upstream-pion-webrtc/examples/data-channels-simple/demo.html

<!DOCTYPE html>
<html>
  <!--
		SPDX-FileCopyrightText: 2026 The Pion community <https://pion.ly>
		SPDX-License-Identifier: MIT
	-->
<head>
  <meta charset="utf-8">
  <title>DataChannel Test</title>
</head>
<body>
  <h2>📡 WebRTC DataChannel Test</h2>
  <input id="msg" placeholder="Message">
  <button id="sendBtn" disabled onclick="sendMsg()">Send</button>
  <pre id="log"></pre>

  <script>
    const pc = new RTCPeerConnection({iceServers:[{urls:"stun:stun.l.google.com:19302"}]});
    const channel = pc.createDataChannel("chat");

    // Connection state monitoring
    pc.onconnectionstatechange = () => log(`🔄 Connection state: ${pc.connectionState}`);
    pc.oniceconnectionstatechange = () => log(`🧊 ICE state: ${pc.iceConnectionState}`);
    pc.onsignalingstatechange = () => log(`📞 Signaling state: ${pc.signalingState}`);

    channel.onopen = () => {
      log("✅ DataChannel opened");
      document.getElementById("sendBtn").disabled = false;
    }
    channel.onmessage = e => log(`📩 Server: ${e.data}`);

    pc.onicecandidate = event => {
      if(event.candidate){
        fetch("/candidate", {
          method: "POST",
          headers: {"Content-Type": "application/json"},
          body: JSON.stringify(event.candidate),
        });
      }
    };

    async function start(){
      try {
        const offer = await pc.createOffer();
        await pc.setLocalDescription(offer);

        const res = await fetch("/offer", {
          method: "POST",
          headers: {"Content-Type": "application/json"},
          body: JSON.stringify(offer),
        })

        if (!res.ok) {
          throw new Error(`HTTP ${res.status}: ${res.statusText}`);
        }

        const answer = await res.json();
        await pc.setRemoteDescription(answer);

      } catch (err) {
        log(`❌ Connection failed: ${err.message}`);
        console.error("Connection error:", err);
      }
    }

    function sendMsg(){
      if(channel.readyState !== "open"){
        log("❌ Channel not open yet");
        return;
      }

      const msg = document.getElementById("msg").value;

      if (msg.trim()) {
        channel.send(msg);
        log(`You: ${msg}`);
        document.getElementById("msg").value = "";
      }
    }

    function log(msg){
      document.getElementById("log").textContent+=msg+"\n";
    }

    start();
  </script>
</body>
</html>