snapshot of https://github.com/pion/webrtc.git (main, 2026-09-15; blobs > 131072B omitted)

examples/data-channels/README.md

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+# data-channels
+data-channels is Pion's sample WebRTC app that lets you send and receive DataChannel messages from a web browser.
+
+## Brief Overview
+This example will result in messages being sent between a browser and a self-hosted data-channels server. The connection is made by grabbing the browser's generated session description, or SDP, and passing it into the server. The server uses the browser's SDP to then return a new SDP from the server based on the browser's SDP. The server's SDP then gets passed back into the browser which confirms the handshake and forms a connection!
+
+Once the connection is established, messages will automatically be sent from the data-channels server to the browser every 5 seconds. The browser has a button that lets you send a message back to the server when you click on it.
+
+## Instructions
+### 1. Download the data-channels server
+```
+go install github.com/pion/webrtc/v4/examples/data-channels@latest
+```
+
+### 2. Open JSFiddle
+[Open this JSFiddle example page.](https://jsfiddle.net/e41tgovp/)
+The top of the JSFiddle example page contains a text box containing your browser's session description (SDP).
+Press `Copy browser SDP to clipboard` or copy the base64 string manually.
+
+### 3. Send the browser's SDP to the server
+Depending on your OS:
+
+#### Linux/macOS (including WSL)
+In the following command, replace `$BROWSER_SDP` with the copied string.
+Run `echo $BROWSER_SDP | data-channels`.
+
+#### Windows
+1. Paste the copied string into a file.
+2. Run `data-channels < my_file`.
+
+### 4. Send the server's SDP back to the browser
+The server will automatically print out a base64 string. Copy it and paste it into the second textbox in the JSFiddle page.
+
+### 5. Start the session!
+Under Start Session you should see 'Checking' as it starts connecting. If everything worked you should see `New DataChannel foo 1`.
+
+Pion WebRTC will send random messages every 5 seconds that will appear in your browser.
+
+### 6. Send a message from the browser to the server!
+You can put whatever you want in the `Message` text area, and when you hit `Send Message` it should appear in your terminal!
+
+## Example finished!
+Congrats, you have used Pion WebRTC! Now start building something cool :)
+
+## Architecture Overview
+
+```mermaid
+flowchart TB
+    Browser--Copy Offer from TextArea-->Pion
+    Pion--Copy Text Print to Console-->Browser
+    subgraph Pion[Go Peer]
+        p1[Create PeerConnection]
+        p2[OnConnectionState Handler]
+        p3[Print Connection State]
+        p2-->p3
+        p4[OnDataChannel Handler]
+        p5[OnDataChannel Open]
+        p6[Send Random Message every 5 seconds to DataChannel]
+        p4-->p5-->p6
+        p7[OnDataChannel Message]
+        p8[Log Incoming Message to Console]
+        p4-->p7-->p8
+        p9[Read Session Description from Standard Input]
+        p10[SetRemoteDescription with Session Description from Standard Input]
+        p11[Create Answer]
+        p12[Block until ICE Gathering is Complete]
+        p13[Print Answer with ICE Candidatens included to Standard Output]
+    end
+    subgraph Browser[Browser Peer]
+        b1[Create PeerConnection]
+        b2[Create DataChannel 'foo']
+        b3[OnDataChannel Message]
+        b4[Log Incoming Message to Console]
+        b3-->b4
+        b5[Create Offer]
+        b6[SetLocalDescription with Offer]
+        b7[Print Offer with ICE Candidates included]
+
+    end
+```

examples/data-channels/jsfiddle/demo.css

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+/*
+    SPDX-FileCopyrightText: 2026 The Pion community <https://pion.ly>
+    SPDX-License-Identifier: MIT
+*/
+textarea {
+    width: 500px;
+    min-height: 75px;
+}

examples/data-channels/jsfiddle/demo.details

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+---
+# SPDX-FileCopyrightText: 2026 The Pion community <https://pion.ly>
+# SPDX-License-Identifier: MIT
+
+name: data-channels
+description: Example of using Pion WebRTC to communicate with a web browser using bi-direction DataChannels
+authors:
+  - Sean DuBois

examples/data-channels/jsfiddle/demo.html

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+<!--
+	SPDX-FileCopyrightText: 2026 The Pion community <https://pion.ly>
+	SPDX-License-Identifier: MIT
+-->
+Browser base64 Session Description<br />
+<textarea id="localSessionDescription" readonly="true"></textarea> <br />
+<button onclick="window.copySDP()">
+	Copy browser SDP to clipboard
+</button>
+<br />
+<br />
+
+Golang base64 Session Description<br />
+<textarea id="remoteSessionDescription"></textarea><br/>
+<button onclick="window.startSession()">Start Session</button><br />
+
+<br />
+
+Message<br />
+<textarea id="message">This is my DataChannel message!</textarea> <br/>
+<button onclick="window.sendMessage()">Send Message</button> <br />
+
+<br />
+Logs<br />
+<div id="logs"></div>

