From b1441d004478ea931e007eeccacc5f86457f8e91 Mon Sep 17 00:00:00 2001
From: James Tucker <james@tailscale.com>
Date: Wed, 23 Nov 2022 14:45:44 -0800
Subject: [PATCH] cmd/stunc: add command for making debug stun requests

Signed-off-by: James Tucker <james@tailscale.com>
---
 cmd/stunc/stunc.go | 58 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100644 cmd/stunc/stunc.go

diff --git a/cmd/stunc/stunc.go b/cmd/stunc/stunc.go
new file mode 100644
index 000000000..34cc4f2e5
--- /dev/null
+++ b/cmd/stunc/stunc.go
@@ -0,0 +1,58 @@
+// Copyright (c) 2022 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.
+
+// Command stunc makes a STUN request to a STUN server and prints the result.
+package main
+
+import (
+	"log"
+	"net"
+	"os"
+
+	"tailscale.com/net/stun"
+)
+
+func main() {
+	log.SetFlags(0)
+
+	if len(os.Args) != 2 {
+		log.Fatalf("usage: %s <hostname>", os.Args[0])
+	}
+	host := os.Args[1]
+
+	uaddr, err := net.ResolveUDPAddr("udp", host+":3478")
+	if err != nil {
+		log.Fatal(err)
+	}
+	c, err := net.ListenUDP("udp", nil)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	txID := stun.NewTxID()
+	req := stun.Request(txID)
+
+	_, err = c.WriteToUDP(req, uaddr)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	var buf [1024]byte
+	n, raddr, err := c.ReadFromUDPAddrPort(buf[:])
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	tid, saddr, err := stun.ParseResponse(buf[:n])
+	if err != nil {
+		log.Fatal(err)
+	}
+	if tid != txID {
+		log.Fatalf("txid mismatch: got %v, want %v", tid, txID)
+	}
+
+	log.Printf("sent addr: %v", uaddr)
+	log.Printf("from addr: %v", raddr)
+	log.Printf("stun addr: %v", saddr)
+}