cmd/tailscaled: add subcommand on darwin to install+start tailscaled under launchd

Tangentially related to #987, #177, #594, #925.

cmd/tailscaled/install_darwin.go

@@ -0,0 +1,104 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"os/exec"
+)
+
+func init() {
+	installSystemDaemon = installSystemDaemonDarwin
+}
+
+// darwinLaunchdPlist is the launchd.plist that's written to
+// /Library/LaunchDaemons/com.tailscale.tailscaled.plist or (in the
+// future) a user-specific location.
+//
+// See man launchd.plist.
+const darwinLaunchdPlist = `
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+
+  <key>Label</key>
+  <string>com.tailscale.tailscaled</string>
+
+  <key>ProgramArguments</key>
+  <array>
+    <string>/usr/local/bin/tailscaled</string>
+  </array>
+
+  <key>RunAtLoad</key>
+  <true/>
+
+</dict>
+</plist>
+`
+
+const sysPlist = "/Library/LaunchDaemons/com.tailscale.tailscaled.plist"
+const targetBin = "/usr/local/bin/tailscaled"
+const service = "system/com.tailscale.tailscaled"
+
+func installSystemDaemonDarwin() (err error) {
+	defer func() {
+		if err != nil && os.Getuid() != 0 {
+			err = fmt.Errorf("%w; try running tailscaled with sudo", err)
+		}
+	}()
+
+	// Copy ourselves to /usr/local/bin/tailscaled.
+	exe, err := os.Executable()
+	if err != nil {
+		return fmt.Errorf("failed to find our own executable path: %w", err)
+	}
+	tmpBin := targetBin + ".tmp"
+	f, err := os.Create(tmpBin)
+	if err != nil {
+		return err
+	}
+	self, err := os.Open(exe)
+	if err != nil {
+		f.Close()
+		return err
+	}
+	_, err = io.Copy(f, self)
+	self.Close()
+	if err != nil {
+		f.Close()
+		return err
+	}
+	if err := f.Close(); err != nil {
+		return err
+	}
+	if err := os.Chmod(tmpBin, 0755); err != nil {
+		return err
+	}
+	if err := os.Rename(tmpBin, targetBin); err != nil {
+		return err
+	}
+
+	// Two best effort commands to stop a previous run.
+	exec.Command("launchctl", "stop", "system/com.tailscale.tailscaled").Run()
+	exec.Command("launchctl", "unload", sysPlist).Run()
+
+	if err := ioutil.WriteFile(sysPlist, []byte(darwinLaunchdPlist), 0700); err != nil {
+		return err
+	}
+
+	if out, err := exec.Command("launchctl", "load", sysPlist).CombinedOutput(); err != nil {
+		return fmt.Errorf("error running launchctl load %s: %v, %s", sysPlist, err, out)
+	}
+
+	if out, err := exec.Command("launchctl", "start", service).CombinedOutput(); err != nil {
+		return fmt.Errorf("error running launchctl start %s: %v, %s", service, err, out)
+	}
+
+	return nil
+}

cmd/tailscaled/tailscaled.go

@@ -71,6 +71,8 @@ var args struct {
 	verbose    int
 }
 
+var installSystemDaemon func() error // non-nil on some platforms
+
 func main() {
 	// We aren't very performance sensitive, and the parts that are
 	// performance sensitive (wireguard) try hard not to do any memory
@@ -91,11 +93,23 @@ func main() {
 	flag.StringVar(&args.socketpath, "socket", paths.DefaultTailscaledSocket(), "path of the service unix socket")
 	flag.BoolVar(&printVersion, "version", false, "print version information and exit")
 
-	if len(os.Args) > 1 && os.Args[1] == "debug" {
-		if err := debugMode(os.Args[2:]); err != nil {
-			log.Fatal(err)
+	if len(os.Args) > 1 {
+		switch os.Args[1] {
+		case "debug":
+			if err := debugMode(os.Args[2:]); err != nil {
+				log.Fatal(err)
+			}
+			return
+		case "install-system-daemon":
+			if f := installSystemDaemon; f == nil {
+				log.SetFlags(0)
+				log.Fatalf("install-system-daemon not available on %v", runtime.GOOS)
+			} else if err := f(); err != nil {
+				log.SetFlags(0)
+				log.Fatal(err)
+			}
+			return
 		}
-		return
 	}
 
 	if beWindowsSubprocess() {