examples/data-channels/jsfiddle/demo.js

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+/* eslint-env browser */
+
+// SPDX-FileCopyrightText: 2026 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+const pc = new RTCPeerConnection({
+  iceServers: [
+    {
+      urls: 'stun:stun.l.google.com:19302'
+    }
+  ]
+})
+const log = msg => {
+  document.getElementById('logs').innerHTML += msg + '<br>'
+}
+
+const sendChannel = pc.createDataChannel('foo')
+sendChannel.onclose = () => console.log('sendChannel has closed')
+sendChannel.onopen = () => console.log('sendChannel has opened')
+sendChannel.onmessage = e => log(`Message from DataChannel '${sendChannel.label}' payload '${e.data}'`)
+
+pc.oniceconnectionstatechange = e => log(pc.iceConnectionState)
+pc.onicecandidate = event => {
+  if (event.candidate === null) {
+    document.getElementById('localSessionDescription').value = btoa(JSON.stringify(pc.localDescription))
+  }
+}
+
+pc.onnegotiationneeded = e =>
+  pc.createOffer().then(d => pc.setLocalDescription(d)).catch(log)
+
+window.sendMessage = () => {
+  const message = document.getElementById('message').value
+  if (message === '') {
+    return alert('Message must not be empty')
+  }
+
+  sendChannel.send(message)
+}
+
+window.startSession = () => {
+  const sd = document.getElementById('remoteSessionDescription').value
+  if (sd === '') {
+    return alert('Session Description must not be empty')
+  }
+
+  try {
+    pc.setRemoteDescription(JSON.parse(atob(sd)))
+  } catch (e) {
+    alert(e)
+  }
+}
+
+window.copySDP = () => {
+  const browserSDP = document.getElementById('localSessionDescription')
+
+  browserSDP.focus()
+  browserSDP.select()
+
+  try {
+    const successful = document.execCommand('copy')
+    const msg = successful ? 'successful' : 'unsuccessful'
+    log('Copying SDP was ' + msg)
+  } catch (err) {
+    log('Unable to copy SDP ' + err)
+  }
+}

