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