small refactor*

server/pkg/cowutils/cowutils.go

@@ -0,0 +1,14 @@
+package cowutils
+
+import (
+	"errors"
+)
+
+// ErrNotSupported is returned by Always() if the operation is not
+// supported on the current operating system. Auto() will never return this
+// error.
+var (
+	ErrNotSupported = errors.New("cow is not supported on this OS")
+	ErrFailed       = errors.New("cow is not supported on this OS or file")
+	ErrTooSmall     = errors.New("file is too smaller then filesystem block size")
+)

server/pkg/cowutils/dedupe.go

@@ -0,0 +1,88 @@
+package cowutils
+
+import (
+	"context"
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+func DedupeFiles(ctx context.Context, paths []string) (deduped uint64, err error) {
+	srcF, err := os.Open(paths[0])
+	if err != nil {
+		return deduped, err
+	}
+	defer srcF.Close()
+	srcStat, err := srcF.Stat()
+	if err != nil {
+		return deduped, err
+	}
+
+	srcFd := int(srcF.Fd())
+	srcSize := srcStat.Size()
+
+	fsStat := unix.Statfs_t{}
+	err = unix.Fstatfs(srcFd, &fsStat)
+	if err != nil {
+		return deduped, err
+	}
+
+	if int64(fsStat.Bsize) > srcSize { // for btrfs it means file residing in metadata and can't be deduplicated
+		return deduped, nil
+	}
+
+	blockSize := uint64((srcSize % int64(fsStat.Bsize)) * int64(fsStat.Bsize))
+
+	fdr := unix.FileDedupeRange{
+		Src_offset: 0,
+		Src_length: blockSize,
+		Info:       []unix.FileDedupeRangeInfo{},
+	}
+
+	for _, dst := range paths[1:] {
+		if ctx.Err() != nil {
+			return deduped, ctx.Err()
+		}
+
+		destF, err := os.OpenFile(dst, os.O_RDWR, os.ModePerm)
+		if err != nil {
+			return deduped, err
+		}
+
+		// defer in cycle is intended, file must be closed only at the end of the function,
+		// and, most importantly, this keeps GC from closing descriptor while dudupe in progress
+		defer destF.Close()
+
+		fdr.Info = append(fdr.Info, unix.FileDedupeRangeInfo{
+			Dest_fd:     int64(destF.Fd()),
+			Dest_offset: 0,
+		})
+	}
+
+	if len(fdr.Info) == 0 {
+		return deduped, nil
+	}
+
+	if ctx.Err() != nil {
+		return deduped, ctx.Err()
+	}
+
+	fdr.Src_offset = 0
+	for i := range fdr.Info {
+		fdr.Info[i].Dest_offset = 0
+	}
+
+	err = unix.IoctlFileDedupeRange(srcFd, &fdr)
+	if err != nil {
+		return deduped, err
+	}
+
+	for i := range fdr.Info {
+		deduped += fdr.Info[i].Bytes_deduped
+
+		fdr.Info[i].Status = 0
+		fdr.Info[i].Bytes_deduped = 0
+	}
+
+	return deduped, nil
+}

server/pkg/cowutils/reflink.go

@@ -0,0 +1,54 @@
+package cowutils
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
+)
+
+// Reflink performs the reflink operation on the passed files, replacing
+// dst's contents with src. If fallback is true and reflink fails,
+// copy_file_range will be used first, and if that fails too io.Copy will
+// be used to copy the data.
+func Reflink(ctx context.Context, dst, src *os.File, fallback bool) error {
+	err := reflink(dst, src)
+	if (err != nil) && fallback {
+		// reflink failed, but we can fallback, but first we need to know the file's size
+		var st fs.FileInfo
+		st, err = src.Stat()
+		if err != nil {
+			// couldn't stat source, this can't be helped
+			return fmt.Errorf("failed to stat source: %w", err)
+		}
+		_, err = copyFileRange(dst, src, 0, 0, st.Size())
+		if err != nil {
+			// copyFileRange failed too, switch to simple io copy
+			reader := io.NewSectionReader(src, 0, st.Size())
+			writer := &sectionWriter{w: dst}
+			_ = dst.Truncate(0) // assuming any error in trucate will result in copy error
+			_, err = io.Copy(writer, reader)
+		}
+	}
+	return err
+}
+
+// ReflinkRange performs a range reflink operation on the passed files, replacing
+// part of dst's contents with data from src. If fallback is true and reflink
+// fails, copy_file_range will be used first, and if that fails too io.CopyN
+// will be used to copy the data.
+func ReflinkRange(ctx context.Context, dst, src *os.File, dstOffset, srcOffset, n int64, fallback bool) error {
+	err := reflinkRange(dst, src, dstOffset, srcOffset, n)
+	if (err != nil) && fallback {
+		_, err = copyFileRange(dst, src, dstOffset, srcOffset, n)
+	}
+
+	if (err != nil) && fallback {
+		// seek both src & dst
+		reader := io.NewSectionReader(src, srcOffset, n)
+		writer := &sectionWriter{w: dst, base: dstOffset}
+		_, err = io.CopyN(writer, reader, n)
+	}
+	return err
+}

server/pkg/cowutils/reflink_unix.go

@@ -0,0 +1,53 @@
+//!build +unix
+
+package cowutils
+
+import (
+	"errors"
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+// reflink performs the actual reflink action without worrying about fallback
+func reflink(dst, src *os.File) error {
+	srcFd := int(src.Fd())
+	dstFd := int(dst.Fd())
+
+	err := unix.IoctlFileClone(dstFd, srcFd)
+
+	if err != nil && errors.Is(err, unix.ENOTSUP) {
+		return ErrNotSupported
+	}
+
+	return err
+}
+
+func reflinkRange(dst, src *os.File, dstOffset, srcOffset, n int64) error {
+	srcFd := int(src.Fd())
+	dstFd := int(dst.Fd())
+
+	req := &unix.FileCloneRange{
+		Src_fd:      int64(srcFd),
+		Src_offset:  uint64(srcOffset),
+		Src_length:  uint64(n),
+		Dest_offset: uint64(dstOffset),
+	}
+
+	err := unix.IoctlFileCloneRange(dstFd, req)
+	if err != nil && errors.Is(err, unix.ENOTSUP) {
+		return ErrNotSupported
+	}
+
+	return err
+}
+
+func copyFileRange(dst, src *os.File, dstOffset, srcOffset, n int64) (int64, error) {
+	srcFd := int(src.Fd())
+	dstFd := int(dst.Fd())
+
+	resN, err := unix.CopyFileRange(srcFd, &srcOffset, dstFd, &dstOffset, int(n), 0)
+
+	return int64(resN), err
+
+}

server/pkg/cowutils/writer.go

@@ -0,0 +1,39 @@
+package cowutils
+
+import (
+	"errors"
+	"io"
+)
+
+// sectionWriter is a helper used when we need to fallback into copying data manually
+type sectionWriter struct {
+	w    io.WriterAt // target file
+	base int64       // base position in file
+	off  int64       // current relative offset
+}
+
+// Write writes & updates offset
+func (s *sectionWriter) Write(p []byte) (int, error) {
+	n, err := s.w.WriteAt(p, s.base+s.off)
+	s.off += int64(n)
+	return n, err
+}
+
+func (s *sectionWriter) Seek(offset int64, whence int) (int64, error) {
+	switch whence {
+	case io.SeekStart:
+		// nothing needed
+	case io.SeekCurrent:
+		offset += s.off
+	case io.SeekEnd:
+		// we don't support io.SeekEnd
+		fallthrough
+	default:
+		return s.off, errors.New("Seek: invalid whence")
+	}
+	if offset < 0 {
+		return s.off, errors.New("Seek: invalid offset")
+	}
+	s.off = offset
+	return offset, nil
+}

server/pkg/ctxbilly/change.go

@@ -0,0 +1,27 @@
+package ctxbilly
+
+import (
+	"context"
+	"os"
+	"time"
+)
+
+// Change abstract the FileInfo change related operations in a storage-agnostic
+// interface as an extension to the Basic interface
+type Change interface {
+	// Chmod changes the mode of the named file to mode. If the file is a
+	// symbolic link, it changes the mode of the link's target.
+	Chmod(ctx context.Context, name string, mode os.FileMode) error
+	// Lchown changes the numeric uid and gid of the named file. If the file is
+	// a symbolic link, it changes the uid and gid of the link itself.
+	Lchown(ctx context.Context, name string, uid, gid int) error
+	// Chown changes the numeric uid and gid of the named file. If the file is a
+	// symbolic link, it changes the uid and gid of the link's target.
+	Chown(ctx context.Context, name string, uid, gid int) error
+	// Chtimes changes the access and modification times of the named file,
+	// similar to the Unix utime() or utimes() functions.
+	//
+	// The underlying filesystem may truncate or round the values to a less
+	// precise time unit.
+	Chtimes(ctx context.Context, name string, atime time.Time, mtime time.Time) error
+}

server/pkg/ctxbilly/fs.go

@@ -0,0 +1,97 @@
+package ctxbilly
+
+import (
+	"context"
+	"io"
+	"os"
+
+	"github.com/royalcat/ctxio"
+)
+
+type Filesystem interface {
+	// Create creates the named file with mode 0666 (before umask), truncating
+	// it if it already exists. If successful, methods on the returned File can
+	// be used for I/O; the associated file descriptor has mode O_RDWR.
+	Create(ctx context.Context, filename string) (File, error)
+	// OpenFile is the generalized open call; most users will use Open or Create
+	// instead. It opens the named file with specified flag (O_RDONLY etc.) and
+	// perm, (0666 etc.) if applicable. If successful, methods on the returned
+	// File can be used for I/O.
+	OpenFile(ctx context.Context, filename string, flag int, perm os.FileMode) (File, error)
+	// Stat returns a FileInfo describing the named file.
+	Stat(ctx context.Context, filename string) (os.FileInfo, error)
+	// Rename renames (moves) oldpath to newpath. If newpath already exists and
+	// is not a directory, Rename replaces it. OS-specific restrictions may
+	// apply when oldpath and newpath are in different directories.
+	Rename(ctx context.Context, oldpath, newpath string) error
+	// Remove removes the named file or directory.
+	Remove(ctx context.Context, filename string) error
+	// Join joins any number of path elements into a single path, adding a
+	// Separator if necessary. Join calls filepath.Clean on the result; in
+	// particular, all empty strings are ignored. On Windows, the result is a
+	// UNC path if and only if the first path element is a UNC path.
+	Join(elem ...string) string
+
+	// ReadDir reads the directory named by d(irname and returns a list of
+	// directory entries sorted by filename.
+	ReadDir(ctx context.Context, path string) ([]os.FileInfo, error)
+	// MkdirAll creates a directory named path, along with any necessary
+	// parents, and returns nil, or else returns an error. The permission bits
+	// perm are used for all directories that MkdirAll creates. If path is/
+	// already a directory, MkdirAll does nothing and returns nil.
+	MkdirAll(ctx context.Context, filename string, perm os.FileMode) error
+
+	// Lstat returns a FileInfo describing the named file. If the file is a
+	// symbolic link, the returned FileInfo describes the symbolic link. Lstat
+	// makes no attempt to follow the link.
+	Lstat(ctx context.Context, filename string) (os.FileInfo, error)
+	// Symlink creates a symbolic-link from link to target. target may be an
+	// absolute or relative path, and need not refer to an existing node.
+	// Parent directories of link are created as necessary.
+	Symlink(ctx context.Context, target, link string) error
+	// Readlink returns the target path of link.
+	Readlink(ctx context.Context, link string) (string, error)
+
+	// // Chroot returns a new filesystem from the same type where the new root is
+	// // the given path. Files outside of the designated directory tree cannot be
+	// // accessed.
+	// Chroot(path string) (Filesystem, error)
+	// // Root returns the root path of the filesystem.
+	// Root() string
+}
+
+type TempFileFS interface {
+	// TempFile creates a new temporary file in the directory dir with a name
+	// beginning with prefix, opens the file for reading and writing, and
+	// returns the resulting *os.File. If dir is the empty string, TempFile
+	// uses the default directory for temporary files (see os.TempDir).
+	// Multiple programs calling TempFile simultaneously will not choose the
+	// same file. The caller can use f.Name() to find the pathname of the file.
+	// It is the caller's responsibility to remove the file when no longer
+	// needed.
+	TempFile(ctx context.Context, dir, prefix string) (File, error)
+}
+
+type File interface {
+	// Name returns the name of the file as presented to Open.
+	Name() string
+	ctxio.Writer
+	ctxio.WriterAt
+	ctxio.Reader
+	ctxio.ReaderAt
+	io.Seeker
+	ctxio.Closer
+}
+
+type LockFile interface {
+	// Lock locks the file like e.g. flock. It protects against access from
+	// other processes.
+	Lock() error
+	// Unlock unlocks the file.
+	Unlock() error
+}
+
+type TruncateFile interface {
+	// Truncate the file.
+	Truncate(ctx context.Context, size int64) error
+}

server/pkg/ctxbilly/mem.go

@@ -0,0 +1,175 @@
+package ctxbilly
+
+import (
+	"context"
+	"io/fs"
+
+	"github.com/go-git/go-billy/v5"
+)
+
+func WrapFileSystem(bf billy.Filesystem) Filesystem {
+	return &wrapFS{
+		Filesystem: bf,
+	}
+}
+
+type wrapFS struct {
+	billy.Filesystem
+}
+
+var _ Filesystem = (*wrapFS)(nil)
+
+// Create implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Create of MemFS.Filesystem.
+func (m *wrapFS) Create(ctx context.Context, filename string) (File, error) {
+	bf, err := m.Filesystem.Create(filename)
+	if err != nil {
+		return nil, err
+	}
+	return &wrapFile{bf}, nil
+}
+
+// Lstat implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Lstat of MemFS.Filesystem.
+func (m *wrapFS) Lstat(ctx context.Context, filename string) (fs.FileInfo, error) {
+	return m.Filesystem.Lstat(filename)
+}
+
+// MkdirAll implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).MkdirAll of MemFS.Filesystem.
+func (m *wrapFS) MkdirAll(ctx context.Context, filename string, perm fs.FileMode) error {
+	return m.Filesystem.MkdirAll(filename, perm)
+}
+
+// Open implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Open of MemFS.Filesystem.
+func (m *wrapFS) Open(ctx context.Context, filename string) (File, error) {
+	bf, err := m.Filesystem.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+	return WrapFile(bf), nil
+}
+
+// OpenFile implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).OpenFile of MemFS.Filesystem.
+func (m *wrapFS) OpenFile(ctx context.Context, filename string, flag int, perm fs.FileMode) (File, error) {
+	bf, err := m.Filesystem.OpenFile(filename, flag, perm)
+	if err != nil {
+		return nil, err
+	}
+	return WrapFile(bf), nil
+}
+
+// ReadDir implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).ReadDir of MemFS.Filesystem.
+func (m *wrapFS) ReadDir(ctx context.Context, path string) ([]fs.FileInfo, error) {
+	return m.Filesystem.ReadDir(path)
+}
+
+// Readlink implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Readlink of MemFS.Filesystem.
+func (m *wrapFS) Readlink(ctx context.Context, link string) (string, error) {
+	return m.Filesystem.Readlink(link)
+}
+
+// Remove implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Remove of MemFS.Filesystem.
+func (m *wrapFS) Remove(ctx context.Context, filename string) error {
+	return m.Filesystem.Remove(filename)
+}
+
+// Rename implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Rename of MemFS.Filesystem.
+func (m *wrapFS) Rename(ctx context.Context, oldpath string, newpath string) error {
+	return m.Filesystem.Rename(oldpath, newpath)
+}
+
+// Stat implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Stat of MemFS.Filesystem.
+func (m *wrapFS) Stat(ctx context.Context, filename string) (fs.FileInfo, error) {
+	return m.Filesystem.Stat(filename)
+}
+
+// Symlink implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Symlink of MemFS.Filesystem.
+func (m *wrapFS) Symlink(ctx context.Context, target string, link string) error {
+	return m.Filesystem.Symlink(target, link)
+}
+
+// TempFile implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).TempFile of MemFS.Filesystem.
+func (m *wrapFS) TempFile(ctx context.Context, dir string, prefix string) (File, error) {
+	file, err := m.Filesystem.TempFile(dir, prefix)
+	if err != nil {
+		return nil, err
+	}
+	return WrapFile(file), nil
+}
+
+func WrapFile(bf billy.File) File {
+	return &wrapFile{File: bf}
+}
+
+type wrapFile struct {
+	billy.File
+}
+
+var _ File = (*wrapFile)(nil)
+
+// Close implements File.
+// Subtle: this method shadows the method (File).Close of MemFile.File.
+func (m *wrapFile) Close(ctx context.Context) error {
+	return m.File.Close()
+}
+
+// Lock implements File.
+// Subtle: this method shadows the method (File).Lock of MemFile.File.
+func (m *wrapFile) Lock() error {
+	return m.File.Lock()
+}
+
+// Name implements File.
+// Subtle: this method shadows the method (File).Name of MemFile.File.
+func (m *wrapFile) Name() string {
+	return m.File.Name()
+}
+
+// Truncate implements File.
+// Subtle: this method shadows the method (File).Truncate of memFile.File.
+func (m *wrapFile) Truncate(ctx context.Context, size int64) error {
+	return m.File.Truncate(size)
+}
+
+// Read implements File.
+// Subtle: this method shadows the method (File).Read of MemFile.File.
+func (m *wrapFile) Read(ctx context.Context, p []byte) (n int, err error) {
+	return m.File.Read(p)
+}
+
+// ReadAt implements File.
+// Subtle: this method shadows the method (File).ReadAt of MemFile.File.
+func (m *wrapFile) ReadAt(ctx context.Context, p []byte, off int64) (n int, err error) {
+	return m.File.ReadAt(p, off)
+}
+
+// Unlock implements File.
+// Subtle: this method shadows the method (File).Unlock of MemFile.File.
+func (m *wrapFile) Unlock() error {
+	return m.File.Unlock()
+}
+
+// Write implements File.
+// Subtle: this method shadows the method (File).Write of MemFile.File.
+func (m *wrapFile) Write(ctx context.Context, p []byte) (n int, err error) {
+	return m.File.Write(p)
+}
+
+// WriteAt implements File.
+func (m *wrapFile) WriteAt(ctx context.Context, p []byte, off int64) (n int, err error) {
+	_, err = m.File.Seek(off, 0)
+	if err != nil {
+		return 0, err
+	}
+	return m.File.Write(p)
+}

server/pkg/ctxbilly/uring.go

@@ -0,0 +1,355 @@
+package ctxbilly
+
+// import (
+// 	"context"
+// 	"errors"
+// 	"fmt"
+// 	"os"
+// 	"path/filepath"
+// 	"strings"
+
+// 	securejoin "github.com/cyphar/filepath-securejoin"
+// 	"github.com/iceber/iouring-go"
+// )
+
+// func NewURingFS() (*UringFS, error) {
+// 	ur, err := iouring.New(64, iouring.WithAsync())
+// 	if err != nil {
+// 		return nil, err
+// 	}
+
+// 	return &UringFS{
+// 		ur: ur,
+// 	}, nil
+// }
+
+// var _ Filesystem = (*UringFS)(nil)
+
+// const (
+// 	defaultDirectoryMode = 0o755
+// 	defaultCreateMode    = 0o666
+// )
+
+// // UringFS is a fs implementation based on the OS filesystem which is bound to
+// // a base dir.
+// // Prefer this fs implementation over ChrootOS.
+// //
+// // Behaviours of note:
+// //  1. Read and write operations can only be directed to files which descends
+// //     from the base dir.
+// //  2. Symlinks don't have their targets modified, and therefore can point
+// //     to locations outside the base dir or to non-existent paths.
+// //  3. Readlink and Lstat ensures that the link file is located within the base
+// //     dir, evaluating any symlinks that file or base dir may contain.
+// type UringFS struct {
+// 	ur      *iouring.IOURing
+// 	baseDir string
+// }
+
+// func newBoundOS(d string) *UringFS {
+// 	return &UringFS{baseDir: d}
+// }
+
+// func (fs *UringFS) Create(ctx context.Context, filename string) (File, error) {
+// 	return fs.OpenFile(ctx, filename, os.O_RDWR|os.O_CREATE|os.O_TRUNC, defaultCreateMode)
+// }
+
+// func (fs *UringFS) OpenFile(ctx context.Context, filename string, flag int, perm os.FileMode) (File, error) {
+// 	fn, err := fs.abs(filename)
+// 	if err != nil {
+// 		return nil, err
+// 	}
+
+// 	f, err := os.OpenFile(fn, flag, perm)
+// 	if err != nil {
+// 		return nil, err
+// 	}
+
+// 	return newFile(fs.ur, f)
+// }
+
+// func (fs *UringFS) ReadDir(ctx context.Context, path string) ([]os.FileInfo, error) {
+// 	dir, err := fs.abs(path)
+// 	if err != nil {
+// 		return nil, err
+// 	}
+
+// 	entries, err := os.ReadDir(dir)
+// 	if err != nil {
+// 		return nil, err
+// 	}
+// 	infos := make([]os.FileInfo, 0, len(entries))
+// 	for _, v := range entries {
+// 		info, err := v.Info()
+// 		if err != nil {
+// 			return nil, err
+// 		}
+
+// 		infos = append(infos, info)
+// 	}
+
+// 	return infos, nil
+// }
+
+// func (fs *UringFS) Rename(ctx context.Context, from, to string) error {
+// 	f, err := fs.abs(from)
+// 	if err != nil {
+// 		return err
+// 	}
+// 	t, err := fs.abs(to)
+// 	if err != nil {
+// 		return err
+// 	}
+
+// 	// MkdirAll for target name.
+// 	if err := fs.createDir(t); err != nil {
+// 		return err
+// 	}
+
+// 	return os.Rename(f, t)
+// }
+
+// func (fs *UringFS) MkdirAll(ctx context.Context, path string, perm os.FileMode) error {
+// 	dir, err := fs.abs(path)
+// 	if err != nil {
+// 		return err
+// 	}
+// 	return os.MkdirAll(dir, perm)
+// }
+
+// func (fs *UringFS) Stat(ctx context.Context, filename string) (os.FileInfo, error) {
+// 	filename, err := fs.abs(filename)
+// 	if err != nil {
+// 		return nil, err
+// 	}
+// 	return os.Stat(filename)
+// }
+
+// func (fs *UringFS) Remove(ctx context.Context, filename string) error {
+// 	fn, err := fs.abs(filename)
+// 	if err != nil {
+// 		return err
+// 	}
+// 	return os.Remove(fn)
+// }
+
+// func (fs *UringFS) Join(elem ...string) string {
+// 	return filepath.Join(elem...)
+// }
+
+// func (fs *UringFS) RemoveAll(path string) error {
+// 	dir, err := fs.abs(path)
+// 	if err != nil {
+// 		return err
+// 	}
+// 	return os.RemoveAll(dir)
+// }
+
+// func (fs *UringFS) Symlink(ctx context.Context, target, link string) error {
+// 	ln, err := fs.abs(link)
+// 	if err != nil {
+// 		return err
+// 	}
+// 	// MkdirAll for containing dir.
+// 	if err := fs.createDir(ln); err != nil {
+// 		return err
+// 	}
+// 	return os.Symlink(target, ln)
+// }
+
+// func (fs *UringFS) Lstat(ctx context.Context, filename string) (os.FileInfo, error) {
+// 	filename = filepath.Clean(filename)
+// 	if !filepath.IsAbs(filename) {
+// 		filename = filepath.Join(fs.baseDir, filename)
+// 	}
+// 	if ok, err := fs.insideBaseDirEval(filename); !ok {
+// 		return nil, err
+// 	}
+// 	return os.Lstat(filename)
+// }
+
+// func (fs *UringFS) Readlink(ctx context.Context, link string) (string, error) {
+// 	if !filepath.IsAbs(link) {
+// 		link = filepath.Clean(filepath.Join(fs.baseDir, link))
+// 	}
+// 	if ok, err := fs.insideBaseDirEval(link); !ok {
+// 		return "", err
+// 	}
+// 	return os.Readlink(link)
+// }
+
+// // Chroot returns a new OS filesystem, with the base dir set to the
+// // result of joining the provided path with the underlying base dir.
+// // func (fs *UringFS) Chroot(path string) (Filesystem, error) {
+// // 	joined, err := securejoin.SecureJoin(fs.baseDir, path)
+// // 	if err != nil {
+// // 		return nil, err
+// // 	}
+// // 	return newBoundOS(joined), nil
+// // }
+
+// // Root returns the current base dir of the billy.Filesystem.
+// // This is required in order for this implementation to be a drop-in
+// // replacement for other upstream implementations (e.g. memory and osfs).
+// func (fs *UringFS) Root() string {
+// 	return fs.baseDir
+// }
+
+// func (fs *UringFS) createDir(fullpath string) error {
+// 	dir := filepath.Dir(fullpath)
+// 	if dir != "." {
+// 		if err := os.MkdirAll(dir, defaultDirectoryMode); err != nil {
+// 			return err
+// 		}
+// 	}
+
+// 	return nil
+// }
+
+// // abs transforms filename to an absolute path, taking into account the base dir.
+// // Relative paths won't be allowed to ascend the base dir, so `../file` will become
+// // `/working-dir/file`.
+// //
+// // Note that if filename is a symlink, the returned address will be the target of the
+// // symlink.
+// func (fs *UringFS) abs(filename string) (string, error) {
+// 	if filename == fs.baseDir {
+// 		filename = string(filepath.Separator)
+// 	}
+
+// 	path, err := securejoin.SecureJoin(fs.baseDir, filename)
+// 	if err != nil {
+// 		return "", nil
+// 	}
+
+// 	return path, nil
+// }
+
+// // insideBaseDirEval checks whether filename is contained within
+// // a dir that is within the fs.baseDir, by first evaluating any symlinks
+// // that either filename or fs.baseDir may contain.
+// func (fs *UringFS) insideBaseDirEval(filename string) (bool, error) {
+// 	dir, err := filepath.EvalSymlinks(filepath.Dir(filename))
+// 	if dir == "" || os.IsNotExist(err) {
+// 		dir = filepath.Dir(filename)
+// 	}
+// 	wd, err := filepath.EvalSymlinks(fs.baseDir)
+// 	if wd == "" || os.IsNotExist(err) {
+// 		wd = fs.baseDir
+// 	}
+// 	if filename != wd && dir != wd && !strings.HasPrefix(dir, wd+string(filepath.Separator)) {
+// 		return false, fmt.Errorf("path outside base dir")
+// 	}
+// 	return true, nil
+// }
+
+// func newFile(fsur *iouring.IOURing, f *os.File) (*URingFile, error) {
+// 	ur, err := iouring.New(64, iouring.WithAttachWQ(fsur))
+// 	if err != nil {
+// 		return nil, err
+// 	}
+
+// 	return &URingFile{
+// 		ur: ur,
+// 		f:  f,
+// 	}, nil
+// }
+
+// type URingFile struct {
+// 	ur *iouring.IOURing
+// 	f  *os.File
+// }
+
+// // Close implements File.
+// func (o *URingFile) Close(ctx context.Context) error {
+// 	return errors.Join(o.ur.UnregisterFile(o.f), o.Close(ctx))
+// }
+
+// // Name implements File.
+// func (o *URingFile) Name() string {
+// 	return o.f.Name()
+// }
+
+// // Read implements File.
+// func (o *URingFile) Read(ctx context.Context, p []byte) (n int, err error) {
+// 	req, err := o.ur.Read(o.f, p, nil)
+// 	if err != nil {
+// 		return 0, err
+// 	}
+// 	defer req.Cancel()
+
+// 	select {
+// 	case <-req.Done():
+// 		return req.GetRes()
+// 	case <-ctx.Done():
+// 		req.Cancel()
+// 		<-req.Done()
+// 		return req.GetRes()
+// 	}
+// }
+
+// // ReadAt implements File.
+// func (o *URingFile) ReadAt(ctx context.Context, p []byte, off int64) (n int, err error) {
+// 	req, err := o.ur.Pread(o.f, p, uint64(off), nil)
+// 	if err != nil {
+// 		return 0, err
+// 	}
+// 	defer req.Cancel()
+
+// 	select {
+// 	case <-req.Done():
+// 		return req.GetRes()
+// 	case <-ctx.Done():
+// 		req.Cancel()
+// 		<-req.Done()
+// 		return req.GetRes()
+// 	}
+// }
+
+// // Write implements File.
+// func (o *URingFile) Write(ctx context.Context, p []byte) (n int, err error) {
+// 	req, err := o.ur.Write(o.f, p, nil)
+// 	if err != nil {
+// 		return 0, err
+// 	}
+// 	defer req.Cancel()
+
+// 	select {
+// 	case <-req.Done():
+// 		return req.GetRes()
+// 	case <-ctx.Done():
+// 		req.Cancel()
+// 		<-req.Done()
+// 		return req.GetRes()
+// 	}
+// }
+
+// // WriteAt implements File.
+// func (o *URingFile) WriteAt(ctx context.Context, p []byte, off int64) (n int, err error) {
+// 	req, err := o.ur.Pwrite(o.f, p, uint64(off), nil)
+// 	if err != nil {
+// 		return 0, err
+// 	}
+// 	defer req.Cancel()
+
+// 	select {
+// 	case <-req.Done():
+// 		return req.GetRes()
+// 	case <-ctx.Done():
+// 		req.Cancel()
+// 		<-req.Done()
+// 		return req.GetRes()
+// 	}
+// }
+
+// // Seek implements File.
+// func (o *URingFile) Seek(offset int64, whence int) (int64, error) {
+// 	return o.f.Seek(offset, whence)
+// }
+
+// // Truncate implements File.
+// func (o *URingFile) Truncate(ctx context.Context, size int64) error {
+// 	return o.f.Truncate(size)
+// }
+
+// var _ File = (*URingFile)(nil)

server/pkg/go-nfs/.github/dependabot.yml

@@ -0,0 +1,11 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for all configuration options:
+# https://help.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
+version: 2
+updates:
+  - package-ecosystem: "gomod"
+    directory: "/" # Location of package manifests
+    schedule:
+      interval: "daily"

server/pkg/go-nfs/.github/workflows/codeql-analysis.yml

@@ -0,0 +1,51 @@
+name: "Code scanning - action"
+
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: '0 18 * * 3'
+
+jobs:
+  CodeQL-Build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v2
+      with:
+        # We must fetch at least the immediate parents so that if this is
+        # a pull request then we can checkout the head.
+        fetch-depth: 2
+
+    # If this run was triggered by a pull request event, then checkout
+    # the head of the pull request instead of the merge commit.
+    - run: git checkout HEAD^2
+      if: ${{ github.event_name == 'pull_request' }}
+      
+    # Initializes the CodeQL tools for scanning.
+    - name: Initialize CodeQL
+      uses: github/codeql-action/init@v1
+      # Override language selection by uncommenting this and choosing your languages
+      # with:
+      #   languages: go, javascript, csharp, python, cpp, java
+
+    # Autobuild attempts to build any compiled languages  (C/C++, C#, or Java).
+    # If this step fails, then you should remove it and run the build manually (see below)
+    - name: Autobuild
+      uses: github/codeql-action/autobuild@v1
+
+    # ℹ️ Command-line programs to run using the OS shell.
+    # 📚 https://git.io/JvXDl
+
+    # ✏️ If the Autobuild fails above, remove it and uncomment the following three lines
+    #    and modify them (or add more) to build your code if your project
+    #    uses a compiled language
+
+    #- run: |
+    #   make bootstrap
+    #   make release
+
+    - name: Perform CodeQL Analysis
+      uses: github/codeql-action/analyze@v1

server/pkg/go-nfs/.github/workflows/go.yml

@@ -0,0 +1,36 @@
+name: Go
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    steps:
+    - name: Set up Go 1.x
+      uses: actions/setup-go@v3
+      with:
+        go-version: ^1.19
+      id: go
+
+    - name: Check out code into the Go module directory
+      uses: actions/checkout@v3
+
+    - name: Get dependencies
+      run: go get -v -t -d ./...
+
+    - name: Build
+      run: go build -v ./...
+
+    - name: golangci-lint
+      uses: golangci/golangci-lint-action@v3
+
+    - name: Test
+      run: go test -v .

