fix new file contents getting appended to end of file

fs/content_cache.go

@@ -2,6 +2,7 @@ package fs
 
 import (
 	"io"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -27,15 +28,15 @@ func (l *LoopbackCache) contentPath(id string) string {
 	return filepath.Join(l.directory, id)
 }
 
-// GetContent reads a file's content from disk.
+// Get reads a file's content from disk.
 func (l *LoopbackCache) Get(id string) []byte {
-	content, _ := os.ReadFile(l.contentPath(id))
+	content, _ := ioutil.ReadFile(l.contentPath(id))
 	return content
 }
 
 // InsertContent writes file content to disk in a single bulk insert.
 func (l *LoopbackCache) Insert(id string, content []byte) error {
-	return os.WriteFile(l.contentPath(id), content, 0600)
+	return ioutil.WriteFile(l.contentPath(id), content, 0600)
 }
 
 // InsertStream inserts a stream of data
@@ -47,12 +48,13 @@ func (l *LoopbackCache) InsertStream(id string, reader io.Reader) (int64, error)
 	return io.Copy(fd, reader)
 }
 
-// DeleteContent deletes content from disk.
+// Delete closes the fd AND deletes content from disk.
 func (l *LoopbackCache) Delete(id string) error {
+	l.Close(id)
 	return os.Remove(l.contentPath(id))
 }
 
-// MoveContent moves content from one ID to another
+// Move moves content from one ID to another
 func (l *LoopbackCache) Move(oldID string, newID string) error {
 	return os.Rename(l.contentPath(oldID), l.contentPath(newID))
 }
@@ -75,7 +77,7 @@ func (l *LoopbackCache) HasContent(id string) bool {
 	return err == nil
 }
 
-// OpenContent returns a filehandle for subsequent access
+// Open returns a filehandle for subsequent access
 func (l *LoopbackCache) Open(id string) (*os.File, error) {
 	if fd, ok := l.fds.Load(id); ok {
 		// already opened, return existing fd
@@ -96,6 +98,7 @@ func (l *LoopbackCache) Open(id string) (*os.File, error) {
 	return fd, nil
 }
 
+// Close closes the currently open fd
 func (l *LoopbackCache) Close(id string) {
 	if fd, ok := l.fds.Load(id); ok {
 		file := fd.(*os.File)

fs/fs.go

@@ -513,8 +513,11 @@ func (f *Filesystem) Open(cancel <-chan struct{}, in *fuse.OpenIn, out *fuse.Ope
 	ctx.Info().Msg(
 		"Not using cached item due to file hash mismatch, fetching content from API.",
 	)
+	// explicitly purge existing file content
+	fd.Seek(0, 0)
+	fd.Truncate(0)
 	size, err := graph.GetItemContentStream(id, f.auth, fd)
-	if err != nil {
+	if err != nil || !inode.VerifyChecksum(graph.QuickXORHashStream(fd)) {
 		ctx.Error().Err(err).Msg("Failed to fetch remote content.")
 		return fuse.EREMOTEIO
 	}
@@ -761,6 +764,7 @@ func (f *Filesystem) SetAttr(cancel <-chan struct{}, in *fuse.SetAttrIn, out *fu
 			Uint64("newSize", size).
 			Msg("")
 		fd, _ := f.content.Open(i.DriveItem.ID)
+		// the unix syscall does not update the seek position, so neither should we
 		fd.Truncate(int64(size))
 		i.DriveItem.Size = size
 		i.hasChanges = true

fs/graph/drive_item.go

@@ -122,8 +122,10 @@ func GetItemContent(id string, auth *Auth) ([]byte, uint64, error) {
 	return buf.Bytes(), uint64(n), err
 }
 
-// GetItemContentStream is the same as GetItemContent, but writes data to an output
-// reader
+// GetItemContentStream is the same as GetItemContent, but writes data to an
+// output reader. This function assumes a brand-new io.Writer is used, so
+// "output" must be truncated if there is content already in the io.Writer
+// prior to use.
 func GetItemContentStream(id string, auth *Auth, output io.Writer) (uint64, error) {
 	// determine the size of the item
 	item, err := GetItem(id, auth)