XL: CompleteMultipart should ignore last part is 0bytes. (#1931)

Fixes #1917

erasure-createfile.go

@@ -39,20 +39,34 @@ func erasureCreateFile(disks []StorageAPI, volume string, path string, partName
 	// Read until io.EOF, erasure codes data and writes to all disks.
 	for {
 		var n int
+		var blocks [][]byte
 		n, err = io.ReadFull(data, buf)
 		if err == io.EOF {
+			// We have reached EOF on the first byte read, io.Reader
+			// must be 0bytes, we don't need to erasure code
+			// data. Will create a 0byte file instead.
+			if size == 0 {
+				blocks = make([][]byte, len(disks))
+				err = appendFile(disks, volume, path, blocks, eInfo.Distribution, hashWriters, writeQuorum)
+				if err != nil {
+					return nil, 0, err
+				}
+			} // else we have reached EOF after few reads, no need to
+			// add an additional 0bytes at the end.
 			break
 		}
 		if err != nil && err != io.ErrUnexpectedEOF {
 			return nil, 0, err
 		}
 		size += int64(n)
-		var blocks [][]byte
 		// Returns encoded blocks.
-		blocks, err = encodeData(buf[:n], eInfo.DataBlocks, eInfo.ParityBlocks)
-		if err != nil {
-			return nil, 0, err
+		var enErr error
+		blocks, enErr = encodeData(buf[:n], eInfo.DataBlocks, eInfo.ParityBlocks)
+		if enErr != nil {
+			return nil, 0, enErr
 		}
+
+		// Write to all disks.
 		err = appendFile(disks, volume, path, blocks, eInfo.Distribution, hashWriters, writeQuorum)
 		if err != nil {
 			return nil, 0, err

xl-v1-metadata.go

@@ -171,11 +171,6 @@ func (m xlMetaV1) ObjectToPartOffset(offset int64) (partIndex int, partOffset in
 	// Seek until object offset maps to a particular part offset.
 	for i, part := range m.Parts {
 		partIndex = i
-		// Last part can be of '0' bytes, treat it specially and
-		// return right here.
-		if part.Size == 0 {
-			return partIndex, partOffset, nil
-		}
 		// Offset is smaller than size we have reached the proper part offset.
 		if partOffset < part.Size {
 			return partIndex, partOffset, nil

xl-v1-multipart.go

@@ -579,17 +579,28 @@ func (xl xlObjects) CompleteMultipartUpload(bucket string, object string, upload
 	// Validate each part and then commit to disk.
 	for i, part := range parts {
 		partIdx := currentXLMeta.ObjectPartIndex(part.PartNumber)
+		// All parts should have same part number.
 		if partIdx == -1 {
 			return "", InvalidPart{}
 		}
+
+		// All parts should have same ETag as previously generated.
 		if currentXLMeta.Parts[partIdx].ETag != part.ETag {
 			return "", BadDigest{}
 		}
+
 		// All parts except the last part has to be atleast 5MB.
 		if (i < len(parts)-1) && !isMinAllowedPartSize(currentXLMeta.Parts[partIdx].Size) {
 			return "", PartTooSmall{}
 		}
 
+		// Last part could have been uploaded as 0bytes, do not need
+		// to save it in final `xl.json`.
+		if (i == len(parts)-1) && currentXLMeta.Parts[partIdx].Size == 0 {
+			xlMeta.Parts = xlMeta.Parts[:i] // Skip the part.
+			continue
+		}
+
 		// Save for total object size.
 		objectSize += currentXLMeta.Parts[partIdx].Size