cmd/{derper,derpprobe}: add --version flag

Fixes #11582

Change-Id: If99fc1ab6b89d624fbb07bd104dd882d2c7b50b4
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/derper/derper.go

@@ -36,10 +36,12 @@ import (
 	"tailscale.com/tsweb"
 	"tailscale.com/types/key"
 	"tailscale.com/types/logger"
+	"tailscale.com/version"
 )
 
 var (
 	dev         = flag.Bool("dev", false, "run in localhost development mode (overrides -a)")
+	versionFlag = flag.Bool("version", false, "print version and exit")
 	addr        = flag.String("a", ":443", "server HTTP/HTTPS listen address, in form \":port\", \"ip:port\", or for IPv6 \"[ip]:port\". If the IP is omitted, it defaults to all interfaces. Serves HTTPS if the port is 443 and/or -certmode is manual, otherwise HTTP.")
 	httpPort    = flag.Int("http-port", 80, "The port on which to serve HTTP. Set to -1 to disable. The listener is bound to the same IP (if any) as specified in the -a flag.")
 	stunPort    = flag.Int("stun-port", 3478, "The UDP port on which to serve STUN. The listener is bound to the same IP (if any) as specified in the -a flag.")
@@ -129,6 +131,10 @@ func writeNewConfig() config {
 
 func main() {
 	flag.Parse()
+	if *versionFlag {
+		fmt.Println(version.Long())
+		return
+	}
 
 	ctx, cancel := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
 	defer cancel()

cmd/derpprobe/derpprobe.go

@@ -16,10 +16,12 @@ import (
 
 	"tailscale.com/prober"
 	"tailscale.com/tsweb"
+	"tailscale.com/version"
 )
 
 var (
 	derpMapURL   = flag.String("derp-map", "https://login.tailscale.com/derpmap/default", "URL to DERP map (https:// or file://)")
+	versionFlag  = flag.Bool("version", false, "print version and exit")
 	listen       = flag.String("listen", ":8030", "HTTP listen address")
 	probeOnce    = flag.Bool("once", false, "probe once and print results, then exit; ignores the listen flag")
 	spread       = flag.Bool("spread", true, "whether to spread probing over time")
@@ -33,6 +35,10 @@ var (
 
 func main() {
 	flag.Parse()
+	if *versionFlag {
+		fmt.Println(version.Long())
+		return
+	}
 
 	p := prober.New().WithSpread(*spread).WithOnce(*probeOnce).WithMetricNamespace("derpprobe")
 	opts := []prober.DERPOpt{