s3: use multipart uploads only when multiple parts are needed

Fixes #2016

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

internal/vfs/s3fs.go

@@ -306,7 +306,7 @@ func (fs *S3Fs) Create(name string, flag, checks int) (File, PipeWriter, func(),
 		} else {
 			contentType = mime.TypeByExtension(path.Ext(name))
 		}
-		err := fs.handleMultipartUpload(ctx, r, name, contentType)
+		err := fs.handleUpload(ctx, r, name, contentType)
 		r.CloseWithError(err) //nolint:errcheck
 		p.Done(err)
 		fsLog(fs, logger.LevelDebug, "upload completed, path: %q, acl: %q, readed bytes: %d, err: %+v",
@@ -890,7 +890,36 @@ func (fs *S3Fs) abortMultipartUpload(name, uploadID string) error {
 	return err
 }
 
-func (fs *S3Fs) handleMultipartUpload(ctx context.Context, reader io.Reader, name, contentType string) error {
+func (fs *S3Fs) singlePartUpload(ctx context.Context, name, contentType string, data []byte) error {
+	contentLength := int64(len(data))
+	_, err := fs.svc.PutObject(ctx, &s3.PutObjectInput{
+		Bucket:               aws.String(fs.config.Bucket),
+		Key:                  aws.String(name),
+		ACL:                  types.ObjectCannedACL(fs.config.ACL),
+		Body:                 bytes.NewReader(data),
+		ContentType:          util.NilIfEmpty(contentType),
+		ContentLength:        &contentLength,
+		SSECustomerKey:       util.NilIfEmpty(fs.sseCustomerKey),
+		SSECustomerAlgorithm: util.NilIfEmpty(fs.sseCustomerAlgo),
+		SSECustomerKeyMD5:    util.NilIfEmpty(fs.sseCustomerKeyMD5),
+		StorageClass:         types.StorageClass(fs.config.StorageClass),
+	})
+	return err
+}
+
+func (fs *S3Fs) handleUpload(ctx context.Context, reader io.Reader, name, contentType string) error {
+	pool := newBufferAllocator(int(fs.config.UploadPartSize))
+	defer pool.free()
+
+	firstBuf := pool.getBuffer()
+	firstReadSize, err := readFill(reader, firstBuf)
+	if err == io.EOF {
+		return fs.singlePartUpload(ctx, name, contentType, firstBuf[:firstReadSize])
+	}
+	if err != nil {
+		return err
+	}
+
 	uploadID, err := fs.initiateMultipartUpload(ctx, name, contentType)
 	if err != nil {
 		return err
@@ -905,9 +934,6 @@ func (fs *S3Fs) handleMultipartUpload(ctx context.Context, reader io.Reader, nam
 	var errOnce sync.Once
 	var partNumber int32
 
-	pool := newBufferAllocator(int(fs.config.UploadPartSize))
-	defer pool.free()
-
 	poolCtx, poolCancel := context.WithCancel(ctx)
 	defer poolCancel()
 
@@ -921,32 +947,7 @@ func (fs *S3Fs) handleMultipartUpload(ctx context.Context, reader io.Reader, nam
 		}
 	}
 
-	for partNumber = 1; !finished; partNumber++ {
-		buf := pool.getBuffer()
-
-		n, err := readFill(reader, buf)
-		if err == io.EOF {
-			if n == 0 && partNumber > 1 {
-				pool.releaseBuffer(buf)
-				break
-			}
-			finished = true
-		} else if err != nil {
-			pool.releaseBuffer(buf)
-			errOnce.Do(func() {
-				finalizeFailedUpload(err)
-			})
-			return err
-		}
-		guard <- struct{}{}
-		if hasError.Load() {
-			fsLog(fs, logger.LevelError, "pool error, upload for part %d not started", partNumber)
-			pool.releaseBuffer(buf)
-			break
-		}
-
-		wg.Add(1)
-		go func(partNum int32, buf []byte, bytesRead int) {
+	uploadPart := func(partNum int32, buf []byte, bytesRead int) {
 		defer func() {
 			pool.releaseBuffer(buf)
 			<-guard
@@ -966,7 +967,40 @@ func (fs *S3Fs) handleMultipartUpload(ctx context.Context, reader io.Reader, nam
 			ETag:       etag,
 		})
 		partMutex.Unlock()
-		}(partNumber, buf, n)
+	}
+
+	partNumber = 1
+	guard <- struct{}{}
+
+	wg.Add(1)
+	go uploadPart(partNumber, firstBuf, firstReadSize)
+
+	for partNumber = 2; !finished; partNumber++ {
+		buf := pool.getBuffer()
+
+		n, err := readFill(reader, buf)
+		if err == io.EOF {
+			if n == 0 {
+				pool.releaseBuffer(buf)
+				break
+			}
+			finished = true
+		} else if err != nil {
+			pool.releaseBuffer(buf)
+			errOnce.Do(func() {
+				finalizeFailedUpload(err)
+			})
+			return err
+		}
+		guard <- struct{}{}
+		if hasError.Load() {
+			fsLog(fs, logger.LevelError, "pool error, upload for part %d not started", partNumber)
+			pool.releaseBuffer(buf)
+			break
+		}
+
+		wg.Add(1)
+		go uploadPart(partNumber, buf, n)
 	}
 
 	wg.Wait()