small refactor*

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)
+}