copyObject: No need to verify md5sum. (#1520)

Multipart objects are kept in non hex md5sum format.
This format doesn't comply with hex, so decoding
would fail invariably.

This is not necessary to validate and its not expected
error during a CopyObject operation.

Fixes #1519

object-handlers.go

@@ -393,16 +393,6 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 		return
 	}
 
-	var md5Bytes []byte
-	if objInfo.MD5Sum != "" {
-		md5Bytes, err = hex.DecodeString(objInfo.MD5Sum)
-		if err != nil {
-			errorIf(err, "Decoding md5 failed.", nil)
-			writeErrorResponse(w, r, ErrInvalidDigest, r.URL.Path)
-			return
-		}
-	}
-
 	startOffset := int64(0) // Read the whole file.
 	// Get the object.
 	readCloser, err := api.ObjectAPI.GetObject(sourceBucket, sourceObject, startOffset)
@@ -414,12 +404,8 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 	// Size of object.
 	size := objInfo.Size
 
-	// Save metadata.
-	metadata := make(map[string]string)
-	metadata["md5Sum"] = hex.EncodeToString(md5Bytes)
-
 	// Create the object.
-	md5Sum, err := api.ObjectAPI.PutObject(bucket, object, size, readCloser, metadata)
+	md5Sum, err := api.ObjectAPI.PutObject(bucket, object, size, readCloser, nil)
 	if err != nil {
 		errorIf(err, "PutObject failed.", nil)
 		writeErrorResponse(w, r, toAPIErrorCode(err), r.URL.Path)