feat(storage/transfermanager): add SkipIfExists option

storage/transfermanager/downloader.go

@@ -161,15 +161,22 @@ func (d *Downloader) DownloadDirectory(ctx context.Context, input *DownloadDirec
 		}
 
 		// Check if the file exists.
-		// TODO: add skip option.
+		fileExists := false
+
 		filePath := filepath.Join(input.LocalDirectory, attrs.Name)
 		if _, err := os.Stat(filePath); err == nil {
-			return fmt.Errorf("transfermanager: failed to create file(%q): %w", filePath, os.ErrExist)
+			fileExists = true
+			if !d.config.skipIfExists {
+				return fmt.Errorf("transfermanager: failed to create file(%q): %w", filePath, os.ErrExist)
+			}
 		} else if !errors.Is(err, os.ErrNotExist) {
+			// Encountered an error other than file does not exist.
 			return fmt.Errorf("transfermanager: failed to create file(%q): %w", filePath, err)
 		}
 
-		objectsToQueue = append(objectsToQueue, attrs.Name)
+		if !(d.config.skipIfExists && fileExists) {
+			objectsToQueue = append(objectsToQueue, attrs.Name)
+		}
 	}
 
 	outs := make(chan DownloadOutput, len(objectsToQueue))

storage/transfermanager/integration_test.go

@@ -185,22 +185,37 @@ func TestIntegration_DownloadDirectoryAsync(t *testing.T) {
 	multiTransportTest(context.Background(), t, func(t *testing.T, ctx context.Context, c *storage.Client, tb downloadTestBucket) {
 		localDir := t.TempDir()
 
-		numCallbacks := 0
-		callbackMu := sync.Mutex{}
-
 		d, err := NewDownloader(c, WithWorkers(2), WithPartSize(maxObjectSize/2), WithCallbacks())
 		if err != nil {
 			t.Fatalf("NewDownloader: %v", err)
 		}
 
+		// Test download options - only download directory "dir".
 		// In lex order we have:
-		// "dir/nested/again/obj1", -- excluded
+		// "dir/nested/again/obj1", -- excluded by StartOffset
 		// "dir/nested/objA", -- included
 		// "dir/file" -- excluded by MatchGlob
 		// "dir/objA", -- included
 		// "dir/objB", -- included
-		// "dir/objC", -- excluded
-		wantObjs := 3
+		// "dir/objC", -- excluded by EndOffset
+		includedObjs := []string{"dir/nested/objA", "dir/objA", "dir/objB"}
+
+		objectDownloaded := make(chan bool)
+		done := make(chan bool)
+
+		trackObjectsDownloaded := func(numObjects *int) {
+			for {
+				select {
+				case <-done:
+					return
+				case <-objectDownloaded:
+					*numObjects++
+				}
+			}
+		}
+
+		objectsDownloaded := 0
+		go trackObjectsDownloaded(&objectsDownloaded)
 
 		if err := d.DownloadDirectory(ctx, &DownloadDirectoryInput{
 			Bucket:         tb.bucket,
@@ -210,9 +225,7 @@ func TestIntegration_DownloadDirectoryAsync(t *testing.T) {
 			EndOffset:      "dir/objC",
 			MatchGlob:      "**obj**",
 			OnObjectDownload: func(got *DownloadOutput) {
-				callbackMu.Lock()
-				numCallbacks++
-				callbackMu.Unlock()
+				objectDownloaded <- true
 
 				if got.Err != nil {
 					t.Errorf("result.Err: %v", got.Err)
@@ -240,8 +253,8 @@ func TestIntegration_DownloadDirectoryAsync(t *testing.T) {
 				got.Object = "modifying this shouldn't be a problem"
 			},
 			Callback: func(outs []DownloadOutput) {
-				if len(outs) != wantObjs {
-					t.Errorf("expected to receive %d results, got %d results", wantObjs, len(outs))
+				if len(outs) != len(includedObjs) {
+					t.Errorf("expected to receive %d results, got %d results", len(includedObjs), len(outs))
 				}
 
 				for _, got := range outs {
@@ -275,21 +288,22 @@ func TestIntegration_DownloadDirectoryAsync(t *testing.T) {
 			t.Errorf("d.DownloadDirectory: %v", err)
 		}
 
-		if _, err = d.WaitAndClose(); err != nil {
-			t.Fatalf("d.WaitAndClose: %v", err)
+		if _, err := d.WaitAndClose(); err != nil {
+			t.Errorf("d.WaitAndClose: %v", err)
 		}
+		done <- true
 
