Fix bugs in sftp retrying

* Fixed a bug caused by nil sftp client during retry
* Simplify the rework logic in UploadFile
* Change the number of tries from 6 to 8

src/duplicacy_sftpstorage.go

@@ -91,7 +91,7 @@ func CreateSFTPStorage(server string, port int, username string, storageDir stri
 		storageDir:      storageDir,
 		minimumNesting:  minimumNesting,
 		numberOfThreads: threads,
-		numberOfTries:   6,
+		numberOfTries:   8,
 		serverAddress:   serverAddress,
 		sftpConfig:      sftpConfig,
 	}
@@ -129,22 +129,19 @@ func (storage *SFTPStorage) retry(f func () error) error {
 			delay *= 2
 
 			storage.clientLock.Lock()
-			if storage.client != nil {
-				storage.client.Close()
-				storage.client = nil
-			}
-
 			connection, err := ssh.Dial("tcp", storage.serverAddress, storage.sftpConfig)
 			if err != nil {
+				LOG_WARN("SFT_RECONNECT", "Failed to connect to %s: %v; retrying", storage.serverAddress, err)
 				storage.clientLock.Unlock()
-				return err
+				continue
 			}
 
 			client, err := sftp.NewClient(connection)
 			if err != nil {
+				LOG_WARN("SFT_RECONNECT", "Failed to create a new SFTP client to %s: %v; retrying", storage.serverAddress, err)
 				connection.Close()
 				storage.clientLock.Unlock()
-				return err
+				continue
 			}
 			storage.client = client
 			storage.clientLock.Unlock()
@@ -275,36 +272,19 @@ func (storage *SFTPStorage) UploadFile(threadIndex int, filePath string, content
 	fullPath := path.Join(storage.storageDir, filePath)
 
 	dirs := strings.Split(filePath, "/")
-	if len(dirs) > 1 {
-		fullDir := path.Dir(fullPath)
-		err = storage.retry(func() error {
-			_, err := storage.getSFTPClient().Stat(fullDir)
-			return err
-		})
-		if err != nil {
-			// The error may be caused by a non-existent fullDir, or a broken connection.  In either case,
-			// we just assume it is the former because there isn't a way to tell which is the case.
-			for i := range dirs[1 : len(dirs)-1] {
-				subDir := path.Join(storage.storageDir, path.Join(dirs[0:i+2]...))
-				// We don't check the error; just keep going blindly but always store the last err
-				err = storage.getSFTPClient().Mkdir(subDir)
-			}
+	fullDir := path.Dir(fullPath)
+	return storage.retry(func() error {
 
-			// If there is an error creating the dirs, we check fullDir one more time, because another thread
-			// may happen to create the same fullDir ahead of this thread
-			if err != nil {
-				err = storage.retry(func() error {
-					_, err := storage.getSFTPClient().Stat(fullDir)
-					return err
-				})
-				if err != nil {
-					return err
+		if len(dirs) > 1 {
+			_, err := storage.getSFTPClient().Stat(fullDir)
+			if os.IsNotExist(err) {
+				for i := range dirs[1 : len(dirs)-1] {
+					subDir := path.Join(storage.storageDir, path.Join(dirs[0:i+2]...))
+					// We don't check the error; just keep going blindly
+					storage.getSFTPClient().Mkdir(subDir)
 				}
 			}
 		}
-	}
-
-	return storage.retry(func() error {
 
 		letters := "abcdefghijklmnopqrstuvwxyz"
 		suffix := make([]byte, 8)