vfs: fix stale data when using --vfs-cache-mode full

Before this change the VFS cache could get into a state where when an
object was updated remotely, the fingerprint of the item was correct
for the new object but the data in the VFS cache was for the old
object.

This fixes the problem by updating the fingerprint of the item at the
point we remove the stale data. The empty cache item now represents
the new item even though it has no data in.

This stops the fallback code for an empty fingerprint running (used
when we are writing items to the cache instead of reading them) which
was causing the problem.

Fixes #6053
See: https://forum.rclone.org/t/cached-webdav-mount-fingerprints-get-nuked-on-ls/43974/

vfs/read_write_test.go

@@ -714,3 +714,47 @@ func TestRWCacheRename(t *testing.T) {
 	assert.False(t, vfs.cache.Exists("rename_me"))
 	assert.True(t, vfs.cache.Exists("i_was_renamed"))
 }
+
+// Test the cache reading a file that is updated externally
+//
+// See: https://github.com/rclone/rclone/issues/6053
+func TestRWCacheUpdate(t *testing.T) {
+	opt := vfscommon.DefaultOpt
+	opt.CacheMode = vfscommon.CacheModeFull
+	opt.WriteBack = writeBackDelay
+	opt.DirCacheTime = 100 * time.Millisecond
+	r, vfs := newTestVFSOpt(t, &opt)
+
+	if r.Fremote.Precision() == fs.ModTimeNotSupported {
+		t.Skip("skip as modtime not supported")
+	}
+
+	const filename = "TestRWCacheUpdate"
+
+	modTime := time.Now().Add(-time.Hour)
+	for i := 0; i < 10; i++ {
+		modTime = modTime.Add(time.Minute)
+		// Refresh test file
+		contents := fmt.Sprintf("TestRWCacheUpdate%03d", i)
+		// Increase the size for second half of test
+		for j := 5; j < i; j++ {
+			contents += "*"
+		}
+		file1 := r.WriteObject(context.Background(), filename, contents, modTime)
+		r.CheckRemoteItems(t, file1)
+
+		// Wait for directory cache to expire
+		time.Sleep(2 * opt.DirCacheTime)
+
+		// Check the file is OK via the VFS
+		data, err := vfs.ReadFile(filename)
+		require.NoError(t, err)
+		require.Equal(t, contents, string(data))
+
+		// Check Stat
+		fi, err := vfs.Stat(filename)
+		require.NoError(t, err)
+		assert.Equal(t, int64(len(contents)), fi.Size())
+		fstest.AssertTimeEqualWithPrecision(t, filename, modTime, fi.ModTime(), r.Fremote.Precision())
+	}
+}

vfs/vfscache/item.go

@@ -810,6 +810,7 @@ func (item *Item) _checkObject(o fs.Object) error {
 				if !item.info.Dirty {
 					fs.Debugf(item.name, "vfs cache: removing cached entry as stale (remote fingerprint %q != cached fingerprint %q)", remoteFingerprint, item.info.Fingerprint)
 					item._remove("stale (remote is different)")
+					item.info.Fingerprint = remoteFingerprint
 				} else {
 					fs.Debugf(item.name, "vfs cache: remote object has changed but local object modified - keeping it (remote fingerprint %q != cached fingerprint %q)", remoteFingerprint, item.info.Fingerprint)
 				}

vfs/vfscache/item_test.go

@@ -409,8 +409,14 @@ func TestItemReloadCacheStale(t *testing.T) {
 	assert.NotEqual(t, contents, contents2)
 
 	// Re-open with updated object
+	oldFingerprint := item.info.Fingerprint
+	assert.NotEqual(t, "", oldFingerprint)
 	require.NoError(t, item.Open(obj))
 
+	// Make sure fingerprint was updated
+	assert.NotEqual(t, oldFingerprint, item.info.Fingerprint)
+	assert.NotEqual(t, "", item.info.Fingerprint)
+
 	// Check size is now 110
 	size, err = item.GetSize()
 	require.NoError(t, err)