For GCS if size cannot be found use tempfile.

This is added as a fallback option instead of returning
an error we can just add a limit reader upto 5GB and
attempt to upload the file instead.

Related to restic/restic#996

api-put-object-progress.go

@@ -17,6 +17,7 @@
 package minio
 
 import (
+	"fmt"
 	"io"
 	"strings"
 
@@ -85,17 +86,14 @@ func (c Client) PutObjectWithMetadata(bucketName, objectName string, reader io.R
 	// NOTE: Google Cloud Storage does not implement Amazon S3 Compatible multipart PUT.
 	// So we fall back to single PUT operation with the maximum limit of 5GiB.
 	if s3utils.IsGoogleEndpoint(c.endpointURL) {
-		if size <= -1 {
+		if size > maxSinglePutObjectSize {
 			return 0, ErrorResponse{
 				Code:       "NotImplemented",
-				Message:    "Content-Length cannot be negative for file uploads to Google Cloud Storage.",
+				Message:    fmt.Sprintf("Invalid Content-Length %d for file uploads to Google Cloud Storage.", size),
 				Key:        objectName,
 				BucketName: bucketName,
 			}
 		}
-		if size > maxSinglePutObjectSize {
-			return 0, ErrEntityTooLarge(size, maxSinglePutObjectSize, bucketName, objectName)
-		}
 		// Do not compute MD5 for Google Cloud Storage. Uploads up to 5GiB in size.
 		return c.putObjectNoChecksum(bucketName, objectName, reader, size, metaData, progress)
 	}

api-put-object.go

@@ -170,6 +170,30 @@ func (c Client) putObjectNoChecksum(bucketName, objectName string, reader io.Rea
 		return 0, ErrEntityTooLarge(size, maxSinglePutObjectSize, bucketName, objectName)
 	}
 
+	if size <= -1 {
+		// Initialize a new temporary file.
+		var tmpFile *tempFile
+		tmpFile, err = newTempFile("single$-putobject-single")
+		if err != nil {
+			return 0, err
+		}
+		defer tmpFile.Close()
+		size, err = io.Copy(tmpFile, io.LimitReader(reader, maxSinglePutObjectSize))
+		if err != nil {
+			return 0, err
+		}
+		// Seek back to beginning of the temporary file.
+		if _, err = tmpFile.Seek(0, 0); err != nil {
+			return 0, err
+		}
+		reader = tmpFile
+	} else {
+		readerAt, ok := reader.(io.ReaderAt)
+		if ok {
+			reader = io.NewSectionReader(readerAt, 0, size)
+		}
+	}
+
 	// Update progress reader appropriately to the latest offset as we
 	// read from the source.
 	readSeeker := newHook(reader, progress)