added relay

https://github.com/libp2p/go-libp2p-relay-daemon is deprecated and the relay server needs to use this now
go run ./cmd/relay -identity "path-to/identity.key"

cmd/relay/README.md

@@ -0,0 +1,5 @@
+https://github.com/libp2p/go-libp2p-relay-daemon is deprecated and the relay server needs to use this now
+
+```
+go run ./cmd/relay -identity "path-to/identity.key"
+```

cmd/relay/main.go

@@ -0,0 +1,88 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"time"
+
+	libp2p "github.com/libp2p/go-libp2p"
+	"github.com/libp2p/go-libp2p/core/crypto"
+	"github.com/libp2p/go-libp2p/core/peer"
+	relayv2 "github.com/libp2p/go-libp2p/p2p/protocol/circuitv2/relay"
+	"github.com/multiformats/go-multiaddr"
+)
+
+// ReadIdentity reads a private key from the given path and returns it.
+func ReadIdentity(path string) (crypto.PrivKey, error) {
+	bytes, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+
+	return crypto.UnmarshalPrivateKey(bytes)
+}
+
+func main() {
+	// Define a command-line flag for the identity key path
+	idPath := flag.String("identity", "", "Path to the identity.key file")
+	flag.Parse()
+
+	if *idPath == "" {
+		log.Fatalf("You must specify a path to the identity.key file using the -identity flag")
+	}
+
+	// Read the private key from the file
+	privKey, err := ReadIdentity(*idPath)
+	if err != nil {
+		log.Fatalf("Failed to read identity key: %v", err)
+	}
+
+	// Generate the Peer ID from the private key
+	peerID, err := peer.IDFromPrivateKey(privKey)
+	if err != nil {
+		log.Fatalf("Failed to generate peer ID: %v", err)
+	}
+
+	fmt.Printf("Using Peer ID: %s\n", peerID.String())
+
+	// Define listen addresses
+	listenAddrs := []multiaddr.Multiaddr{
+		multiaddr.StringCast("/ip4/0.0.0.0/tcp/4001"),
+		multiaddr.StringCast("/ip4/0.0.0.0/udp/4001/quic-v1"),
+		multiaddr.StringCast("/ip4/0.0.0.0/udp/4001/quic-v1/webtransport"),
+	}
+
+	// Define relay service options with resources and limits
+	relayOpts := []relayv2.Option{
+		relayv2.WithResources(relayv2.Resources{
+			Limit: &relayv2.RelayLimit{
+				Duration: 120 * time.Second, // Duration in seconds
+				Data:     17179869184,       // Data limit in bytes (16 GiB)
+			},
+			MaxReservations:        512,
+			MaxCircuits:            512,
+			MaxReservationsPerPeer: 16,
+			MaxReservationsPerIP:   32,
+			MaxReservationsPerASN:  64,
+			ReservationTTL:         360 * time.Hour, // TTL in hours
+			BufferSize:             8192,
+		}),
+	}
+
+	h, err := libp2p.New(
+		libp2p.ListenAddrs(listenAddrs...),
+		libp2p.Identity(privKey), // Use the private key for identity
+		libp2p.EnableRelayService(relayOpts...),
+	)
+	if err != nil {
+		log.Fatalf("Failed to create libp2p host: %v", err)
+	}
+
+	for _, addr := range h.Addrs() {
+		fmt.Printf("Listening on %s/p2p/%s\n", addr, h.ID().String())
+	}
+
+	select {}
+}