Include remote error when pure SSH protocol fails

bk2204 · bk2204 · commit 5dbbf1324673 · 2024-03-12T13:21:29.000Z
Right now, if spawning the remote command fails for some reason, we get
a message like the following in the trace output:

  pure SSH protocol connection failed: Unable to negotiate version with remote side (unable to read capabilities): EOF

However, all we know is that we failed to connect to the remote
`git-lfs-transfer` process.  That could be for any number of reasons:
the remote program doesn't exist or is not in `PATH`, the user has
misconfigured something locally or remotely, or any number of other
problems.  We won't know unless we log the output, so let's do that so
we can get more information.
diff --git a/ssh/connection.go b/ssh/connection.go
@@ -1,10 +1,14 @@
 package ssh
 
 import (
+	"bytes"
+	"fmt"
 	"sync"
 
 	"github.com/git-lfs/git-lfs/v3/config"
+	"github.com/git-lfs/git-lfs/v3/errors"
 	"github.com/git-lfs/git-lfs/v3/subprocess"
+	"github.com/git-lfs/git-lfs/v3/tr"
 	"github.com/git-lfs/pktline"
 	"github.com/rubyist/tracerx"
 )
@@ -39,6 +43,7 @@ func NewSSHTransfer(osEnv config.Environment, gitEnv config.Environment, meta *S
 
 func startConnection(id int, osEnv config.Environment, gitEnv config.Environment, meta *SSHMetadata, operation string, multiplexControlPath string) (conn *PktlineConnection, multiplexing bool, controlPath string, err error) {
 	tracerx.Printf("spawning pure SSH connection")
+	var errbuf bytes.Buffer
 	exe, args, multiplexing, controlPath := GetLFSExeAndArgs(osEnv, gitEnv, meta, "git-lfs-transfer", operation, true, multiplexControlPath)
 	cmd, err := subprocess.ExecCommand(exe, args...)
 	if err != nil {
@@ -52,6 +57,7 @@ func startConnection(id int, osEnv config.Environment, gitEnv config.Environment
 	if err != nil {
 		return nil, false, "", err
 	}
+	cmd.Stderr = &errbuf
 	err = cmd.Start()
 	if err != nil {
 		return nil, false, "", err
@@ -74,6 +80,7 @@ func startConnection(id int, osEnv config.Environment, gitEnv config.Environment
 		r.Close()
 		w.Close()
 		cmd.Wait()
+		err = errors.Combine([]error{err, fmt.Errorf(tr.Tr.Get("Failed to connect to remote SSH server: %s", cmd.Stderr))})
 	}
 	tracerx.Printf("pure SSH connection successful")
 	return conn, multiplexing, controlPath, err
