From 28f69f25a001923ca880192e8b4960f7bf58496b Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Sat, 22 Feb 2020 10:37:01 +0000
Subject: [PATCH] ftp: fix lockup when using concurrency limit on failed
 connections #3984

Before this change if rclone failed to make an FTP connection for some
reason it would leak a concurrency token. When all the tokens were
leaked then rclone would lock up.

The fix returns the concurrency token if creating the FTP connection
returns an error.
---
 backend/ftp/ftp.go | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/backend/ftp/ftp.go b/backend/ftp/ftp.go
index 7631209da..58bd8cab6 100644
--- a/backend/ftp/ftp.go
+++ b/backend/ftp/ftp.go
@@ -190,7 +190,11 @@ func (f *Fs) getFtpConnection() (c *ftp.ServerConn, err error) {
 	if c != nil {
 		return c, nil
 	}
-	return f.ftpConnection()
+	c, err = f.ftpConnection()
+	if err != nil && f.opt.Concurrency > 0 {
+		f.tokens.Put()
+	}
+	return c, err
 }
 
 // Return an FTP connection to the pool