-		if numCallbacks != wantObjs {
-			t.Errorf("expected to receive %d results, got %d callbacks", (wantObjs), numCallbacks)
+		if want, got := len(includedObjs), objectsDownloaded; want != got {
+			t.Errorf("expected to receive %d callbacks, got %d", want, got)
 		}
 
 		entries, err := os.ReadDir(filepath.Join(localDir, "dir"))
 		if err != nil {
 			t.Fatalf("os.ReadDir: %v", err)
 		}
 
-		if len(entries) != wantObjs {
-			t.Errorf("expected %d entries in dir, got %d", (wantObjs), len(entries))
+		if len(entries) != len(includedObjs) {
+			t.Errorf("expected %d entries in dir, got %d", len(includedObjs), len(entries))
 		}
 
 		for _, entry := range entries {
@@ -300,6 +314,65 @@ func TestIntegration_DownloadDirectoryAsync(t *testing.T) {
 				t.Errorf("unexpected file %q in dir", entry.Name())
 			}
 		}
+
+		// Test SkipIfExists() by attempting to download the entire directory.
+		// The files previously downloaded (ie. includedObjects) should be skipped.
+		d, err = NewDownloader(c, WithWorkers(2), SkipIfExists())
+		if err != nil {
+			t.Fatalf("NewDownloader: %v", err)
+		}
+
+		objectsDownloaded = 0
+		go trackObjectsDownloaded(&objectsDownloaded)
+
+		if err := d.DownloadDirectory(ctx, &DownloadDirectoryInput{
+			Bucket:         tb.bucket,
+			LocalDirectory: localDir,
+			OnObjectDownload: func(got *DownloadOutput) {
+				objectDownloaded <- true
+
+				if got.Err != nil {
+					t.Errorf("result.Err: %v", got.Err)
+				}
+
+				for _, obj := range includedObjs {
+					if strings.EqualFold(got.Object, obj) {
+						t.Errorf("should have skipped download of object %s", got.Object)
+					}
+				}
+
+				if got, want := got.Attrs.Size, tb.objectSizes[got.Object]; want != got {
+					t.Errorf("expected object size %d, got %d", want, got)
+				}
+
+				path := filepath.Join(localDir, got.Object)
+				f, err := os.Open(path)
+				if err != nil {
+					t.Errorf("os.Open(%q): %v", path, err)
+				}
+				defer f.Close()
+
+				b := bytes.NewBuffer(make([]byte, 0, got.Attrs.Size))
+				if _, err := io.Copy(b, f); err != nil {
+					t.Errorf("io.Copy: %v", err)
+				}
+
+				if wantCRC, gotCRC := tb.contentHashes[got.Object], crc32c(b.Bytes()); gotCRC != wantCRC {
+					t.Errorf("object(%q) at filepath(%q): content crc32c does not match; got: %v, expected: %v", got.Object, path, gotCRC, wantCRC)
+				}
+			},
+		}); err != nil {
+			t.Errorf("d.DownloadDirectory: %v", err)
+		}
+
+		if _, err := d.WaitAndClose(); err != nil {
+			t.Errorf("d.WaitAndClose: %v", err)
+		}
+		done <- true
+
+		if want, got := len(tb.objects)-len(includedObjs), objectsDownloaded; want != got {
+			t.Errorf("expected to receive %d callbacks, got %d", want, got)
+		}
 	})
 }
 
@@ -1007,6 +1080,8 @@ func (tb *downloadTestBucket) Create(prefix string) error {
 	ctx := context.Background()
 
 	tb.bucket = prefix + uidSpace.New()
+	// Note: some tests depend on these object names.
+	// Verify that tests pass when adding or removing objects.
 	tb.objects = []string{
 		"!#$&'()*+,:;=,?@,[] and spaces",
 		"./obj",

storage/transfermanager/option.go

@@ -91,6 +91,21 @@ func (wps withPartSize) apply(tm *transferManagerConfig) {
 	tm.partSize = wps.partSize
 }
 
+// SkipIfExists returns a TransferManagerOption that will not download files
+// that already exist in the local directory.
+//
+// By default, if a file already exists the operation will abort and return an error.
+func SkipIfExists() Option {
+	return &skipIfExists{}
+}
+
+type skipIfExists struct {
+}
+
+func (sie skipIfExists) apply(tm *transferManagerConfig) {
+	tm.skipIfExists = true
+}
+
 type transferManagerConfig struct {
 	// Workers in thread pool; default numCPU/2 based on previous benchmarks?
 	numWorkers int
@@ -107,6 +122,10 @@ type transferManagerConfig struct {
 	// If true, callbacks are used instead of returning results synchronously
 	// in a slice at the end.
 	asynchronous bool
+
+	// If true, files that already exist in the local directory will not be
+	// downloaded.
+	skipIfExists bool
 }
 
 func defaultTransferManagerConfig() *transferManagerConfig {