cmd/tailscaled: use the standard flag page instead of getopt

Per discussion with @crawshaw. The CLI tool already used std flag anyway.
If either of them, it would've made more sense for the CLI to use getopt.

cmd/tailscaled/depaware.txt

@@ -19,7 +19,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         github.com/klauspost/compress/zstd/internal/xxhash           from github.com/klauspost/compress/zstd
    L 💣 github.com/mdlayher/netlink                                  from github.com/jsimonetti/rtnetlink+
    L 💣 github.com/mdlayher/netlink/nlenc                            from github.com/jsimonetti/rtnetlink+
-        github.com/pborman/getopt/v2                                 from tailscale.com/cmd/tailscaled
    W 💣 github.com/tailscale/winipcfg-go                             from tailscale.com/net/interfaces+
      💣 github.com/tailscale/wireguard-go/conn                       from github.com/tailscale/wireguard-go/device+
      💣 github.com/tailscale/wireguard-go/device                     from tailscale.com/wgengine+
@@ -76,6 +75,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
   DW    tailscale.com/tempfork/osexec                                from tailscale.com/portlist
    W    tailscale.com/tsconst                                        from tailscale.com/net/interfaces
         tailscale.com/types/empty                                    from tailscale.com/control/controlclient+
+        tailscale.com/types/flagtype                                 from tailscale.com/cmd/tailscaled
         tailscale.com/types/key                                      from tailscale.com/derp+
         tailscale.com/types/logger                                   from tailscale.com/cmd/tailscaled+
         tailscale.com/types/nettype                                  from tailscale.com/wgengine/magicsock
@@ -181,7 +181,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         encoding/pem                                                 from crypto/tls+
         errors                                                       from bufio+
         expvar                                                       from tailscale.com/derp+
-   L    flag                                                         from tailscale.com/net/netns
+        flag                                                         from tailscale.com/cmd/tailscaled+
         fmt                                                          from compress/flate+
         hash                                                         from compress/zlib+
         hash/adler32                                                 from compress/zlib

cmd/tailscaled/tailscaled.go

@@ -11,6 +11,7 @@ package main // import "tailscale.com/cmd/tailscaled"
 
 import (
 	"context"
+	"flag"
 	"log"
 	"net/http"
 	"net/http/pprof"
@@ -22,10 +23,10 @@ import (
 	"time"
 
 	"github.com/apenwarr/fixconsole"
-	"github.com/pborman/getopt/v2"
 	"tailscale.com/ipn/ipnserver"
 	"tailscale.com/logpolicy"
 	"tailscale.com/paths"
+	"tailscale.com/types/flagtype"
 	"tailscale.com/types/logger"
 	"tailscale.com/wgengine"
 	"tailscale.com/wgengine/magicsock"
@@ -71,28 +72,22 @@ func main() {
 		debug.SetGCPercent(10)
 	}
 
-	// Set default values for getopt.
-	args.tunname = defaultTunName()
-	args.port = magicsock.DefaultPort
-	args.statepath = paths.DefaultTailscaledStateFile()
-	args.socketpath = paths.DefaultTailscaledSocket()
-
-	getopt.FlagLong(&args.cleanup, "cleanup", 0, "clean up system state and exit")
-	getopt.FlagLong(&args.fake, "fake", 0, "fake tunnel+routing instead of tuntap")
-	getopt.FlagLong(&args.debug, "debug", 0, "address of debug server")
-	getopt.FlagLong(&args.tunname, "tun", 0, "tunnel interface name")
-	getopt.FlagLong(&args.port, "port", 'p', "WireGuard port (0=autoselect)")
-	getopt.FlagLong(&args.statepath, "state", 0, "path of state file")
-	getopt.FlagLong(&args.socketpath, "socket", 's', "path of the service unix socket")
+	flag.BoolVar(&args.cleanup, "cleanup", false, "clean up system state and exit")
+	flag.BoolVar(&args.fake, "fake", false, "use userspace fake tunnel+routing instead of kernel TUN interface")
+	flag.StringVar(&args.debug, "debug", "", "listen address ([ip]:port) of optional debug server")
+	flag.StringVar(&args.tunname, "tun", defaultTunName(), "tunnel interface name")
+	flag.Var(flagtype.PortValue(&args.port, magicsock.DefaultPort), "port", "UDP port to listen on for WireGuard and peer-to-peer traffic; 0 means automatically select")
+	flag.StringVar(&args.statepath, "state", paths.DefaultTailscaledStateFile(), "path of state file")
+	flag.StringVar(&args.socketpath, "socket", paths.DefaultTailscaledSocket(), "path of the service unix socket")
 
 	err := fixconsole.FixConsoleIfNeeded()
 	if err != nil {
 		log.Fatalf("fixConsoleOutput: %v", err)
 	}
 
-	getopt.Parse()
-	if len(getopt.Args()) > 0 {
-		log.Fatalf("too many non-flag arguments: %#v", getopt.Args()[0])
+	flag.Parse()
+	if flag.NArg() > 0 {
+		log.Fatalf("tailscaled does not take non-flag arguments: %q", flag.Args())
 	}
 
 	if args.statepath == "" {
@@ -136,7 +131,7 @@ func run() error {
 
 	var e wgengine.Engine
 	if args.fake {
-		e, err = wgengine.NewFakeUserspaceEngine(logf, 0)
+		e, err = wgengine.NewFakeUserspaceEngine(logf, args.port)
 	} else {
 		e, err = wgengine.NewUserspaceEngine(logf, args.tunname, args.port)
 	}

types/flagtype/flagtype.go

@@ -0,0 +1,41 @@
+// Copyright (c) 2020 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 flagtype defines flag.Value types.
+package flagtype
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+)
+
+type portValue struct{ n *uint16 }
+
+func PortValue(dst *uint16, defaultPort uint16) flag.Value {
+	*dst = defaultPort
+	return portValue{dst}
+}
+
+func (p portValue) String() string { return fmt.Sprint(p.n) }
+func (p portValue) Set(v string) error {
+	if v == "" {
+		return errors.New("can't be the empty string")
+	}
+	if strings.Contains(v, ":") {
+		return errors.New("expecting just a port number, without a colon")
+	}
+	n, err := strconv.ParseUint(v, 10, 64) // use 64 instead of 16 to return nicer error message
+	if err != nil {
+		return fmt.Errorf("not a valid number")
+	}
+	if n > math.MaxUint16 {
+		return errors.New("out of range for port number")
+	}
+	*p.n = uint16(n)
+	return nil
+}