operations: fix missing metadata for multipart transfers to local disk

Before this change multipart downloads to the local disk with
--metadata failed to have their metadata set properly.

This was because the OpenWriterAt interface doesn't receive metadata
when creating the object.

This patch fixes the problem by using the recently introduced
Object.SetMetadata method to set the metadata on the object after the
download has completed (when using --metadata). If the backend we are
copying to is using OpenWriterAt but the Object doesn't support
SetMetadata then it will write an ERROR level log but complete
successfully. This should not happen at the moment as only the local
backend supports metadata and OpenWriterAt but it may in the future.

It also adds a test to check metadata is preserved when doing
multipart transfers.

Fixes #7424

fs/operations/multithread.go

@@ -131,6 +131,7 @@ func multiThreadCopy(ctx context.Context, f fs.Fs, remote string, src fs.Object,
 	openChunkWriter := f.Features().OpenChunkWriter
 	ci := fs.GetConfig(ctx)
 	noBuffering := false
+	usingOpenWriterAt := false
 	if openChunkWriter == nil {
 		openWriterAt := f.Features().OpenWriterAt
 		if openWriterAt == nil {
@@ -140,6 +141,7 @@ func multiThreadCopy(ctx context.Context, f fs.Fs, remote string, src fs.Object,
 		// If we are using OpenWriterAt we don't seek the chunks so don't need to buffer
 		fs.Debugf(src, "multi-thread copy: disabling buffering because destination uses OpenWriterAt")
 		noBuffering = true
+		usingOpenWriterAt = true
 	} else if src.Fs().Features().IsLocal {
 		// If the source fs is local we don't need to buffer
 		fs.Debugf(src, "multi-thread copy: disabling buffering because source is local disk")
@@ -241,7 +243,26 @@ func multiThreadCopy(ctx context.Context, f fs.Fs, remote string, src fs.Object,
 		return nil, fmt.Errorf("multi-thread copy: failed to find object after copy: %w", err)
 	}
 
-	if f.Features().PartialUploads {
+	// OpenWriterAt doesn't set metadata so we need to set it on completion
+	if usingOpenWriterAt {
+		setModTime := true
+		if ci.Metadata {
+			do, ok := obj.(fs.SetMetadataer)
+			if ok {
+				meta, err := fs.GetMetadataOptions(ctx, f, src, options)
+				if err != nil {
+					return nil, fmt.Errorf("multi-thread copy: failed to read metadata from source object: %w", err)
+				}
+				err = do.SetMetadata(ctx, meta)
+				if err != nil {
+					return nil, fmt.Errorf("multi-thread copy: failed to set metadata: %w", err)
+				}
+				setModTime = false
+			} else {
+				fs.Errorf(obj, "multi-thread copy: can't set metadata as SetMetadata isn't implemented in: %v", f)
+			}
+		}
+		if setModTime {
 			err = obj.SetModTime(ctx, src.ModTime(ctx))
 			switch err {
 			case nil, fs.ErrorCantSetModTime, fs.ErrorCantSetModTimeWithoutDelete:
@@ -249,6 +270,7 @@ func multiThreadCopy(ctx context.Context, f fs.Fs, remote string, src fs.Object,
 				return nil, fmt.Errorf("multi-thread copy: failed to set modification time: %w", err)
 			}
 		}
+	}
 
 	fs.Debugf(src, "Finished multi-thread copy with %d parts of size %v", mc.numChunks, fs.SizeSuffix(mc.partSize))
 	return obj, nil

fs/operations/multithread_test.go

@@ -146,6 +146,9 @@ func TestMultithreadCopy(t *testing.T) {
 	r := fstest.NewRun(t)
 	ctx := context.Background()
 	chunkSize := skipIfNotMultithread(ctx, t, r)
+	// Check every other transfer for metadata
+	checkMetadata := false
+	ctx, ci := fs.AddConfig(ctx)
 