examples/data-channels/jsfiddle/main.go

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+// SPDX-FileCopyrightText: 2026 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+//go:build js && wasm
+// +build js,wasm
+
+package main
+
+import (
+	"bufio"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"syscall/js"
+
+	"github.com/pion/webrtc/v4"
+)
+
+func main() {
+	// Configure and create a new PeerConnection.
+	config := webrtc.Configuration{
+		ICEServers: []webrtc.ICEServer{
+			{
+				URLs: []string{"stun:stun.l.google.com:19302"},
+			},
+		},
+	}
+	pc, err := webrtc.NewPeerConnection(config)
+	if err != nil {
+		handleError(err)
+	}
+
+	// Create DataChannel.
+	sendChannel, err := pc.CreateDataChannel("foo", nil)
+	if err != nil {
+		handleError(err)
+	}
+	sendChannel.OnClose(func() {
+		fmt.Println("sendChannel has closed")
+	})
+	sendChannel.OnClosing(func() {
+		fmt.Println("sendChannel is closing")
+	})
+	sendChannel.OnError(func(err error) {
+		fmt.Println("sendChannel error", err)
+	})
+	sendChannel.OnOpen(func() {
+		fmt.Println("sendChannel has opened")
+
+		candidatePair, err := pc.SCTP().Transport().ICETransport().GetSelectedCandidatePair()
+
+		fmt.Println(candidatePair)
+		fmt.Println(err)
+	})
+	sendChannel.OnMessage(func(msg webrtc.DataChannelMessage) {
+		log(fmt.Sprintf("Message from DataChannel %s payload %s", sendChannel.Label(), string(msg.Data)))
+	})
+
+	// Create offer
+	offer, err := pc.CreateOffer(nil)
+	if err != nil {
+		handleError(err)
+	}
+	if err := pc.SetLocalDescription(offer); err != nil {
+		handleError(err)
+	}
+
+	// Add handlers for setting up the connection.
+	pc.OnICEConnectionStateChange(func(state webrtc.ICEConnectionState) {
+		log(fmt.Sprint(state))
+	})
+	pc.OnICECandidate(func(candidate *webrtc.ICECandidate) {
+		if candidate != nil {
+			encodedDescr := encode(pc.LocalDescription())
+			el := getElementByID("localSessionDescription")
+			el.Set("value", encodedDescr)
+		}
+	})
+
+	// Set up global callbacks which will be triggered on button clicks.
+	js.Global().Set("sendMessage", js.FuncOf(func(_ js.Value, _ []js.Value) any {
+		go func() {
+			el := getElementByID("message")
+			message := el.Get("value").String()
+			if message == "" {
+				js.Global().Call("alert", "Message must not be empty")
+				return
+			}
+			if err := sendChannel.SendText(message); err != nil {
+				handleError(err)
+			}
+		}()
+		return js.Undefined()
+	}))
+	js.Global().Set("startSession", js.FuncOf(func(_ js.Value, _ []js.Value) any {
+		go func() {
+			el := getElementByID("remoteSessionDescription")
+			sd := el.Get("value").String()
+			if sd == "" {
+				js.Global().Call("alert", "Session Description must not be empty")
+				return
+			}
+
+			descr := webrtc.SessionDescription{}
+			decode(sd, &descr)
+			if err := pc.SetRemoteDescription(descr); err != nil {
+				handleError(err)
+			}
+		}()
+		return js.Undefined()
+	}))
+	js.Global().Set("copySDP", js.FuncOf(func(_ js.Value, _ []js.Value) any {
+		go func() {
+			defer func() {
+				if e := recover(); e != nil {
+					switch e := e.(type) {
+					case error:
+						handleError(e)
+					default:
+						handleError(fmt.Errorf("recovered with non-error value: (%T) %s", e, e))
+					}
+				}
+			}()
+
+			browserSDP := getElementByID("localSessionDescription")
+
+			browserSDP.Call("focus")
+			browserSDP.Call("select")
+
+			copyStatus := js.Global().Get("document").Call("execCommand", "copy")
+			if copyStatus.Bool() {
+				log("Copying SDP was successful")
+			} else {
+				log("Copying SDP was unsuccessful")
+			}
+		}()
+		return js.Undefined()
+	}))
+
+	// Stay alive
+	select {}
+}
+
+func log(msg string) {
+	el := getElementByID("logs")
+	el.Set("innerHTML", el.Get("innerHTML").String()+msg+"<br>")
+}
+
+func handleError(err error) {
+	log("Unexpected error. Check console.")
+	panic(err)
+}
+
+func getElementByID(id string) js.Value {
+	return js.Global().Get("document").Call("getElementById", id)
+}
+
+// Read from stdin until we get a newline
+func readUntilNewline() (in string) {
+	var err error
+
+	r := bufio.NewReader(os.Stdin)
+	for {
+		in, err = r.ReadString('\n')
+		if err != nil && !errors.Is(err, io.EOF) {
+			panic(err)
+		}
+
+		if in = strings.TrimSpace(in); len(in) > 0 {
+			break
+		}
+	}
+
+	fmt.Println("")
+	return
+}
+
+// JSON encode + base64 a SessionDescription
+func encode(obj *webrtc.SessionDescription) string {
+	b, err := json.Marshal(obj)
+	if err != nil {
+		panic(err)
+	}
+
+	return base64.StdEncoding.EncodeToString(b)
+}
+
+// Decode a base64 and unmarshal JSON into a SessionDescription
+func decode(in string, obj *webrtc.SessionDescription) {
+	b, err := base64.StdEncoding.DecodeString(in)
+	if err != nil {
+		panic(err)
+	}
+
+	if err = json.Unmarshal(b, obj); err != nil {
+		panic(err)
+	}
+}