server/pkg/go-nfs/CONTRIBUTING.md

@@ -0,0 +1,11 @@
+# Contributing Guidelines
+
+We appreciate your interest in improving go-nfs!
+
+## Looking for ways to contribute?
+
+There are several ways you can contribute:
+- Start contributing immediately via the [opened](https://github.com/willscott/go-nfs/issues) issues on GitHub.
+  Defined issues provide an excellent starting point.
+- Reporting issues, bugs, mistakes, or inconsistencies.
+  As many open source projects, we are short-staffed, we thus kindly ask you to be open to contribute a fix for discovered issues.

server/pkg/go-nfs/LICENSE

@@ -0,0 +1,202 @@
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
+
+      "License" shall mean the terms and conditions for use, reproduction,
+      and distribution as defined by Sections 1 through 9 of this document.
+
+      "Licensor" shall mean the copyright owner or entity authorized by
+      the copyright owner that is granting the License.
+
+      "Legal Entity" shall mean the union of the acting entity and all
+      other entities that control, are controlled by, or are under common
+      control with that entity. For the purposes of this definition,
+      "control" means (i) the power, direct or indirect, to cause the
+      direction or management of such entity, whether by contract or
+      otherwise, or (ii) ownership of fifty percent (50%) or more of the
+      outstanding shares, or (iii) beneficial ownership of such entity.
+
+      "You" (or "Your") shall mean an individual or Legal Entity
+      exercising permissions granted by this License.
+
+      "Source" form shall mean the preferred form for making modifications,
+      including but not limited to software source code, documentation
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+      transformation or translation of a Source form, including but
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+
+      "Work" shall mean the work of authorship, whether in Source or
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+      copyright notice that is included in or attached to the work
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+      "Derivative Works" shall mean any work, whether in Source or Object
+      form, that is based on (or derived from) the Work and for which the
+      editorial revisions, annotations, elaborations, or other modifications
+      represent, as a whole, an original work of authorship. For the purposes
+      of this License, Derivative Works shall not include works that remain
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+      "Contribution" shall mean any work of authorship, including
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+      to that Work or Derivative Works thereof, that is intentionally
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+      to the Licensor or its representatives, including but not limited to
+      communication on electronic mailing lists, source code control systems,
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+      designated in writing by the copyright owner as "Not a Contribution."
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+      "Contributor" shall mean Licensor and any individual or Legal Entity
+      on behalf of whom a Contribution has been received by Licensor and
+      subsequently incorporated within the Work.
+
+   2. Grant of Copyright License. Subject to the terms and conditions of
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+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
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+      (except as stated in this section) patent license to make, have made,
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+      institute patent litigation against any entity (including a
+      cross-claim or counterclaim in a lawsuit) alleging that the Work
+      or a Contribution incorporated within the Work constitutes direct
+      or contributory patent infringement, then any patent licenses
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+
+   4. Redistribution. You may reproduce and distribute copies of the
+      Work or Derivative Works thereof in any medium, with or without
+      modifications, and in Source or Object form, provided that You
+      meet the following conditions:
+
+      (a) You must give any other recipients of the Work or
+          Derivative Works a copy of this License; and
+
+      (b) You must cause any modified files to carry prominent notices
+          stating that You changed the files; and
+
+      (c) You must retain, in the Source form of any Derivative Works
+          that You distribute, all copyright, patent, trademark, and
+          attribution notices from the Source form of the Work,
+          excluding those notices that do not pertain to any part of
+          the Derivative Works; and
+
+      (d) If the Work includes a "NOTICE" text file as part of its
+          distribution, then any Derivative Works that You distribute must
+          include a readable copy of the attribution notices contained
+          within such NOTICE file, excluding those notices that do not
+          pertain to any part of the Derivative Works, in at least one
+          of the following places: within a NOTICE text file distributed
+          as part of the Derivative Works; within the Source form or
+          documentation, if provided along with the Derivative Works; or,
+          within a display generated by the Derivative Works, if and
+          wherever such third-party notices normally appear. The contents
+          of the NOTICE file are for informational purposes only and
+          do not modify the License. You may add Your own attribution
+          notices within Derivative Works that You distribute, alongside
+          or as an addendum to the NOTICE text from the Work, provided
+          that such additional attribution notices cannot be construed
+          as modifying the License.
+
+      You may add Your own copyright statement to Your modifications and
+      may provide additional or different license terms and conditions
+      for use, reproduction, or distribution of Your modifications, or
+      for any such Derivative Works as a whole, provided Your use,
+      reproduction, and distribution of the Work otherwise complies with
+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
+
+   6. Trademarks. This License does not grant permission to use the trade
+      names, trademarks, service marks, or product names of the Licensor,
+      except as required for reasonable and customary use in describing the
+      origin of the Work and reproducing the content of the NOTICE file.
+
+   7. Disclaimer of Warranty. Unless required by applicable law or
+      agreed to in writing, Licensor provides the Work (and each
+      Contributor provides its Contributions) on an "AS IS" BASIS,
+      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+      implied, including, without limitation, any warranties or conditions
+      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+      PARTICULAR PURPOSE. You are solely responsible for determining the
+      appropriateness of using or redistributing the Work and assume any
+      risks associated with Your exercise of permissions under this License.
+
+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
+      liable to You for damages, including any direct, indirect, special,
+      incidental, or consequential damages of any character arising as a
+      result of this License or out of the use or inability to use the
+      Work (including but not limited to damages for loss of goodwill,
+      work stoppage, computer failure or malfunction, or any and all
+      other commercial damages or losses), even if such Contributor
+      has been advised of the possibility of such damages.
+
+   9. Accepting Warranty or Additional Liability. While redistributing
+      the Work or Derivative Works thereof, You may choose to offer,
+      and charge a fee for, acceptance of support, warranty, indemnity,
+      or other liability obligations and/or rights consistent with this
+      License. However, in accepting such obligations, You may act only
+      on Your own behalf and on Your sole responsibility, not on behalf
+      of any other Contributor, and only if You agree to indemnify,
+      defend, and hold each Contributor harmless for any liability
+      incurred by, or claims asserted against, such Contributor by reason
+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS
+
+   APPENDIX: How to apply the Apache License to your work.
+
+      To apply the Apache License to your work, attach the following
+      boilerplate notice, with the fields enclosed by brackets "[]"
+      replaced with your own identifying information. (Don't include
+      the brackets!)  The text should be enclosed in the appropriate
+      comment syntax for the file format. We also recommend that a
+      file or class name and description of purpose be included on the
+      same "printed page" as the copyright notice for easier
+      identification within third-party archives.
+
+   Copyright [yyyy] [name of copyright owner]
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.

server/pkg/go-nfs/README.md

@@ -0,0 +1,96 @@
+Golang Network File Server
+===
+
+NFSv3 protocol implementation in pure Golang.
+
+Current Status:
+* Minimally tested
+* Mounts, read-only and read-write support
+
+Usage
+===
+
+The most interesting demo is currently in `example/osview`. 
+
+Start the server
+`go run ./example/osview .`.
+
+The local folder at `.` will be the initial view in the mount. mutations to metadata or contents
+will be stored purely in memory and not written back to the OS. When run, this
+demo will print the port it is listening on.
+
+The mount can be accessed using a command similar to 
+`mount -o port=<n>,mountport=<n> -t nfs localhost:/mount <mountpoint>` (For Mac users)
+
+or
+
+`mount -o port=<n>,mountport=<n>,nfsvers=3,noacl,tcp -t nfs localhost:/mount <mountpoint>` (For Linux users)
+
+API
+===
+
+The NFS server runs on a `net.Listener` to export a file system to NFS clients.
+Usage is structured similarly to many other golang network servers.
+
+```golang
+package main
+
+import (
+	"fmt"
+	"log"
+	"net"
+
+	"github.com/go-git/go-billy/v5/memfs"
+	nfs "github.com/willscott/go-nfs"
+	nfshelper "github.com/willscott/go-nfs/helpers"
+)
+
+func main() {
+	listener, err := net.Listen("tcp", ":0")
+	panicOnErr(err, "starting TCP listener")
+	fmt.Printf("Server running at %s\n", listener.Addr())
+	mem := memfs.New()
+	f, err := mem.Create("hello.txt")
+	panicOnErr(err, "creating file")
+	_, err = f.Write([]byte("hello world"))
+	panicOnErr(err, "writing data")
+	f.Close()
+	handler := nfshelper.NewNullAuthHandler(mem)
+	cacheHelper := nfshelper.NewCachingHandler(handler, 1)
+	panicOnErr(nfs.Serve(listener, cacheHelper), "serving nfs")
+}
+
+func panicOnErr(err error, desc ...interface{}) {
+	if err == nil {
+		return
+	}
+	log.Println(desc...)
+	log.Panicln(err)
+}
+```
+
+Notes
+---
+
+* Ports are typically determined through portmap. The need for running portmap 
+(which is the only part that needs a privileged listening port) can be avoided
+through specific mount options. e.g. 
+`mount -o port=n,mountport=n -t nfs host:/mount /localmount`
+
+* This server currently uses [billy](https://github.com/go-git/go-billy/) to
+provide a file system abstraction layer. There are some edges of the NFS protocol
+which do not translate to this abstraction.
+  * NFS expects access to an `inode` or equivalent unique identifier to reference
+  files in a file system. These are considered opaque identifiers here, which
+  means they will not work as expected in cases of hard linking.
+  * The billy abstraction layer does not extend to exposing `uid` and `gid`
+  ownership of files. If ownership is important to your file system, you
+  will need to ensure that the `os.FileInfo` meets additional constraints.
+  In particular, the `Sys()` escape hatch is queried by this library, and
+  if your file system populates a [`syscall.Stat_t`](https://golang.org/pkg/syscall/#Stat_t)
+  concrete struct, the ownership specified in that object will be used.
+
+* Relevant RFCS:
+[5531 - RPC protocol](https://tools.ietf.org/html/rfc5531),
+[1813 - NFSv3](https://tools.ietf.org/html/rfc1813),
+[1094 - NFS](https://tools.ietf.org/html/rfc1094)

server/pkg/go-nfs/SECURITY.md

@@ -0,0 +1,11 @@
+# Security Policy
+
+## Supported Versions
+
+The latest release reflects the current best recommendation / supported version at this time.
+
+## Reporting a Vulnerability
+
+Please email Will (the git commit author) if you need to report issues privately.
+I will endeavor to respond within a day, but if I am offline, responses may be delayed longer than that.
+If you need a stronger SLA to have confidence in using this code, feel free to reach out.

server/pkg/go-nfs/capability_check.go

@@ -0,0 +1,9 @@
+package nfs
+
+import (
+	billy "github.com/go-git/go-billy/v5"
+)
+
+func CapabilityCheck(fs Filesystem, cap billy.Capability) bool {
+	return true
+}

server/pkg/go-nfs/conn.go

@@ -0,0 +1,344 @@
+package nfs
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+
+	xdr2 "github.com/rasky/go-xdr/xdr2"
+	"github.com/willscott/go-nfs-client/nfs/rpc"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/codes"
+)
+
+var (
+	// ErrInputInvalid is returned when input cannot be parsed
+	ErrInputInvalid = errors.New("invalid input")
+	// ErrAlreadySent is returned when writing a header/status multiple times
+	ErrAlreadySent = errors.New("response already started")
+)
+
+// ResponseCode is a combination of accept_stat and reject_stat.
+type ResponseCode uint32
+
+// ResponseCode Codes
+const (
+	ResponseCodeSuccess ResponseCode = iota
+	ResponseCodeProgUnavailable
+	ResponseCodeProcUnavailable
+	ResponseCodeGarbageArgs
+	ResponseCodeSystemErr
+	ResponseCodeRPCMismatch
+	ResponseCodeAuthError
+)
+
+type conn struct {
+	*Server
+	writeSerializer chan []byte
+	net.Conn
+}
+
+var tracer = otel.Tracer("git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs")
+
+func (c *conn) serve() {
+	ctx := context.Background() // TODO implement correct timeout on serve side
+
+	c.writeSerializer = make(chan []byte, 1)
+	go c.serializeWrites(ctx)
+
+	bio := bufio.NewReader(c.Conn)
+	for {
+		w, err := c.readRequestHeader(ctx, bio)
+		if err != nil {
+			if err == io.EOF {
+				// Clean close.
+				c.Close()
+				return
+			}
+			return
+		}
+		Log.Tracef("request: %v", w.req)
+		err = c.handle(ctx, w)
+		respErr := w.finish(ctx)
+		if err != nil {
+			Log.Errorf("error handling req: %v", err)
+			// failure to handle at a level needing to close the connection.
+			c.Close()
+			return
+		}
+		if respErr != nil {
+			Log.Errorf("error sending response: %v", respErr)
+			c.Close()
+			return
+		}
+	}
+}
+
+func (c *conn) serializeWrites(ctx context.Context) {
+	// todo: maybe don't need the extra buffer
+	writer := bufio.NewWriter(c.Conn)
+	var fragmentBuf [4]byte
+	var fragmentInt uint32
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case msg, ok := <-c.writeSerializer:
+			if !ok {
+				return
+			}
+			// prepend the fragmentation header
+			fragmentInt = uint32(len(msg))
+			fragmentInt |= (1 << 31)
+			binary.BigEndian.PutUint32(fragmentBuf[:], fragmentInt)
+			n, err := writer.Write(fragmentBuf[:])
+			if n < 4 || err != nil {
+				return
+			}
+			n, err = writer.Write(msg)
+			if err != nil {
+				return
+			}
+			if n < len(msg) {
+				panic("todo: ensure writes complete fully.")
+			}
+			if err = writer.Flush(); err != nil {
+				return
+			}
+		}
+	}
+}
+
+// Handle a request. errors from this method indicate a failure to read or
+// write on the network stream, and trigger a disconnection of the connection.
+func (c *conn) handle(ctx context.Context, w *response) (err error) {
+	ctx, span := tracer.Start(ctx, fmt.Sprintf("nfs.handle.%s", NFSProcedure(w.req.Header.Proc).String()))
+	defer span.End()
+	defer func() {
+		if err != nil {
+			span.SetStatus(codes.Error, err.Error())
+		} else {
+			span.SetStatus(codes.Ok, "")
+		}
+	}()
+
+	handler := c.Server.handlerFor(w.req.Header.Prog, w.req.Header.Proc)
+	if handler == nil {
+		Log.Errorf("No handler for %d.%d", w.req.Header.Prog, w.req.Header.Proc)
+		if err := w.drain(ctx); err != nil {
+			return err
+		}
+		return c.err(ctx, w, &ResponseCodeProcUnavailableError{})
+	}
+	appError := handler(ctx, w, c.Server.Handler)
+	if drainErr := w.drain(ctx); drainErr != nil {
+		return drainErr
+	}
+	if appError != nil && !w.responded {
+		Log.Errorf("call to %+v failed: %v", handler, appError)
+		if err := c.err(ctx, w, appError); err != nil {
+			return err
+		}
+	}
+	if !w.responded {
+		Log.Errorf("Handler did not indicate response status via writing or erroring")
+		if err := c.err(ctx, w, &ResponseCodeSystemError{}); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (c *conn) err(ctx context.Context, w *response, err error) error {
+	select {
+	case <-ctx.Done():
+		return nil
+	default:
+	}
+
+	if w.err == nil {
+		w.err = err
+	}
+
+	if w.responded {
+		return nil
+	}
+
+	rpcErr := w.errorFmt(err)
+	if writeErr := w.writeHeader(rpcErr.Code()); writeErr != nil {
+		return writeErr
+	}
+
+	body, _ := rpcErr.MarshalBinary()
+	return w.Write(body)
+}
+
+type request struct {
+	xid uint32
+	rpc.Header
+	Body io.Reader
+}
+
+func (r *request) String() string {
+	if r.Header.Prog == nfsServiceID {
+		return fmt.Sprintf("RPC #%d (nfs.%s)", r.xid, NFSProcedure(r.Header.Proc))
+	} else if r.Header.Prog == mountServiceID {
+		return fmt.Sprintf("RPC #%d (mount.%s)", r.xid, MountProcedure(r.Header.Proc))
+	}
+	return fmt.Sprintf("RPC #%d (%d.%d)", r.xid, r.Header.Prog, r.Header.Proc)
+}
+
+type response struct {
+	*conn
+	writer    *bytes.Buffer
+	responded bool
+	err       error
+	errorFmt  func(error) RPCError
+	req       *request
+}
+
+func (w *response) writeXdrHeader() error {
+	err := xdr.Write(w.writer, &w.req.xid)
+	if err != nil {
+		return err
+	}
+	respType := uint32(1)
+	err = xdr.Write(w.writer, &respType)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func (w *response) writeHeader(code ResponseCode) error {
+	if w.responded {
+		return ErrAlreadySent
+	}
+	w.responded = true
+	if err := w.writeXdrHeader(); err != nil {
+		return err
+	}
+
+	status := rpc.MsgAccepted
+	if code == ResponseCodeAuthError || code == ResponseCodeRPCMismatch {
+		status = rpc.MsgDenied
+	}
+
+	err := xdr.Write(w.writer, &status)
+	if err != nil {
+		return err
+	}
+
+	if status == rpc.MsgAccepted {
+		// Write opaque_auth header.
+		err = xdr.Write(w.writer, &rpc.AuthNull)
+		if err != nil {
+			return err
+		}
+	}
+
+	return xdr.Write(w.writer, &code)
+}
+
+// Write a response to an xdr message
+func (w *response) Write(dat []byte) error {
+	if !w.responded {
+		if err := w.writeHeader(ResponseCodeSuccess); err != nil {
+			return err
+		}
+	}
+
+	acc := 0
+	for acc < len(dat) {
+		n, err := w.writer.Write(dat[acc:])
+		if err != nil {
+			return err
+		}
+		acc += n
+	}
+	return nil
+}
+
+// drain reads the rest of the request frame if not consumed by the handler.
+func (w *response) drain(ctx context.Context) error {
+	if reader, ok := w.req.Body.(*io.LimitedReader); ok {
+		if reader.N == 0 {
+			return nil
+		}
+		// todo: wrap body in a context reader.
+		_, err := io.CopyN(io.Discard, w.req.Body, reader.N)
+		if err == nil || err == io.EOF {
+			return nil
+		}
+		return err
+	}
+	return io.ErrUnexpectedEOF
+}
+
+func (w *response) finish(ctx context.Context) error {
+	select {
+	case w.conn.writeSerializer <- w.writer.Bytes():
+		return nil
+	case <-ctx.Done():
+		return ctx.Err()
+	}
+}
+
+func (c *conn) readRequestHeader(ctx context.Context, reader *bufio.Reader) (w *response, err error) {
+	fragment, err := xdr.ReadUint32(reader)
+	if err != nil {
+		if xdrErr, ok := err.(*xdr2.UnmarshalError); ok {
+			if xdrErr.Err == io.EOF {
+				return nil, io.EOF
+			}
+		}
+		return nil, err
+	}
+	if fragment&(1<<31) == 0 {
+		Log.Warnf("Warning: haven't implemented fragment reconstruction.\n")
+		return nil, ErrInputInvalid
+	}
+	reqLen := fragment - uint32(1<<31)
+	if reqLen < 40 {
+		return nil, ErrInputInvalid
+	}
+
+	r := io.LimitedReader{R: reader, N: int64(reqLen)}
+
+	xid, err := xdr.ReadUint32(&r)
+	if err != nil {
+		return nil, err
+	}
+	reqType, err := xdr.ReadUint32(&r)
+	if err != nil {
+		return nil, err
+	}
+	if reqType != 0 { // 0 = request, 1 = response
+		return nil, ErrInputInvalid
+	}
+
+	req := request{
+		xid,
+		rpc.Header{},
+		&r,
+	}
+	if err = xdr.Read(&r, &req.Header); err != nil {
+		return nil, err
+	}
+
+	w = &response{
+		conn:     c,
+		req:      &req,
+		errorFmt: basicErrorFormatter,
+		// TODO: use a pool for these.
+		writer: bytes.NewBuffer([]byte{}),
+	}
+	return w, nil
+}

server/pkg/go-nfs/errors.go

@@ -0,0 +1,230 @@
+package nfs
+
+import (
+	"encoding"
+	"encoding/binary"
+	"errors"
+	"fmt"
+)
+
+// RPCError provides the error interface for errors thrown by
+// procedures to be transmitted over the XDR RPC channel
+type RPCError interface {
+	// An RPCError is an `error` with this method
+	Error() string
+	// Code is the RPC Response code to send
+	Code() ResponseCode
+	// BinaryMarshaler is the on-wire representation of this error
+	encoding.BinaryMarshaler
+}
+
+// AuthStat is an enumeration of why authentication ahs failed
+type AuthStat uint32
+
+// AuthStat Codes
+const (
+	AuthStatOK AuthStat = iota
+	AuthStatBadCred
+	AuthStatRejectedCred
+	AuthStatBadVerifier
+	AuthStatRejectedVerfier
+	AuthStatTooWeak
+	AuthStatInvalidResponse
+	AuthStatFailed
+	AuthStatKerbGeneric
+	AuthStatTimeExpire
+	AuthStatTktFile
+	AuthStatDecode
+	AuthStatNetAddr
+	AuthStatRPCGSSCredProblem
+	AuthStatRPCGSSCTXProblem
+)
+
+// AuthError is an RPCError
+type AuthError struct {
+	AuthStat
+}
+
+// Code for AuthErrors is ResponseCodeAuthError
+func (a *AuthError) Code() ResponseCode {
+	return ResponseCodeAuthError
+}
+
+// Error is a textual representaiton of the auth error. From the RFC
+func (a *AuthError) Error() string {
+	switch a.AuthStat {
+	case AuthStatOK:
+		return "Auth Status: OK"
+	case AuthStatBadCred:
+		return "Auth Status: bad credential"
+	case AuthStatRejectedCred:
+		return "Auth Status: client must begin new session"
+	case AuthStatBadVerifier:
+		return "Auth Status: bad verifier"
+	case AuthStatRejectedVerfier:
+		return "Auth Status: verifier expired or replayed"
+	case AuthStatTooWeak:
+		return "Auth Status: rejected for security reasons"
+	case AuthStatInvalidResponse:
+		return "Auth Status: bogus response verifier"
+	case AuthStatFailed:
+		return "Auth Status: reason unknown"
+	case AuthStatKerbGeneric:
+		return "Auth Status: kerberos generic error"
+	case AuthStatTimeExpire:
+		return "Auth Status: time of credential expired"
+	case AuthStatTktFile:
+		return "Auth Status: problem with ticket file"
+	case AuthStatDecode:
+		return "Auth Status: can't decode authenticator"
+	case AuthStatNetAddr:
+		return "Auth Status: wrong net address in ticket"
+	case AuthStatRPCGSSCredProblem:
+		return "Auth Status: no credentials for user"
+	case AuthStatRPCGSSCTXProblem:
+		return "Auth Status: problem with context"
+	}
+	return "Auth Status: Unknown"
+}
+
+// MarshalBinary sends the specific auth status
+func (a *AuthError) MarshalBinary() (data []byte, err error) {
+	var resp [4]byte
+	binary.LittleEndian.PutUint32(resp[:], uint32(a.AuthStat))
+	return resp[:], nil
+}
+
+// RPCMismatchError is an RPCError
+type RPCMismatchError struct {
+	Low  uint32
+	High uint32
+}
+
+// Code for RPCMismatchError is ResponseCodeRPCMismatch
+func (r *RPCMismatchError) Code() ResponseCode {
+	return ResponseCodeRPCMismatch
+}
+
+func (r *RPCMismatchError) Error() string {
+	return fmt.Sprintf("RPC Mismatch: Expected version between %d and %d.", r.Low, r.High)
+}
+
+// MarshalBinary sends the specific rpc mismatch range
+func (r *RPCMismatchError) MarshalBinary() (data []byte, err error) {
+	var resp [8]byte
+	binary.LittleEndian.PutUint32(resp[0:4], uint32(r.Low))
+	binary.LittleEndian.PutUint32(resp[4:8], uint32(r.High))
+	return resp[:], nil
+}
+
+// ResponseCodeProcUnavailableError is an RPCError
+type ResponseCodeProcUnavailableError struct {
+}
+
+// Code for ResponseCodeProcUnavailableError
+func (r *ResponseCodeProcUnavailableError) Code() ResponseCode {
+	return ResponseCodeProcUnavailable
+}
+
+func (r *ResponseCodeProcUnavailableError) Error() string {
+	return "The requested procedure is unexported"
+}
+
+// MarshalBinary - this error has no associated body
+func (r *ResponseCodeProcUnavailableError) MarshalBinary() (data []byte, err error) {
+	return []byte{}, nil
+}
+
+// ResponseCodeSystemError is an RPCError
+type ResponseCodeSystemError struct {
+}
+
+// Code for ResponseCodeSystemError
+func (r *ResponseCodeSystemError) Code() ResponseCode {
+	return ResponseCodeSystemErr
+}
+
+func (r *ResponseCodeSystemError) Error() string {
+	return "memory allocation failure"
+}
+
+// MarshalBinary - this error has no associated body
+func (r *ResponseCodeSystemError) MarshalBinary() (data []byte, err error) {
+	return []byte{}, nil
+}
+
+// basicErrorFormatter is the default error handler for response errors.
+// if the error is already formatted, it is directly written. Otherwise,
+// ResponseCodeSystemError is sent to the client.
+func basicErrorFormatter(err error) RPCError {
+	var rpcErr RPCError
+	if errors.As(err, &rpcErr) {
+		return rpcErr
+	}
+	return &ResponseCodeSystemError{}
+}
+
+// NFSStatusError represents an error at the NFS level.
+type NFSStatusError struct {
+	NFSStatus
+	WrappedErr error
+}
+
+// Error is The wrapped error
+func (s *NFSStatusError) Error() string {
+	message := s.NFSStatus.String()
+	if s.WrappedErr != nil {
+		message = fmt.Sprintf("%s: %v", message, s.WrappedErr)
+	}
+	return message
+}
+
+// Code for NFS issues are successful RPC responses
+func (s *NFSStatusError) Code() ResponseCode {
+	return ResponseCodeSuccess
+}
+
+// MarshalBinary - The binary form of the code.
+func (s *NFSStatusError) MarshalBinary() (data []byte, err error) {
+	var resp [4]byte
+	binary.BigEndian.PutUint32(resp[0:4], uint32(s.NFSStatus))
+	return resp[:], nil
+}
+
+// Unwrap unpacks wrapped errors
+func (s *NFSStatusError) Unwrap() error {
+	return s.WrappedErr
+}
+
+// StatusErrorWithBody is an NFS error with a payload.
+type StatusErrorWithBody struct {
+	NFSStatusError
+	Body []byte
+}
+
+// MarshalBinary provides the wire format of the error response
+func (s *StatusErrorWithBody) MarshalBinary() (data []byte, err error) {
+	head, err := s.NFSStatusError.MarshalBinary()
+	return append(head, s.Body...), err
+}
+
+// errFormatterWithBody appends a provided body to errors
+func errFormatterWithBody(body []byte) func(err error) RPCError {
+	return func(err error) RPCError {
+		if nerr, ok := err.(*NFSStatusError); ok {
+			return &StatusErrorWithBody{*nerr, body[:]}
+		}
+		var rErr RPCError
+		if errors.As(err, &rErr) {
+			return rErr
+		}
+		return &ResponseCodeSystemError{}
+	}
+}
+
+var (
+	opAttrErrorBody       = [4]byte{}
+	opAttrErrorFormatter  = errFormatterWithBody(opAttrErrorBody[:])
+	wccDataErrorBody      = [8]byte{}
+	wccDataErrorFormatter = errFormatterWithBody(wccDataErrorBody[:])
+)

server/pkg/go-nfs/example/helloworld/main.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"net"
+
+	"github.com/go-git/go-billy/v5"
+	"github.com/go-git/go-billy/v5/memfs"
+
+	nfs "git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs"
+	"git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs/helpers"
+	nfshelper "git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs/helpers"
+)
+
+// ROFS is an intercepter for the filesystem indicating it should
+// be read only. The undelrying billy.Memfs indicates it supports
+// writing, but does not in implement billy.Change to support
+// modification of permissions / modTimes, and as such cannot be
+// used as RW system.
+type ROFS struct {
+	nfs.Filesystem
+}
+
+// Capabilities exports the filesystem as readonly
+func (ROFS) Capabilities() billy.Capability {
+	return billy.ReadCapability | billy.SeekCapability
+}
+
+func main() {
+	ctx := context.Background()
+
+	listener, err := net.Listen("tcp", ":0")
+	if err != nil {
+		fmt.Printf("Failed to listen: %v\n", err)
+		return
+	}
+	fmt.Printf("Server running at %s\n", listener.Addr())
+
+	mem := helpers.WrapBillyFS(memfs.New())
+	f, err := mem.Create(ctx, "hello.txt")
+	if err != nil {
+		fmt.Printf("Failed to create file: %v\n", err)
+		return
+	}
+	_, _ = f.Write(ctx, []byte("hello world"))
+	_ = f.Close(ctx)
+
+	handler := nfshelper.NewNullAuthHandler(ROFS{mem})
+	cacheHelper := nfshelper.NewCachingHandler(handler, 1024)
+	fmt.Printf("%v", nfs.Serve(listener, cacheHelper))
+}

server/pkg/go-nfs/example/osnfs/changeos.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"os"
+	"time"
+
+	"github.com/go-git/go-billy/v5"
+)
+
+// NewChangeOSFS wraps billy osfs to add the change interface
+func NewChangeOSFS(fs billy.Filesystem) billy.Filesystem {
+	return COS{fs}
+}
+
+// COS or OSFS + Change wraps a billy.FS to not fail the `Change` interface.
+type COS struct {
+	billy.Filesystem
+}
+
+// Chmod changes mode
+func (fs COS) Chmod(name string, mode os.FileMode) error {
+	return os.Chmod(fs.Join(fs.Root(), name), mode)
+}
+
+// Lchown changes ownership
+func (fs COS) Lchown(name string, uid, gid int) error {
+	return os.Lchown(fs.Join(fs.Root(), name), uid, gid)
+}
+
+// Chown changes ownership
+func (fs COS) Chown(name string, uid, gid int) error {
+	return os.Chown(fs.Join(fs.Root(), name), uid, gid)
+}
+
+// Chtimes changes access time
+func (fs COS) Chtimes(name string, atime time.Time, mtime time.Time) error {
+	return os.Chtimes(fs.Join(fs.Root(), name), atime, mtime)
+}

server/pkg/go-nfs/example/osnfs/changeos_unix.go

@@ -0,0 +1,28 @@
+//go:build darwin || dragonfly || freebsd || linux || nacl || netbsd || openbsd || solaris
+
+package main
+
+import (
+	"golang.org/x/sys/unix"
+)
+
+func (fs COS) Mknod(path string, mode uint32, major uint32, minor uint32) error {
+	dev := unix.Mkdev(major, minor)
+	return unix.Mknod(fs.Join(fs.Root(), path), mode, int(dev))
+}
+
+func (fs COS) Mkfifo(path string, mode uint32) error {
+	return unix.Mkfifo(fs.Join(fs.Root(), path), mode)
+}
+
+func (fs COS) Link(path string, link string) error {
+	return unix.Link(fs.Join(fs.Root(), path), link)
+}
+
+func (fs COS) Socket(path string) error {
+	fd, err := unix.Socket(unix.AF_UNIX, unix.SOCK_STREAM, 0)
+	if err != nil {
+		return err
+	}
+	return unix.Bind(fd, &unix.SockaddrUnix{Name: fs.Join(fs.Root(), path)})
+}

server/pkg/go-nfs/example/osnfs/main.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+	"fmt"
+	"net"
+	"os"
+
+	nfs "git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs"
+	"git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs/helpers"
+	nfshelper "git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs/helpers"
+	osfs "github.com/go-git/go-billy/v5/osfs"
+)
+
+func main() {
+	port := ""
+	if len(os.Args) < 2 {
+		fmt.Printf("Usage: osnfs </path/to/folder> [port]\n")
+		return
+	} else if len(os.Args) == 3 {
+		port = os.Args[2]
+	}
+
+	listener, err := net.Listen("tcp", ":"+port)
+	if err != nil {
+		fmt.Printf("Failed to listen: %v\n", err)
+		return
+	}
+	fmt.Printf("osnfs server running at %s\n", listener.Addr())
+
+	bfs := osfs.New(os.Args[1])
+	bfsPlusChange := helpers.WrapBillyFS(NewChangeOSFS(bfs))
+
+	handler := nfshelper.NewNullAuthHandler(bfsPlusChange)
+	cacheHelper := nfshelper.NewCachingHandler(handler, 1024)
+	fmt.Printf("%v", nfs.Serve(listener, cacheHelper))
+}

