Add CID listener example

Adds an example for setting up a CID-enabled DTLS listener.

Signed-off-by: Daniel Mangum <[email protected]>

Author: hasheddan

examples/listen/cid/main.go

@@ -0,0 +1,77 @@
+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+// Package main implements a DTLS server using a pre-shared key.
+package main
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"time"
+
+	"github.com/pion/dtls/v2"
+	"github.com/pion/dtls/v2/examples/util"
+)
+
+func main() {
+	// Prepare the IP to connect to
+	addr := &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: 4444}
+
+	// Create parent context to cleanup handshaking connections on exit.
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	//
+	// Everything below is the pion-DTLS API! Thanks for using it ❤️.
+	//
+
+	// Prepare the configuration of the DTLS connection
+	config := &dtls.Config{
+		PSK: func(hint []byte) ([]byte, error) {
+			fmt.Printf("Client's hint: %s \n", hint)
+			return []byte{0xAB, 0xC1, 0x23}, nil
+		},
+		PSKIdentityHint:      []byte("Pion DTLS Client"),
+		CipherSuites:         []dtls.CipherSuiteID{dtls.TLS_PSK_WITH_AES_128_CCM_8},
+		ExtendedMasterSecret: dtls.RequireExtendedMasterSecret,
+		// Create timeout context for accepted connection.
+		ConnectContextMaker: func() (context.Context, func()) {
+			return context.WithTimeout(ctx, 30*time.Second)
+		},
+		ConnectionIDGenerator: dtls.RandomCIDGenerator(8),
+	}
+
+	// Connect to a DTLS server
+	listener, err := dtls.Listen("udp", addr, config)
+	util.Check(err)
+	defer func() {
+		util.Check(listener.Close())
+	}()
+
+	fmt.Println("Listening")
+
+	// Simulate a chat session
+	hub := util.NewHub()
+
+	go func() {
+		for {
+			// Wait for a connection.
+			conn, err := listener.Accept()
+			util.Check(err)
+			// defer conn.Close() // TODO: graceful shutdown
+
+			// `conn` is of type `net.Conn` but may be casted to `dtls.Conn`
+			// using `dtlsConn := conn.(*dtls.Conn)` in order to to expose
+			// functions like `ConnectionState` etc.
+
+			// Register the connection with the chat hub
+			if err == nil {
+				hub.Register(conn)
+			}
+		}
+	}()
+
+	// Start chatting
+	hub.Chat()
+}