Add a rotating buffer functionality to the s3 driver

storagedriver/s3/s3.go

@@ -284,6 +284,7 @@ func (d *Driver) WriteStream(path string, offset int64, reader io.Reader) (total
 
 	partNumber := 1
 	bytesRead := 0
+	var putErrChan chan error
 	parts := []s3.Part{}
 	var part s3.Part
 
@@ -303,6 +304,12 @@ func (d *Driver) WriteStream(path string, offset int64, reader io.Reader) (total
 	// multipart upload, which will eventually be cleaned up, but we will lose all of the progress
 	// made prior to the machine crashing.
 	defer func() {
+		if putErrChan != nil {
+			if putErr := <-putErrChan; putErr != nil {
+				err = putErr
+			}
+		}
+
 		if len(parts) > 0 {
 			if multi == nil {
 				// Parts should be empty if the multi is not initialized
@@ -356,16 +363,31 @@ func (d *Driver) WriteStream(path string, offset int64, reader io.Reader) (total
 			}
 		}
 
+		if putErrChan == nil {
+			putErrChan = make(chan error)
+		} else {
+			if putErr := <-putErrChan; putErr != nil {
+				putErrChan = nil
+				return putErr
+			}
+		}
+
+		go func(bytesRead int, from int64, buf []byte) {
+			// parts and partNumber are safe, because this function is the only one modifying them and we
+			// force it to be executed serially.
 			if bytesRead > 0 {
-			part, err = multi.PutPart(int(partNumber), bytes.NewReader(buf[0:int64(bytesRead)+from]))
+				part, putErr := multi.PutPart(int(partNumber), bytes.NewReader(buf[0:int64(bytesRead)+from]))
-			if err != nil {
+				if putErr != nil {
-				return err
+					putErrChan <- putErr
 				}
 
 				parts = append(parts, part)
 				partNumber++
 			}
+			putErrChan <- nil
+		}(bytesRead, from, buf)
 
+		buf = make([]byte, d.ChunkSize)
 		return nil
 	}