server/pkg/go-nfs/example/osview/main.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"fmt"
+	"net"
+	"os"
+
+	"github.com/willscott/memphis"
+
+	nfs "git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs"
+	"git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs/helpers"
+	nfshelper "git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs/helpers"
+)
+
+func main() {
+	port := ""
+	if len(os.Args) < 2 {
+		fmt.Printf("Usage: osview </path/to/folder> [port]\n")
+		return
+	} else if len(os.Args) == 3 {
+		port = os.Args[2]
+	}
+
+	listener, err := net.Listen("tcp", ":"+port)
+	if err != nil {
+		fmt.Printf("Failed to listen: %v\n", err)
+		return
+	}
+	fmt.Printf("Server running at %s\n", listener.Addr())
+
+	fs := memphis.FromOS(os.Args[1])
+	bfs := helpers.WrapBillyFS(fs.AsBillyFS(0, 0))
+
+	handler := nfshelper.NewNullAuthHandler(bfs)
+	cacheHelper := nfshelper.NewCachingHandler(handler, 1024)
+	fmt.Printf("%v", nfs.Serve(listener, cacheHelper))
+}

server/pkg/go-nfs/file.go

@@ -0,0 +1,379 @@
+package nfs
+
+import (
+	"context"
+	"errors"
+	"hash/fnv"
+	"io"
+	"math"
+	"os"
+	"time"
+
+	"git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs/file"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+// FileAttribute holds metadata about a filesystem object
+type FileAttribute struct {
+	Type                FileType
+	FileMode            uint32
+	Nlink               uint32
+	UID                 uint32
+	GID                 uint32
+	Filesize            uint64
+	Used                uint64
+	SpecData            [2]uint32
+	FSID                uint64
+	Fileid              uint64
+	Atime, Mtime, Ctime FileTime
+}
+
+// FileType represents a NFS File Type
+type FileType uint32
+
+// Enumeration of NFS FileTypes
+const (
+	FileTypeRegular FileType = iota + 1
+	FileTypeDirectory
+	FileTypeBlock
+	FileTypeCharacter
+	FileTypeLink
+	FileTypeSocket
+	FileTypeFIFO
+)
+
+func (f FileType) String() string {
+	switch f {
+	case FileTypeRegular:
+		return "Regular"
+	case FileTypeDirectory:
+		return "Directory"
+	case FileTypeBlock:
+		return "Block Device"
+	case FileTypeCharacter:
+		return "Character Device"
+	case FileTypeLink:
+		return "Symbolic Link"
+	case FileTypeSocket:
+		return "Socket"
+	case FileTypeFIFO:
+		return "FIFO"
+	default:
+		return "Unknown"
+	}
+}
+
+// Mode provides the OS interpreted mode of the file attributes
+func (f *FileAttribute) Mode() os.FileMode {
+	return os.FileMode(f.FileMode)
+}
+
+// FileCacheAttribute is the subset of FileAttribute used by
+// wcc_attr
+type FileCacheAttribute struct {
+	Filesize     uint64
+	Mtime, Ctime FileTime
+}
+
+// AsCache provides the wcc view of the file attributes
+func (f FileAttribute) AsCache() *FileCacheAttribute {
+	wcc := FileCacheAttribute{
+		Filesize: f.Filesize,
+		Mtime:    f.Mtime,
+		Ctime:    f.Ctime,
+	}
+	return &wcc
+}
+
+// ToFileAttribute creates an NFS fattr3 struct from an OS.FileInfo
+func ToFileAttribute(info os.FileInfo, filePath string) *FileAttribute {
+	f := FileAttribute{}
+
+	m := info.Mode()
+	f.FileMode = uint32(m)
+	if info.IsDir() {
+		f.Type = FileTypeDirectory
+	} else if m&os.ModeSymlink != 0 {
+		f.Type = FileTypeLink
+	} else if m&os.ModeCharDevice != 0 {
+		f.Type = FileTypeCharacter
+	} else if m&os.ModeDevice != 0 {
+		f.Type = FileTypeBlock
+	} else if m&os.ModeSocket != 0 {
+		f.Type = FileTypeSocket
+	} else if m&os.ModeNamedPipe != 0 {
+		f.Type = FileTypeFIFO
+	} else {
+		f.Type = FileTypeRegular
+	}
+	// The number of hard links to the file.
+	f.Nlink = 1
+
+	if a := file.GetInfo(info); a != nil {
+		f.Nlink = a.Nlink
+		f.UID = a.UID
+		f.GID = a.GID
+		f.SpecData = [2]uint32{a.Major, a.Minor}
+		f.Fileid = a.Fileid
+	} else {
+		hasher := fnv.New64()
+		_, _ = hasher.Write([]byte(filePath))
+		f.Fileid = hasher.Sum64()
+	}
+
+	f.Filesize = uint64(info.Size())
+	f.Used = uint64(info.Size())
+	f.Atime = ToNFSTime(info.ModTime())
+	f.Mtime = f.Atime
+	f.Ctime = f.Atime
+	return &f
+}
+
+// tryStat attempts to create a FileAttribute from a path.
+func tryStat(ctx context.Context, fs Filesystem, path []string) *FileAttribute {
+	fullPath := fs.Join(path...)
+	attrs, err := fs.Lstat(ctx, fullPath)
+	if err != nil || attrs == nil {
+		Log.Errorf("err loading attrs for %s: %v", fs.Join(path...), err)
+		return nil
+	}
+	return ToFileAttribute(attrs, fullPath)
+}
+
+// WriteWcc writes the `wcc_data` representation of an object.
+func WriteWcc(writer io.Writer, pre *FileCacheAttribute, post *FileAttribute) error {
+	if pre == nil {
+		if err := xdr.Write(writer, uint32(0)); err != nil {
+			return err
+		}
+	} else {
+		if err := xdr.Write(writer, uint32(1)); err != nil {
+			return err
+		}
+		if err := xdr.Write(writer, *pre); err != nil {
+			return err
+		}
+	}
+	if post == nil {
+		if err := xdr.Write(writer, uint32(0)); err != nil {
+			return err
+		}
+	} else {
+		if err := xdr.Write(writer, uint32(1)); err != nil {
+			return err
+		}
+		if err := xdr.Write(writer, *post); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// WritePostOpAttrs writes the `post_op_attr` representation of a files attributes
+func WritePostOpAttrs(writer io.Writer, post *FileAttribute) error {
+	if post == nil {
+		if err := xdr.Write(writer, uint32(0)); err != nil {
+			return err
+		}
+	} else {
+		if err := xdr.Write(writer, uint32(1)); err != nil {
+			return err
+		}
+		if err := xdr.Write(writer, *post); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// SetFileAttributes represents a command to update some metadata
+// about a file.
+type SetFileAttributes struct {
+	SetMode  *uint32
+	SetUID   *uint32
+	SetGID   *uint32
+	SetSize  *uint64
+	SetAtime *time.Time
+	SetMtime *time.Time
+}
+
+// Apply uses a `Change` implementation to set defined attributes on a
+// provided file.
+func (s *SetFileAttributes) Apply(ctx context.Context, changer Change, fs Filesystem, file string) error {
+	curOS, err := fs.Lstat(ctx, file)
+	if errors.Is(err, os.ErrNotExist) {
+		return &NFSStatusError{NFSStatusNoEnt, os.ErrNotExist}
+	} else if errors.Is(err, os.ErrPermission) {
+		return &NFSStatusError{NFSStatusAccess, os.ErrPermission}
+	} else if err != nil {
+		return nil
+	}
+	curr := ToFileAttribute(curOS, file)
+
+	if s.SetMode != nil {
+		mode := os.FileMode(*s.SetMode) & os.ModePerm
+		if mode != curr.Mode().Perm() {
+			if changer == nil {
+				return &NFSStatusError{NFSStatusNotSupp, os.ErrPermission}
+			}
+			if err := changer.Chmod(ctx, file, mode); err != nil {
+				if errors.Is(err, os.ErrPermission) {
+					return &NFSStatusError{NFSStatusAccess, os.ErrPermission}
+				}
+				return err
+			}
+		}
+	}
+	if s.SetUID != nil || s.SetGID != nil {
+		euid := curr.UID
+		if s.SetUID != nil {
+			euid = *s.SetUID
+		}
+		egid := curr.GID
+		if s.SetGID != nil {
+			egid = *s.SetGID
+		}
+		if euid != curr.UID || egid != curr.GID {
+			if changer == nil {
+				return &NFSStatusError{NFSStatusNotSupp, os.ErrPermission}
+			}
+			if err := changer.Lchown(ctx, file, int(euid), int(egid)); err != nil {
+				if errors.Is(err, os.ErrPermission) {
+					return &NFSStatusError{NFSStatusAccess, os.ErrPermission}
+				}
+				return err
+			}
+		}
+	}
+	if s.SetSize != nil {
+		if curr.Mode()&os.ModeSymlink != 0 {
+			return &NFSStatusError{NFSStatusNotSupp, os.ErrInvalid}
+		}
+		fp, err := fs.OpenFile(ctx, file, os.O_WRONLY|os.O_EXCL, 0)
+		if errors.Is(err, os.ErrPermission) {
+			return &NFSStatusError{NFSStatusAccess, err}
+		} else if err != nil {
+			return err
+		}
+		defer fp.Close(ctx)
+
+		if *s.SetSize > math.MaxInt64 {
+			return &NFSStatusError{NFSStatusInval, os.ErrInvalid}
+		}
+		if err := fp.Truncate(ctx, int64(*s.SetSize)); err != nil {
+			return err
+		}
+		if err := fp.Close(ctx); err != nil {
+			return err
+		}
+	}
+
+	if s.SetAtime != nil || s.SetMtime != nil {
+		atime := curr.Atime.Native()
+		if s.SetAtime != nil {
+			atime = s.SetAtime
+		}
+		mtime := curr.Mtime.Native()
+		if s.SetMtime != nil {
+			mtime = s.SetMtime
+		}
+		if atime != curr.Atime.Native() || mtime != curr.Mtime.Native() {
+			if changer == nil {
+				return &NFSStatusError{NFSStatusNotSupp, os.ErrPermission}
+			}
+			if err := changer.Chtimes(ctx, file, *atime, *mtime); err != nil {
+				if errors.Is(err, os.ErrPermission) {
+					return &NFSStatusError{NFSStatusAccess, err}
+				}
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// Mode returns a mode if specified or the provided default mode.
+func (s *SetFileAttributes) Mode(def os.FileMode) os.FileMode {
+	if s.SetMode != nil {
+		return os.FileMode(*s.SetMode) & os.ModePerm
+	}
+	return def
+}
+
+// ReadSetFileAttributes reads an sattr3 xdr stream into a go struct.
+func ReadSetFileAttributes(r io.Reader) (*SetFileAttributes, error) {
+	attrs := SetFileAttributes{}
+	hasMode, err := xdr.ReadUint32(r)
+	if err != nil {
+		return nil, err
+	}
+	if hasMode != 0 {
+		mode, err := xdr.ReadUint32(r)
+		if err != nil {
+			return nil, err
+		}
+		attrs.SetMode = &mode
+	}
+	hasUID, err := xdr.ReadUint32(r)
+	if err != nil {
+		return nil, err
+	}
+	if hasUID != 0 {
+		uid, err := xdr.ReadUint32(r)
+		if err != nil {
+			return nil, err
+		}
+		attrs.SetUID = &uid
+	}
+	hasGID, err := xdr.ReadUint32(r)
+	if err != nil {
+		return nil, err
+	}
+	if hasGID != 0 {
+		gid, err := xdr.ReadUint32(r)
+		if err != nil {
+			return nil, err
+		}
+		attrs.SetGID = &gid
+	}
+	hasSize, err := xdr.ReadUint32(r)
+	if err != nil {
+		return nil, err
+	}
+	if hasSize != 0 {
+		var size uint64
+		attrs.SetSize = &size
+		if err := xdr.Read(r, &size); err != nil {
+			return nil, err
+		}
+	}
+	aTime, err := xdr.ReadUint32(r)
+	if err != nil {
+		return nil, err
+	}
+	if aTime == 1 {
+		now := time.Now()
+		attrs.SetAtime = &now
+	} else if aTime == 2 {
+		t := FileTime{}
+		if err := xdr.Read(r, &t); err != nil {
+			return nil, err
+		}
+		attrs.SetAtime = t.Native()
+	}
+	mTime, err := xdr.ReadUint32(r)
+	if err != nil {
+		return nil, err
+	}
+	if mTime == 1 {
+		now := time.Now()
+		attrs.SetMtime = &now
+	} else if mTime == 2 {
+		t := FileTime{}
+		if err := xdr.Read(r, &t); err != nil {
+			return nil, err
+		}
+		attrs.SetMtime = t.Native()
+	}
+	return &attrs, nil
+}

server/pkg/go-nfs/file/file.go

@@ -0,0 +1,17 @@
+package file
+
+import "os"
+
+type FileInfo struct {
+	Nlink  uint32
+	UID    uint32
+	GID    uint32
+	Major  uint32
+	Minor  uint32
+	Fileid uint64
+}
+
+// GetInfo extracts some non-standardized items from the result of a Stat call.
+func GetInfo(fi os.FileInfo) *FileInfo {
+	return getInfo(fi)
+}

server/pkg/go-nfs/file/file_unix.go

@@ -0,0 +1,24 @@
+//go:build darwin || dragonfly || freebsd || linux || nacl || netbsd || openbsd || solaris
+
+package file
+
+import (
+	"os"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+func getInfo(info os.FileInfo) *FileInfo {
+	fi := &FileInfo{}
+	if s, ok := info.Sys().(*syscall.Stat_t); ok {
+		fi.Nlink = uint32(s.Nlink)
+		fi.UID = s.Uid
+		fi.GID = s.Gid
+		fi.Major = unix.Major(uint64(s.Rdev))
+		fi.Minor = unix.Minor(uint64(s.Rdev))
+		fi.Fileid = s.Ino
+		return fi
+	}
+	return nil
+}

server/pkg/go-nfs/file/file_windows.go

@@ -0,0 +1,12 @@
+//go:build windows
+
+package file
+
+import "os"
+
+func getInfo(info os.FileInfo) *FileInfo {
+	// https://godoc.org/golang.org/x/sys/windows#GetFileInformationByHandle
+	// can be potentially used to populate Nlink
+
+	return nil
+}

server/pkg/go-nfs/filesystem.go

@@ -0,0 +1,97 @@
+package nfs
+
+import (
+	"context"
+	"io"
+	"os"
+	"time"
+
+	"github.com/royalcat/ctxio"
+)
+
+// FSStat returns metadata about a file system
+type FSStat struct {
+	TotalSize      uint64
+	FreeSize       uint64
+	AvailableSize  uint64
+	TotalFiles     uint64
+	FreeFiles      uint64
+	AvailableFiles uint64
+	// CacheHint is called "invarsec" in the nfs standard
+	CacheHint time.Duration
+}
+
+type Filesystem interface {
+	// Create creates the named file with mode 0666 (before umask), truncating
+	// it if it already exists. If successful, methods on the returned File can
+	// be used for I/O; the associated file descriptor has mode O_RDWR.
+	Create(ctx context.Context, filename string) (File, error)
+	// OpenFile is the generalized open call; most users will use Open or Create
+	// instead. It opens the named file with specified flag (O_RDONLY etc.) and
+	// perm, (0666 etc.) if applicable. If successful, methods on the returned
+	// File can be used for I/O.
+	OpenFile(ctx context.Context, filename string, flag int, perm os.FileMode) (File, error)
+	// Stat returns a FileInfo describing the named file.
+	Stat(ctx context.Context, filename string) (os.FileInfo, error)
+	// Rename renames (moves) oldpath to newpath. If newpath already exists and
+	// is not a directory, Rename replaces it. OS-specific restrictions may
+	// apply when oldpath and newpath are in different directories.
+	Rename(ctx context.Context, oldpath, newpath string) error
+	// Remove removes the named file or directory.
+	Remove(ctx context.Context, filename string) error
+	// Join joins any number of path elements into a single path, adding a
+	// Separator if necessary. Join calls filepath.Clean on the result; in
+	// particular, all empty strings are ignored. On Windows, the result is a
+	// UNC path if and only if the first path element is a UNC path.
+	Join(elem ...string) string
+
+	// ReadDir reads the directory named by d(irname and returns a list of
+	// directory entries sorted by filename.
+	ReadDir(ctx context.Context, path string) ([]os.FileInfo, error)
+	// MkdirAll creates a directory named path, along with any necessary
+	// parents, and returns nil, or else returns an error. The permission bits
+	// perm are used for all directories that MkdirAll creates. If path is/
+	// already a directory, MkdirAll does nothing and returns nil.
+	MkdirAll(ctx context.Context, filename string, perm os.FileMode) error
+
+	// Lstat returns a FileInfo describing the named file. If the file is a
+	// symbolic link, the returned FileInfo describes the symbolic link. Lstat
+	// makes no attempt to follow the link.
+	Lstat(ctx context.Context, filename string) (os.FileInfo, error)
+	// Symlink creates a symbolic-link from link to target. target may be an
+	// absolute or relative path, and need not refer to an existing node.
+	// Parent directories of link are created as necessary.
+	Symlink(ctx context.Context, target, link string) error
+	// Readlink returns the target path of link.
+	Readlink(ctx context.Context, link string) (string, error)
+}
+
+type File interface {
+	// Name returns the name of the file as presented to Open.
+	Name() string
+	ctxio.Writer
+	// ctxio.Reader
+	ctxio.ReaderAt
+	io.Seeker
+	ctxio.Closer
+
+	// Truncate the file.
+	Truncate(ctx context.Context, size int64) error
+}
+
+// Change abstract the FileInfo change related operations in a storage-agnostic
+// interface as an extension to the Basic interface
+type Change interface {
+	// Chmod changes the mode of the named file to mode. If the file is a
+	// symbolic link, it changes the mode of the link's target.
+	Chmod(ctx context.Context, name string, mode os.FileMode) error
+	// Lchown changes the numeric uid and gid of the named file. If the file is
+	// a symbolic link, it changes the uid and gid of the link itself.
+	Lchown(ctx context.Context, name string, uid, gid int) error
+	// Chtimes changes the access and modification times of the named file,
+	// similar to the Unix utime() or utimes() functions.
+	//
+	// The underlying filesystem may truncate or round the values to a less
+	// precise time unit.
+	Chtimes(ctx context.Context, name string, atime time.Time, mtime time.Time) error
+}

server/pkg/go-nfs/handler.go

@@ -0,0 +1,52 @@
+package nfs
+
+import (
+	"context"
+	"io/fs"
+	"net"
+
+	"git.kmsign.ru/royalcat/tstor/server/pkg/ctxbilly"
+)
+
+// Handler represents the interface of the file system / vfs being exposed over NFS
+type Handler interface {
+	// Required methods
+
+	Mount(context.Context, net.Conn, MountRequest) (MountStatus, Filesystem, []AuthFlavor)
+
+	// Change can return 'nil' if filesystem is read-only
+	// If the returned value can be cast to `UnixChange`, mknod and link RPCs will be available.
+	Change(Filesystem) Change
+
+	// Optional methods - generic helpers or trivial implementations can be sufficient depending on use case.
+
+	// Fill in information about a file system's free space.
+	FSStat(context.Context, Filesystem, *FSStat) error
+
+	// represent file objects as opaque references
+	// Can be safely implemented via helpers/cachinghandler.
+	ToHandle(ctx context.Context, fs Filesystem, path []string) []byte
+	FromHandle(ctx context.Context, fh []byte) (Filesystem, []string, error)
+	InvalidateHandle(context.Context, Filesystem, []byte) error
+
+	// How many handles can be safely maintained by the handler.
+	HandleLimit() int
+}
+
+// UnixChange extends the billy `Change` interface with support for special files.
+type UnixChange interface {
+	ctxbilly.Change
+	Mknod(ctx context.Context, path string, mode uint32, major uint32, minor uint32) error
+	Mkfifo(ctx context.Context, path string, mode uint32) error
+	Socket(ctx context.Context, path string) error
+	Link(ctx context.Context, path string, link string) error
+}
+
+// CachingHandler represents the optional caching work that a user may wish to over-ride with
+// their own implementations, but which can be otherwise provided through defaults.
+type CachingHandler interface {
+	VerifierFor(path string, contents []fs.FileInfo) uint64
+
+	// fs.FileInfo needs to be sorted by Name(), nil in case of a cache-miss
+	DataForVerifier(path string, verifier uint64) []fs.FileInfo
+}

server/pkg/go-nfs/helpers/billlyfs.go

@@ -0,0 +1,157 @@
+package helpers
+
+import (
+	"context"
+	"io/fs"
+
+	"git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs"
+	"github.com/go-git/go-billy/v5"
+)
+
+func WrapBillyFS(bf billy.Filesystem) nfs.Filesystem {
+	return &wrapFS{
+		Filesystem: bf,
+	}
+}
+
+type wrapFS struct {
+	billy.Filesystem
+}
+
+var _ nfs.Filesystem = (*wrapFS)(nil)
+
+// Create implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Create of MemFS.Filesystem.
+func (m *wrapFS) Create(ctx context.Context, filename string) (nfs.File, error) {
+	bf, err := m.Filesystem.Create(filename)
+	if err != nil {
+		return nil, err
+	}
+	return &wrapFile{bf}, nil
+}
+
+// Lstat implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Lstat of MemFS.Filesystem.
+func (m *wrapFS) Lstat(ctx context.Context, filename string) (fs.FileInfo, error) {
+	return m.Filesystem.Lstat(filename)
+}
+
+// MkdirAll implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).MkdirAll of MemFS.Filesystem.
+func (m *wrapFS) MkdirAll(ctx context.Context, filename string, perm fs.FileMode) error {
+	return m.Filesystem.MkdirAll(filename, perm)
+}
+
+// Open implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Open of MemFS.Filesystem.
+func (m *wrapFS) Open(ctx context.Context, filename string) (nfs.File, error) {
+	bf, err := m.Filesystem.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+	return WrapFile(bf), nil
+}
+
+// OpenFile implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).OpenFile of MemFS.Filesystem.
+func (m *wrapFS) OpenFile(ctx context.Context, filename string, flag int, perm fs.FileMode) (nfs.File, error) {
+	bf, err := m.Filesystem.OpenFile(filename, flag, perm)
+	if err != nil {
+		return nil, err
+	}
+	return WrapFile(bf), nil
+}
+
+// ReadDir implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).ReadDir of MemFS.Filesystem.
+func (m *wrapFS) ReadDir(ctx context.Context, path string) ([]fs.FileInfo, error) {
+	return m.Filesystem.ReadDir(path)
+}
+
+// Readlink implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Readlink of MemFS.Filesystem.
+func (m *wrapFS) Readlink(ctx context.Context, link string) (string, error) {
+	return m.Filesystem.Readlink(link)
+}
+
+// Remove implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Remove of MemFS.Filesystem.
+func (m *wrapFS) Remove(ctx context.Context, filename string) error {
+	return m.Filesystem.Remove(filename)
+}
+
+// Rename implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Rename of MemFS.Filesystem.
+func (m *wrapFS) Rename(ctx context.Context, oldpath string, newpath string) error {
+	return m.Filesystem.Rename(oldpath, newpath)
+}
+
+// Stat implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Stat of MemFS.Filesystem.
+func (m *wrapFS) Stat(ctx context.Context, filename string) (fs.FileInfo, error) {
+	return m.Filesystem.Stat(filename)
+}
+
+// Symlink implements Filesystem.
+// Subtle: this method shadows the method (Filesystem).Symlink of MemFS.Filesystem.
+func (m *wrapFS) Symlink(ctx context.Context, target string, link string) error {
+	return m.Filesystem.Symlink(target, link)
+}
+
+func WrapFile(bf billy.File) nfs.File {
+	return &wrapFile{File: bf}
+}
+
+type wrapFile struct {
+	billy.File
+}
+
+var _ nfs.File = (*wrapFile)(nil)
+
+// Close implements File.
+// Subtle: this method shadows the method (File).Close of MemFile.File.
+func (m *wrapFile) Close(ctx context.Context) error {
+	return m.File.Close()
+}
+
+// Lock implements File.
+// Subtle: this method shadows the method (File).Lock of MemFile.File.
+func (m *wrapFile) Lock() error {
+	return m.File.Lock()
+}
+
+// Name implements File.
+// Subtle: this method shadows the method (File).Name of MemFile.File.
+func (m *wrapFile) Name() string {
+	return m.File.Name()
+}
+
+// Truncate implements File.
+// Subtle: this method shadows the method (File).Truncate of memFile.File.
+func (m *wrapFile) Truncate(ctx context.Context, size int64) error {
+	return m.File.Truncate(size)
+}
+
+// Read implements File.
+// Subtle: this method shadows the method (File).Read of MemFile.File.
+func (m *wrapFile) Read(ctx context.Context, p []byte) (n int, err error) {
+	return m.File.Read(p)
+}
+
+// ReadAt implements File.
+// Subtle: this method shadows the method (File).ReadAt of MemFile.File.
+func (m *wrapFile) ReadAt(ctx context.Context, p []byte, off int64) (n int, err error) {
+	return m.File.ReadAt(p, off)
+}
+
+// Unlock implements File.
+// Subtle: this method shadows the method (File).Unlock of MemFile.File.
+func (m *wrapFile) Unlock() error {
+	return m.File.Unlock()
+}
+
+// Write implements File.
+// Subtle: this method shadows the method (File).Write of MemFile.File.
+func (m *wrapFile) Write(ctx context.Context, p []byte) (n int, err error) {
+	return m.File.Write(p)
+}

server/pkg/go-nfs/helpers/cachinghandler.go

@@ -0,0 +1,199 @@
+package helpers
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/binary"
+	"io/fs"
+	"reflect"
+
+	"git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs"
+
+	"github.com/google/uuid"
+	lru "github.com/hashicorp/golang-lru/v2"
+)
+
+// NewCachingHandler wraps a handler to provide a basic to/from-file handle cache.
+func NewCachingHandler(h nfs.Handler, limit int) nfs.Handler {
+	return NewCachingHandlerWithVerifierLimit(h, limit, limit)
+}
+
+// NewCachingHandlerWithVerifierLimit provides a basic to/from-file handle cache that can be tuned with a smaller cache of active directory listings.
+func NewCachingHandlerWithVerifierLimit(h nfs.Handler, limit int, verifierLimit int) nfs.Handler {
+	if limit < 2 || verifierLimit < 2 {
+		nfs.Log.Warnf("Caching handler created with insufficient cache to support directory listing", "size", limit, "verifiers", verifierLimit)
+	}
+	cache, _ := lru.New[uuid.UUID, entry](limit)
+	reverseCache := make(map[string][]uuid.UUID)
+	verifiers, _ := lru.New[uint64, verifier](verifierLimit)
+	return &CachingHandler{
+		Handler:         h,
+		activeHandles:   cache,
+		reverseHandles:  reverseCache,
+		activeVerifiers: verifiers,
+		cacheLimit:      limit,
+	}
+}
+
+// CachingHandler implements to/from handle via an LRU cache.
+type CachingHandler struct {
+	nfs.Handler
+	activeHandles   *lru.Cache[uuid.UUID, entry]
+	reverseHandles  map[string][]uuid.UUID
+	activeVerifiers *lru.Cache[uint64, verifier]
+	cacheLimit      int
+}
+
+type entry struct {
+	f nfs.Filesystem
+	p []string
+}
+
+// ToHandle takes a file and represents it with an opaque handle to reference it.
+// In stateless nfs (when it's serving a unix fs) this can be the device + inode
+// but we can generalize with a stateful local cache of handed out IDs.
+func (c *CachingHandler) ToHandle(ctx context.Context, f nfs.Filesystem, path []string) []byte {
+	joinedPath := f.Join(path...)
+
+	if handle := c.searchReverseCache(f, joinedPath); handle != nil {
+		return handle
+	}
+
+	id := uuid.New()
+
+	newPath := make([]string, len(path))
+
+	copy(newPath, path)
+	evictedKey, evictedPath, ok := c.activeHandles.GetOldest()
+	if evicted := c.activeHandles.Add(id, entry{f, newPath}); evicted && ok {
+		rk := evictedPath.f.Join(evictedPath.p...)
+		c.evictReverseCache(rk, evictedKey)
+	}
+
+	if _, ok := c.reverseHandles[joinedPath]; !ok {
+		c.reverseHandles[joinedPath] = []uuid.UUID{}
+	}
+	c.reverseHandles[joinedPath] = append(c.reverseHandles[joinedPath], id)
+	b, _ := id.MarshalBinary()
+
+	return b
+}
+
+// FromHandle converts from an opaque handle to the file it represents
+func (c *CachingHandler) FromHandle(ctx context.Context, fh []byte) (nfs.Filesystem, []string, error) {
+	id, err := uuid.FromBytes(fh)
+	if err != nil {
+		return nil, []string{}, err
+	}
+
+	if f, ok := c.activeHandles.Get(id); ok {
+		for _, k := range c.activeHandles.Keys() {
+			candidate, _ := c.activeHandles.Peek(k)
+			if hasPrefix(f.p, candidate.p) {
+				_, _ = c.activeHandles.Get(k)
+			}
+		}
+		if ok {
+			newP := make([]string, len(f.p))
+			copy(newP, f.p)
+			return f.f, newP, nil
+		}
+	}
+	return nil, []string{}, &nfs.NFSStatusError{NFSStatus: nfs.NFSStatusStale}
+}
+
+func (c *CachingHandler) searchReverseCache(f nfs.Filesystem, path string) []byte {
+	uuids, exists := c.reverseHandles[path]
+
+	if !exists {
+		return nil
+	}
+
+	for _, id := range uuids {
+		if candidate, ok := c.activeHandles.Get(id); ok {
+			if reflect.DeepEqual(candidate.f, f) {
+				return id[:]
+			}
+		}
+	}
+
+	return nil
+}
+
+func (c *CachingHandler) evictReverseCache(path string, handle uuid.UUID) {
+	uuids, exists := c.reverseHandles[path]
+
+	if !exists {
+		return
+	}
+	for i, u := range uuids {
+		if u == handle {
+			uuids = append(uuids[:i], uuids[i+1:]...)
+			c.reverseHandles[path] = uuids
+			return
+		}
+	}
+}
+
+func (c *CachingHandler) InvalidateHandle(ctx context.Context, fs nfs.Filesystem, handle []byte) error {
+	//Remove from cache
+	id, _ := uuid.FromBytes(handle)
+	entry, ok := c.activeHandles.Get(id)
+	if ok {
+		rk := entry.f.Join(entry.p...)
+		c.evictReverseCache(rk, id)
+	}
+	c.activeHandles.Remove(id)
+	return nil
+}
+
+// HandleLimit exports how many file handles can be safely stored by this cache.
+func (c *CachingHandler) HandleLimit() int {
+	return c.cacheLimit
+}
+
+func hasPrefix(path, prefix []string) bool {
+	if len(prefix) > len(path) {
+		return false
+	}
+	for i, e := range prefix {
+		if path[i] != e {
+			return false
+		}
+	}
+	return true
+}
+
+type verifier struct {
+	path     string
+	contents []fs.FileInfo
+}
+
+func hashPathAndContents(path string, contents []fs.FileInfo) uint64 {
+	//calculate a cookie-verifier.
+	vHash := sha256.New()
+
+	// Add the path to avoid collisions of directories with the same content
+	vHash.Write(binary.BigEndian.AppendUint64([]byte{}, uint64(len(path))))
+	vHash.Write([]byte(path))
+
+	for _, c := range contents {
+		vHash.Write([]byte(c.Name())) // Never fails according to the docs
+	}
+
+	verify := vHash.Sum(nil)[0:8]
+	return binary.BigEndian.Uint64(verify)
+}
+
+func (c *CachingHandler) VerifierFor(path string, contents []fs.FileInfo) uint64 {
+	id := hashPathAndContents(path, contents)
+	c.activeVerifiers.Add(id, verifier{path, contents})
+	return id
+}
+
+func (c *CachingHandler) DataForVerifier(path string, id uint64) []fs.FileInfo {
+	if cache, ok := c.activeVerifiers.Get(id); ok {
+		return cache.contents
+	}
+	return nil
+}

