WriteObject() encoded data in go routine, fix another multipart issue

pkg/donut/bucket.go

@@ -417,13 +417,22 @@ func (b bucket) writeObjectData(k, m uint8, writers []io.WriteCloser, objectData
 			return 0, 0, iodine.New(err, nil)
 		}
 		totalLength = totalLength + len(chunk.Data)
-		encodedBlocks, _ := encoder.Encode(chunk.Data)
+		encodedBlocks, err := encoder.Encode(chunk.Data)
+		if err != nil {
+			return 0, 0, iodine.New(err, nil)
+		}
+
 		sumMD5.Write(chunk.Data)
 		sum256.Write(chunk.Data)
 		sum512.Write(chunk.Data)
 		for blockIndex, block := range encodedBlocks {
-			_, err := io.Copy(writers[blockIndex], bytes.NewBuffer(block))
-			if err != nil {
+			errCh := make(chan error, 1)
+			go func(writer io.Writer, reader io.Reader) {
+				defer close(errCh)
+				_, err := io.Copy(writers[blockIndex], bytes.NewReader(block))
+				errCh <- err
+			}(writers[blockIndex], bytes.NewReader(block))
+			if err := <-errCh; err != nil {
 				return 0, 0, iodine.New(err, nil)
 			}
 		}

pkg/donut/multipart.go

@@ -281,12 +281,12 @@ func (donut API) CompleteMultipartUpload(bucket, key, uploadID string, data io.R
 	}
 	var size int64
 	var fullObject bytes.Buffer
-	for i := 1; i <= len(parts.Part); i++ {
-		recvMD5 := parts.Part[i-1].ETag
-		object, ok := donut.multiPartObjects[uploadID].Get(parts.Part[i-1].PartNumber)
+	for i := 0; i < len(parts.Part); i++ {
+		recvMD5 := parts.Part[i].ETag
+		object, ok := donut.multiPartObjects[uploadID].Get(parts.Part[i].PartNumber)
 		if ok == false {
 			donut.lock.Unlock()
-			return ObjectMetadata{}, iodine.New(errors.New("missing part: "+strconv.Itoa(i)), nil)
+			return ObjectMetadata{}, iodine.New(errors.New("missing part: "+strconv.Itoa(parts.Part[i].PartNumber)), nil)
 		}
 		size += int64(len(object))
 		calcMD5Bytes := md5.Sum(object)