From 54fda3422e70540f14edd8db1504cf09b92edfbc Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Thu, 4 Jun 2020 12:02:48 +0100
Subject: [PATCH] atexit: implement OnError for cancelling multpart uploads

---
 lib/atexit/atexit.go | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/lib/atexit/atexit.go b/lib/atexit/atexit.go
index 1976d5a2a..d52d50371 100644
--- a/lib/atexit/atexit.go
+++ b/lib/atexit/atexit.go
@@ -77,3 +77,23 @@ func Run() {
 		}
 	})
 }
+
+// OnError registers fn with atexit and returns a function which
+// runs fn() if *perr != nil and deregisters fn
+//
+// It should be used in a defer statement normally so
+//
+//     defer OnError(&err, cancelFunc)()
+//
+// So cancelFunc will be run if the function exits with an error or
+// at exit.
+func OnError(perr *error, fn func()) func() {
+	handle := Register(fn)
+	return func() {
+		defer Unregister(handle)
+		if *perr != nil {
+			fn()
+		}
+	}
+
+}