server/pkg/go-nfs/helpers/memfs/memfs.go

@@ -0,0 +1,414 @@
+// Package memfs is a variant of "github.com/go-git/go-billy/v5/memfs" with
+// stable mtimes for items.
+package memfs
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"syscall"
+	"time"
+
+	"github.com/go-git/go-billy/v5"
+	"github.com/go-git/go-billy/v5/helper/chroot"
+	"github.com/go-git/go-billy/v5/util"
+)
+
+const separator = filepath.Separator
+
+// Memory a very convenient filesystem based on memory files
+type Memory struct {
+	s *storage
+}
+
+// New returns a new Memory filesystem.
+func New() billy.Filesystem {
+	fs := &Memory{s: newStorage()}
+	return chroot.New(fs, string(separator))
+}
+
+func (fs *Memory) Create(filename string) (billy.File, error) {
+	return fs.OpenFile(filename, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0666)
+}
+
+func (fs *Memory) Open(filename string) (billy.File, error) {
+	return fs.OpenFile(filename, os.O_RDONLY, 0)
+}
+
+func (fs *Memory) OpenFile(filename string, flag int, perm os.FileMode) (billy.File, error) {
+	f, has := fs.s.Get(filename)
+	if !has {
+		if !isCreate(flag) {
+			return nil, os.ErrNotExist
+		}
+
+		var err error
+		f, err = fs.s.New(filename, perm, flag)
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		if isExclusive(flag) {
+			return nil, os.ErrExist
+		}
+
+		if target, isLink := fs.resolveLink(filename, f); isLink {
+			return fs.OpenFile(target, flag, perm)
+		}
+	}
+
+	if f.mode.IsDir() {
+		return nil, fmt.Errorf("cannot open directory: %s", filename)
+	}
+
+	return f.Duplicate(filename, perm, flag), nil
+}
+
+func (fs *Memory) resolveLink(fullpath string, f *file) (target string, isLink bool) {
+	if !isSymlink(f.mode) {
+		return fullpath, false
+	}
+
+	target = string(f.content.bytes)
+	if !isAbs(target) {
+		target = fs.Join(filepath.Dir(fullpath), target)
+	}
+
+	return target, true
+}
+
+// On Windows OS, IsAbs validates if a path is valid based on if stars with a
+// unit (eg.: `C:\`)  to assert that is absolute, but in this mem implementation
+// any path starting by `separator` is also considered absolute.
+func isAbs(path string) bool {
+	return filepath.IsAbs(path) || strings.HasPrefix(path, string(separator))
+}
+
+func (fs *Memory) Stat(filename string) (os.FileInfo, error) {
+	f, has := fs.s.Get(filename)
+	if !has {
+		return nil, os.ErrNotExist
+	}
+
+	fi, _ := f.Stat()
+
+	var err error
+	if target, isLink := fs.resolveLink(filename, f); isLink {
+		fi, err = fs.Stat(target)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	// the name of the file should always the name of the stated file, so we
+	// overwrite the Stat returned from the storage with it, since the
+	// filename may belong to a link.
+	fi.(*fileInfo).name = filepath.Base(filename)
+	return fi, nil
+}
+
+func (fs *Memory) Lstat(filename string) (os.FileInfo, error) {
+	f, has := fs.s.Get(filename)
+	if !has {
+		return nil, os.ErrNotExist
+	}
+
+	return f.Stat()
+}
+
+type ByName []os.FileInfo
+
+func (a ByName) Len() int           { return len(a) }
+func (a ByName) Less(i, j int) bool { return a[i].Name() < a[j].Name() }
+func (a ByName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+
+func (fs *Memory) ReadDir(path string) ([]os.FileInfo, error) {
+	if f, has := fs.s.Get(path); has {
+		if target, isLink := fs.resolveLink(path, f); isLink {
+			return fs.ReadDir(target)
+		}
+	} else {
+		return nil, &os.PathError{Op: "open", Path: path, Err: syscall.ENOENT}
+	}
+
+	var entries []os.FileInfo
+	for _, f := range fs.s.Children(path) {
+		fi, _ := f.Stat()
+		entries = append(entries, fi)
+	}
+
+	sort.Sort(ByName(entries))
+
+	return entries, nil
+}
+
+func (fs *Memory) MkdirAll(path string, perm os.FileMode) error {
+	_, err := fs.s.New(path, perm|os.ModeDir, 0)
+	return err
+}
+
+func (fs *Memory) TempFile(dir, prefix string) (billy.File, error) {
+	return util.TempFile(fs, dir, prefix)
+}
+
+func (fs *Memory) Rename(from, to string) error {
+	return fs.s.Rename(from, to)
+}
+
+func (fs *Memory) Remove(filename string) error {
+	return fs.s.Remove(filename)
+}
+
+func (fs *Memory) Join(elem ...string) string {
+	return filepath.Join(elem...)
+}
+
+func (fs *Memory) Symlink(target, link string) error {
+	_, err := fs.Stat(link)
+	if err == nil {
+		return os.ErrExist
+	}
+
+	if !os.IsNotExist(err) {
+		return err
+	}
+
+	return util.WriteFile(fs, link, []byte(target), 0777|os.ModeSymlink)
+}
+
+func (fs *Memory) Readlink(link string) (string, error) {
+	f, has := fs.s.Get(link)
+	if !has {
+		return "", os.ErrNotExist
+	}
+
+	if !isSymlink(f.mode) {
+		return "", &os.PathError{
+			Op:   "readlink",
+			Path: link,
+			Err:  fmt.Errorf("not a symlink"),
+		}
+	}
+
+	return string(f.content.bytes), nil
+}
+
+// Capabilities implements the Capable interface.
+func (fs *Memory) Capabilities() billy.Capability {
+	return billy.WriteCapability |
+		billy.ReadCapability |
+		billy.ReadAndWriteCapability |
+		billy.SeekCapability |
+		billy.TruncateCapability
+}
+
+type file struct {
+	name     string
+	content  *content
+	position int64
+	flag     int
+	mode     os.FileMode
+	mtime    time.Time
+
+	isClosed bool
+}
+
+func (f *file) Name() string {
+	return f.name
+}
+
+func (f *file) Read(b []byte) (int, error) {
+	n, err := f.ReadAt(b, f.position)
+	f.position += int64(n)
+
+	if err == io.EOF && n != 0 {
+		err = nil
+	}
+
+	return n, err
+}
+
+func (f *file) ReadAt(b []byte, off int64) (int, error) {
+	if f.isClosed {
+		return 0, os.ErrClosed
+	}
+
+	if !isReadAndWrite(f.flag) && !isReadOnly(f.flag) {
+		return 0, errors.New("read not supported")
+	}
+
+	n, err := f.content.ReadAt(b, off)
+
+	return n, err
+}
+
+func (f *file) Seek(offset int64, whence int) (int64, error) {
+	if f.isClosed {
+		return 0, os.ErrClosed
+	}
+
+	switch whence {
+	case io.SeekCurrent:
+		f.position += offset
+	case io.SeekStart:
+		f.position = offset
+	case io.SeekEnd:
+		f.position = int64(f.content.Len()) + offset
+	}
+
+	return f.position, nil
+}
+
+func (f *file) Write(p []byte) (int, error) {
+	return f.WriteAt(p, f.position)
+}
+
+func (f *file) WriteAt(p []byte, off int64) (int, error) {
+	if f.isClosed {
+		return 0, os.ErrClosed
+	}
+
+	if !isReadAndWrite(f.flag) && !isWriteOnly(f.flag) {
+		return 0, errors.New("write not supported")
+	}
+
+	n, err := f.content.WriteAt(p, off)
+	f.position = off + int64(n)
+	f.mtime = time.Now()
+
+	return n, err
+}
+
+func (f *file) Close() error {
+	if f.isClosed {
+		return os.ErrClosed
+	}
+
+	f.isClosed = true
+	return nil
+}
+
+func (f *file) Truncate(size int64) error {
+	if size < int64(len(f.content.bytes)) {
+		f.content.bytes = f.content.bytes[:size]
+	} else if more := int(size) - len(f.content.bytes); more > 0 {
+		f.content.bytes = append(f.content.bytes, make([]byte, more)...)
+	}
+	f.mtime = time.Now()
+
+	return nil
+}
+
+func (f *file) Duplicate(filename string, mode os.FileMode, flag int) billy.File {
+	new := &file{
+		name:    filename,
+		content: f.content,
+		mode:    mode,
+		flag:    flag,
+		mtime:   time.Now(),
+	}
+
+	if isTruncate(flag) {
+		new.content.Truncate()
+	}
+
+	if isAppend(flag) {
+		new.position = int64(new.content.Len())
+	}
+
+	return new
+}
+
+func (f *file) Stat() (os.FileInfo, error) {
+	return &fileInfo{
+		name:  f.Name(),
+		mode:  f.mode,
+		size:  f.content.Len(),
+		mtime: f.mtime,
+	}, nil
+}
+
+// Lock is a no-op in memfs.
+func (f *file) Lock() error {
+	return nil
+}
+
+// Unlock is a no-op in memfs.
+func (f *file) Unlock() error {
+	return nil
+}
+
+type fileInfo struct {
+	name  string
+	size  int
+	mode  os.FileMode
+	mtime time.Time
+}
+
+func (fi *fileInfo) Name() string {
+	return fi.name
+}
+
+func (fi *fileInfo) Size() int64 {
+	return int64(fi.size)
+}
+
+func (fi *fileInfo) Mode() os.FileMode {
+	return fi.mode
+}
+
+func (fi *fileInfo) ModTime() time.Time {
+	return fi.mtime
+}
+
+func (fi *fileInfo) IsDir() bool {
+	return fi.mode.IsDir()
+}
+
+func (*fileInfo) Sys() interface{} {
+	return nil
+}
+
+func (c *content) Truncate() {
+	c.bytes = make([]byte, 0)
+}
+
+func (c *content) Len() int {
+	return len(c.bytes)
+}
+
+func isCreate(flag int) bool {
+	return flag&os.O_CREATE != 0
+}
+
+func isExclusive(flag int) bool {
+	return flag&os.O_EXCL != 0
+}
+
+func isAppend(flag int) bool {
+	return flag&os.O_APPEND != 0
+}
+
+func isTruncate(flag int) bool {
+	return flag&os.O_TRUNC != 0
+}
+
+func isReadAndWrite(flag int) bool {
+	return flag&os.O_RDWR != 0
+}
+
+func isReadOnly(flag int) bool {
+	return flag == os.O_RDONLY
+}
+
+func isWriteOnly(flag int) bool {
+	return flag&os.O_WRONLY != 0
+}
+
+func isSymlink(m os.FileMode) bool {
+	return m&os.ModeSymlink != 0
+}

server/pkg/go-nfs/helpers/memfs/storage.go

@@ -0,0 +1,243 @@
+package memfs
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+	"time"
+)
+
+type storage struct {
+	files    map[string]*file
+	children map[string]map[string]*file
+}
+
+func newStorage() *storage {
+	return &storage{
+		files:    make(map[string]*file, 0),
+		children: make(map[string]map[string]*file, 0),
+	}
+}
+
+func (s *storage) Has(path string) bool {
+	path = clean(path)
+
+	_, ok := s.files[path]
+	return ok
+}
+
+func (s *storage) New(path string, mode os.FileMode, flag int) (*file, error) {
+	path = clean(path)
+	if s.Has(path) {
+		if !s.MustGet(path).mode.IsDir() {
+			return nil, fmt.Errorf("file already exists %q", path)
+		}
+
+		return nil, nil
+	}
+
+	name := filepath.Base(path)
+
+	f := &file{
+		name:    name,
+		content: &content{name: name},
+		mode:    mode,
+		flag:    flag,
+		mtime:   time.Now(),
+	}
+
+	s.files[path] = f
+	if err := s.createParent(path, mode, f); err != nil {
+		return nil, err
+	}
+	return f, nil
+}
+
+func (s *storage) createParent(path string, mode os.FileMode, f *file) error {
+	base := filepath.Dir(path)
+	base = clean(base)
+	if f.Name() == string(separator) {
+		return nil
+	}
+
+	if _, err := s.New(base, mode.Perm()|os.ModeDir, 0); err != nil {
+		return err
+	}
+
+	if _, ok := s.children[base]; !ok {
+		s.children[base] = make(map[string]*file, 0)
+	}
+
+	s.children[base][f.Name()] = f
+	return nil
+}
+
+func (s *storage) Children(path string) []*file {
+	path = clean(path)
+
+	l := make([]*file, 0)
+	for _, f := range s.children[path] {
+		l = append(l, f)
+	}
+
+	return l
+}
+
+func (s *storage) MustGet(path string) *file {
+	f, ok := s.Get(path)
+	if !ok {
+		panic(fmt.Errorf("couldn't find %q", path))
+	}
+
+	return f
+}
+
+func (s *storage) Get(path string) (*file, bool) {
+	path = clean(path)
+	if !s.Has(path) {
+		return nil, false
+	}
+
+	file, ok := s.files[path]
+	return file, ok
+}
+
+func (s *storage) Rename(from, to string) error {
+	from = clean(from)
+	to = clean(to)
+
+	if !s.Has(from) {
+		return os.ErrNotExist
+	}
+
+	move := [][2]string{{from, to}}
+
+	for pathFrom := range s.files {
+		if pathFrom == from || !strings.HasPrefix(pathFrom, from) {
+			continue
+		}
+
+		rel, _ := filepath.Rel(from, pathFrom)
+		pathTo := filepath.Join(to, rel)
+
+		move = append(move, [2]string{pathFrom, pathTo})
+	}
+
+	for _, ops := range move {
+		from := ops[0]
+		to := ops[1]
+
+		if err := s.move(from, to); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (s *storage) move(from, to string) error {
+	s.files[to] = s.files[from]
+	s.files[to].name = filepath.Base(to)
+	s.children[to] = s.children[from]
+
+	defer func() {
+		delete(s.children, from)
+		delete(s.files, from)
+		delete(s.children[filepath.Dir(from)], filepath.Base(from))
+	}()
+
+	return s.createParent(to, 0644, s.files[to])
+}
+
+func (s *storage) Remove(path string) error {
+	path = clean(path)
+
+	f, has := s.Get(path)
+	if !has {
+		return os.ErrNotExist
+	}
+
+	if f.mode.IsDir() && len(s.children[path]) != 0 {
+		return fmt.Errorf("dir: %s contains files", path)
+	}
+
+	base, file := filepath.Split(path)
+	base = filepath.Clean(base)
+
+	delete(s.children[base], file)
+	delete(s.files, path)
+	return nil
+}
+
+func clean(path string) string {
+	return filepath.Clean(filepath.FromSlash(path))
+}
+
+type content struct {
+	name  string
+	bytes []byte
+
+	m sync.RWMutex
+}
+
+func (c *content) WriteAt(p []byte, off int64) (int, error) {
+	if off < 0 {
+		return 0, &os.PathError{
+			Op:   "writeat",
+			Path: c.name,
+			Err:  errors.New("negative offset"),
+		}
+	}
+
+	c.m.Lock()
+	prev := len(c.bytes)
+
+	diff := int(off) - prev
+	if diff > 0 {
+		c.bytes = append(c.bytes, make([]byte, diff)...)
+	}
+
+	c.bytes = append(c.bytes[:off], p...)
+	if len(c.bytes) < prev {
+		c.bytes = c.bytes[:prev]
+	}
+	c.m.Unlock()
+
+	return len(p), nil
+}
+
+func (c *content) ReadAt(b []byte, off int64) (n int, err error) {
+	if off < 0 {
+		return 0, &os.PathError{
+			Op:   "readat",
+			Path: c.name,
+			Err:  errors.New("negative offset"),
+		}
+	}
+
+	c.m.RLock()
+	size := int64(len(c.bytes))
+	if off >= size {
+		c.m.RUnlock()
+		return 0, io.EOF
+	}
+
+	l := int64(len(b))
+	if off+l > size {
+		l = size - off
+	}
+
+	btr := c.bytes[off : off+l]
+	n = copy(b, btr)
+
+	if len(btr) < len(b) {
+		err = io.EOF
+	}
+	c.m.RUnlock()
+
+	return
+}

server/pkg/go-nfs/helpers/nullauthhandler.go

@@ -0,0 +1,59 @@
+package helpers
+
+import (
+	"context"
+	"net"
+
+	"git.kmsign.ru/royalcat/tstor/server/pkg/ctxbilly"
+	nfs "git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs"
+)
+
+// NewNullAuthHandler creates a handler for the provided filesystem
+func NewNullAuthHandler(fs nfs.Filesystem) nfs.Handler {
+	return &NullAuthHandler{fs}
+}
+
+// NullAuthHandler returns a NFS backing that exposes a given file system in response to all mount requests.
+type NullAuthHandler struct {
+	fs nfs.Filesystem
+}
+
+// Mount backs Mount RPC Requests, allowing for access control policies.
+func (h *NullAuthHandler) Mount(ctx context.Context, conn net.Conn, req nfs.MountRequest) (status nfs.MountStatus, hndl nfs.Filesystem, auths []nfs.AuthFlavor) {
+	status = nfs.MountStatusOk
+	hndl = h.fs
+	auths = []nfs.AuthFlavor{nfs.AuthFlavorNull}
+	return
+}
+
+// Change provides an interface for updating file attributes.
+func (h *NullAuthHandler) Change(fs nfs.Filesystem) nfs.Change {
+	if c, ok := h.fs.(ctxbilly.Change); ok {
+		return c
+	}
+	return nil
+}
+
+// FSStat provides information about a filesystem.
+func (h *NullAuthHandler) FSStat(context.Context, nfs.Filesystem, *nfs.FSStat) error {
+	return nil
+}
+
+// ToHandle handled by CachingHandler
+func (h *NullAuthHandler) ToHandle(context.Context, nfs.Filesystem, []string) []byte {
+	return []byte{}
+}
+
+// FromHandle handled by CachingHandler
+func (h *NullAuthHandler) FromHandle(context.Context, []byte) (nfs.Filesystem, []string, error) {
+	return nil, []string{}, nil
+}
+
+func (c *NullAuthHandler) InvalidateHandle(context.Context, nfs.Filesystem, []byte) error {
+	return nil
+}
+
+// HandleLImit handled by cachingHandler
+func (h *NullAuthHandler) HandleLimit() int {
+	return -1
+}

server/pkg/go-nfs/log.go

@@ -0,0 +1,216 @@
+package nfs
+
+import (
+	"fmt"
+	"log"
+	"os"
+)
+
+var (
+	Log Logger = &DefaultLogger{}
+)
+
+type LogLevel int
+
+const (
+	PanicLevel LogLevel = iota
+	FatalLevel
+	ErrorLevel
+	WarnLevel
+	InfoLevel
+	DebugLevel
+	TraceLevel
+
+	panicLevelStr string = "[PANIC] "
+	fatalLevelStr string = "[FATAL] "
+	errorLevelStr string = "[ERROR] "
+	warnLevelStr  string = "[WARN] "
+	infoLevelStr  string = "[INFO] "
+	debugLevelStr string = "[DEBUG] "
+	traceLevelStr string = "[TRACE] "
+)
+
+type Logger interface {
+	SetLevel(level LogLevel)
+	GetLevel() LogLevel
+	ParseLevel(level string) (LogLevel, error)
+
+	Panic(args ...interface{})
+	Fatal(args ...interface{})
+	Error(args ...interface{})
+	Warn(args ...interface{})
+	Info(args ...interface{})
+	Debug(args ...interface{})
+	Trace(args ...interface{})
+	Print(args ...interface{})
+
+	Panicf(format string, args ...interface{})
+	Fatalf(format string, args ...interface{})
+	Errorf(format string, args ...interface{})
+	Warnf(format string, args ...interface{})
+	Infof(format string, args ...interface{})
+	Debugf(format string, args ...interface{})
+	Tracef(format string, args ...interface{})
+	Printf(format string, args ...interface{})
+}
+
+type DefaultLogger struct {
+	Level LogLevel
+}
+
+func SetLogger(logger Logger) {
+	Log = logger
+}
+
+func init() {
+	if os.Getenv("LOG_LEVEL") != "" {
+		if level, err := Log.ParseLevel(os.Getenv("LOG_LEVEL")); err == nil {
+			Log.SetLevel(level)
+		}
+	} else {
+		// set default log level to info
+		Log.SetLevel(InfoLevel)
+	}
+}
+
+func (l *DefaultLogger) GetLevel() LogLevel {
+	return l.Level
+}
+
+func (l *DefaultLogger) SetLevel(level LogLevel) {
+	l.Level = level
+}
+
+func (l *DefaultLogger) ParseLevel(level string) (LogLevel, error) {
+	switch level {
+	case "panic":
+		return PanicLevel, nil
+	case "fatal":
+		return FatalLevel, nil
+	case "error":
+		return ErrorLevel, nil
+	case "warn":
+		return WarnLevel, nil
+	case "info":
+		return InfoLevel, nil
+	case "debug":
+		return DebugLevel, nil
+	case "trace":
+		return TraceLevel, nil
+	}
+	var ll LogLevel
+	return ll, fmt.Errorf("invalid log level %q", level)
+}
+
+func (l *DefaultLogger) Panic(args ...interface{}) {
+	if l.Level < PanicLevel {
+		return
+	}
+	args = append([]interface{}{panicLevelStr}, args...)
+	log.Print(args...)
+}
+
+func (l *DefaultLogger) Panicf(format string, args ...interface{}) {
+	if l.Level < PanicLevel {
+		return
+	}
+	log.Printf(panicLevelStr+format, args...)
+}
+
+func (l *DefaultLogger) Fatal(args ...interface{}) {
+	if l.Level < FatalLevel {
+		return
+	}
+	args = append([]interface{}{fatalLevelStr}, args...)
+	log.Print(args...)
+}
+
+func (l *DefaultLogger) Fatalf(format string, args ...interface{}) {
+	if l.Level < FatalLevel {
+		return
+	}
+	log.Printf(fatalLevelStr+format, args...)
+}
+
+func (l *DefaultLogger) Error(args ...interface{}) {
+	if l.Level < ErrorLevel {
+		return
+	}
+	args = append([]interface{}{errorLevelStr}, args...)
+	log.Print(args...)
+}
+
+func (l *DefaultLogger) Errorf(format string, args ...interface{}) {
+	if l.Level < ErrorLevel {
+		return
+	}
+	log.Printf(errorLevelStr+format, args...)
+}
+
+func (l *DefaultLogger) Warn(args ...interface{}) {
+	if l.Level < WarnLevel {
+		return
+	}
+	args = append([]interface{}{warnLevelStr}, args...)
+	log.Print(args...)
+}
+
+func (l *DefaultLogger) Warnf(format string, args ...interface{}) {
+	if l.Level < WarnLevel {
+		return
+	}
+	log.Printf(warnLevelStr+format, args...)
+}
+
+func (l *DefaultLogger) Info(args ...interface{}) {
+	if l.Level < InfoLevel {
+		return
+	}
+	args = append([]interface{}{infoLevelStr}, args...)
+	log.Print(args...)
+}
+
+func (l *DefaultLogger) Infof(format string, args ...interface{}) {
+	if l.Level < InfoLevel {
+		return
+	}
+	log.Printf(infoLevelStr+format, args...)
+}
+
+func (l *DefaultLogger) Debug(args ...interface{}) {
+	if l.Level < DebugLevel {
+		return
+	}
+	args = append([]interface{}{debugLevelStr}, args...)
+	log.Print(args...)
+}
+
+func (l *DefaultLogger) Debugf(format string, args ...interface{}) {
+	if l.Level < DebugLevel {
+		return
+	}
+	log.Printf(debugLevelStr+format, args...)
+}
+
+func (l *DefaultLogger) Trace(args ...interface{}) {
+	if l.Level < TraceLevel {
+		return
+	}
+	args = append([]interface{}{traceLevelStr}, args...)
+	log.Print(args...)
+}
+
+func (l *DefaultLogger) Tracef(format string, args ...interface{}) {
+	if l.Level < TraceLevel {
+		return
+	}
+	log.Printf(traceLevelStr+format, args...)
+}
+
+func (l *DefaultLogger) Print(args ...interface{}) {
+	log.Print(args...)
+}
+
+func (l *DefaultLogger) Printf(format string, args ...interface{}) {
+	log.Printf(format, args...)
+}

server/pkg/go-nfs/mount.go

@@ -0,0 +1,58 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+const (
+	mountServiceID = 100005
+)
+
+func init() {
+	_ = RegisterMessageHandler(mountServiceID, uint32(MountProcNull), onMountNull)
+	_ = RegisterMessageHandler(mountServiceID, uint32(MountProcMount), onMount)
+	_ = RegisterMessageHandler(mountServiceID, uint32(MountProcUmnt), onUMount)
+}
+
+func onMountNull(ctx context.Context, w *response, userHandle Handler) error {
+	return w.writeHeader(ResponseCodeSuccess)
+}
+
+func onMount(ctx context.Context, w *response, userHandle Handler) error {
+	// TODO: auth check.
+	dirpath, err := xdr.ReadOpaque(w.req.Body)
+	if err != nil {
+		return err
+	}
+	mountReq := MountRequest{Header: w.req.Header, Dirpath: dirpath}
+	status, handle, flavors := userHandle.Mount(ctx, w.conn, mountReq)
+
+	if err := w.writeHeader(ResponseCodeSuccess); err != nil {
+		return err
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(status)); err != nil {
+		return err
+	}
+
+	rootHndl := userHandle.ToHandle(ctx, handle, []string{})
+
+	if status == MountStatusOk {
+		_ = xdr.Write(writer, rootHndl)
+		_ = xdr.Write(writer, flavors)
+	}
+	return w.Write(writer.Bytes())
+}
+
+func onUMount(ctx context.Context, w *response, userHandle Handler) error {
+	_, err := xdr.ReadOpaque(w.req.Body)
+	if err != nil {
+		return err
+	}
+
+	return w.writeHeader(ResponseCodeSuccess)
+}

server/pkg/go-nfs/mountinterface.go

@@ -0,0 +1,90 @@
+package nfs
+
+import (
+	"github.com/willscott/go-nfs-client/nfs/rpc"
+)
+
+// FHSize is the maximum size of a FileHandle
+const FHSize = 64
+
+// MNTNameLen is the maximum size of a mount name
+const MNTNameLen = 255
+
+// MntPathLen is the maximum size of a mount path
+const MntPathLen = 1024
+
+// FileHandle maps to a fhandle3
+type FileHandle []byte
+
+// MountStatus defines the response to the Mount Procedure
+type MountStatus uint32
+
+// MountStatus Codes
+const (
+	MountStatusOk             MountStatus = 0
+	MountStatusErrPerm        MountStatus = 1
+	MountStatusErrNoEnt       MountStatus = 2
+	MountStatusErrIO          MountStatus = 5
+	MountStatusErrAcces       MountStatus = 13
+	MountStatusErrNotDir      MountStatus = 20
+	MountStatusErrInval       MountStatus = 22
+	MountStatusErrNameTooLong MountStatus = 63
+	MountStatusErrNotSupp     MountStatus = 10004
+	MountStatusErrServerFault MountStatus = 10006
+)
+
+// MountProcedure is the valid RPC calls for the mount service.
+type MountProcedure uint32
+
+// MountProcedure Codes
+const (
+	MountProcNull MountProcedure = iota
+	MountProcMount
+	MountProcDump
+	MountProcUmnt
+	MountProcUmntAll
+	MountProcExport
+)
+
+func (m MountProcedure) String() string {
+	switch m {
+	case MountProcNull:
+		return "Null"
+	case MountProcMount:
+		return "Mount"
+	case MountProcDump:
+		return "Dump"
+	case MountProcUmnt:
+		return "Umnt"
+	case MountProcUmntAll:
+		return "UmntAll"
+	case MountProcExport:
+		return "Export"
+	default:
+		return "Unknown"
+	}
+}
+
+// AuthFlavor is a form of authentication, per rfc1057 section 7.2
+type AuthFlavor uint32
+
+// AuthFlavor Codes
+const (
+	AuthFlavorNull  AuthFlavor = 0
+	AuthFlavorUnix  AuthFlavor = 1
+	AuthFlavorShort AuthFlavor = 2
+	AuthFlavorDES   AuthFlavor = 3
+)
+
+// MountRequest contains the format of a client request to open a mount.
+type MountRequest struct {
+	rpc.Header
+	Dirpath []byte
+}
+
+// MountResponse is the server's response with status `MountStatusOk`
+type MountResponse struct {
+	rpc.Header
+	FileHandle
+	AuthFlavors []int
+}

server/pkg/go-nfs/nfs.go

@@ -0,0 +1,38 @@
+package nfs
+
+import (
+	"context"
+)
+
+const (
+	nfsServiceID = 100003
+)
+
+func init() {
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureNull), onNull)               // 0
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureGetAttr), onGetAttr)         // 1
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureSetAttr), onSetAttr)         // 2
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureLookup), onLookup)           // 3
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureAccess), onAccess)           // 4
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureReadlink), onReadLink)       // 5
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureRead), onRead)               // 6
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureWrite), onWrite)             // 7
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureCreate), onCreate)           // 8
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureMkDir), onMkdir)             // 9
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureSymlink), onSymlink)         // 10
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureMkNod), onMknod)             // 11
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureRemove), onRemove)           // 12
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureRmDir), onRmDir)             // 13
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureRename), onRename)           // 14
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureLink), onLink)               // 15
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureReadDir), onReadDir)         // 16
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureReadDirPlus), onReadDirPlus) // 17
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureFSStat), onFSStat)           // 18
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureFSInfo), onFSInfo)           // 19
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedurePathConf), onPathConf)       // 20
+	_ = RegisterMessageHandler(nfsServiceID, uint32(NFSProcedureCommit), onCommit)           // 21
+}
+
+func onNull(ctx context.Context, w *response, userHandle Handler) error {
+	return w.Write([]byte{})
+}

server/pkg/go-nfs/nfs_onaccess.go

@@ -0,0 +1,45 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+
+	billy "github.com/go-git/go-billy/v5"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+func onAccess(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = opAttrErrorFormatter
+	roothandle, err := xdr.ReadOpaque(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	fs, path, err := userHandle.FromHandle(ctx, roothandle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+	mask, err := xdr.ReadUint32(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if !CapabilityCheck(fs, billy.WriteCapability) {
+		mask = mask & (1 | 2 | 0x20)
+	}
+
+	if err := xdr.Write(writer, mask); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_oncommit.go

@@ -0,0 +1,51 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"os"
+
+	billy "github.com/go-git/go-billy/v5"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+// onCommit - note this is a no-op, as we always push writes to the backing store.
+func onCommit(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = wccDataErrorFormatter
+	handle, err := xdr.ReadOpaque(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	// The conn will drain the unread offset and count arguments.
+
+	fs, path, err := userHandle.FromHandle(ctx, handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+
+	if !CapabilityCheck(fs, billy.WriteCapability) {
+		return &NFSStatusError{NFSStatusServerFault, os.ErrPermission}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return err
+	}
+
+	// no pre-op cache data.
+	if err := xdr.Write(writer, uint32(0)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	// write the 8 bytes of write verification.
+	if err := xdr.Write(writer, w.Server.ID); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_oncreate.go