 	for _, upload := range []bool{false, true} {
 		for _, test := range []struct {
@@ -156,6 +159,8 @@ func TestMultithreadCopy(t *testing.T) {
 			{size: chunkSize * 2, streams: 2},
 			{size: chunkSize*2 + 1, streams: 2},
 		} {
+			checkMetadata = !checkMetadata
+			ci.Metadata = checkMetadata
 			fileName := fmt.Sprintf("test-multithread-copy-%v-%d-%d", upload, test.size, test.streams)
 			t.Run(fmt.Sprintf("upload=%v,size=%v,streams=%v", upload, test.size, test.streams), func(t *testing.T) {
 				if *fstest.SizeLimit > 0 && int64(test.size) > *fstest.SizeLimit {
@@ -167,21 +172,41 @@ func TestMultithreadCopy(t *testing.T) {
 					file1        fstest.Item
 					src, dst     fs.Object
 					err          error
+					testMetadata = fs.Metadata{
+						// System metadata supported by all backends
+						"mtime": t1.Format(time.RFC3339Nano),
+						// User metadata
+						"potato": "jersey",
+					}
 				)
 
+				var fSrc, fDst fs.Fs
 				if upload {
 					file1 = r.WriteFile(fileName, contents, t1)
 					r.CheckRemoteItems(t)
 					r.CheckLocalItems(t, file1)
-					src, err = r.Flocal.NewObject(ctx, fileName)
+					fDst, fSrc = r.Fremote, r.Flocal
 				} else {
 					file1 = r.WriteObject(ctx, fileName, contents, t1)
 					r.CheckRemoteItems(t, file1)
 					r.CheckLocalItems(t)
-					src, err = r.Fremote.NewObject(ctx, fileName)
+					fDst, fSrc = r.Flocal, r.Fremote
 				}
+				src, err = fSrc.NewObject(ctx, fileName)
 				require.NoError(t, err)
 
+				do, canSetMetadata := src.(fs.SetMetadataer)
+				if checkMetadata && canSetMetadata {
+					// Set metadata on the source if required
+					err := do.SetMetadata(ctx, testMetadata)
+					if err == fs.ErrorNotImplemented {
+						canSetMetadata = false
+					} else {
+						require.NoError(t, err)
+						fstest.CheckEntryMetadata(ctx, t, r.Flocal, src, testMetadata)
+					}
+				}
+
 				accounting.GlobalStats().ResetCounters()
 				tr := accounting.GlobalStats().NewTransfer(src, nil)
 
@@ -189,19 +214,21 @@ func TestMultithreadCopy(t *testing.T) {
 					tr.Done(ctx, err)
 				}()
 
-				if upload {
+				dst, err = multiThreadCopy(ctx, fDst, fileName, src, test.streams, tr)
-					dst, err = multiThreadCopy(ctx, r.Fremote, fileName, src, test.streams, tr)
-				} else {
-					dst, err = multiThreadCopy(ctx, r.Flocal, fileName, src, test.streams, tr)
-				}
-
 				require.NoError(t, err)
+
 				assert.Equal(t, src.Size(), dst.Size())
 				assert.Equal(t, fileName, dst.Remote())
-				fstest.CheckListingWithPrecision(t, r.Fremote, []fstest.Item{file1}, nil, fs.GetModifyWindow(ctx, r.Flocal, r.Fremote))
+				fstest.CheckListingWithPrecision(t, fSrc, []fstest.Item{file1}, nil, fs.GetModifyWindow(ctx, fDst, fSrc))
-				fstest.CheckListingWithPrecision(t, r.Flocal, []fstest.Item{file1}, nil, fs.GetModifyWindow(ctx, r.Flocal, r.Fremote))
+				fstest.CheckListingWithPrecision(t, fDst, []fstest.Item{file1}, nil, fs.GetModifyWindow(ctx, fDst, fSrc))
+
+				if checkMetadata && canSetMetadata && fDst.Features().ReadMetadata {
+					fstest.CheckEntryMetadata(ctx, t, fDst, dst, testMetadata)
+				}
+
 				require.NoError(t, dst.Remove(ctx))
 				require.NoError(t, src.Remove(ctx))
+
 			})
 		}
 	}