examples/data-channels/main.go

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+// SPDX-FileCopyrightText: 2026 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+// data-channels is a Pion WebRTC application that shows how you can send/recv DataChannel messages from a web browser
+package main
+
+import (
+	"bufio"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/pion/randutil"
+	"github.com/pion/webrtc/v4"
+)
+
+// nolint:cyclop
+func main() {
+	// Everything below is the Pion WebRTC API! Thanks for using it ❤️.
+
+	// Prepare the configuration
+	config := webrtc.Configuration{
+		ICEServers: []webrtc.ICEServer{
+			{
+				URLs: []string{"stun:stun.l.google.com:19302"},
+			},
+		},
+	}
+
+	// Create a new RTCPeerConnection
+	peerConnection, err := webrtc.NewPeerConnection(config)
+	if err != nil {
+		panic(err)
+	}
+	defer func() {
+		if cErr := peerConnection.Close(); cErr != nil {
+			fmt.Printf("cannot close peerConnection: %v\n", cErr)
+		}
+	}()
+
+	// Set the handler for Peer connection state
+	// This will notify you when the peer has connected/disconnected
+	peerConnection.OnConnectionStateChange(func(state webrtc.PeerConnectionState) {
+		fmt.Printf("Peer Connection State has changed: %s\n", state.String())
+
+		if state == webrtc.PeerConnectionStateFailed {
+			// Wait until PeerConnection has had no network activity for 30 seconds or another failure.
+			// It may be reconnected using an ICE Restart.
+			// Use webrtc.PeerConnectionStateDisconnected if you are interested in detecting faster timeout.
+			// Note that the PeerConnection may come back from PeerConnectionStateDisconnected.
+			fmt.Println("Peer Connection has gone to failed exiting")
+			os.Exit(0)
+		}
+
+		if state == webrtc.PeerConnectionStateClosed {
+			// PeerConnection was explicitly closed. This usually happens from a DTLS CloseNotify
+			fmt.Println("Peer Connection has gone to closed exiting")
+			os.Exit(0)
+		}
+	})
+
+	// Register data channel creation handling
+	peerConnection.OnDataChannel(func(dataChannel *webrtc.DataChannel) {
+		fmt.Printf("New DataChannel %s %d\n", dataChannel.Label(), dataChannel.ID())
+
+		// Register channel opening handling
+		dataChannel.OnOpen(func() {
+			fmt.Printf(
+				"Data channel '%s'-'%d' open. Random messages will now be sent to any connected DataChannels every 5 seconds\n",
+				dataChannel.Label(), dataChannel.ID(),
+			)
+
+			ticker := time.NewTicker(5 * time.Second)
+			defer ticker.Stop()
+			for range ticker.C {
+				message, sendErr := randutil.GenerateCryptoRandomString(15, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
+				if sendErr != nil {
+					panic(sendErr)
+				}
+
+				// Send the message as text
+				fmt.Printf("Sending '%s'\n", message)
+				if sendErr = dataChannel.SendText(message); sendErr != nil {
+					panic(sendErr)
+				}
+			}
+		})
+
+		// Register text message handling
+		dataChannel.OnMessage(func(msg webrtc.DataChannelMessage) {
+			fmt.Printf("Message from DataChannel '%s': '%s'\n", dataChannel.Label(), string(msg.Data))
+		})
+	})
+
+	// Wait for the offer to be pasted
+	offer := webrtc.SessionDescription{}
+	decode(readUntilNewline(), &offer)
+
+	// Set the remote SessionDescription
+	err = peerConnection.SetRemoteDescription(offer)
+	if err != nil {
+		panic(err)
+	}
+
+	// Create an answer
+	answer, err := peerConnection.CreateAnswer(nil)
+	if err != nil {
+		panic(err)
+	}
+
+	// Create channel that is blocked until ICE Gathering is complete
+	gatherComplete := webrtc.GatheringCompletePromise(peerConnection)
+
+	// Sets the LocalDescription, and starts our UDP listeners
+	err = peerConnection.SetLocalDescription(answer)
+	if err != nil {
+		panic(err)
+	}
+
+	// Block until ICE Gathering is complete, disabling trickle ICE
+	// we do this because we only can exchange one signaling message
+	// in a production application you should exchange ICE Candidates via OnICECandidate
+	<-gatherComplete
+
+	// Output the answer in base64 so we can paste it in browser
+	fmt.Println(encode(peerConnection.LocalDescription()))
+
+	// Block forever
+	select {}
+}
+
+// Read from stdin until we get a newline.
+func readUntilNewline() (in string) {
+	var err error
+
+	r := bufio.NewReader(os.Stdin)
+	for {
+		in, err = r.ReadString('\n')
+		if err != nil && !errors.Is(err, io.EOF) {
+			panic(err)
+		}
+
+		if in = strings.TrimSpace(in); len(in) > 0 {
+			break
+		}
+	}
+
+	fmt.Println("")
+
+	return
+}
+
+// JSON encode + base64 a SessionDescription.
+func encode(obj *webrtc.SessionDescription) string {
+	b, err := json.Marshal(obj)
+	if err != nil {
+		panic(err)
+	}
+
+	return base64.StdEncoding.EncodeToString(b)
+}
+
+// Decode a base64 and unmarshal JSON into a SessionDescription.
+func decode(in string, obj *webrtc.SessionDescription) {
+	b, err := base64.StdEncoding.DecodeString(in)
+	if err != nil {
+		panic(err)
+	}
+
+	if err = json.Unmarshal(b, obj); err != nil {
+		panic(err)
+	}
+}