@@ -0,0 +1,125 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"os"
+
+	billy "github.com/go-git/go-billy/v5"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+const (
+	createModeUnchecked = 0
+	createModeGuarded   = 1
+	createModeExclusive = 2
+)
+
+func onCreate(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = wccDataErrorFormatter
+	obj := DirOpArg{}
+	err := xdr.Read(w.req.Body, &obj)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	how, err := xdr.ReadUint32(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	var attrs *SetFileAttributes
+	if how == createModeUnchecked || how == createModeGuarded {
+		sattr, err := ReadSetFileAttributes(w.req.Body)
+		if err != nil {
+			return &NFSStatusError{NFSStatusInval, err}
+		}
+		attrs = sattr
+	} else if how == createModeExclusive {
+		// read createverf3
+		var verf [8]byte
+		if err := xdr.Read(w.req.Body, &verf); err != nil {
+			return &NFSStatusError{NFSStatusInval, err}
+		}
+		Log.Errorf("failing create to indicate lack of support for 'exclusive' mode.")
+		// TODO: support 'exclusive' mode.
+		return &NFSStatusError{NFSStatusNotSupp, os.ErrPermission}
+	} else {
+		// invalid
+		return &NFSStatusError{NFSStatusNotSupp, os.ErrInvalid}
+	}
+
+	fs, path, err := userHandle.FromHandle(ctx, obj.Handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+
+	if !CapabilityCheck(fs, billy.WriteCapability) {
+		return &NFSStatusError{NFSStatusROFS, os.ErrPermission}
+	}
+
+	if len(string(obj.Filename)) > PathNameMax {
+		return &NFSStatusError{NFSStatusNameTooLong, nil}
+	}
+
+	newFile := append(path, string(obj.Filename))
+	newFilePath := fs.Join(newFile...)
+	if s, err := fs.Stat(ctx, newFilePath); err == nil {
+		if s.IsDir() {
+			return &NFSStatusError{NFSStatusExist, nil}
+		}
+		if how == createModeGuarded {
+			return &NFSStatusError{NFSStatusExist, os.ErrPermission}
+		}
+	} else {
+		if s, err := fs.Stat(ctx, fs.Join(path...)); err != nil {
+			return &NFSStatusError{NFSStatusAccess, err}
+		} else if !s.IsDir() {
+			return &NFSStatusError{NFSStatusNotDir, nil}
+		}
+	}
+
+	file, err := fs.Create(ctx, newFilePath)
+	if err != nil {
+		Log.Errorf("Error Creating: %v", err)
+		return &NFSStatusError{NFSStatusAccess, err}
+	}
+	if err := file.Close(ctx); err != nil {
+		Log.Errorf("Error Creating: %v", err)
+		return &NFSStatusError{NFSStatusAccess, err}
+	}
+
+	fp := userHandle.ToHandle(ctx, fs, newFile)
+	changer := userHandle.Change(fs)
+	if err := attrs.Apply(ctx, changer, fs, newFilePath); err != nil {
+		Log.Errorf("Error applying attributes: %v\n", err)
+		return &NFSStatusError{NFSStatusIO, err}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	// "handle follows"
+	if err := xdr.Write(writer, uint32(1)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := xdr.Write(writer, fp); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, []string{file.Name()})); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	// dir_wcc (we don't include pre_op_attr)
+	if err := xdr.Write(writer, uint32(0)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onfsinfo.go

@@ -0,0 +1,89 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+
+	"github.com/go-git/go-billy/v5"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+const (
+	// FSInfoPropertyLink does the FS support hard links?
+	FSInfoPropertyLink = 0x0001
+	// FSInfoPropertySymlink does the FS support soft links?
+	FSInfoPropertySymlink = 0x0002
+	// FSInfoPropertyHomogeneous does the FS need PATHCONF calls for each file
+	FSInfoPropertyHomogeneous = 0x0008
+	// FSInfoPropertyCanSetTime can the FS support setting access/mod times?
+	FSInfoPropertyCanSetTime = 0x0010
+)
+
+func onFSInfo(ctx context.Context, w *response, userHandle Handler) error {
+	roothandle, err := xdr.ReadOpaque(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	fs, path, err := userHandle.FromHandle(ctx, roothandle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	type fsinfores struct {
+		Rtmax       uint32
+		Rtpref      uint32
+		Rtmult      uint32
+		Wtmax       uint32
+		Wtpref      uint32
+		Wtmult      uint32
+		Dtpref      uint32
+		Maxfilesize uint64
+		TimeDelta   uint64
+		Properties  uint32
+	}
+
+	res := fsinfores{
+		Rtmax:       1 << 30,
+		Rtpref:      1 << 30,
+		Rtmult:      4096,
+		Wtmax:       1 << 30,
+		Wtpref:      1 << 30,
+		Wtmult:      4096,
+		Dtpref:      8192,
+		Maxfilesize: 1 << 62, // wild guess. this seems big.
+		TimeDelta:   1,       // nanosecond precision.
+		Properties:  0,
+	}
+
+	// TODO: these aren't great indications of support, really.
+	// if _, ok := fs.(billy.Symlink); ok {
+	// 	res.Properties |= FSInfoPropertyLink
+	// 	res.Properties |= FSInfoPropertySymlink
+	// }
+	// TODO: if the nfs share spans multiple virtual mounts, may need
+	// to support granular PATHINFO responses.
+	res.Properties |= FSInfoPropertyHomogeneous
+	// TODO: not a perfect indicator
+
+	if CapabilityCheck(fs, billy.WriteCapability) {
+		res.Properties |= FSInfoPropertyCanSetTime
+	}
+
+	// TODO: this whole struct should be specifiable by the userhandler.
+
+	if err := xdr.Write(writer, res); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onfsstat.go

@@ -0,0 +1,59 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+
+	billy "github.com/go-git/go-billy/v5"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+func onFSStat(ctx context.Context, w *response, userHandle Handler) error {
+	roothandle, err := xdr.ReadOpaque(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	fs, path, err := userHandle.FromHandle(ctx, roothandle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+
+	defaults := FSStat{
+		TotalSize:      1 << 62,
+		FreeSize:       1 << 62,
+		AvailableSize:  1 << 62,
+		TotalFiles:     1 << 62,
+		FreeFiles:      1 << 62,
+		AvailableFiles: 1 << 62,
+		CacheHint:      0,
+	}
+
+	if !CapabilityCheck(fs, billy.WriteCapability) {
+		defaults.AvailableFiles = 0
+		defaults.AvailableSize = 0
+	}
+
+	err = userHandle.FSStat(ctx, fs, &defaults)
+	if err != nil {
+		if _, ok := err.(*NFSStatusError); ok {
+			return err
+		}
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := xdr.Write(writer, defaults); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_ongetattr.go

@@ -0,0 +1,48 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"os"
+
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+func onGetAttr(ctx context.Context, w *response, userHandle Handler) error {
+	handle, err := xdr.ReadOpaque(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	fs, path, err := userHandle.FromHandle(ctx, handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+
+	fullPath := fs.Join(path...)
+	info, err := fs.Lstat(ctx, fullPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &NFSStatusError{NFSStatusNoEnt, err}
+		}
+		if errors.Is(err, context.DeadlineExceeded) {
+			return &NFSStatusError{timeoutStatus, err}
+		}
+		return &NFSStatusError{NFSStatusIO, err}
+	}
+	attr := ToFileAttribute(info, fullPath)
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := xdr.Write(writer, attr); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onlink.go

@@ -0,0 +1,94 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"os"
+
+	"github.com/go-git/go-billy/v5"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+// Backing billy.FS doesn't support hard links
+func onLink(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = wccDataErrorFormatter
+	obj := DirOpArg{}
+	err := xdr.Read(w.req.Body, &obj)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	attrs, err := ReadSetFileAttributes(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	target, err := xdr.ReadOpaque(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	fs, path, err := userHandle.FromHandle(ctx, obj.Handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+	if !CapabilityCheck(fs, billy.WriteCapability) {
+		return &NFSStatusError{NFSStatusROFS, os.ErrPermission}
+	}
+
+	if len(string(obj.Filename)) > PathNameMax {
+		return &NFSStatusError{NFSStatusNameTooLong, os.ErrInvalid}
+	}
+
+	newFilePath := fs.Join(append(path, string(obj.Filename))...)
+	if _, err := fs.Stat(ctx, newFilePath); err == nil {
+		return &NFSStatusError{NFSStatusExist, os.ErrExist}
+	}
+	if s, err := fs.Stat(ctx, fs.Join(path...)); err != nil {
+		return &NFSStatusError{NFSStatusAccess, err}
+	} else if !s.IsDir() {
+		return &NFSStatusError{NFSStatusNotDir, nil}
+	}
+
+	fp := userHandle.ToHandle(ctx, fs, append(path, string(obj.Filename)))
+	changer := userHandle.Change(fs)
+	if changer == nil {
+		return &NFSStatusError{NFSStatusAccess, err}
+	}
+	cos, ok := changer.(UnixChange)
+	if !ok {
+		return &NFSStatusError{NFSStatusAccess, err}
+	}
+
+	err = cos.Link(ctx, string(target), newFilePath)
+	if err != nil {
+		return &NFSStatusError{NFSStatusAccess, err}
+	}
+	if err := attrs.Apply(ctx, changer, fs, newFilePath); err != nil {
+		return &NFSStatusError{NFSStatusIO, err}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	// "handle follows"
+	if err := xdr.Write(writer, uint32(1)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := xdr.Write(writer, fp); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, append(path, string(obj.Filename)))); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := WriteWcc(writer, nil, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onlookup.go

@@ -0,0 +1,86 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"os"
+
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+func lookupSuccessResponse(ctx context.Context, handle []byte, entPath, dirPath []string, fs Filesystem) ([]byte, error) {
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return nil, err
+	}
+	if err := xdr.Write(writer, handle); err != nil {
+		return nil, err
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, entPath)); err != nil {
+		return nil, err
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, dirPath)); err != nil {
+		return nil, err
+	}
+	return writer.Bytes(), nil
+}
+
+func onLookup(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = opAttrErrorFormatter
+	obj := DirOpArg{}
+	err := xdr.Read(w.req.Body, &obj)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	fs, p, err := userHandle.FromHandle(ctx, obj.Handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+	dirInfo, err := fs.Lstat(ctx, fs.Join(p...))
+	if err != nil || !dirInfo.IsDir() {
+		return &NFSStatusError{NFSStatusNotDir, err}
+	}
+
+	// Special cases for "." and ".."
+	if bytes.Equal(obj.Filename, []byte(".")) {
+		resp, err := lookupSuccessResponse(ctx, obj.Handle, p, p, fs)
+		if err != nil {
+			return &NFSStatusError{NFSStatusServerFault, err}
+		}
+		if err := w.Write(resp); err != nil {
+			return &NFSStatusError{NFSStatusServerFault, err}
+		}
+		return nil
+	}
+	if bytes.Equal(obj.Filename, []byte("..")) {
+		if len(p) == 0 {
+			return &NFSStatusError{NFSStatusAccess, os.ErrPermission}
+		}
+		pPath := p[0 : len(p)-1]
+		pHandle := userHandle.ToHandle(ctx, fs, pPath)
+		resp, err := lookupSuccessResponse(ctx, pHandle, pPath, p, fs)
+		if err != nil {
+			return &NFSStatusError{NFSStatusServerFault, err}
+		}
+		if err := w.Write(resp); err != nil {
+			return &NFSStatusError{NFSStatusServerFault, err}
+		}
+		return nil
+	}
+
+	reqPath := append(p, string(obj.Filename))
+	if _, err = fs.Lstat(ctx, fs.Join(reqPath...)); err != nil {
+		return &NFSStatusError{NFSStatusNoEnt, os.ErrNotExist}
+	}
+
+	newHandle := userHandle.ToHandle(ctx, fs, reqPath)
+	resp, err := lookupSuccessResponse(ctx, newHandle, reqPath, p, fs)
+	if err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := w.Write(resp); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onmkdir.go

@@ -0,0 +1,94 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"os"
+
+	"github.com/go-git/go-billy/v5"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+const (
+	mkdirDefaultMode = 755
+)
+
+func onMkdir(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = wccDataErrorFormatter
+	obj := DirOpArg{}
+	err := xdr.Read(w.req.Body, &obj)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	attrs, err := ReadSetFileAttributes(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	fs, path, err := userHandle.FromHandle(ctx, obj.Handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+	if !CapabilityCheck(fs, billy.WriteCapability) {
+		return &NFSStatusError{NFSStatusROFS, os.ErrPermission}
+	}
+
+	if len(string(obj.Filename)) > PathNameMax {
+		return &NFSStatusError{NFSStatusNameTooLong, os.ErrInvalid}
+	}
+	if string(obj.Filename) == "." || string(obj.Filename) == ".." {
+		return &NFSStatusError{NFSStatusExist, os.ErrExist}
+	}
+
+	newFolder := append(path, string(obj.Filename))
+	newFolderPath := fs.Join(newFolder...)
+	if s, err := fs.Stat(ctx, newFolderPath); err == nil {
+		if s.IsDir() {
+			return &NFSStatusError{NFSStatusExist, nil}
+		}
+	} else {
+		if s, err := fs.Stat(ctx, fs.Join(path...)); err != nil {
+			return &NFSStatusError{NFSStatusAccess, err}
+		} else if !s.IsDir() {
+			return &NFSStatusError{NFSStatusNotDir, nil}
+		}
+	}
+
+	if err := fs.MkdirAll(ctx, newFolderPath, attrs.Mode(mkdirDefaultMode)); err != nil {
+		return &NFSStatusError{NFSStatusAccess, err}
+	}
+
+	fp := userHandle.ToHandle(ctx, fs, newFolder)
+	changer := userHandle.Change(fs)
+	if changer != nil {
+		if err := attrs.Apply(ctx, changer, fs, newFolderPath); err != nil {
+			return &NFSStatusError{NFSStatusIO, err}
+		}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	// "handle follows"
+	if err := xdr.Write(writer, uint32(1)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := xdr.Write(writer, fp); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, newFolder)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := WriteWcc(writer, nil, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onmknod.go

@@ -0,0 +1,158 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"os"
+
+	billy "github.com/go-git/go-billy/v5"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+type nfs_ftype int32
+
+const (
+	FTYPE_NF3REG  nfs_ftype = 1
+	FTYPE_NF3DIR  nfs_ftype = 2
+	FTYPE_NF3BLK  nfs_ftype = 3
+	FTYPE_NF3CHR  nfs_ftype = 4
+	FTYPE_NF3LNK  nfs_ftype = 5
+	FTYPE_NF3SOCK nfs_ftype = 6
+	FTYPE_NF3FIFO nfs_ftype = 7
+)
+
+// Backing billy.FS doesn't support creation of
+// char, block, socket, or fifo pipe nodes
+func onMknod(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = wccDataErrorFormatter
+	obj := DirOpArg{}
+	err := xdr.Read(w.req.Body, &obj)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	ftype, err := xdr.ReadUint32(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	// see if the filesystem supports mknod
+	fs, path, err := userHandle.FromHandle(ctx, obj.Handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+
+	if !CapabilityCheck(fs, billy.WriteCapability) {
+		return &NFSStatusError{NFSStatusROFS, os.ErrPermission}
+	}
+
+	c := userHandle.Change(fs)
+	if c == nil {
+		return &NFSStatusError{NFSStatusAccess, os.ErrPermission}
+	}
+	cu, ok := c.(UnixChange)
+	if !ok {
+		return &NFSStatusError{NFSStatusAccess, os.ErrPermission}
+	}
+
+	if len(string(obj.Filename)) > PathNameMax {
+		return &NFSStatusError{NFSStatusNameTooLong, os.ErrInvalid}
+	}
+
+	newFilePath := fs.Join(append(path, string(obj.Filename))...)
+	if _, err := fs.Stat(ctx, newFilePath); err == nil {
+		return &NFSStatusError{NFSStatusExist, os.ErrExist}
+	}
+	parent, err := fs.Stat(ctx, fs.Join(path...))
+	if err != nil {
+		return &NFSStatusError{NFSStatusAccess, err}
+	} else if !parent.IsDir() {
+		return &NFSStatusError{NFSStatusNotDir, nil}
+	}
+	fp := userHandle.ToHandle(ctx, fs, append(path, string(obj.Filename)))
+
+	switch nfs_ftype(ftype) {
+	case FTYPE_NF3CHR:
+	case FTYPE_NF3BLK:
+		// read devicedata3 = {sattr3, specdata3}
+		attrs, err := ReadSetFileAttributes(w.req.Body)
+		if err != nil {
+			return &NFSStatusError{NFSStatusInval, err}
+		}
+		specData1, err := xdr.ReadUint32(w.req.Body)
+		if err != nil {
+			return &NFSStatusError{NFSStatusInval, err}
+		}
+		specData2, err := xdr.ReadUint32(w.req.Body)
+		if err != nil {
+			return &NFSStatusError{NFSStatusInval, err}
+		}
+
+		err = cu.Mknod(ctx, newFilePath, uint32(attrs.Mode(parent.Mode())), specData1, specData2)
+		if err != nil {
+			return &NFSStatusError{NFSStatusAccess, err}
+		}
+		if err = attrs.Apply(ctx, cu, fs, newFilePath); err != nil {
+			return &NFSStatusError{NFSStatusServerFault, err}
+		}
+
+	case FTYPE_NF3SOCK:
+		// read sattr3
+		attrs, err := ReadSetFileAttributes(w.req.Body)
+		if err != nil {
+			return &NFSStatusError{NFSStatusInval, err}
+		}
+		if err := cu.Socket(ctx, newFilePath); err != nil {
+			return &NFSStatusError{NFSStatusAccess, err}
+		}
+		if err = attrs.Apply(ctx, cu, fs, newFilePath); err != nil {
+			return &NFSStatusError{NFSStatusServerFault, err}
+		}
+
+	case FTYPE_NF3FIFO:
+		// read sattr3
+		attrs, err := ReadSetFileAttributes(w.req.Body)
+		if err != nil {
+			return &NFSStatusError{NFSStatusInval, err}
+		}
+		err = cu.Mkfifo(ctx, newFilePath, uint32(attrs.Mode(parent.Mode())))
+		if err != nil {
+			return &NFSStatusError{NFSStatusAccess, err}
+		}
+		if err = attrs.Apply(ctx, cu, fs, newFilePath); err != nil {
+			return &NFSStatusError{NFSStatusServerFault, err}
+		}
+
+	default:
+		return &NFSStatusError{NFSStatusBadType, os.ErrInvalid}
+		// end of input.
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	// "handle follows"
+	if err := xdr.Write(writer, uint32(1)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	// fh3
+	if err := xdr.Write(writer, fp); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	// attr
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, append(path, string(obj.Filename)))); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	// wcc
+	if err := WriteWcc(writer, nil, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	return nil
+}

server/pkg/go-nfs/nfs_onpathconf.go

@@ -0,0 +1,55 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+// PathNameMax is the maximum length for a file name
+const PathNameMax = 255
+
+func onPathConf(ctx context.Context, w *response, userHandle Handler) error {
+	roothandle, err := xdr.ReadOpaque(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	fs, path, err := userHandle.FromHandle(ctx, roothandle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	type PathConf struct {
+		LinkMax         uint32
+		NameMax         uint32
+		NoTrunc         uint32
+		ChownRestricted uint32
+		CaseInsensitive uint32
+		CasePreserving  uint32
+	}
+
+	defaults := PathConf{
+		LinkMax:         1,
+		NameMax:         PathNameMax,
+		NoTrunc:         1,
+		ChownRestricted: 0,
+		CaseInsensitive: 0,
+		CasePreserving:  1,
+	}
+	if err := xdr.Write(writer, defaults); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onread.go

@@ -0,0 +1,98 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"io"
+	"os"
+
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+type nfsReadArgs struct {
+	Handle []byte
+	Offset uint64
+	Count  uint32
+}
+
+type nfsReadResponse struct {
+	Count uint32
+	EOF   uint32
+	Data  []byte
+}
+
+// MaxRead is the advertised largest buffer the server is willing to read
+const MaxRead = 1 << 24
+
+// CheckRead is a size where - if a request to read is larger than this,
+// the server will stat the file to learn it's actual size before allocating
+// a buffer to read into.
+const CheckRead = 1 << 15
+
+func onRead(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = opAttrErrorFormatter
+	var obj nfsReadArgs
+	err := xdr.Read(w.req.Body, &obj)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	fs, path, err := userHandle.FromHandle(ctx, obj.Handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+
+	fh, err := fs.OpenFile(ctx, fs.Join(path...), os.O_RDONLY, 0)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &NFSStatusError{NFSStatusNoEnt, err}
+		}
+		if errors.Is(err, context.DeadlineExceeded) {
+			return &NFSStatusError{timeoutStatus, err}
+		}
+		return &NFSStatusError{NFSStatusAccess, err}
+	}
+	defer fh.Close(ctx)
+
+	resp := nfsReadResponse{}
+
+	if obj.Count > CheckRead {
+		info, err := fs.Stat(ctx, fs.Join(path...))
+		if err != nil {
+			return &NFSStatusError{NFSStatusAccess, err}
+		}
+		if info.Size()-int64(obj.Offset) < int64(obj.Count) {
+			obj.Count = uint32(uint64(info.Size()) - obj.Offset)
+		}
+	}
+	if obj.Count > MaxRead {
+		obj.Count = MaxRead
+	}
+	resp.Data = make([]byte, obj.Count)
+	// todo: multiple reads if size isn't full
+	cnt, err := fh.ReadAt(ctx, resp.Data, int64(obj.Offset))
+	if err != nil && !errors.Is(err, io.EOF) {
+		return &NFSStatusError{NFSStatusIO, err}
+	}
+	resp.Count = uint32(cnt)
+	resp.Data = resp.Data[:resp.Count]
+	if errors.Is(err, io.EOF) {
+		resp.EOF = 1
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := xdr.Write(writer, resp); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onreaddir.go

@@ -0,0 +1,195 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"crypto/sha256"
+	"encoding/binary"
+	"errors"
+	"io"
+	"io/fs"
+	"os"
+	"path"
+	"sort"
+
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+type readDirArgs struct {
+	Handle      []byte
+	Cookie      uint64
+	CookieVerif uint64
+	Count       uint32
+}
+
+type readDirEntity struct {
+	FileID uint64
+	Name   []byte
+	Cookie uint64
+	Next   bool
+}
+
+func onReadDir(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = opAttrErrorFormatter
+	obj := readDirArgs{}
+	err := xdr.Read(w.req.Body, &obj)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	if obj.Count < 1024 {
+		return &NFSStatusError{NFSStatusTooSmall, io.ErrShortBuffer}
+	}
+
+	fs, p, err := userHandle.FromHandle(ctx, obj.Handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+
+	contents, verifier, err := getDirListingWithVerifier(ctx, userHandle, obj.Handle, obj.CookieVerif)
+	if err != nil {
+		return err
+	}
+	if obj.Cookie > 0 && obj.CookieVerif > 0 && verifier != obj.CookieVerif {
+		return &NFSStatusError{NFSStatusBadCookie, nil}
+	}
+
+	entities := make([]readDirEntity, 0)
+	maxBytes := uint32(100) // conservative overhead measure
+
+	started := obj.Cookie == 0
+	if started {
+		// add '.' and '..' to entities
+		dotdotFileID := uint64(0)
+		if len(p) > 0 {
+			dda := tryStat(ctx, fs, p[0:len(p)-1])
+			if dda != nil {
+				dotdotFileID = dda.Fileid
+			}
+		}
+		dotFileID := uint64(0)
+		da := tryStat(ctx, fs, p)
+		if da != nil {
+			dotFileID = da.Fileid
+		}
+		entities = append(entities,
+			readDirEntity{Name: []byte("."), Cookie: 0, Next: true, FileID: dotFileID},
+			readDirEntity{Name: []byte(".."), Cookie: 1, Next: true, FileID: dotdotFileID},
+		)
+	}
+
+	eof := true
+	maxEntities := userHandle.HandleLimit() / 2
+	for i, c := range contents {
+		// cookie equates to index within contents + 2 (for '.' and '..')
+		cookie := uint64(i + 2)
+		if started {
+			maxBytes += 512 // TODO: better estimation.
+			if maxBytes > obj.Count || len(entities) > maxEntities {
+				eof = false
+				break
+			}
+
+			attrs := ToFileAttribute(c, path.Join(append(p, c.Name())...))
+			entities = append(entities, readDirEntity{
+				FileID: attrs.Fileid,
+				Name:   []byte(c.Name()),
+				Cookie: cookie,
+				Next:   true,
+			})
+		} else if cookie == obj.Cookie {
+			started = true
+		}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, p)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := xdr.Write(writer, verifier); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := xdr.Write(writer, len(entities) > 0); err != nil { // next
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if len(entities) > 0 {
+		entities[len(entities)-1].Next = false
+		// no next for last entity
+
+		for _, e := range entities {
+			if err := xdr.Write(writer, e); err != nil {
+				return &NFSStatusError{NFSStatusServerFault, err}
+			}
+		}
+	}
+	if err := xdr.Write(writer, eof); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	// TODO: track writer size at this point to validate maxcount estimation and stop early if needed.
+
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}
+
+func getDirListingWithVerifier(ctx context.Context, userHandle Handler, fsHandle []byte, verifier uint64) ([]fs.FileInfo, uint64, error) {
+	// figure out what directory it is.
+	fs, p, err := userHandle.FromHandle(ctx, fsHandle)
+	if err != nil {
+		return nil, 0, &NFSStatusError{NFSStatusStale, err}
+	}
+
+	path := fs.Join(p...)
+	// see if the verifier has this dir cached:
+	if vh, ok := userHandle.(CachingHandler); verifier != 0 && ok {
+		entries := vh.DataForVerifier(path, verifier)
+		if entries != nil {
+			return entries, verifier, nil
+		}
+	}
+	// load the entries.
+	contents, err := fs.ReadDir(ctx, path)
+	if err != nil {
+		if os.IsPermission(err) {
+			return nil, 0, &NFSStatusError{NFSStatusAccess, err}
+		}
+		if errors.Is(err, context.DeadlineExceeded) {
+			return nil, 0, &NFSStatusError{timeoutStatus, err}
+		}
+		return nil, 0, &NFSStatusError{NFSStatusIO, err}
+	}
+
+	sort.Slice(contents, func(i, j int) bool {
+		return contents[i].Name() < contents[j].Name()
+	})
+
+	if vh, ok := userHandle.(CachingHandler); ok {
+		// let the user handler make a verifier if it can.
+		v := vh.VerifierFor(path, contents)
+		return contents, v, nil
+	}
+
+	id := hashPathAndContents(path, contents)
+	return contents, id, nil
+}
+
+func hashPathAndContents(path string, contents []fs.FileInfo) uint64 {
+	//calculate a cookie-verifier.
+	vHash := sha256.New()
+
+	// Add the path to avoid collisions of directories with the same content
+	vHash.Write([]byte(path))
+
+	for _, c := range contents {
+		vHash.Write([]byte(c.Name())) // Never fails according to the docs
+	}
+
+	verify := vHash.Sum(nil)[0:8]
+	return binary.BigEndian.Uint64(verify)
+}

server/pkg/go-nfs/nfs_onreaddirplus.go

@@ -0,0 +1,153 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"path"
+
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+type readDirPlusArgs struct {
+	Handle      []byte
+	Cookie      uint64
+	CookieVerif uint64
+	DirCount    uint32
+	MaxCount    uint32
+}
+
+type readDirPlusEntity struct {
+	FileID     uint64
+	Name       []byte
+	Cookie     uint64
+	Attributes *FileAttribute `xdr:"optional"`
+	Handle     *[]byte        `xdr:"optional"`
+	Next       bool
+}
+
+func joinPath(parent []string, elements ...string) []string {
+	joinedPath := make([]string, 0, len(parent)+len(elements))
+	joinedPath = append(joinedPath, parent...)
+	joinedPath = append(joinedPath, elements...)
+	return joinedPath
+}
+
+func onReadDirPlus(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = opAttrErrorFormatter
+	obj := readDirPlusArgs{}
+	if err := xdr.Read(w.req.Body, &obj); err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	// in case of test, nfs-client send:
+	// DirCount = 512
+	// MaxCount = 4096
+	if obj.DirCount < 512 || obj.MaxCount < 4096 {
+		return &NFSStatusError{NFSStatusTooSmall, nil}
+	}
+
+	fs, p, err := userHandle.FromHandle(ctx, obj.Handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+
+	contents, verifier, err := getDirListingWithVerifier(ctx, userHandle, obj.Handle, obj.CookieVerif)
+	if err != nil {
+		return err
+	}
+	if obj.Cookie > 0 && obj.CookieVerif > 0 && verifier != obj.CookieVerif {
+		return &NFSStatusError{NFSStatusBadCookie, nil}
+	}
+
+	entities := make([]readDirPlusEntity, 0)
+	dirBytes := uint32(0)
+	maxBytes := uint32(100) // conservative overhead measure
+
+	started := obj.Cookie == 0
+	if started {
+		// add '.' and '..' to entities
+		dotdotFileID := uint64(0)
+		if len(p) > 0 {
+			dda := tryStat(ctx, fs, p[0:len(p)-1])
+			if dda != nil {
+				dotdotFileID = dda.Fileid
+			}
+		}
+		dotFileID := uint64(0)
+		da := tryStat(ctx, fs, p)
+		if da != nil {
+			dotFileID = da.Fileid
+		}
+		entities = append(entities,
+			readDirPlusEntity{Name: []byte("."), Cookie: 0, Next: true, FileID: dotFileID, Attributes: da},
+			readDirPlusEntity{Name: []byte(".."), Cookie: 1, Next: true, FileID: dotdotFileID},
+		)
+	}
+
+	eof := true
+	maxEntities := userHandle.HandleLimit() / 2
+	fb := 0
+	fss := 0
+	for i, c := range contents {
+		// cookie equates to index within contents + 2 (for '.' and '..')
+		cookie := uint64(i + 2)
+		fb++
+		if started {
+			fss++
+			dirBytes += uint32(len(c.Name()) + 20)
+			maxBytes += 512 // TODO: better estimation.
+			if dirBytes > obj.DirCount || maxBytes > obj.MaxCount || len(entities) > maxEntities {
+				eof = false
+				break
+			}
+
+			filePath := joinPath(p, c.Name())
+			handle := userHandle.ToHandle(ctx, fs, filePath)
+			attrs := ToFileAttribute(c, path.Join(filePath...))
+			entities = append(entities, readDirPlusEntity{
+				FileID:     attrs.Fileid,
+				Name:       []byte(c.Name()),
+				Cookie:     cookie,
+				Attributes: attrs,
+				Handle:     &handle,
+				Next:       true,
+			})
+		} else if cookie == obj.Cookie {
+			started = true
+		}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, p)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := xdr.Write(writer, verifier); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := xdr.Write(writer, len(entities) > 0); err != nil { // next
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if len(entities) > 0 {
+		entities[len(entities)-1].Next = false
+		// no next for last entity
+
+		for _, e := range entities {
+			if err := xdr.Write(writer, e); err != nil {
+				return &NFSStatusError{NFSStatusServerFault, err}
+			}
+		}
+	}
+	if err := xdr.Write(writer, eof); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	// TODO: track writer size at this point to validate maxcount estimation and stop early if needed.
+
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onreadlink.go

@@ -0,0 +1,55 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"os"
+
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+func onReadLink(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = opAttrErrorFormatter
+	handle, err := xdr.ReadOpaque(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	fs, path, err := userHandle.FromHandle(ctx, handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+
+	out, err := fs.Readlink(ctx, fs.Join(path...))
+	if err != nil {
+		if info, err := fs.Stat(ctx, fs.Join(path...)); err == nil {
+			if info.Mode()&os.ModeSymlink == 0 {
+				return &NFSStatusError{NFSStatusInval, err}
+			}
+		}
+		if os.IsNotExist(err) {
+			return &NFSStatusError{NFSStatusNoEnt, err}
+		}
+		if errors.Is(err, context.DeadlineExceeded) {
+			return &NFSStatusError{timeoutStatus, err}
+		}
+
+		return &NFSStatusError{NFSStatusAccess, err}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := xdr.Write(writer, out); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onremove.go

@@ -0,0 +1,85 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"os"
+
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+func onRemove(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = wccDataErrorFormatter
+	obj := DirOpArg{}
+	if err := xdr.Read(w.req.Body, &obj); err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	fs, path, err := userHandle.FromHandle(ctx, obj.Handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+
+	// TODO
+	// if !CapabilityCheck(fs, billy.WriteCapability) {
+	// 	return &NFSStatusError{NFSStatusROFS, os.ErrPermission}
+	// }
+
+	if len(string(obj.Filename)) > PathNameMax {
+		return &NFSStatusError{NFSStatusNameTooLong, nil}
+	}
+
+	fullPath := fs.Join(path...)
+	dirInfo, err := fs.Stat(ctx, fullPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &NFSStatusError{NFSStatusNoEnt, err}
+		}
+		if os.IsPermission(err) {
+			return &NFSStatusError{NFSStatusAccess, err}
+		}
+		if errors.Is(err, context.DeadlineExceeded) {
+			return &NFSStatusError{timeoutStatus, err}
+		}
+		return &NFSStatusError{NFSStatusIO, err}
+	}
+	if !dirInfo.IsDir() {
+		return &NFSStatusError{NFSStatusNotDir, nil}
+	}
+	preCacheData := ToFileAttribute(dirInfo, fullPath).AsCache()
+
+	toDelete := fs.Join(append(path, string(obj.Filename))...)
+	toDeleteHandle := userHandle.ToHandle(ctx, fs, append(path, string(obj.Filename)))
+
+	err = fs.Remove(ctx, toDelete)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &NFSStatusError{NFSStatusNoEnt, err}
+		}
+		if os.IsPermission(err) {
+			return &NFSStatusError{NFSStatusAccess, err}
+		}
+		if errors.Is(err, context.DeadlineExceeded) {
+			return &NFSStatusError{timeoutStatus, err}
+		}
+		return &NFSStatusError{NFSStatusIO, err}
+	}
+
+	if err := userHandle.InvalidateHandle(ctx, fs, toDeleteHandle); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := WriteWcc(writer, preCacheData, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onrename.go

