feat: Set SSH env vars: `SSH_CLIENT`, `SSH_CONNECTION` and `SSH_TTY` (#3622)

Fixes #2339

agent/agent.go

@@ -404,6 +404,15 @@ func (a *agent) createCommand(ctx context.Context, rawCommand string, env []stri
 	unixExecutablePath := strings.ReplaceAll(executablePath, "\\", "/")
 	cmd.Env = append(cmd.Env, fmt.Sprintf(`GIT_SSH_COMMAND=%s gitssh --`, unixExecutablePath))
 
+	// Set SSH connection environment variables (these are also set by OpenSSH
+	// and thus expected to be present by SSH clients). Since the agent does
+	// networking in-memory, trying to provide accurate values here would be
+	// nonsensical. For now, we hard code these values so that they're present.
+	srcAddr, srcPort := "0.0.0.0", "0"
+	dstAddr, dstPort := "0.0.0.0", "0"
+	cmd.Env = append(cmd.Env, fmt.Sprintf("SSH_CLIENT=%s %s %s", srcAddr, srcPort, dstPort))
+	cmd.Env = append(cmd.Env, fmt.Sprintf("SSH_CONNECTION=%s %s %s %s", srcAddr, srcPort, dstAddr, dstPort))
+
 	// Load environment variables passed via the agent.
 	// These should override all variables we manually specify.
 	for envKey, value := range metadata.EnvironmentVariables {
@@ -441,6 +450,8 @@ func (a *agent) handleSSHSession(session ssh.Session) (retErr error) {
 	sshPty, windowSize, isPty := session.Pty()
 	if isPty {
 		cmd.Env = append(cmd.Env, fmt.Sprintf("TERM=%s", sshPty.Term))
+
+		// The pty package sets `SSH_TTY` on supported platforms.
 		ptty, process, err := pty.Start(cmd)
 		if err != nil {
 			return xerrors.Errorf("start command: %w", err)

agent/agent_test.go

@@ -252,6 +252,29 @@ func TestAgent(t *testing.T) {
 		}
 	})
 
+	t.Run("SSH connection env vars", func(t *testing.T) {
+		t.Parallel()
+
+		// Note: the SSH_TTY environment variable should only be set for TTYs.
+		// For some reason this test produces a TTY locally and a non-TTY in CI
+		// so we don't test for the absence of SSH_TTY.
+		for _, key := range []string{"SSH_CONNECTION", "SSH_CLIENT"} {
+			key := key
+			t.Run(key, func(t *testing.T) {
+				t.Parallel()
+
+				session := setupSSHSession(t, agent.Metadata{})
+				command := "sh -c 'echo $" + key + "'"
+				if runtime.GOOS == "windows" {
+					command = "cmd.exe /c echo %" + key + "%"
+				}
+				output, err := session.Output(command)
+				require.NoError(t, err)
+				require.NotEmpty(t, strings.TrimSpace(string(output)))
+			})
+		}
+	})
+
 	t.Run("StartupScript", func(t *testing.T) {
 		t.Parallel()
 		tempPath := filepath.Join(t.TempDir(), "content.txt")

pty/start_other.go

@@ -4,6 +4,7 @@
 package pty
 
 import (
+	"fmt"
 	"os/exec"
 	"runtime"
 	"strings"
@@ -18,6 +19,8 @@ func startPty(cmd *exec.Cmd) (PTY, Process, error) {
 	if err != nil {
 		return nil, nil, xerrors.Errorf("open: %w", err)
 	}
+
+	cmd.Env = append(cmd.Env, fmt.Sprintf("SSH_PTY=%s", tty.Name()))
 	cmd.SysProcAttr = &syscall.SysProcAttr{
 		Setsid:  true,
 		Setctty: true,

pty/start_other_test.go

@@ -1,5 +1,4 @@
 //go:build !windows
-// +build !windows
 
 package pty_test
 
@@ -40,4 +39,12 @@ func TestStart(t *testing.T) {
 		require.True(t, xerrors.As(err, &exitErr))
 		assert.NotEqual(t, 0, exitErr.ExitCode())
 	})
+
+	t.Run("SSH_PTY", func(t *testing.T) {
+		t.Parallel()
+		pty, ps := ptytest.Start(t, exec.Command("env"))
+		pty.ExpectMatch("SSH_PTY=/dev/")
+		err := ps.Wait()
+		require.NoError(t, err)
+	})
 }