feat(storage): support single-shot uploads in gRPC (#8348)

When ChunkSize is zero, use a single shot upload (leaving the stream open between messages) rather than a resumable session. This matches better with what we do in JSON. Also reduce the buffer size to the minimum (256k).

Fixes #7798

storage/grpc_client.go

@@ -1044,11 +1044,13 @@ func (c *grpcStorageClient) OpenWriter(params *openWriterParams, opts ...storage
 			}
 
 			// The chunk buffer is full, but there is no end in sight. This
-			// means that a resumable upload will need to be used to send
+			// means that either:
+			// 1. A resumable upload will need to be used to send
 			// multiple chunks, until we are done reading data. Start a
 			// resumable upload if it has not already been started.
-			// Otherwise, all data will be sent over a single gRPC stream.
-			if !doneReading && gw.upid == "" {
+			// 2. ChunkSize of zero may also have a full buffer, but a resumable
+			// session should not be initiated in this case.
+			if !doneReading && gw.upid == "" && params.chunkSize != 0 {
 				err = gw.startResumableUpload()
 				if err != nil {
 					err = checkCanceled(err)
@@ -1065,11 +1067,15 @@ func (c *grpcStorageClient) OpenWriter(params *openWriterParams, opts ...storage
 				pr.CloseWithError(err)
 				return
 			}
+
 			// At this point, the current buffer has been uploaded. For resumable
-			// uploads, capture the committed offset here in case the upload was not
-			// finalized and another chunk is to be uploaded.
-			if gw.upid != "" {
+			// uploads and chunkSize = 0, capture the committed offset here in case
+			// the upload was not finalized and another chunk is to be uploaded. Call
+			// the progress function for resumable uploads only.
+			if gw.upid != "" || gw.chunkSize == 0 {
 				offset = off
+			}
+			if gw.upid != "" {
 				progress(offset)
 			}
 
@@ -1485,14 +1491,11 @@ func newGRPCWriter(c *grpcStorageClient, params *openWriterParams, r io.Reader)
 		size += googleapi.MinUploadChunkSize - (size % googleapi.MinUploadChunkSize)
 	}
 
+	// A completely bufferless upload is not possible as it is in JSON because
+	// the buffer must be provided to the message. However use the minimum size
+	// possible in this case.
 	if params.chunkSize == 0 {
-		// TODO: Should we actually use the minimum of 256 KB here when the user
-		// indicates they want minimal memory usage? We cannot do a zero-copy,
-		// bufferless upload like HTTP/JSON can.
-		// TODO: We need to determine if we can avoid starting a
-		// resumable upload when the user *plans* to send more than bufSize but
-		// with a bufferless upload.
-		size = maxPerMessageWriteSize
+		size = googleapi.MinUploadChunkSize
 	}
 
 	return &gRPCWriter{
@@ -1505,6 +1508,7 @@ func newGRPCWriter(c *grpcStorageClient, params *openWriterParams, r io.Reader)
 		conds:         params.conds,
 		encryptionKey: params.encryptionKey,
 		sendCRC32C:    params.sendCRC32C,
+		chunkSize:     params.chunkSize,
 	}
 }
 
@@ -1524,6 +1528,7 @@ type gRPCWriter struct {
 	settings      *settings
 
 	sendCRC32C bool
+	chunkSize  int
 
 	// The gRPC client-stream used for sending buffers.
 	stream storagepb.Storage_WriteObjectClient
@@ -1589,7 +1594,6 @@ func (w *gRPCWriter) uploadBuffer(recvd int, start int64, doneReading bool) (*st
 	offset := start
 	toWrite := w.buf[:recvd]
 	for {
-		first := sent == 0
 		// This indicates that this is the last message and the remaining
 		// data fits in one message.
 		belowLimit := recvd-sent <= limit
@@ -1612,10 +1616,10 @@ func (w *gRPCWriter) uploadBuffer(recvd int, start int64, doneReading bool) (*st
 			FinishWrite: finishWrite,
 		}
 
-		// Open a new stream and set the first_message field on the request.
-		// The first message on the WriteObject stream must either be the
-		// Object or the Resumable Upload ID.
-		if first {
+		// Open a new stream if necessary and set the first_message field on
+		// the request. The first message on the WriteObject stream must either
+		// be the Object or the Resumable Upload ID.
+		if w.stream == nil {
 			ctx := gapic.InsertMetadata(w.ctx, metadata.Pairs("x-goog-request-params", fmt.Sprintf("bucket=projects/_/buckets/%s", url.QueryEscape(w.bucket))))
 			w.stream, err = w.c.raw.WriteObject(ctx)
 			if err != nil {
@@ -1678,6 +1682,13 @@ func (w *gRPCWriter) uploadBuffer(recvd int, start int64, doneReading bool) (*st
 			continue
 		}
 
+		// The buffer has been uploaded and there is still more data to be
+		// uploaded, but this is not a resumable upload session. Therefore
+		// keep the stream open and don't commit yet.
+		if !finishWrite && w.chunkSize == 0 {
+			return nil, offset, false, nil
+		}
+
 		// Done sending data. Close the stream to "commit" the data sent.
 		resp, finalized, err := w.commit()
 		// Retriable errors mean we should start over and attempt to

storage/integration_test.go

@@ -2393,6 +2393,15 @@ func TestIntegration_WriterChunksize(t *testing.T) {
 				if callbacks != test.wantCallbacks {
 					t.Errorf("ProgressFunc was called %d times, expected %d", callbacks, test.wantCallbacks)
 				}
+
+				// Confirm all bytes were uploaded.
+				attrs, err := obj.Attrs(ctx)
+				if err != nil {
+					t.Fatalf("obj.Attrs: %v", err)
+				}
+				if attrs.Size != int64(objSize) {
+					t.Errorf("incorrect number of bytes written; got %v, want %v", attrs.Size, objSize)
+				}
 			})
 		}
 	})