@@ -0,0 +1,120 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"os"
+	"reflect"
+
+	"github.com/go-git/go-billy/v5"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+var doubleWccErrorBody = [16]byte{}
+
+func onRename(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = errFormatterWithBody(doubleWccErrorBody[:])
+	from := DirOpArg{}
+	err := xdr.Read(w.req.Body, &from)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	fs, fromPath, err := userHandle.FromHandle(ctx, from.Handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+
+	to := DirOpArg{}
+	if err = xdr.Read(w.req.Body, &to); err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	fs2, toPath, err := userHandle.FromHandle(ctx, to.Handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+	// check the two fs are the same
+	if !reflect.DeepEqual(fs, fs2) {
+		return &NFSStatusError{NFSStatusNotSupp, os.ErrPermission}
+	}
+
+	if !CapabilityCheck(fs, billy.WriteCapability) {
+		return &NFSStatusError{NFSStatusROFS, os.ErrPermission}
+	}
+
+	if len(string(from.Filename)) > PathNameMax || len(string(to.Filename)) > PathNameMax {
+		return &NFSStatusError{NFSStatusNameTooLong, os.ErrInvalid}
+	}
+
+	fromDirPath := fs.Join(fromPath...)
+	fromDirInfo, err := fs.Stat(ctx, fromDirPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &NFSStatusError{NFSStatusNoEnt, err}
+		}
+		if errors.Is(err, context.DeadlineExceeded) {
+			return &NFSStatusError{timeoutStatus, err}
+		}
+		return &NFSStatusError{NFSStatusIO, err}
+	}
+	if !fromDirInfo.IsDir() {
+		return &NFSStatusError{NFSStatusNotDir, nil}
+	}
+	preCacheData := ToFileAttribute(fromDirInfo, fromDirPath).AsCache()
+
+	toDirPath := fs.Join(toPath...)
+	toDirInfo, err := fs.Stat(ctx, toDirPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &NFSStatusError{NFSStatusNoEnt, err}
+		}
+		if errors.Is(err, context.DeadlineExceeded) {
+			return &NFSStatusError{timeoutStatus, err}
+		}
+		return &NFSStatusError{NFSStatusIO, err}
+	}
+	if !toDirInfo.IsDir() {
+		return &NFSStatusError{NFSStatusNotDir, nil}
+	}
+	preDestData := ToFileAttribute(toDirInfo, toDirPath).AsCache()
+
+	oldHandle := userHandle.ToHandle(ctx, fs, append(fromPath, string(from.Filename)))
+
+	fromLoc := fs.Join(append(fromPath, string(from.Filename))...)
+	toLoc := fs.Join(append(toPath, string(to.Filename))...)
+
+	err = fs.Rename(ctx, fromLoc, toLoc)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &NFSStatusError{NFSStatusNoEnt, err}
+		}
+		if os.IsPermission(err) {
+			return &NFSStatusError{NFSStatusAccess, err}
+		}
+		if errors.Is(err, context.DeadlineExceeded) {
+			return &NFSStatusError{timeoutStatus, err}
+		}
+		return &NFSStatusError{NFSStatusIO, err}
+	}
+
+	if err := userHandle.InvalidateHandle(ctx, fs, oldHandle); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := WriteWcc(writer, preCacheData, tryStat(ctx, fs, fromPath)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WriteWcc(writer, preDestData, tryStat(ctx, fs, toPath)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onrmdir.go

@@ -0,0 +1,9 @@
+package nfs
+
+import (
+	"context"
+)
+
+func onRmDir(ctx context.Context, w *response, userHandle Handler) error {
+	return onRemove(ctx, w, userHandle)
+}

server/pkg/go-nfs/nfs_onsetattr.go

@@ -0,0 +1,80 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"os"
+
+	"github.com/go-git/go-billy/v5"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+func onSetAttr(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = wccDataErrorFormatter
+	handle, err := xdr.ReadOpaque(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	fs, path, err := userHandle.FromHandle(ctx, handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+	attrs, err := ReadSetFileAttributes(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	fullPath := fs.Join(path...)
+	info, err := fs.Lstat(ctx, fullPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &NFSStatusError{NFSStatusNoEnt, err}
+		}
+		if errors.Is(err, context.DeadlineExceeded) {
+			return &NFSStatusError{timeoutStatus, err}
+		}
+		return &NFSStatusError{NFSStatusAccess, err}
+	}
+
+	// see if there's a "guard"
+	if guard, err := xdr.ReadUint32(w.req.Body); err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	} else if guard != 0 {
+		// read the ctime.
+		t := FileTime{}
+		if err := xdr.Read(w.req.Body, &t); err != nil {
+			return &NFSStatusError{NFSStatusInval, err}
+		}
+		attr := ToFileAttribute(info, fullPath)
+		if t != attr.Ctime {
+			return &NFSStatusError{NFSStatusNotSync, nil}
+		}
+	}
+
+	if !CapabilityCheck(fs, billy.WriteCapability) {
+		return &NFSStatusError{NFSStatusROFS, os.ErrPermission}
+	}
+
+	changer := userHandle.Change(fs)
+	if err := attrs.Apply(ctx, changer, fs, fs.Join(path...)); err != nil {
+		// Already an nfsstatuserror
+		return err
+	}
+
+	preAttr := ToFileAttribute(info, fullPath).AsCache()
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WriteWcc(writer, preAttr, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onsymlink.go

@@ -0,0 +1,88 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"os"
+
+	"github.com/go-git/go-billy/v5"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+func onSymlink(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = wccDataErrorFormatter
+	obj := DirOpArg{}
+	err := xdr.Read(w.req.Body, &obj)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+	attrs, err := ReadSetFileAttributes(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	target, err := xdr.ReadOpaque(w.req.Body)
+	if err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	fs, path, err := userHandle.FromHandle(ctx, obj.Handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+	if !CapabilityCheck(fs, billy.WriteCapability) {
+		return &NFSStatusError{NFSStatusROFS, os.ErrPermission}
+	}
+
+	if len(string(obj.Filename)) > PathNameMax {
+		return &NFSStatusError{NFSStatusNameTooLong, os.ErrInvalid}
+	}
+
+	newFilePath := fs.Join(append(path, string(obj.Filename))...)
+	if _, err := fs.Stat(ctx, newFilePath); err == nil {
+		return &NFSStatusError{NFSStatusExist, os.ErrExist}
+	}
+	if s, err := fs.Stat(ctx, fs.Join(path...)); err != nil {
+		return &NFSStatusError{NFSStatusAccess, err}
+	} else if !s.IsDir() {
+		return &NFSStatusError{NFSStatusNotDir, nil}
+	}
+
+	err = fs.Symlink(ctx, string(target), newFilePath)
+	if err != nil {
+		return &NFSStatusError{NFSStatusAccess, err}
+	}
+
+	fp := userHandle.ToHandle(ctx, fs, append(path, string(obj.Filename)))
+	changer := userHandle.Change(fs)
+	if changer != nil {
+		if err := attrs.Apply(ctx, changer, fs, newFilePath); err != nil {
+			return &NFSStatusError{NFSStatusIO, err}
+		}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	// "handle follows"
+	if err := xdr.Write(writer, uint32(1)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := xdr.Write(writer, fp); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := WritePostOpAttrs(writer, tryStat(ctx, fs, append(path, string(obj.Filename)))); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := WriteWcc(writer, nil, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_onwrite.go

@@ -0,0 +1,117 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"io"
+	"math"
+	"os"
+
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+// writeStability is the level of durability requested with the write
+type writeStability uint32
+
+const (
+	unstable writeStability = 0
+	dataSync writeStability = 1
+	fileSync writeStability = 2
+)
+
+type writeArgs struct {
+	Handle []byte
+	Offset uint64
+	Count  uint32
+	How    uint32
+	Data   []byte
+}
+
+func onWrite(ctx context.Context, w *response, userHandle Handler) error {
+	w.errorFmt = wccDataErrorFormatter
+	var req writeArgs
+	if err := xdr.Read(w.req.Body, &req); err != nil {
+		return &NFSStatusError{NFSStatusInval, err}
+	}
+
+	fs, path, err := userHandle.FromHandle(ctx, req.Handle)
+	if err != nil {
+		return &NFSStatusError{NFSStatusStale, err}
+	}
+	// TODO
+	// if !CapabilityCheck(fs, billy.WriteCapability) {
+	// 	return &NFSStatusError{NFSStatusROFS, os.ErrPermission}
+	// }
+	if len(req.Data) > math.MaxInt32 || req.Count > math.MaxInt32 {
+		return &NFSStatusError{NFSStatusFBig, os.ErrInvalid}
+	}
+	if req.How != uint32(unstable) && req.How != uint32(dataSync) && req.How != uint32(fileSync) {
+		return &NFSStatusError{NFSStatusInval, os.ErrInvalid}
+	}
+
+	// stat first for pre-op wcc.
+	fullPath := fs.Join(path...)
+	info, err := fs.Stat(ctx, fullPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &NFSStatusError{NFSStatusNoEnt, err}
+		}
+		if errors.Is(err, context.DeadlineExceeded) {
+			return &NFSStatusError{timeoutStatus, err}
+		}
+		return &NFSStatusError{NFSStatusAccess, err}
+	}
+	if !info.Mode().IsRegular() {
+		return &NFSStatusError{NFSStatusInval, os.ErrInvalid}
+	}
+	preOpCache := ToFileAttribute(info, fullPath).AsCache()
+
+	// now the actual op.
+	file, err := fs.OpenFile(ctx, fs.Join(path...), os.O_RDWR, info.Mode().Perm())
+	if err != nil {
+		return &NFSStatusError{NFSStatusAccess, err}
+	}
+	defer file.Close(ctx)
+	if req.Offset > 0 {
+		if _, err := file.Seek(int64(req.Offset), io.SeekStart); err != nil {
+			return &NFSStatusError{NFSStatusIO, err}
+		}
+	}
+	end := req.Count
+	if len(req.Data) < int(end) {
+		end = uint32(len(req.Data))
+	}
+	writtenCount, err := file.Write(ctx, req.Data[:end])
+	if err != nil {
+		Log.Errorf("Error writing: %v", err)
+		return &NFSStatusError{NFSStatusIO, err}
+	}
+	if err := file.Close(ctx); err != nil {
+		Log.Errorf("error closing: %v", err)
+		return &NFSStatusError{NFSStatusIO, err}
+	}
+
+	writer := bytes.NewBuffer([]byte{})
+	if err := xdr.Write(writer, uint32(NFSStatusOk)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := WriteWcc(writer, preOpCache, tryStat(ctx, fs, path)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := xdr.Write(writer, uint32(writtenCount)); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := xdr.Write(writer, fileSync); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	if err := xdr.Write(writer, w.Server.ID); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+
+	if err := w.Write(writer.Bytes()); err != nil {
+		return &NFSStatusError{NFSStatusServerFault, err}
+	}
+	return nil
+}

server/pkg/go-nfs/nfs_test.go

@@ -0,0 +1,294 @@
+package nfs_test
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"net"
+	"os"
+	"reflect"
+	"sort"
+	"testing"
+
+	nfs "git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs"
+	"git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs/helpers"
+	"git.kmsign.ru/royalcat/tstor/server/pkg/go-nfs/helpers/memfs"
+
+	nfsc "github.com/willscott/go-nfs-client/nfs"
+	rpc "github.com/willscott/go-nfs-client/nfs/rpc"
+	"github.com/willscott/go-nfs-client/nfs/util"
+	"github.com/willscott/go-nfs-client/nfs/xdr"
+)
+
+func TestNFS(t *testing.T) {
+	ctx := context.Background()
+
+	if testing.Verbose() {
+		util.DefaultLogger.SetDebug(true)
+	}
+
+	// make an empty in-memory server.
+	listener, err := net.Listen("tcp", "localhost:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	mem := helpers.WrapBillyFS(memfs.New())
+	// File needs to exist in the root for memfs to acknowledge the root exists.
+	_, _ = mem.Create(ctx, "/test")
+
+	handler := helpers.NewNullAuthHandler(mem)
+	cacheHelper := helpers.NewCachingHandler(handler, 1024)
+	go func() {
+		_ = nfs.Serve(listener, cacheHelper)
+	}()
+
+	c, err := rpc.DialTCP(listener.Addr().Network(), listener.Addr().(*net.TCPAddr).String(), false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer c.Close()
+
+	var mounter nfsc.Mount
+	mounter.Client = c
+	target, err := mounter.Mount("/", rpc.AuthNull)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		_ = mounter.Unmount()
+	}()
+
+	_, err = target.FSInfo()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Validate sample file creation
+	_, err = target.Create("/helloworld.txt", 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if info, err := mem.Stat(ctx, "/helloworld.txt"); err != nil {
+		t.Fatal(err)
+	} else {
+		if info.Size() != 0 || info.Mode().Perm() != 0666 {
+			t.Fatal("incorrect creation.")
+		}
+	}
+
+	// Validate writing to a file.
+	f, err := target.OpenFile("/helloworld.txt", 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+	b := []byte("hello world")
+	_, err = f.Write(b)
+	if err != nil {
+		t.Fatal(err)
+	}
+	mf, _ := mem.OpenFile(ctx, "/helloworld.txt", os.O_RDONLY, 0)
+	buf := make([]byte, len(b))
+	if _, err = mf.ReadAt(ctx, buf[:], 0); err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(buf, b) {
+		t.Fatal("written does not match expected")
+	}
+
+	// for test nfs.ReadDirPlus in case of many files
+	dirF1, err := mem.ReadDir(ctx, "/")
+	if err != nil {
+		t.Fatal(err)
+	}
+	shouldBeNames := []string{}
+	for _, f := range dirF1 {
+		shouldBeNames = append(shouldBeNames, f.Name())
+	}
+	for i := 0; i < 2000; i++ {
+		fName := fmt.Sprintf("f-%04d.txt", i)
+		shouldBeNames = append(shouldBeNames, fName)
+		f, err := mem.Create(ctx, fName)
+		if err != nil {
+			t.Fatal(err)
+		}
+		f.Close(ctx)
+	}
+
+	manyEntitiesPlus, err := target.ReadDirPlus("/")
+	if err != nil {
+		t.Fatal(err)
+	}
+	actualBeNamesPlus := []string{}
+	for _, e := range manyEntitiesPlus {
+		actualBeNamesPlus = append(actualBeNamesPlus, e.Name())
+	}
+
+	as := sort.StringSlice(shouldBeNames)
+	bs := sort.StringSlice(actualBeNamesPlus)
+	as.Sort()
+	bs.Sort()
+	if !reflect.DeepEqual(as, bs) {
+		t.Fatal("nfs.ReadDirPlus error")
+	}
+
+	// for test nfs.ReadDir in case of many files
+	manyEntities, err := readDir(target, "/")
+	if err != nil {
+		t.Fatal(err)
+	}
+	actualBeNames := []string{}
+	for _, e := range manyEntities {
+		actualBeNames = append(actualBeNames, e.FileName)
+	}
+
+	as2 := sort.StringSlice(shouldBeNames)
+	bs2 := sort.StringSlice(actualBeNames)
+	as2.Sort()
+	bs2.Sort()
+	if !reflect.DeepEqual(as2, bs2) {
+		fmt.Printf("should be %v\n", as2)
+		fmt.Printf("actual be %v\n", bs2)
+		t.Fatal("nfs.ReadDir error")
+	}
+
+	// confirm rename works as expected
+	oldFA, _, err := target.Lookup("/f-0010.txt", false)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if err := target.Rename("/f-0010.txt", "/g-0010.txt"); err != nil {
+		t.Fatal(err)
+	}
+	new, _, err := target.Lookup("/g-0010.txt", false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if new.Sys() != oldFA.Sys() {
+		t.Fatal("rename failed to update")
+	}
+	_, _, err = target.Lookup("/f-0010.txt", false)
+	if err == nil {
+		t.Fatal("old handle should be invalid")
+	}
+
+	// for test nfs.ReadDirPlus in case of empty directory
+	_, err = target.Mkdir("/empty", 0755)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	emptyEntitiesPlus, err := target.ReadDirPlus("/empty")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(emptyEntitiesPlus) != 0 {
+		t.Fatal("nfs.ReadDirPlus error reading empty dir")
+	}
+
+	// for test nfs.ReadDir in case of empty directory
+	emptyEntities, err := readDir(target, "/empty")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(emptyEntities) != 0 {
+		t.Fatal("nfs.ReadDir error reading empty dir")
+	}
+}
+
+type readDirEntry struct {
+	FileId   uint64
+	FileName string
+	Cookie   uint64
+}
+
+// readDir implementation "appropriated" from go-nfs-client implementation of READDIRPLUS
+func readDir(target *nfsc.Target, dir string) ([]*readDirEntry, error) {
+	_, fh, err := target.Lookup(dir)
+	if err != nil {
+		return nil, err
+	}
+
+	type readDirArgs struct {
+		rpc.Header
+		Handle      []byte
+		Cookie      uint64
+		CookieVerif uint64
+		Count       uint32
+	}
+
+	type readDirList struct {
+		IsSet bool         `xdr:"union"`
+		Entry readDirEntry `xdr:"unioncase=1"`
+	}
+
+	type readDirListOK struct {
+		DirAttrs   nfsc.PostOpAttr
+		CookieVerf uint64
+	}
+
+	cookie := uint64(0)
+	cookieVerf := uint64(0)
+	eof := false
+
+	var entries []*readDirEntry
+	for !eof {
+		res, err := target.Call(&readDirArgs{
+			Header: rpc.Header{
+				Rpcvers: 2,
+				Vers:    nfsc.Nfs3Vers,
+				Prog:    nfsc.Nfs3Prog,
+				Proc:    uint32(nfs.NFSProcedureReadDir),
+				Cred:    rpc.AuthNull,
+				Verf:    rpc.AuthNull,
+			},
+			Handle:      fh,
+			Cookie:      cookie,
+			CookieVerif: cookieVerf,
+			Count:       4096,
+		})
+		if err != nil {
+			return nil, err
+		}
+
+		status, err := xdr.ReadUint32(res)
+		if err != nil {
+			return nil, err
+		}
+
+		if err = nfsc.NFS3Error(status); err != nil {
+			return nil, err
+		}
+
+		dirListOK := new(readDirListOK)
+		if err = xdr.Read(res, dirListOK); err != nil {
+			return nil, err
+		}
+
+		for {
+			var item readDirList
+			if err = xdr.Read(res, &item); err != nil {
+				return nil, err
+			}
+
+			if !item.IsSet {
+				break
+			}
+
+			cookie = item.Entry.Cookie
+			if item.Entry.FileName == "." || item.Entry.FileName == ".." {
+				continue
+			}
+			entries = append(entries, &item.Entry)
+		}
+
+		if err = xdr.Read(res, &eof); err != nil {
+			return nil, err
+		}
+
+		cookieVerf = dirListOK.CookieVerf
+	}
+
+	return entries, nil
+}

server/pkg/go-nfs/nfsinterface.go

@@ -0,0 +1,190 @@
+package nfs
+
+// NFSProcedure is the valid RPC calls for the nfs service.
+type NFSProcedure uint32
+
+// NfsProcedure Codes
+const (
+	NFSProcedureNull NFSProcedure = iota
+	NFSProcedureGetAttr
+	NFSProcedureSetAttr
+	NFSProcedureLookup
+	NFSProcedureAccess
+	NFSProcedureReadlink
+	NFSProcedureRead
+	NFSProcedureWrite
+	NFSProcedureCreate
+	NFSProcedureMkDir
+	NFSProcedureSymlink
+	NFSProcedureMkNod
+	NFSProcedureRemove
+	NFSProcedureRmDir
+	NFSProcedureRename
+	NFSProcedureLink
+	NFSProcedureReadDir
+	NFSProcedureReadDirPlus
+	NFSProcedureFSStat
+	NFSProcedureFSInfo
+	NFSProcedurePathConf
+	NFSProcedureCommit
+)
+
+func (n NFSProcedure) String() string {
+	switch n {
+	case NFSProcedureNull:
+		return "Null"
+	case NFSProcedureGetAttr:
+		return "GetAttr"
+	case NFSProcedureSetAttr:
+		return "SetAttr"
+	case NFSProcedureLookup:
+		return "Lookup"
+	case NFSProcedureAccess:
+		return "Access"
+	case NFSProcedureReadlink:
+		return "ReadLink"
+	case NFSProcedureRead:
+		return "Read"
+	case NFSProcedureWrite:
+		return "Write"
+	case NFSProcedureCreate:
+		return "Create"
+	case NFSProcedureMkDir:
+		return "Mkdir"
+	case NFSProcedureSymlink:
+		return "Symlink"
+	case NFSProcedureMkNod:
+		return "Mknod"
+	case NFSProcedureRemove:
+		return "Remove"
+	case NFSProcedureRmDir:
+		return "Rmdir"
+	case NFSProcedureRename:
+		return "Rename"
+	case NFSProcedureLink:
+		return "Link"
+	case NFSProcedureReadDir:
+		return "ReadDir"
+	case NFSProcedureReadDirPlus:
+		return "ReadDirPlus"
+	case NFSProcedureFSStat:
+		return "FSStat"
+	case NFSProcedureFSInfo:
+		return "FSInfo"
+	case NFSProcedurePathConf:
+		return "PathConf"
+	case NFSProcedureCommit:
+		return "Commit"
+	default:
+		return "Unknown"
+	}
+}
+
+const timeoutStatus = NFSStatusIO
+
+// NFSStatus (nfsstat3) is a result code for nfs rpc calls
+type NFSStatus uint32
+
+// NFSStatus codes
+const (
+	NFSStatusOk          NFSStatus = 0
+	NFSStatusPerm        NFSStatus = 1
+	NFSStatusNoEnt       NFSStatus = 2
+	NFSStatusIO          NFSStatus = 5
+	NFSStatusNXIO        NFSStatus = 6
+	NFSStatusAccess      NFSStatus = 13
+	NFSStatusExist       NFSStatus = 17
+	NFSStatusXDev        NFSStatus = 18
+	NFSStatusNoDev       NFSStatus = 19
+	NFSStatusNotDir      NFSStatus = 20
+	NFSStatusIsDir       NFSStatus = 21
+	NFSStatusInval       NFSStatus = 22
+	NFSStatusFBig        NFSStatus = 27
+	NFSStatusNoSPC       NFSStatus = 28
+	NFSStatusROFS        NFSStatus = 30
+	NFSStatusMlink       NFSStatus = 31
+	NFSStatusNameTooLong NFSStatus = 63
+	NFSStatusNotEmpty    NFSStatus = 66
+	NFSStatusDQuot       NFSStatus = 69
+	NFSStatusStale       NFSStatus = 70
+	NFSStatusRemote      NFSStatus = 71
+	NFSStatusBadHandle   NFSStatus = 10001
+	NFSStatusNotSync     NFSStatus = 10002
+	NFSStatusBadCookie   NFSStatus = 10003
+	NFSStatusNotSupp     NFSStatus = 10004
+	NFSStatusTooSmall    NFSStatus = 10005
+	NFSStatusServerFault NFSStatus = 10006
+	NFSStatusBadType     NFSStatus = 10007
+	NFSStatusJukebox     NFSStatus = 10008
+)
+
+func (s NFSStatus) String() string {
+	switch s {
+	case NFSStatusOk:
+		return "Call Completed Successfull"
+	case NFSStatusPerm:
+		return "Not Owner"
+	case NFSStatusNoEnt:
+		return "No such file or directory"
+	case NFSStatusIO:
+		return "I/O error"
+	case NFSStatusNXIO:
+		return "I/O error: No such device"
+	case NFSStatusAccess:
+		return "Permission denied"
+	case NFSStatusExist:
+		return "File exists"
+	case NFSStatusXDev:
+		return "Attempt to do a cross device hard link"
+	case NFSStatusNoDev:
+		return "No such device"
+	case NFSStatusNotDir:
+		return "Not a directory"
+	case NFSStatusIsDir:
+		return "Is a directory"
+	case NFSStatusInval:
+		return "Invalid argument"
+	case NFSStatusFBig:
+		return "File too large"
+	case NFSStatusNoSPC:
+		return "No space left on device"
+	case NFSStatusROFS:
+		return "Read only file system"
+	case NFSStatusMlink:
+		return "Too many hard links"
+	case NFSStatusNameTooLong:
+		return "Name too long"
+	case NFSStatusNotEmpty:
+		return "Not empty"
+	case NFSStatusDQuot:
+		return "Resource quota exceeded"
+	case NFSStatusStale:
+		return "Invalid file handle"
+	case NFSStatusRemote:
+		return "Too many levels of remote in path"
+	case NFSStatusBadHandle:
+		return "Illegal NFS file handle"
+	case NFSStatusNotSync:
+		return "Synchronization mismatch"
+	case NFSStatusBadCookie:
+		return "Cookie is Stale"
+	case NFSStatusNotSupp:
+		return "Operation not supported"
+	case NFSStatusTooSmall:
+		return "Buffer or request too small"
+	case NFSStatusServerFault:
+		return "Unmapped error (EIO)"
+	case NFSStatusBadType:
+		return "Type not supported"
+	case NFSStatusJukebox:
+		return "Initiated, but too slow. Try again with new txn"
+	default:
+		return "unknown"
+	}
+}
+
+// DirOpArg is a common serialization used for referencing an object in a directory
+type DirOpArg struct {
+	Handle   []byte
+	Filename []byte
+}

server/pkg/go-nfs/server.go

@@ -0,0 +1,102 @@
+package nfs
+
+import (
+	"bytes"
+	"context"
+	"crypto/rand"
+	"errors"
+	"net"
+	"time"
+)
+
+// Server is a handle to the listening NFS server.
+type Server struct {
+	Handler
+	ID [8]byte
+}
+
+// RegisterMessageHandler registers a handler for a specific
+// XDR procedure.
+func RegisterMessageHandler(protocol uint32, proc uint32, handler HandleFunc) error {
+	if registeredHandlers == nil {
+		registeredHandlers = make(map[registeredHandlerID]HandleFunc)
+	}
+	for k := range registeredHandlers {
+		if k.protocol == protocol && k.proc == proc {
+			return errors.New("already registered")
+		}
+	}
+	id := registeredHandlerID{protocol, proc}
+	registeredHandlers[id] = handler
+	return nil
+}
+
+// HandleFunc represents a handler for a specific protocol message.
+type HandleFunc func(ctx context.Context, w *response, userHandler Handler) error
+
+// TODO: store directly as a uint64 for more efficient lookups
+type registeredHandlerID struct {
+	protocol uint32
+	proc     uint32
+}
+
+var registeredHandlers map[registeredHandlerID]HandleFunc
+
+// Serve listens on the provided listener port for incoming client requests.
+func (s *Server) Serve(l net.Listener) error {
+	defer l.Close()
+	if bytes.Equal(s.ID[:], []byte{0, 0, 0, 0, 0, 0, 0, 0}) {
+		if _, err := rand.Reader.Read(s.ID[:]); err != nil {
+			return err
+		}
+	}
+
+	var tempDelay time.Duration
+
+	for {
+		conn, err := l.Accept()
+		if err != nil {
+			if ne, ok := err.(net.Error); ok && ne.Timeout() {
+				if tempDelay == 0 {
+					tempDelay = 5 * time.Millisecond
+				} else {
+					tempDelay *= 2
+				}
+				if max := 1 * time.Second; tempDelay > max {
+					tempDelay = max
+				}
+				time.Sleep(tempDelay)
+				continue
+			}
+			return err
+		}
+		tempDelay = 0
+		c := s.newConn(conn)
+		go c.serve()
+	}
+}
+
+func (s *Server) newConn(nc net.Conn) *conn {
+	c := &conn{
+		Server: s,
+		Conn:   nc,
+	}
+	return c
+}
+
+// TODO: keep an immutable map for each server instance to have less
+// chance of races.
+func (s *Server) handlerFor(prog uint32, proc uint32) HandleFunc {
+	for k, v := range registeredHandlers {
+		if k.protocol == prog && k.proc == proc {
+			return v
+		}
+	}
+	return nil
+}
+
+// Serve is a singleton listener paralleling http.Serve
+func Serve(l net.Listener, handler Handler) error {
+	srv := &Server{Handler: handler}
+	return srv.Serve(l)
+}

server/pkg/go-nfs/time.go

@@ -0,0 +1,32 @@
+package nfs
+
+import (
+	"time"
+)
+
+// FileTime is the NFS wire time format
+// This is equivalent to go-nfs-client/nfs.NFS3Time
+type FileTime struct {
+	Seconds  uint32
+	Nseconds uint32
+}
+
+// ToNFSTime generates the nfs 64bit time format from a golang time.
+func ToNFSTime(t time.Time) FileTime {
+	return FileTime{
+		Seconds:  uint32(t.Unix()),
+		Nseconds: uint32(t.UnixNano() % int64(time.Second)),
+	}
+}
+
+// Native generates a golang time from an nfs time spec
+func (t FileTime) Native() *time.Time {
+	ts := time.Unix(int64(t.Seconds), int64(t.Nseconds))
+	return &ts
+}
+
+// EqualTimespec returns if this time is equal to a local time spec
+func (t FileTime) EqualTimespec(sec int64, nsec int64) bool {
+	// TODO: bounds check on sec/nsec overflow
+	return t.Nseconds == uint32(nsec) && t.Seconds == uint32(sec)
+}

server/pkg/ioutils/cachereader.go

@@ -0,0 +1,71 @@
+package ioutils
+
+import (
+	"context"
+	"errors"
+	"io"
+	"sync"
+
+	"github.com/royalcat/ctxio"
+)
+
+type FileReader interface {
+	ctxio.ReaderAt
+	ctxio.Reader
+	ctxio.Closer
+}
+
+type CacheReader struct {
+	m sync.Mutex
+
+	fo int64
+	fr *FileBuffer
+	to int64
+	tr ctxio.Reader
+}
+
+var _ FileReader = (*CacheReader)(nil)
+
+func NewCacheReader(r ctxio.Reader) (FileReader, error) {
+	fr := NewFileBuffer(nil)
+	tr := ctxio.TeeReader(r, fr)
+	return &CacheReader{fr: fr, tr: tr}, nil
+}
+
+func (dtr *CacheReader) ReadAt(ctx context.Context, p []byte, off int64) (int, error) {
+	dtr.m.Lock()
+	defer dtr.m.Unlock()
+	tb := off + int64(len(p))
+
+	if tb > dtr.fo {
+		w, err := ctxio.CopyN(ctx, ctxio.Discard, dtr.tr, tb-dtr.fo)
+		dtr.to += w
+		if err != nil && err != io.EOF {
+			return 0, err
+		}
+	}
+
+	n, err := dtr.fr.ReadAt(ctx, p, off)
+	dtr.fo += int64(n)
+	return n, err
+}
+
+func (dtr *CacheReader) Read(ctx context.Context, p []byte) (n int, err error) {
+	dtr.m.Lock()
+	defer dtr.m.Unlock()
+	// use directly tee reader here
+	n, err = dtr.tr.Read(ctx, p)
+	dtr.to += int64(n)
+	return
+}
+
+func (dtr *CacheReader) Close(ctx context.Context) error {
+	frcloser := dtr.fr.Close(ctx)
+
+	var closeerr error
+	if rc, ok := dtr.tr.(ctxio.ReadCloser); ok {
+		closeerr = rc.Close(ctx)
+	}
+
+	return errors.Join(frcloser, closeerr)
+}

