From e8eb658ba5b2cda4d525c39eb815f548fd0b8288 Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Tue, 25 Feb 2020 11:38:13 +0000
Subject: [PATCH] ftp: fix lockup on failed upload when using concurrency limit
 #3984

Before this change if rclone failed to upload a file 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 regardless of the error state.
---
 backend/ftp/ftp.go | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/backend/ftp/ftp.go b/backend/ftp/ftp.go
index 58bd8cab6..a818dd87b 100644
--- a/backend/ftp/ftp.go
+++ b/backend/ftp/ftp.go
@@ -207,7 +207,13 @@ func (f *Fs) putFtpConnection(pc **ftp.ServerConn, err error) {
 	if f.opt.Concurrency > 0 {
 		defer f.tokens.Put()
 	}
+	if pc == nil {
+		return
+	}
 	c := *pc
+	if c == nil {
+		return
+	}
 	*pc = nil
 	if err != nil {
 		// If not a regular FTP error code then check the connection
@@ -861,6 +867,7 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 	if err != nil {
 		_ = c.Quit() // toss this connection to avoid sync errors
 		remove()
+		o.fs.putFtpConnection(nil, err)
 		return errors.Wrap(err, "update stor")
 	}
 	o.fs.putFtpConnection(&c, nil)