fix: Improve disconnect logic for ssh-bin

Previously we were only closing stdin, and normally that's enough, but
not always: if the connection is gone, but ssh doesn't know about it
(e.g. if the OS was suspended for long enough time, and then resumed),
then the connection kept hanging.

This commit provides custom context for the external ssh command, and
cancels it when we need to disconnect.

Author: dimonomid

core/shell_transport_ssh_bin.go

@@ -2,6 +2,7 @@ package core
 
 import (
 	"bufio"
+	"context"
 	"fmt"
 	"io"
 	"os/exec"
@@ -91,7 +92,8 @@ func (s *ShellTransportSSHBin) doConnect(
 	}
 	logger.Infof("Executing external ssh command: %q", sshCmdDebug)
 
-	cmd := exec.Command("ssh", sshArgs...)
+	ctx, cancel := context.WithCancel(context.Background())
+	cmd := exec.CommandContext(ctx, "ssh", sshArgs...)
 	stdin, err := cmd.StdinPipe()
 	if err != nil {
 		res.Err = errors.Annotatef(err, "getting stdin pipe")
@@ -177,6 +179,8 @@ func (s *ShellTransportSSHBin) doConnect(
 			stdin:  stdin,
 			stdout: clientStdoutR,
 			stderr: stderr,
+
+			ctxCancel: cancel,
 		}
 		return res
 
@@ -198,6 +202,8 @@ type ShellConnSSHBin struct {
 	stdin  io.WriteCloser
 	stdout io.Reader
 	stderr io.Reader
+
+	ctxCancel context.CancelFunc
 }
 
 func (s *ShellConnSSHBin) Stdin() io.Writer {
@@ -213,5 +219,12 @@ func (s *ShellConnSSHBin) Stderr() io.Reader {
 }
 
 func (s *ShellConnSSHBin) Close() {
+	// Close stdin; normally this is enough for the external process to finish
+	// gracefully.
 	s.stdin.Close()
+
+	// Cancel context too, so the external process gets killed (closing stdin is
+	// not always enough; e.g. after the OS gets suspended for long enough time,
+	// and resumed, the connection keeps hanging without it).
+	s.ctxCancel()
 }