server/pkg/ioutils/disk.go

@@ -0,0 +1,72 @@
+package ioutils
+
+import (
+	"context"
+	"io"
+	"os"
+	"sync"
+
+	"github.com/royalcat/ctxio"
+)
+
+type DiskCacheReader struct {
+	m sync.Mutex
+
+	fo int64
+	fr *os.File
+	to int64
+	tr ctxio.Reader
+}
+
+var _ ctxio.ReaderAt = (*DiskCacheReader)(nil)
+var _ ctxio.Reader = (*DiskCacheReader)(nil)
+var _ ctxio.Closer = (*DiskCacheReader)(nil)
+
+func NewDiskCacheReader(r ctxio.Reader) (*DiskCacheReader, error) {
+	tempDir, err := os.MkdirTemp("/tmp", "tstor")
+	if err != nil {
+		return nil, err
+	}
+	fr, err := os.CreateTemp(tempDir, "dtb_tmp")
+	if err != nil {
+		return nil, err
+	}
+
+	tr := ctxio.TeeReader(r, ctxio.WrapIoWriter(fr))
+	return &DiskCacheReader{fr: fr, tr: tr}, nil
+}
+
+func (dtr *DiskCacheReader) ReadAt(ctx context.Context, p []byte, off int64) (int, error) {
+	dtr.m.Lock()
+	defer dtr.m.Unlock()
+	tb := off + int64(len(p))
+
+	if tb > dtr.fo {
+		w, err := ctxio.CopyN(ctx, ctxio.Discard, dtr.tr, tb-dtr.fo)
+		dtr.to += w
+		if err != nil && err != io.EOF {
+			return 0, err
+		}
+	}
+
+	n, err := dtr.fr.ReadAt(p, off)
+	dtr.fo += int64(n)
+	return n, err
+}
+
+func (dtr *DiskCacheReader) Read(ctx context.Context, p []byte) (n int, err error) {
+	dtr.m.Lock()
+	defer dtr.m.Unlock()
+	// use directly tee reader here
+	n, err = dtr.tr.Read(ctx, p)
+	dtr.to += int64(n)
+	return
+}
+
+func (dtr *DiskCacheReader) Close(ctx context.Context) error {
+	if err := dtr.fr.Close(); err != nil {
+		return err
+	}
+
+	return os.Remove(dtr.fr.Name())
+}

server/pkg/ioutils/filebuffer.go

@@ -0,0 +1,205 @@
+package ioutils
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"io"
+	"os"
+	"sync"
+
+	"github.com/royalcat/ctxio"
+)
+
+// FileBuffer implements interfaces implemented by files.
+// The main purpose of this type is to have an in memory replacement for a
+// file.
+type FileBuffer struct {
+	// buff is the backing buffer
+	buff *bytes.Buffer
+	// index indicates where in the buffer we are at
+	index    int64
+	isClosed bool
+	mu       sync.RWMutex
+}
+
+var _ FileReader = (*FileBuffer)(nil)
+var _ ctxio.Writer = (*FileBuffer)(nil)
+
+// NewFileBuffer returns a new populated Buffer
+func NewFileBuffer(b []byte) *FileBuffer {
+	return &FileBuffer{buff: bytes.NewBuffer(b)}
+}
+
+// NewFileBufferFromReader is a convenience method that returns a new populated Buffer
+// whose contents are sourced from a supplied reader by loading it entirely
+// into memory.
+func NewFileBufferFromReader(ctx context.Context, reader ctxio.Reader) (*FileBuffer, error) {
+	data, err := ctxio.ReadAll(ctx, reader)
+	if err != nil {
+		return nil, err
+	}
+	return NewFileBuffer(data), nil
+}
+
+// NewFileBufferFromReader is a convenience method that returns a new populated Buffer
+// whose contents are sourced from a supplied reader by loading it entirely
+// into memory.
+func NewFileBufferFromIoReader(reader io.Reader) (*FileBuffer, error) {
+	data, err := io.ReadAll(reader)
+	if err != nil {
+		return nil, err
+	}
+	return NewFileBuffer(data), nil
+}
+
+// Bytes returns the bytes available until the end of the buffer.
+func (f *FileBuffer) Bytes() []byte {
+	f.mu.RLock()
+	defer f.mu.RUnlock()
+
+	if f.isClosed || f.index >= int64(f.buff.Len()) {
+		return []byte{}
+	}
+	return bytes.Clone(f.buff.Bytes()[f.index:])
+}
+
+// String implements the Stringer interface
+func (f *FileBuffer) String() string {
+	f.mu.RLock()
+	defer f.mu.RUnlock()
+
+	return string(f.buff.Bytes()[f.index:])
+}
+
+// Read implements io.Reader https://golang.org/pkg/io/#Reader
+// Read reads up to len(p) bytes into p. It returns the number of bytes read (0 <= n <= len(p))
+// and any error encountered. Even if Read returns n < len(p), it may use all of p as scratch
+// space during the call. If some data is available but not len(p) bytes, Read conventionally
+// returns what is available instead of waiting for more.
+
+// When Read encounters an error or end-of-file condition after successfully reading n > 0 bytes,
+// it returns the number of bytes read. It may return the (non-nil) error from the same call or
+// return the error (and n == 0) from a subsequent call. An instance of this general case is
+// that a Reader returning a non-zero number of bytes at the end of the input stream may return
+// either err == EOF or err == nil. The next Read should return 0, EOF.
+func (f *FileBuffer) Read(ctx context.Context, b []byte) (n int, err error) {
+	f.mu.RLock()
+	defer f.mu.RUnlock()
+
+	if f.isClosed {
+		return 0, os.ErrClosed
+	}
+	if len(b) == 0 {
+		return 0, nil
+	}
+	if f.index >= int64(f.buff.Len()) {
+		return 0, io.EOF
+	}
+	n, err = bytes.NewBuffer(f.buff.Bytes()[f.index:]).Read(b)
+	f.index += int64(n)
+
+	return n, err
+}
+
+// ReadAt implements io.ReaderAt https://golang.org/pkg/io/#ReaderAt
+// ReadAt reads len(p) bytes into p starting at offset off in the underlying input source.
+// It returns the number of bytes read (0 <= n <= len(p)) and any error encountered.
+//
+// When ReadAt returns n < len(p), it returns a non-nil error explaining why more bytes were not returned.
+// In this respect, ReadAt is stricter than Read.
+//
+// Even if ReadAt returns n < len(p), it may use all of p as scratch space during the call.
+// If some data is available but not len(p) bytes, ReadAt blocks until either all the data is available or an error occurs.
+// In this respect ReadAt is different from Read.
+//
+// If the n = len(p) bytes returned by ReadAt are at the end of the input source,
+// ReadAt may return either err == EOF or err == nil.
+//
+// If ReadAt is reading from an input source with a seek offset,
+// ReadAt should not affect nor be affected by the underlying seek offset.
+// Clients of ReadAt can execute parallel ReadAt calls on the same input source.
+func (f *FileBuffer) ReadAt(ctx context.Context, p []byte, off int64) (n int, err error) {
+	f.mu.RLock()
+	defer f.mu.RUnlock()
+
+	if f.isClosed {
+		return 0, os.ErrClosed
+	}
+	if off < 0 {
+		return 0, errors.New("filebuffer.ReadAt: negative offset")
+	}
+	reqLen := len(p)
+	buffLen := int64(f.buff.Len())
+	if off >= buffLen {
+		return 0, io.EOF
+	}
+
+	n = copy(p, f.buff.Bytes()[off:])
+	if n < reqLen {
+		err = io.EOF
+	}
+	return n, err
+}
+
+// Write implements io.Writer https://golang.org/pkg/io/#Writer
+// by appending the passed bytes to the buffer unless the buffer is closed or index negative.
+func (f *FileBuffer) Write(ctx context.Context, p []byte) (n int, err error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+
+	if f.isClosed {
+		return 0, os.ErrClosed
+	}
+	if f.index < 0 {
+		return 0, io.EOF
+	}
+	// we might have rewinded, let's reset the buffer before appending to it
+	idx := int(f.index)
+	buffLen := f.buff.Len()
+	if idx != buffLen && idx <= buffLen {
+		f.buff = bytes.NewBuffer(f.Bytes()[:f.index])
+	}
+	n, err = f.buff.Write(p)
+
+	f.index += int64(n)
+	return n, err
+}
+
+// Seek implements io.Seeker https://golang.org/pkg/io/#Seeker
+func (f *FileBuffer) Seek(offset int64, whence int) (idx int64, err error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+
+	if f.isClosed {
+		return 0, os.ErrClosed
+	}
+
+	var abs int64
+	switch whence {
+	case 0:
+		abs = offset
+	case 1:
+		abs = int64(f.index) + offset
+	case 2:
+		abs = int64(f.buff.Len()) + offset
+	default:
+		return 0, errors.New("filebuffer.Seek: invalid whence")
+	}
+	if abs < 0 {
+		return 0, errors.New("filebuffer.Seek: negative position")
+	}
+	f.index = abs
+	return abs, nil
+}
+
+// Close implements io.Closer https://golang.org/pkg/io/#Closer
+// It closes the buffer, rendering it unusable for I/O. It returns an error, if any.
+func (f *FileBuffer) Close(ctx context.Context) error {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+
+	f.isClosed = true
+	f.buff = nil
+	return nil
+}

server/pkg/ioutils/readerat.go

@@ -0,0 +1,49 @@
+package ioutils
+
+import (
+	"context"
+	"sync"
+
+	"github.com/royalcat/ctxio"
+)
+
+type ReaderReaderAtWrapper struct {
+	mu     sync.Mutex
+	rat    ctxio.ReaderAt
+	offset int64
+}
+
+func NewReaderReaderAtWrapper(rat ctxio.ReaderAt) *ReaderReaderAtWrapper {
+	return &ReaderReaderAtWrapper{
+		rat: rat,
+	}
+}
+
+var _ ctxio.Reader = (*ReaderReaderAtWrapper)(nil)
+var _ ctxio.ReaderAt = (*ReaderReaderAtWrapper)(nil)
+var _ ctxio.Closer = (*ReaderReaderAtWrapper)(nil)
+
+// Read implements Reader.
+func (r *ReaderReaderAtWrapper) Read(ctx context.Context, p []byte) (n int, err error) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	n, err = r.rat.ReadAt(ctx, p, r.offset)
+	r.offset += int64(n)
+	return n, err
+}
+
+// ReadAt implements ReaderAt.
+func (r *ReaderReaderAtWrapper) ReadAt(ctx context.Context, p []byte, off int64) (n int, err error) {
+	return r.rat.ReadAt(ctx, p, off)
+}
+
+// Close implements Closer.
+func (r *ReaderReaderAtWrapper) Close(ctx context.Context) (err error) {
+	if c, ok := r.rat.(ctxio.Closer); ok {
+		err = c.Close(ctx)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}

server/pkg/ioutils/seeker.go

@@ -0,0 +1,104 @@
+package ioutils
+
+import (
+	"context"
+	"io"
+	"sync"
+
+	"github.com/royalcat/ctxio"
+)
+
+type ioSeekerWrapper struct {
+	ctx context.Context
+
+	mu   sync.Mutex
+	pos  int64
+	size int64
+
+	r ctxio.ReaderAt
+}
+
+func WrapIoReadSeeker(ctx context.Context, r ctxio.ReaderAt, size int64) io.ReadSeeker {
+	return &ioSeekerWrapper{
+		ctx:  ctx,
+		r:    r,
+		size: size,
+	}
+}
+
+func (r *ioSeekerWrapper) Seek(offset int64, whence int) (int64, error) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	switch whence {
+	case io.SeekStart:
+		r.pos = offset
+	case io.SeekCurrent:
+		r.pos = r.pos + offset
+	case io.SeekEnd:
+		r.pos = r.size + offset
+	}
+
+	return r.pos, nil
+}
+
+func (r *ioSeekerWrapper) Read(p []byte) (int, error) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	n, err := r.r.ReadAt(r.ctx, p, r.pos)
+	r.pos += int64(n)
+
+	return n, err
+}
+
+var _ io.ReadSeekCloser = (*ioSeekerCloserWrapper)(nil)
+
+type ioSeekerCloserWrapper struct {
+	ctx context.Context
+
+	mu   sync.Mutex
+	pos  int64
+	size int64
+
+	r FileReader
+}
+
+func IoReadSeekCloserWrapper(ctx context.Context, r FileReader, size int64) io.ReadSeekCloser {
+	return &ioSeekerCloserWrapper{
+		ctx:  ctx,
+		r:    r,
+		size: size,
+	}
+}
+
+func (r *ioSeekerCloserWrapper) Seek(offset int64, whence int) (int64, error) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	switch whence {
+	case io.SeekStart:
+		r.pos = offset
+	case io.SeekCurrent:
+		r.pos = r.pos + offset
+	case io.SeekEnd:
+		r.pos = r.size + offset
+	}
+
+	return r.pos, nil
+}
+
+func (r *ioSeekerCloserWrapper) Read(p []byte) (int, error) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	n, err := r.r.ReadAt(r.ctx, p, r.pos)
+	r.pos += int64(n)
+
+	return n, err
+}
+
+// Close implements io.ReadSeekCloser.
+func (r *ioSeekerCloserWrapper) Close() error {
+	return r.r.Close(r.ctx)
+}

server/pkg/kvsingle/single.go

@@ -0,0 +1,28 @@
+package kvsingle
+
+import (
+	"context"
+
+	"github.com/royalcat/kv"
+)
+
+type Value[K, V any] struct {
+	Key K
+	db  kv.Store[K, V]
+}
+
+func New[K, V any](db kv.Store[K, V], key K) *Value[K, V] {
+	return &Value[K, V]{Key: key, db: db}
+}
+
+func (s *Value[K, V]) Get(ctx context.Context) (V, error) {
+	return s.db.Get(ctx, s.Key)
+}
+
+func (s *Value[K, V]) Set(ctx context.Context, value V) error {
+	return s.db.Set(ctx, s.Key, value)
+}
+
+func (s *Value[K, V]) Edit(ctx context.Context, edit kv.Edit[V]) error {
+	return s.db.Edit(ctx, s.Key, edit)
+}

server/pkg/kvtrace/kvmetrics.go

@@ -0,0 +1,150 @@
+package kvtrace
+
+import (
+	"context"
+
+	"github.com/royalcat/kv"
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/codes"
+	"go.opentelemetry.io/otel/trace"
+)
+
+var tracer = otel.Tracer("github.com/royalcat/kv/tracer")
+
+type traceStore[K, V any] struct {
+	kv    kv.Store[K, V]
+	attrs []attribute.KeyValue
+}
+
+func WrapTracing[K, V any](kv kv.Store[K, V], attrs ...attribute.KeyValue) kv.Store[K, V] {
+	return &traceStore[K, V]{
+		kv:    kv,
+		attrs: attrs,
+	}
+}
+
+// Close implements kv.Store.
+func (m *traceStore[K, V]) Close(ctx context.Context) (err error) {
+	ctx, span := tracer.Start(ctx, "Close", trace.WithAttributes(m.attrs...))
+	defer span.End()
+	defer func() {
+		if err != nil && err != kv.ErrKeyNotFound {
+			span.SetStatus(codes.Error, err.Error())
+		} else {
+			span.SetStatus(codes.Ok, "")
+		}
+	}()
+
+	return m.kv.Close(ctx)
+}
+
+// Delete implements kv.Store.
+func (m *traceStore[K, V]) Delete(ctx context.Context, k K) (err error) {
+	ctx, span := tracer.Start(ctx, "Delete", trace.WithAttributes(m.attrs...))
+	defer span.End()
+	defer func() {
+		if err != nil && err != kv.ErrKeyNotFound {
+			span.SetStatus(codes.Error, err.Error())
+		} else {
+			span.SetStatus(codes.Ok, "")
+		}
+	}()
+
+	return m.kv.Delete(ctx, k)
+}
+
+// Get implements kv.Store.
+func (m *traceStore[K, V]) Get(ctx context.Context, k K) (v V, err error) {
+	ctx, span := tracer.Start(ctx, "Get", trace.WithAttributes(m.attrs...))
+	defer span.End()
+	defer func() {
+		if err != nil && err != kv.ErrKeyNotFound {
+			span.SetStatus(codes.Error, err.Error())
+		} else {
+			span.SetStatus(codes.Ok, "")
+		}
+	}()
+
+	return m.kv.Get(ctx, k)
+}
+
+// Get implements kv.Store.
+func (m *traceStore[K, V]) Edit(ctx context.Context, k K, edit kv.Edit[V]) (err error) {
+	ctx, span := tracer.Start(ctx, "Get", trace.WithAttributes(m.attrs...))
+	defer span.End()
+	defer func() {
+		if err != nil && err != kv.ErrKeyNotFound {
+			span.SetStatus(codes.Error, err.Error())
+		} else {
+			span.SetStatus(codes.Ok, "")
+		}
+	}()
+
+	return m.kv.Edit(ctx, k, edit)
+}
+
+// Range implements kv.Store.
+func (m *traceStore[K, V]) Range(ctx context.Context, iter kv.Iter[K, V]) (err error) {
+	ctx, span := tracer.Start(ctx, "Range", trace.WithAttributes(m.attrs...))
+	defer span.End()
+	defer func() {
+		if err != nil {
+			span.SetStatus(codes.Error, err.Error())
+		} else {
+			span.SetStatus(codes.Ok, "")
+		}
+	}()
+
+	count := 0
+	iterCount := func(k K, v V) error {
+		count++
+		return iter(k, v)
+	}
+	defer func() {
+		span.SetAttributes(attribute.Int("count", count))
+	}()
+
+	return m.kv.Range(ctx, iterCount)
+}
+
+// RangeWithPrefix implements kv.Store.
+func (m *traceStore[K, V]) RangeWithPrefix(ctx context.Context, k K, iter kv.Iter[K, V]) (err error) {
+	ctx, span := tracer.Start(ctx, "RangeWithPrefix", trace.WithAttributes(m.attrs...))
+	defer span.End()
+	defer func() {
+		if err != nil {
+			span.SetStatus(codes.Error, err.Error())
+		} else {
+			span.SetStatus(codes.Ok, "")
+		}
+	}()
+
+	count := 0
+	iterCount := func(k K, v V) error {
+		count++
+		return iter(k, v)
+	}
+	defer func() {
+		span.SetAttributes(attribute.Int("count", count))
+	}()
+
+	return m.kv.Range(ctx, iterCount)
+}
+
+// Set implements kv.Store.
+func (m *traceStore[K, V]) Set(ctx context.Context, k K, v V) (err error) {
+	ctx, span := tracer.Start(ctx, "Set", trace.WithAttributes(m.attrs...))
+	defer span.End()
+	defer func() {
+		if err != nil {
+			span.SetStatus(codes.Error, err.Error())
+		} else {
+			span.SetStatus(codes.Ok, "")
+		}
+	}()
+
+	return m.kv.Set(ctx, k, v)
+}
+
+var _ kv.Store[any, any] = (*traceStore[any, any])(nil)

server/pkg/maxcache/cache.go

@@ -0,0 +1,114 @@
+package maxcache
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	"github.com/cespare/xxhash/v2"
+	"github.com/goware/singleflight"
+	lru "github.com/hashicorp/golang-lru/v2"
+)
+
+func NewCache[K comparable, V any](size int, freshFor, ttl time.Duration) *Cache[K, V] {
+	values, _ := lru.New[K, value[V]](size)
+	return &Cache[K, V]{
+		values: values,
+	}
+}
+
+type Cache[K comparable, V any] struct {
+	values *lru.Cache[K, value[V]]
+
+	mu        sync.RWMutex
+	callGroup singleflight.Group[K, V]
+}
+
+func (c *Cache[K, V]) Get(ctx context.Context, key K, fn singleflight.DoFunc[V]) (V, error) {
+	return c.get(ctx, key, false, fn)
+}
+
+func (c *Cache[K, V]) GetFresh(ctx context.Context, key K, fn singleflight.DoFunc[V]) (V, error) {
+	return c.get(ctx, key, true, fn)
+}
+
+func (c *Cache[K, V]) Set(ctx context.Context, key K, fn singleflight.DoFunc[V]) (V, bool, error) {
+	v, err, shared := c.callGroup.Do(key, c.set(key, fn))
+	return v, shared, err
+}
+
+func (c *Cache[K, V]) get(ctx context.Context, key K, freshOnly bool, fn singleflight.DoFunc[V]) (V, error) {
+	c.mu.RLock()
+	val, ok := c.values.Get(key)
+	c.mu.RUnlock()
+
+	// value exists and is fresh - just return
+	if ok && val.IsFresh() {
+		return val.Value(), nil
+	}
+
+	// value exists and is stale, and we're OK with serving it stale while updating in the background
+	// note: stale means its still okay, but not fresh. but if its expired, then it means its useless.
+	if ok && !freshOnly && !val.IsExpired() {
+		// TODO: technically could be a stampede of goroutines here if the value is expired
+		// and we're OK with serving it stale
+		go c.Set(ctx, key, fn)
+		return val.Value(), nil
+	}
+
+	// value doesn't exist or is expired, or is stale and we need it fresh (freshOnly:true) - sync update
+	v, _, err := c.Set(ctx, key, fn)
+	return v, err
+}
+
+func (c *Cache[K, V]) set(key K, fn singleflight.DoFunc[V]) singleflight.DoFunc[V] {
+	return singleflight.DoFunc[V](func() (V, error) {
+		val, err := fn()
+		if err != nil {
+			return val, err
+		}
+
+		c.mu.Lock()
+		c.values.Add(key, value[V]{
+			v: val,
+		})
+		c.mu.Unlock()
+
+		return val, nil
+	})
+}
+
+type value[V any] struct {
+	v V
+
+	bestBefore time.Time // cache entry freshness cutoff
+	expiry     time.Time // cache entry time to live cutoff
+}
+
+func (v *value[V]) IsFresh() bool {
+	return v.bestBefore.After(time.Now())
+}
+
+func (v *value[V]) IsExpired() bool {
+	return v.expiry.Before(time.Now())
+}
+
+func (v *value[V]) Value() V {
+	return v.v
+}
+
+func BytesToHash(b ...[]byte) uint64 {
+	d := xxhash.New()
+	for _, v := range b {
+		d.Write(v)
+	}
+	return d.Sum64()
+}
+
+func StringToHash(s ...string) uint64 {
+	d := xxhash.New()
+	for _, v := range s {
+		d.WriteString(v)
+	}
+	return d.Sum64()
+}

server/pkg/maxcache/cache_test.go

@@ -0,0 +1,204 @@
+package maxcache_test
+
+import (
+	"context"
+	"io"
+	"log"
+	"net/http"
+	"net/http/httptest"
+	"runtime"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/go-chi/stampede"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGet(t *testing.T) {
+	var count uint64
+	cache := stampede.NewCache(512, time.Duration(2*time.Second), time.Duration(5*time.Second))
+
+	// repeat test multiple times
+	for x := 0; x < 5; x++ {
+		// time.Sleep(1 * time.Second)
+
+		var wg sync.WaitGroup
+		numGoroutines := runtime.NumGoroutine()
+
+		n := 10
+		ctx := context.Background()
+
+		for i := 0; i < n; i++ {
+			t.Logf("numGoroutines now %d", runtime.NumGoroutine())
+
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
+
+				val, err := cache.Get(ctx, "t1", func() (any, error) {
+					t.Log("cache.Get(t1, ...)")
+
+					// some extensive op..
+					time.Sleep(2 * time.Second)
+					atomic.AddUint64(&count, 1)
+
+					return "result1", nil
+				})
+
+				assert.NoError(t, err)
+				assert.Equal(t, "result1", val)
+			}()
+		}
+
+		wg.Wait()
+
+		// ensure single call
+		assert.Equal(t, uint64(1), count)
+
+		// confirm same before/after num of goroutines
+		t.Logf("numGoroutines now %d", runtime.NumGoroutine())
+		assert.Equal(t, numGoroutines, runtime.NumGoroutine())
+
+	}
+}
+
+func TestHandler(t *testing.T) {
+	var numRequests = 30
+
+	var hits uint32
+	var expectedStatus int = 201
+	var expectedBody = []byte("hi")
+
+	app := func(w http.ResponseWriter, r *http.Request) {
+		// log.Println("app handler..")
+
+		atomic.AddUint32(&hits, 1)
+
+		hitsNow := atomic.LoadUint32(&hits)
+		if hitsNow > 1 {
+			// panic("uh oh")
+		}
+
+		// time.Sleep(100 * time.Millisecond) // slow handler
+		w.Header().Set("X-Httpjoin", "test")
+		w.WriteHeader(expectedStatus)
+		w.Write(expectedBody)
+	}
+
+	var count uint32
+	counter := func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			atomic.AddUint32(&count, 1)
+			next.ServeHTTP(w, r)
+			atomic.AddUint32(&count, ^uint32(0))
+			// log.Println("COUNT:", atomic.LoadUint32(&count))
+		})
+	}
+
+	recoverer := func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			defer func() {
+				if r := recover(); r != nil {
+					log.Println("recovered panicing request:", r)
+				}
+			}()
+			next.ServeHTTP(w, r)
+		})
+	}
+
+	h := stampede.Handler(512, 1*time.Second)
+
+	ts := httptest.NewServer(counter(recoverer(h(http.HandlerFunc(app)))))
+	defer ts.Close()
+
+	var wg sync.WaitGroup
+
+	for i := 0; i < numRequests; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			resp, err := http.Get(ts.URL)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			body, err := io.ReadAll(resp.Body)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer resp.Body.Close()
+
+			// log.Println("got resp:", resp, "len:", len(body), "body:", string(body))
+
+			if string(body) != string(expectedBody) {
+				t.Error("expecting response body:", string(expectedBody))
+			}
+
+			if resp.StatusCode != expectedStatus {
+				t.Error("expecting response status:", expectedStatus)
+			}
+
+			assert.Equal(t, "test", resp.Header.Get("X-Httpjoin"), "expecting x-httpjoin test header")
+		}()
+	}
+
+	wg.Wait()
+
+	totalHits := atomic.LoadUint32(&hits)
+	// if totalHits > 1 {
+	// 	t.Error("handler was hit more than once. hits:", totalHits)
+	// }
+	log.Println("total hits:", totalHits)
+
+	finalCount := atomic.LoadUint32(&count)
+	if finalCount > 0 {
+		t.Error("queue count was expected to be empty, but count:", finalCount)
+	}
+	log.Println("final count:", finalCount)
+}
+
+func TestHash(t *testing.T) {
+	h1 := stampede.BytesToHash([]byte{1, 2, 3})
+	assert.Equal(t, uint64(8376154270085342629), h1)
+
+	h2 := stampede.StringToHash("123")
+	assert.Equal(t, uint64(4353148100880623749), h2)
+}
+
+func TestPanic(t *testing.T) {
+	mux := http.NewServeMux()
+	middleware := stampede.Handler(100, 1*time.Hour)
+	mux.Handle("/", middleware(http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+		t.Log(r.Method, r.URL)
+	})))
+
+	ts := httptest.NewServer(mux)
+	defer ts.Close()
+
+	{
+		req, err := http.NewRequest(http.MethodGet, ts.URL, nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+		resp, err := http.DefaultClient.Do(req)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer resp.Body.Close()
+		t.Log(resp.StatusCode)
+	}
+	{
+		req, err := http.NewRequest(http.MethodGet, ts.URL, nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+		resp, err := http.DefaultClient.Do(req)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer resp.Body.Close()
+		t.Log(resp.StatusCode)
+	}
+}

server/pkg/rlog/rlog.go

@@ -0,0 +1,142 @@
+package rlog
+
+import (
+	"context"
+	"log/slog"
+	"os"
+	"runtime"
+	"strings"
+	"time"
+
+	"github.com/rs/zerolog"
+	slogmulti "github.com/samber/slog-multi"
+	slogzerolog "github.com/samber/slog-zerolog"
+)
+
+var (
+	zl       = zerolog.New(&zerolog.ConsoleWriter{Out: os.Stderr})
+	handlers = []slog.Handler{
+		slogzerolog.Option{Logger: &zl}.NewZerologHandler(),
+	}
+	handler       = slogmulti.Fanout(handlers...)
+	defaultLogger = slog.New(handler)
+)
+
+func init() {
+	slog.SetDefault(defaultLogger)
+}
+
+func AddHandler(nh slog.Handler) {
+	handlers = append(handlers, nh)
+	handler = slogmulti.Fanout(handlers...)
+	defaultLogger = slog.New(handler)
+	slog.SetDefault(defaultLogger)
+}
+
+type Logger struct {
+	handler     slog.Handler
+	callNesting int
+	component   []string
+}
+
+const functionKey = "function"
+
+const componentKey = "component"
+const componentSep = "."
+
+func (l *Logger) log(ctx context.Context, level slog.Level, msg string, attrs ...slog.Attr) {
+	var pcs [1]uintptr
+	runtime.Callers(3+l.callNesting, pcs[:])
+	pc := pcs[0]
+	f := runtime.FuncForPC(pc)
+	if f != nil {
+		attrs = append(attrs, slog.String(functionKey, f.Name()))
+	}
+
+	if len(l.component) > 0 {
+		attrs = append(attrs, slog.String(componentKey, strings.Join(l.component, componentSep)))
+	}
+
+	r := slog.NewRecord(time.Now(), level, msg, pc)
+	r.AddAttrs(attrs...)
+	if ctx == nil {
+		ctx = context.Background()
+	}
+
+	_ = l.handler.Handle(ctx, r)
+}
+
+func (l *Logger) Debug(ctx context.Context, msg string, attrs ...slog.Attr) {
+	l.log(ctx, slog.LevelDebug, msg, attrs...)
+}
+
+func (l *Logger) Info(ctx context.Context, msg string, attrs ...slog.Attr) {
+	l.log(ctx, slog.LevelInfo, msg, attrs...)
+}
+
+func (l *Logger) Warn(ctx context.Context, msg string, attrs ...slog.Attr) {
+	l.log(ctx, slog.LevelWarn, msg, attrs...)
+}
+
+func (l *Logger) Error(ctx context.Context, msg string, attrs ...slog.Attr) {
+	l.log(ctx, slog.LevelError, msg, attrs...)
+}
+
+func (log *Logger) WithComponent(name string) *Logger {
+	return &Logger{
+		handler:   log.handler,
+		component: append(log.component, name),
+	}
+}
+
+func (l *Logger) With(attrs ...slog.Attr) *Logger {
+	return &Logger{
+		handler:   l.handler.WithAttrs(attrs),
+		component: l.component,
+	}
+}
+
+func (l *Logger) Nested(callNesting int) *Logger {
+	return &Logger{
+		handler:     l.handler,
+		component:   l.component,
+		callNesting: callNesting,
+	}
+}
+
+// returns a new slog logger with the same attribures as the original logger
+// TODO currently not logging function name
+func (l *Logger) Slog() *slog.Logger {
+	return slog.New(l.handler)
+}
+
+const errKey = "error"
+
+func Error(err error) slog.Attr {
+	return slog.Attr{Key: errKey, Value: errValue(err)}
+}
+
+// errValue returns a slog.GroupValue with keys "msg" and "trace". If the error
+// does not implement interface { StackTrace() errors.StackTrace }, the "trace"
+// key is omitted.
+func errValue(err error) slog.Value {
+	if err == nil {
+		return slog.AnyValue(nil)
+	}
+
+	var groupValues []slog.Attr
+
+	groupValues = append(groupValues,
+		slog.String("msg", err.Error()),
+		slog.Any("value", err),
+	)
+
+	return slog.GroupValue(groupValues...)
+}
+
+func Component(name ...string) *Logger {
+	return &Logger{
+		handler:   handler,
+		component: name,
+	}
+}

server/pkg/slicesutils/intersections.go

@@ -0,0 +1,38 @@
+package slicesutils
+
+func Intersection[T comparable](slices ...[]T) []T {
+	counts := map[T]int{}
+	result := []T{}
+
+	for _, slice := range slices {
+		for _, val := range slice {
+			counts[val]++
+		}
+	}
+
+	for val, count := range counts {
+		if count == len(slices) {
+
+			result = append(result, val)
+
+		}
+	}
+
+	return result
+
+}
+
+func IntersectionFunc[T any](s1 []T, s2 []T, cmp func(T, T) bool) []T {
+	set := make([]T, 0)
+
+	for _, a := range s1 {
+		for _, b := range s2 {
+			if cmp(a, b) {
+				set = append(set, a)
+			}
+		}
+	}
+
+	return set
+
+}

