From 8d07bbf548b99811cf4aab888223cc96c973c0a7 Mon Sep 17 00:00:00 2001
From: Frederik Ring <frederik.ring@gmail.com>
Date: Thu, 29 Feb 2024 19:31:15 +0100
Subject: [PATCH] Also forward exec output when failing to demultiplex

---
 cmd/backup/exec.go | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/cmd/backup/exec.go b/cmd/backup/exec.go
index 1d762f61..754842ad 100644
--- a/cmd/backup/exec.go
+++ b/cmd/backup/exec.go
@@ -45,15 +45,24 @@ func (s *script) exec(containerRef string, command string, user string) ([]byte,
 	}
 	defer resp.Close()
 
-	var outBuf, errBuf bytes.Buffer
+	var outBuf, errBuf, fullRespBuf bytes.Buffer
 	outputDone := make(chan error)
 
+	tee := io.TeeReader(resp.Reader, &fullRespBuf)
+
 	go func() {
-		_, err := stdcopy.StdCopy(&outBuf, &errBuf, resp.Reader)
+		_, err := stdcopy.StdCopy(&outBuf, &errBuf, tee)
 		outputDone <- err
 	}()
 
 	if err := <-outputDone; err != nil {
+		if body, bErr := io.ReadAll(&fullRespBuf); bErr == nil {
+			// if possible, try to append the exec output to the error
+			// as it's likely to be more relevant for users than the error from
+			// calling stdcopy.Copy
+			err = errwrap.Wrap(errors.New(string(body)), err.Error())
+			return nil, nil, errwrap.Wrap(err, "error demultiplexing output")
+		}
 		return nil, nil, errwrap.Wrap(err, "error demultiplexing output")
 	}