Add --pidfile flag to access tcp command

cmd/cloudflared/access/carrier.go

@@ -5,8 +5,10 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"os"
 	"strings"
 
+	"github.com/mitchellh/go-homedir"
 	"github.com/pkg/errors"
 	"github.com/rs/zerolog"
 	"github.com/urfave/cli/v2"
@@ -69,6 +71,10 @@ func ssh(c *cli.Context) error {
 	}
 	log := logger.CreateSSHLoggerFromContext(c, outputTerminal)
 
+	if c.IsSet(sshPidFileFlag) {
+		writePidFile(c.String(sshPidFileFlag), log)
+	}
+
 	// get the hostname from the cmdline and error out if its not provided
 	rawHostName := c.String(sshHostnameFlag)
 	url, err := parseURL(rawHostName)
@@ -145,3 +151,18 @@ func ssh(c *cli.Context) error {
 	}
 	return carrier.StartClient(wsConn, s, options)
 }
+
+func writePidFile(path string, log *zerolog.Logger) {
+	expandedPath, err := homedir.Expand(path)
+	if err != nil {
+		log.Err(err).Str("path", path).Msg("Unable to expand pidfile path")
+		return
+	}
+	file, err := os.Create(expandedPath)
+	if err != nil {
+		log.Err(err).Str("path", expandedPath).Msg("Unable to write pidfile")
+		return
+	}
+	defer file.Close()
+	fmt.Fprintf(file, "%d", os.Getpid())
+}

cmd/cloudflared/access/cmd.go

@@ -38,6 +38,7 @@ const (
 	sshGenCertFlag     = "short-lived-cert"
 	sshConnectTo       = "connect-to"
 	sshDebugStream     = "debug-stream"
+	sshPidFileFlag     = "pidfile"
 	sshConfigTemplate  = `
 Add to your {{.Home}}/.ssh/config:
 
@@ -204,6 +205,11 @@ func Commands() []*cli.Command {
 							Hidden: true,
 							Usage:  "Writes up-to the max provided stream payloads to the logger as debug statements.",
 						},
+						&cli.StringFlag{
+							Name:    sshPidFileFlag,
+							Usage:   "Write the application's PID to this file",
+							EnvVars: []string{"TUNNEL_SERVICE_PIDFILE"},
+						},
 					},
 				},
 				{