filehash random read

src/vfs/hash.go

@@ -5,7 +5,6 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
-	"io"
 )
 
 const chunkSize int64 = 64 * 1024
@@ -18,11 +17,6 @@ func FileHash(ctx context.Context, f File) (Hash, error) {
 	ctx, span := tracer.Start(ctx, "FileHash")
 	defer span.End()
 
-	_, err := f.Seek(0, io.SeekStart)
-	if err != nil {
-		return "", fmt.Errorf("error seeking file: %w", err)
-	}
-	defer f.Seek(0, io.SeekStart)
 	fileSize := f.Size()
 	if fileSize <= 8 {
 		return "", fmt.Errorf("cannot calculate oshash where size < 8 (%d)", fileSize)
@@ -37,20 +31,12 @@ func FileHash(ctx context.Context, f File) (Hash, error) {
 	head := make([]byte, fileChunkSize)
 	tail := make([]byte, fileChunkSize)
 
-	// read the head of the file into the start of the buffer
+	_, err := f.ReadAt(ctx, head, 0)
-	_, err = f.Read(ctx, head)
 	if err != nil {
 		return "", err
 	}
 
-	// seek to the end of the file - the chunk size
+	_, err = f.ReadAt(ctx, tail, fileSize-fileChunkSize)
-	_, err = f.Seek(-fileChunkSize, io.SeekEnd)
-	if err != nil {
-		return "", err
-	}
-
-	// read the tail of the file
-	_, err = f.Read(ctx, tail)
 	if err != nil {
 		return "", err
 	}