server/pkg/uring/file.go

@@ -0,0 +1,112 @@
+package uring
+
+// import (
+// 	"context"
+// 	"os"
+
+// 	"github.com/iceber/iouring-go"
+// 	"go.opentelemetry.io/otel"
+// 	"go.opentelemetry.io/otel/attribute"
+// 	"go.opentelemetry.io/otel/trace"
+// )
+
+// var tracer = otel.Tracer("github.com/royalcat/tstor/pkg/uring")
+
+// type FS struct {
+// 	ur *iouring.IOURing
+// }
+
+// func NewFS(ur *iouring.IOURing) *FS {
+// 	return &FS{
+// 		ur: ur,
+// 	}
+// }
+
+// func (o *FS) OpenFile(ctx context.Context, name string) (File, error) {
+// 	ctx, span := tracer.Start(ctx, "uring.FS.OpenFile", trace.WithAttributes(attribute.String("name", name)))
+// 	defer span.End()
+
+// 	f, err := os.Open(name)
+// 	if err != nil {
+// 		return File{}, err
+// 	}
+
+// 	return File{
+// 		ur: o.ur,
+// 		f:  f,
+// 	}, nil
+// }
+
+// func NewFile(ur *iouring.IOURing, f *os.File) *File {
+// 	return &File{
+// 		ur: ur,
+// 		f:  f,
+// 	}
+// }
+
+// type File struct {
+// 	ur *iouring.IOURing
+// 	f  *os.File
+// }
+
+// func (o *File) pread(ctx context.Context, b []byte, off uint64) (int, error) {
+// 	ctx, span := tracer.Start(ctx, "uring.File.pread", trace.WithAttributes(attribute.Int("size", len(b))))
+// 	defer span.End()
+
+// 	req, err := o.ur.Pread(o.f, b, off, nil)
+// 	if err != nil {
+// 		return 0, err
+// 	}
+
+// 	select {
+// 	case <-req.Done():
+// 		return req.GetRes()
+// 	case <-ctx.Done():
+// 		if _, err := req.Cancel(); err != nil {
+// 			return 0, err
+// 		}
+// 		<-req.Done()
+// 		return 0, ctx.Err()
+// 	}
+// }
+
+// func (f *File) ReadAt(ctx context.Context, b []byte, off int64) (n int, err error) {
+// 	ctx, span := tracer.Start(ctx, "uring.File.ReadAt", trace.WithAttributes(attribute.Int("size", len(b))))
+// 	defer span.End()
+
+// 	return f.f.ReadAt(b, off)
+
+// 	for len(b) > 0 {
+// 		if ctx.Err() != nil {
+// 			err = ctx.Err()
+// 			break
+// 		}
+
+// 		m, e := f.pread(ctx, b, uint64(off))
+// 		if e != nil {
+// 			err = e
+// 			break
+// 		}
+// 		n += m
+// 		b = b[m:]
+// 		off += int64(m)
+// 	}
+
+// 	return n, err
+// }
+
+// func (o *File) Close(ctx context.Context) error {
+// 	return o.f.Close()
+// }
+
+// func waitRequest(ctx context.Context, req iouring.Request) (int, error) {
+// 	select {
+// 	case <-req.Done():
+// 		return req.GetRes()
+// 	case <-ctx.Done():
+// 		if _, err := req.Cancel(); err != nil {
+// 			return 0, err
+// 		}
+// 		return 0, ctx.Err()
+// 	}
+// }

server/pkg/uuid/uuid.go

@@ -0,0 +1,102 @@
+package uuid
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"strconv"
+	"time"
+
+	fuuid "github.com/gofrs/uuid/v5"
+)
+
+var Nil = UUID{}
+
+type UUIDList = []UUID
+
+type UUID struct {
+	fuuid.UUID
+}
+
+func New() UUID {
+	return UUID{fuuid.Must(fuuid.NewV7())}
+}
+
+func NewFromTime(t time.Time) UUID {
+	gen := fuuid.NewGenWithOptions(
+		fuuid.WithEpochFunc(func() time.Time { return t }),
+	)
+	return UUID{fuuid.Must(gen.NewV7())}
+}
+
+func NewP() *UUID {
+	return &UUID{fuuid.Must(fuuid.NewV7())}
+}
+
+func FromString(text string) (UUID, error) {
+	u, err := fuuid.FromString(text)
+	if err != nil {
+		return Nil, err
+	}
+
+	return UUID{u}, nil
+}
+
+func MustFromString(text string) UUID {
+	u, err := fuuid.FromString(text)
+	if err != nil {
+		panic(err)
+	}
+
+	return UUID{u}
+}
+
+func FromBytes(input []byte) (UUID, error) {
+	u, err := fuuid.FromBytes(input)
+	if err != nil {
+		return Nil, err
+	}
+
+	return UUID{u}, nil
+}
+
+func (a *UUID) UnmarshalJSON(b []byte) error {
+	var s string
+	if err := json.Unmarshal(b, &s); err != nil {
+		return err
+	}
+
+	if s == "" {
+		a.UUID = fuuid.Nil
+		return nil
+	}
+
+	return a.UUID.Parse(s)
+}
+
+func (a UUID) MarshalJSON() ([]byte, error) {
+	if a.IsNil() {
+		return json.Marshal("")
+	}
+
+	return json.Marshal(a.UUID)
+}
+
+// UnmarshalGQL implements the graphql.Unmarshaler interface
+func (u *UUID) UnmarshalGQL(v interface{}) error {
+	id, ok := v.(string)
+	if !ok {
+		return fmt.Errorf("uuid must be a string")
+	}
+
+	return u.Parse(id)
+}
+
+// MarshalGQL implements the graphql.Marshaler interface
+func (u UUID) MarshalGQL(w io.Writer) {
+	b := []byte(strconv.Quote(u.String()))
+	_, err := w.Write(b)
+	if err != nil {
+		panic(err)
+	}
+}

server/pkg/ytdlp/client.go

@@ -0,0 +1,9 @@
+package ytdlp
+
+type Client struct {
+	binary string
+}
+
+func New() (*Client, error) {
+	return &Client{binary: "yt-dlp"}, nil
+}

server/pkg/ytdlp/download.go

@@ -0,0 +1,105 @@
+package ytdlp
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+	"os/exec"
+	"strings"
+
+	"github.com/royalcat/ctxprogress"
+	"golang.org/x/sync/errgroup"
+)
+
+type DownloadStatus string
+
+const (
+	StatusDownloading DownloadStatus = "downloading"
+	StatusFinished    DownloadStatus = "finished"
+	StatusErrored     DownloadStatus = "error"
+)
+
+// Progress for the Running call
+type DownloadProgress struct {
+	Status             DownloadStatus `json:"status"`
+	Filename           string         `json:"filename"`
+	TmpFilename        string         `json:"tmpfilename"`
+	DownloadedBytes    int64          `json:"downloaded_bytes"`
+	TotalBytes         int64          `json:"total_bytes"`
+	TotalBytesEstimate float64        `json:"total_bytes_estimate"`
+	Elapsed            float64        `json:"elapsed"`
+	ETA                float64        `json:"eta"`
+	Speed              float64        `json:"speed"`
+	FragmentIndex      int64          `json:"fragment_index"`
+	FragmentCount      int64          `json:"fragment_count"`
+}
+
+// Current implements ctxprogress.Progress.
+func (d DownloadProgress) Progress() (int, int) {
+	if d.TotalBytes != -1 && d.TotalBytes != 0 && d.DownloadedBytes != -1 {
+		return int(d.DownloadedBytes), int(d.TotalBytes)
+	}
+
+	if d.TotalBytesEstimate != -1 && d.TotalBytesEstimate != 0 && d.DownloadedBytes != -1 {
+		return int(d.DownloadedBytes), int(d.TotalBytesEstimate)
+	}
+
+	return int(d.FragmentIndex), int(d.FragmentCount)
+}
+
+const rawProgressTemplate = `download:
+%{
+	"status":"%(progress.status)s",
+	"eta":%(progress.eta|-1)s,
+	"speed":%(progress.speed|0)s,
+	"downloaded_bytes":%(progress.downloaded_bytes|-1)s,
+	"total_bytes": %(progress.total_bytes|-1)s,
+	"total_bytes_estimate": %(progress.total_bytes_estimate|-1)s,
+	"fragment_index":%(progress.fragment_index|-1)s,
+	"fragment_count":%(progress.fragment_count|-1)s
+}`
+
+var progressTemplate = strings.NewReplacer("\n", "", "\t", "", " ", "").Replace(rawProgressTemplate)
+
+func (c *Client) Download(ctx context.Context, url string, w io.Writer) error {
+	args := []string{
+		"--progress", "--newline", "--progress-template", progressTemplate,
+		"-o", "-",
+		url,
+	}
+
+	group, ctx := errgroup.WithContext(ctx)
+
+	stderr, lines, err := lineReader(group)
+	if err != nil {
+		return err
+	}
+	cmd := exec.CommandContext(ctx, c.binary, args...)
+
+	cmd.Stdout = w
+	cmd.Stderr = stderr
+
+	group.Go(func() error {
+		err := cmd.Run()
+		stderr.Close()
+		if err != nil {
+			return err
+		}
+		return nil
+	})
+
+	for line := range lines {
+		if line, ok := strings.CutPrefix(line, "%"); ok {
+			p := DownloadProgress{}
+			err = json.Unmarshal([]byte(line), &p)
+			if err != nil {
+				//TODO: handle error
+				continue
+			}
+
+			ctxprogress.Set(ctx, p)
+		}
+	}
+
+	return group.Wait()
+}

server/pkg/ytdlp/download_test.go

@@ -0,0 +1,27 @@
+package ytdlp_test
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"testing"
+
+	"git.kmsign.ru/royalcat/tstor/server/pkg/ytdlp"
+	"github.com/royalcat/ctxprogress"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDownload(t *testing.T) {
+	require := require.New(t)
+
+	ctx := context.Background()
+	c, err := ytdlp.New()
+	require.NoError(err)
+	ctx = ctxprogress.New(ctx)
+	ctxprogress.AddCallback(ctx, func(p ctxprogress.Progress) {
+		cur, total := p.Progress()
+		fmt.Printf("%d/%d\n", cur, total)
+	})
+	err = c.Download(ctx, "https://www.youtube.com/watch?v=dQw4w9WgXcQ", io.Discard)
+	require.NoError(err)
+}

server/pkg/ytdlp/info.go

@@ -0,0 +1,33 @@
+package ytdlp
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"os/exec"
+)
+
+func (c *Client) Info(ctx context.Context, url string) (*Info, error) {
+	args := []string{
+		"-q", "-J", url,
+	}
+
+	cmd := exec.CommandContext(ctx, c.binary, args...)
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+
+	err := cmd.Run()
+	if err != nil {
+		return nil, err
+	}
+
+	var info Info
+	err = json.Unmarshal(stdout.Bytes(), &info)
+	if err != nil {
+		return nil, err
+	}
+
+	return &info, nil
+}

server/pkg/ytdlp/model.go

@@ -0,0 +1,389 @@
+package ytdlp
+
+type Info struct {
+	ID                   string                        `json:"id"`
+	Title                string                        `json:"title"`
+	Availability         string                        `json:"availability"`
+	ChannelFollowerCount *int64                        `json:"channel_follower_count"`
+	Description          string                        `json:"description"`
+	Tags                 []string                      `json:"tags"`
+	Thumbnails           []Thumbnail                   `json:"thumbnails"`
+	ModifiedDate         *string                       `json:"modified_date,omitempty"`
+	ViewCount            int64                         `json:"view_count"`
+	PlaylistCount        *int64                        `json:"playlist_count,omitempty"`
+	Channel              string                        `json:"channel"`
+	ChannelID            string                        `json:"channel_id"`
+	UploaderID           string                        `json:"uploader_id"`
+	Uploader             string                        `json:"uploader"`
+	ChannelURL           string                        `json:"channel_url"`
+	UploaderURL          string                        `json:"uploader_url"`
+	Type                 string                        `json:"_type"`
+	Entries              []Entry                       `json:"entries,omitempty"`
+	ExtractorKey         string                        `json:"extractor_key"`
+	Extractor            string                        `json:"extractor"`
+	WebpageURL           string                        `json:"webpage_url"`
+	OriginalURL          string                        `json:"original_url"`
+	WebpageURLBasename   string                        `json:"webpage_url_basename"`
+	WebpageURLDomain     string                        `json:"webpage_url_domain"`
+	ReleaseYear          interface{}                   `json:"release_year"`
+	Epoch                int64                         `json:"epoch"`
+	FilesToMove          *FilesToMove                  `json:"__files_to_move,omitempty"`
+	Version              Version                       `json:"_version"`
+	Formats              []Format                      `json:"formats,omitempty"`
+	Thumbnail            *string                       `json:"thumbnail,omitempty"`
+	Duration             *int64                        `json:"duration,omitempty"`
+	AverageRating        interface{}                   `json:"average_rating"`
+	AgeLimit             *int64                        `json:"age_limit,omitempty"`
+	Categories           []string                      `json:"categories,omitempty"`
+	PlayableInEmbed      *bool                         `json:"playable_in_embed,omitempty"`
+	LiveStatus           *string                       `json:"live_status,omitempty"`
+	ReleaseTimestamp     interface{}                   `json:"release_timestamp"`
+	FormatSortFields     []string                      `json:"_format_sort_fields,omitempty"`
+	AutomaticCaptions    map[string][]AutomaticCaption `json:"automatic_captions,omitempty"`
+	Subtitles            *FilesToMove                  `json:"subtitles,omitempty"`
+	CommentCount         *int64                        `json:"comment_count,omitempty"`
+	Chapters             interface{}                   `json:"chapters"`
+	Heatmap              []Heatmap                     `json:"heatmap,omitempty"`
+	LikeCount            *int64                        `json:"like_count,omitempty"`
+	ChannelIsVerified    *bool                         `json:"channel_is_verified,omitempty"`
+	UploadDate           *string                       `json:"upload_date,omitempty"`
+	Timestamp            *int64                        `json:"timestamp,omitempty"`
+	Playlist             interface{}                   `json:"playlist"`
+	PlaylistIndex        interface{}                   `json:"playlist_index"`
+	DisplayID            *string                       `json:"display_id,omitempty"`
+	Fulltitle            *string                       `json:"fulltitle,omitempty"`
+	DurationString       *string                       `json:"duration_string,omitempty"`
+	IsLive               *bool                         `json:"is_live,omitempty"`
+	WasLive              *bool                         `json:"was_live,omitempty"`
+	RequestedSubtitles   interface{}                   `json:"requested_subtitles"`
+	HasDRM               interface{}                   `json:"_has_drm"`
+	RequestedDownloads   []RequestedDownload           `json:"requested_downloads,omitempty"`
+	RequestedFormats     []Format                      `json:"requested_formats,omitempty"`
+	Format               *string                       `json:"format,omitempty"`
+	FormatID             *string                       `json:"format_id,omitempty"`
+	EXT                  *MediaEXT                     `json:"ext,omitempty"`
+	Protocol             *string                       `json:"protocol,omitempty"`
+	Language             *Language                     `json:"language,omitempty"`
+	FormatNote           *string                       `json:"format_note,omitempty"`
+	FilesizeApprox       *int64                        `json:"filesize_approx,omitempty"`
+	Tbr                  *float64                      `json:"tbr,omitempty"`
+	Width                *int64                        `json:"width,omitempty"`
+	Height               *int64                        `json:"height,omitempty"`
+	Resolution           *Resolution                   `json:"resolution,omitempty"`
+	FPS                  *int64                        `json:"fps,omitempty"`
+	DynamicRange         *DynamicRange                 `json:"dynamic_range,omitempty"`
+	Vcodec               *string                       `json:"vcodec,omitempty"`
+	Vbr                  *float64                      `json:"vbr,omitempty"`
+	StretchedRatio       interface{}                   `json:"stretched_ratio"`
+	AspectRatio          *float64                      `json:"aspect_ratio,omitempty"`
+	Acodec               *Acodec                       `json:"acodec,omitempty"`
+	ABR                  *float64                      `json:"abr,omitempty"`
+	ASR                  *int64                        `json:"asr,omitempty"`
+	AudioChannels        *int64                        `json:"audio_channels,omitempty"`
+}
+
+type AutomaticCaption struct {
+	EXT  AutomaticCaptionEXT `json:"ext"`
+	URL  string              `json:"url"`
+	Name string              `json:"name"`
+}
+
+type Entry struct {
+	ID                   string                        `json:"id"`
+	Title                string                        `json:"title"`
+	Formats              []Format                      `json:"formats"`
+	Thumbnails           []Thumbnail                   `json:"thumbnails"`
+	Thumbnail            string                        `json:"thumbnail"`
+	Description          string                        `json:"description"`
+	ChannelID            string                        `json:"channel_id"`
+	ChannelURL           string                        `json:"channel_url"`
+	Duration             int64                         `json:"duration"`
+	ViewCount            int64                         `json:"view_count"`
+	AverageRating        interface{}                   `json:"average_rating"`
+	AgeLimit             int64                         `json:"age_limit"`
+	WebpageURL           string                        `json:"webpage_url"`
+	Categories           []string                      `json:"categories"`
+	Tags                 []string                      `json:"tags"`
+	PlayableInEmbed      bool                          `json:"playable_in_embed"`
+	LiveStatus           string                        `json:"live_status"`
+	ReleaseTimestamp     interface{}                   `json:"release_timestamp"`
+	FormatSortFields     []string                      `json:"_format_sort_fields"`
+	AutomaticCaptions    map[string][]AutomaticCaption `json:"automatic_captions"`
+	Subtitles            FilesToMove                   `json:"subtitles"`
+	CommentCount         int64                         `json:"comment_count"`
+	Chapters             interface{}                   `json:"chapters"`
+	Heatmap              interface{}                   `json:"heatmap"`
+	LikeCount            int64                         `json:"like_count"`
+	Channel              string                        `json:"channel"`
+	ChannelFollowerCount int64                         `json:"channel_follower_count"`
+	Uploader             string                        `json:"uploader"`
+	UploaderID           string                        `json:"uploader_id"`
+	UploaderURL          string                        `json:"uploader_url"`
+	UploadDate           string                        `json:"upload_date"`
+	Timestamp            int64                         `json:"timestamp"`
+	Availability         string                        `json:"availability"`
+	OriginalURL          string                        `json:"original_url"`
+	WebpageURLBasename   string                        `json:"webpage_url_basename"`
+	WebpageURLDomain     string                        `json:"webpage_url_domain"`
+	Extractor            string                        `json:"extractor"`
+	ExtractorKey         string                        `json:"extractor_key"`
+	PlaylistCount        int64                         `json:"playlist_count"`
+	Playlist             string                        `json:"playlist"`
+	PlaylistID           string                        `json:"playlist_id"`
+	PlaylistTitle        string                        `json:"playlist_title"`
+	PlaylistUploader     string                        `json:"playlist_uploader"`
+	PlaylistUploaderID   string                        `json:"playlist_uploader_id"`
+	NEntries             int64                         `json:"n_entries"`
+	PlaylistIndex        int64                         `json:"playlist_index"`
+	LastPlaylistIndex    int64                         `json:"__last_playlist_index"`
+	PlaylistAutonumber   int64                         `json:"playlist_autonumber"`
+	DisplayID            string                        `json:"display_id"`
+	Fulltitle            string                        `json:"fulltitle"`
+	DurationString       string                        `json:"duration_string"`
+	ReleaseYear          interface{}                   `json:"release_year"`
+	IsLive               bool                          `json:"is_live"`
+	WasLive              bool                          `json:"was_live"`
+	RequestedSubtitles   interface{}                   `json:"requested_subtitles"`
+	HasDRM               interface{}                   `json:"_has_drm"`
+	Epoch                int64                         `json:"epoch"`
+	RequestedDownloads   []RequestedDownload           `json:"requested_downloads"`
+	RequestedFormats     []Format                      `json:"requested_formats"`
+	Format               string                        `json:"format"`
+	FormatID             string                        `json:"format_id"`
+	EXT                  string                        `json:"ext"`
+	Protocol             string                        `json:"protocol"`
+	Language             *Language                     `json:"language"`
+	FormatNote           string                        `json:"format_note"`
+	FilesizeApprox       int64                         `json:"filesize_approx"`
+	Tbr                  float64                       `json:"tbr"`
+	Width                int64                         `json:"width"`
+	Height               int64                         `json:"height"`
+	Resolution           Resolution                    `json:"resolution"`
+	FPS                  int64                         `json:"fps"`
+	DynamicRange         DynamicRange                  `json:"dynamic_range"`
+	Vcodec               string                        `json:"vcodec"`
+	Vbr                  float64                       `json:"vbr"`
+	StretchedRatio       interface{}                   `json:"stretched_ratio"`
+	AspectRatio          float64                       `json:"aspect_ratio"`
+	Acodec               Acodec                        `json:"acodec"`
+	ABR                  float64                       `json:"abr"`
+	ASR                  int64                         `json:"asr"`
+	AudioChannels        int64                         `json:"audio_channels"`
+}
+
+type Format struct {
+	FormatID           string             `json:"format_id"`
+	FormatNote         *FormatNote        `json:"format_note,omitempty"`
+	EXT                MediaEXT           `json:"ext"`
+	Protocol           Protocol           `json:"protocol"`
+	Acodec             *Acodec            `json:"acodec,omitempty"`
+	Vcodec             string             `json:"vcodec"`
+	URL                string             `json:"url"`
+	Width              *int64             `json:"width"`
+	Height             *int64             `json:"height"`
+	FPS                *float64           `json:"fps"`
+	Rows               *int64             `json:"rows,omitempty"`
+	Columns            *int64             `json:"columns,omitempty"`
+	Fragments          []Fragment         `json:"fragments,omitempty"`
+	Resolution         Resolution         `json:"resolution"`
+	AspectRatio        *float64           `json:"aspect_ratio"`
+	FilesizeApprox     *int64             `json:"filesize_approx"`
+	HTTPHeaders        HTTPHeaders        `json:"http_headers"`
+	AudioEXT           MediaEXT           `json:"audio_ext"`
+	VideoEXT           MediaEXT           `json:"video_ext"`
+	Vbr                *float64           `json:"vbr"`
+	ABR                *float64           `json:"abr"`
+	Tbr                *float64           `json:"tbr"`
+	Format             string             `json:"format"`
+	FormatIndex        interface{}        `json:"format_index"`
+	ManifestURL        *string            `json:"manifest_url,omitempty"`
+	Language           *Language          `json:"language"`
+	Preference         interface{}        `json:"preference"`
+	Quality            *float64           `json:"quality,omitempty"`
+	HasDRM             *bool              `json:"has_drm,omitempty"`
+	SourcePreference   *int64             `json:"source_preference,omitempty"`
+	ASR                *int64             `json:"asr"`
+	Filesize           *int64             `json:"filesize"`
+	AudioChannels      *int64             `json:"audio_channels"`
+	LanguagePreference *int64             `json:"language_preference,omitempty"`
+	DynamicRange       *DynamicRange      `json:"dynamic_range"`
+	Container          *Container         `json:"container,omitempty"`
+	DownloaderOptions  *DownloaderOptions `json:"downloader_options,omitempty"`
+}
+
+type DownloaderOptions struct {
+	HTTPChunkSize int64 `json:"http_chunk_size"`
+}
+
+type Fragment struct {
+	URL      string  `json:"url"`
+	Duration float64 `json:"duration"`
+}
+
+type HTTPHeaders struct {
+	UserAgent      string         `json:"User-Agent"`
+	Accept         Accept         `json:"Accept"`
+	AcceptLanguage AcceptLanguage `json:"Accept-Language"`
+	SECFetchMode   SECFetchMode   `json:"Sec-Fetch-Mode"`
+}
+
+type RequestedDownload struct {
+	RequestedFormats     []Format     `json:"requested_formats"`
+	Format               string       `json:"format"`
+	FormatID             string       `json:"format_id"`
+	EXT                  string       `json:"ext"`
+	Protocol             string       `json:"protocol"`
+	FormatNote           string       `json:"format_note"`
+	FilesizeApprox       int64        `json:"filesize_approx"`
+	Tbr                  float64      `json:"tbr"`
+	Width                int64        `json:"width"`
+	Height               int64        `json:"height"`
+	Resolution           Resolution   `json:"resolution"`
+	FPS                  int64        `json:"fps"`
+	DynamicRange         DynamicRange `json:"dynamic_range"`
+	Vcodec               string       `json:"vcodec"`
+	Vbr                  float64      `json:"vbr"`
+	AspectRatio          float64      `json:"aspect_ratio"`
+	Acodec               Acodec       `json:"acodec"`
+	ABR                  float64      `json:"abr"`
+	ASR                  int64        `json:"asr"`
+	AudioChannels        int64        `json:"audio_channels"`
+	FilenameOld          string       `json:"_filename"`
+	Filename             string       `json:"filename"`
+	WriteDownloadArchive bool         `json:"__write_download_archive"`
+	Language             *Language    `json:"language,omitempty"`
+}
+
+type FilesToMove struct {
+}
+
+type Thumbnail struct {
+	URL        string  `json:"url"`
+	Preference *int64  `json:"preference,omitempty"`
+	ID         string  `json:"id"`
+	Height     *int64  `json:"height,omitempty"`
+	Width      *int64  `json:"width,omitempty"`
+	Resolution *string `json:"resolution,omitempty"`
+}
+
+type Heatmap struct {
+	StartTime float64 `json:"start_time"`
+	EndTime   float64 `json:"end_time"`
+	Value     float64 `json:"value"`
+}
+
+type Version struct {
+	Version        string      `json:"version"`
+	CurrentGitHead interface{} `json:"current_git_head"`
+	ReleaseGitHead string      `json:"release_git_head"`
+	Repository     string      `json:"repository"`
+}
+
+type Acodec string
+
+const (
+	AcodecNone Acodec = "none"
+	Mp4A402    Acodec = "mp4a.40.2"
+	Mp4A405    Acodec = "mp4a.40.5"
+	Opus       Acodec = "opus"
+)
+
+type AutomaticCaptionEXT string
+
+const (
+	Json3 AutomaticCaptionEXT = "json3"
+	Srv1  AutomaticCaptionEXT = "srv1"
+	Srv2  AutomaticCaptionEXT = "srv2"
+	Srv3  AutomaticCaptionEXT = "srv3"
+	Ttml  AutomaticCaptionEXT = "ttml"
+	Vtt   AutomaticCaptionEXT = "vtt"
+)
+
+type DynamicRange string
+
+const (
+	SDR DynamicRange = "SDR"
+	HDR DynamicRange = "HDR"
+)
+
+type MediaEXT string
+
+const (
+	EXTNone  MediaEXT = "none"
+	EXTMhtml MediaEXT = "mhtml"
+	M4A      MediaEXT = "m4a"
+	Mp4      MediaEXT = "mp4"
+	Webm     MediaEXT = "webm"
+)
+
+type Container string
+
+const (
+	M4ADash  Container = "m4a_dash"
+	Mp4Dash  Container = "mp4_dash"
+	WebmDash Container = "webm_dash"
+)
+
+type FormatNote string
+
+const (
+	Default    FormatNote = "Default"
+	Low        FormatNote = "low"
+	Medium     FormatNote = "medium"
+	Premium    FormatNote = "Premium"
+	Storyboard FormatNote = "storyboard"
+	The1080P   FormatNote = "1080p"
+	The144P    FormatNote = "144p"
+	The240P    FormatNote = "240p"
+	The360P    FormatNote = "360p"
+	The480P    FormatNote = "480p"
+	The720P    FormatNote = "720p"
+)
+
+type Accept string
+
+const (
+	TextHTMLApplicationXHTMLXMLApplicationXMLQ09Q08 Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"
+)
+
+type AcceptLanguage string
+
+const (
+	EnUsEnQ05 AcceptLanguage = "en-us,en;q=0.5"
+)
+
+type SECFetchMode string
+
+const (
+	Navigate SECFetchMode = "navigate"
+)
+
+type Language string
+
+const (
+	En Language = "en"
+)
+
+type Protocol string
+
+const (
+	HTTPS         Protocol = "https"
+	M3U8Native    Protocol = "m3u8_native"
+	ProtocolMhtml Protocol = "mhtml"
+)
+
+type Resolution string
+
+const (
+	AudioOnly    Resolution = "audio only"
+	The1280X720  Resolution = "1280x720"
+	The160X90    Resolution = "160x90"
+	The1920X1080 Resolution = "1920x1080"
+	The256X144   Resolution = "256x144"
+	The320X180   Resolution = "320x180"
+	The426X240   Resolution = "426x240"
+	The48X27     Resolution = "48x27"
+	The640X360   Resolution = "640x360"
+	The80X45     Resolution = "80x45"
+	The854X480   Resolution = "854x480"
+)

server/pkg/ytdlp/playlist.go

@@ -0,0 +1,115 @@
+package ytdlp
+
+import (
+	"bufio"
+	"context"
+	"encoding/json"
+	"errors"
+	"io"
+	"os"
+	"os/exec"
+	"strings"
+
+	"github.com/royalcat/ctxprogress"
+	"golang.org/x/sync/errgroup"
+)
+
+// Progress implements ctxprogress.Progress.
+func (p Entry) Progress() (current int, total int) {
+	return int(p.PlaylistIndex), int(p.PlaylistCount)
+}
+
+// func (p PlaylistEntry) Url() string {
+// 	if p.URL != "" {
+// 		return p.URL
+// 	}
+// 	if p.WebpageURL != "" {
+// 		return p.WebpageURL
+// 	}
+// 	if p.OriginalURL != "" {
+// 		return p.OriginalURL
+// 	}
+
+// 	return ""
+// }
+
+func (yt *Client) Playlist(ctx context.Context, url string) ([]Entry, error) {
+	group, ctx := errgroup.WithContext(ctx)
+	w, lines, err := lineReader(group)
+	if err != nil {
+		return nil, err
+	}
+
+	cmd := exec.CommandContext(ctx, yt.binary, "-j", url)
+
+	cmd.Stdout = w
+
+	group.Go(func() error {
+		err := cmd.Run()
+		if err != nil {
+			return err
+		}
+		return w.Close()
+	})
+
+	playlists := []Entry{}
+	for line := range lines {
+		entry := Entry{}
+		err = json.Unmarshal([]byte(line), &entry)
+		if err != nil {
+			return nil, err
+		}
+
+		playlists = append(playlists, entry)
+	}
+
+	return playlists, nil
+}
+
+func lineReader(group *errgroup.Group) (io.WriteCloser, <-chan string, error) {
+	lines := make(chan string)
+	var r io.Reader
+	r, w := io.Pipe()
+
+	r = io.TeeReader(r, os.Stdout)
+
+	group.Go(func() error {
+		defer close(lines)
+
+		reader := bufio.NewReader(r)
+		for {
+			line, err := reader.ReadString('\n')
+			if err != nil {
+				if err == io.EOF {
+					return w.Close()
+				}
+				return errors.Join(err, w.Close())
+			}
+			line = strings.Trim(line, " \r\t")
+
+			if line == "" {
+				continue
+			}
+
+			lines <- line
+		}
+	})
+
+	return w, lines, nil
+}
+
+var _ ctxprogress.Progress = (*Entry)(nil)
+
+var _ ctxprogress.Progress = (*DownloadProgress)(nil)
+
+func parseProgress(line string) (ctxprogress.Progress, error) {
+	line = strings.Trim(line, " \r\t")
+
+	p := &DownloadProgress{}
+	err := json.Unmarshal([]byte(line), p)
+	if err != nil {
+		return nil, err
+	}
+
+	return p, nil
+}

server/pkg/ytdlp/playlist_test.go

@@ -0,0 +1,27 @@
+package ytdlp_test
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"git.kmsign.ru/royalcat/tstor/server/pkg/ytdlp"
+	"github.com/stretchr/testify/require"
+)
+
+func TestPlaylist(t *testing.T) {
+	require := require.New(t)
+	ctx := context.Background()
+	if deadline, ok := t.Deadline(); ok {
+		var cancel context.CancelFunc
+		ctx, cancel = context.WithDeadlineCause(ctx, deadline, errors.New("test deadline done"))
+		defer cancel()
+	}
+	client, err := ytdlp.New()
+	require.NoError(err)
+	entries, err := client.Playlist(ctx, "https://www.youtube.com/playlist?list=PLUay9m6GhoyCXdloEa-VYtnVeshaKl4AW")
+	require.NoError(err)
+
+	require.NotEmpty(entries)
+	require.Len(entries, int(entries[0].PlaylistCount))
+}