From 2d3e79cf5ec0e7180431b01ab0a0a59d2d8e337f Mon Sep 17 00:00:00 2001
From: Frederik Ring <frederik.ring@gmail.com>
Date: Fri, 1 Mar 2024 09:18:39 +0100
Subject: [PATCH] Also forward exec output when failing to demultiplex (#379)

---
 cmd/backup/exec.go | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/cmd/backup/exec.go b/cmd/backup/exec.go
index 1d762f6..350803c 100644
--- a/cmd/backup/exec.go
+++ b/cmd/backup/exec.go
@@ -45,15 +45,23 @@ 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")
 	}