Rework retry logic when copying objects

* Fix off by one retry logic - fixes #406
  * Retry any retriable errors
  * Restructure code

fs/operations.go

@@ -202,11 +202,12 @@ func Copy(f Fs, dst, src Object) {
 	maxTries := Config.LowLevelRetries
 	tries := 0
 	doUpdate := dst != nil
-	var err, inErr error
-tryAgain:
+	var err error
+	var actionTaken string
+	for {
 		// Try server side copy first - if has optional interface and
 		// is same underlying remote
-	actionTaken := "Copied (server side copy)"
+		actionTaken = "Copied (server side copy)"
 		if fCopy, ok := f.(Copier); ok && src.Fs().Name() == f.Name() {
 			var newDst Object
 			newDst, err = fCopy.Copy(src, src.Remote())
@@ -221,11 +222,8 @@ tryAgain:
 			var in0 io.ReadCloser
 			in0, err = src.Open()
 			if err != nil {
-			Stats.Error()
-			ErrorLog(src, "Failed to open: %v", err)
-			return
-		}
-
+				err = errors.Wrap(err, "failed to open source object")
+			} else {
 				// On big files add a buffer
 				if src.Size() > 10<<20 {
 					in0, _ = newAsyncReader(in0, 4, 4<<20)
@@ -240,21 +238,28 @@ tryAgain:
 					actionTaken = "Copied (new)"
 					dst, err = f.Put(in, src)
 				}
-		inErr = in.Close()
+				closeErr := in.Close()
+				if err == nil {
+					err = closeErr
+				}
+			}
+		}
+		tries++
+		if tries >= maxTries {
+			break
 		}
 		// Retry if err returned a retry error
-	if IsRetryError(err) && tries < maxTries {
-		tries++
+		if IsRetryError(err) || ShouldRetry(err) {
 			Log(src, "Received error: %v - low level retry %d/%d", err, tries, maxTries)
 			if removeFailedCopy(dst) {
 				// If we removed dst, then nil it out and note we are not updating
 				dst = nil
 				doUpdate = false
 			}
-		goto tryAgain
+			continue
 		}
-	if err == nil {
-		err = inErr
+		// otherwise finish
+		break
 	}
 	if err != nil {
 		Stats.Error()