use a single packet conn for all outgoing connections

conn_test.go

 package libp2pquic
 
 import (
+	"bytes"
 	"context"
 	"crypto/rand"
 	"crypto/rsa"
 	"crypto/tls"
 	"crypto/x509"
 	"io/ioutil"
+	"time"
 
 	ic "github.com/libp2p/go-libp2p-crypto"
 	peer "github.com/libp2p/go-libp2p-peer"
@@ -23,12 +25,14 @@ var _ = Describe("Connection", func() {
 		serverID, clientID   peer.ID
 	)
 
-	createPeer := func() ic.PrivKey {
+	createPeer := func() (peer.ID, ic.PrivKey) {
 		key, err := rsa.GenerateKey(rand.Reader, 1024)
 		Expect(err).ToNot(HaveOccurred())
 		priv, err := ic.UnmarshalRsaPrivateKey(x509.MarshalPKCS1PrivateKey(key))
 		Expect(err).ToNot(HaveOccurred())
-		return priv
+		id, err := peer.IDFromPrivateKey(priv)
+		Expect(err).ToNot(HaveOccurred())
+		return id, priv
 	}
 
 	runServer := func(tr tpt.Transport) (ma.Multiaddr, <-chan tpt.Conn) {
@@ -54,13 +58,8 @@ var _ = Describe("Connection", func() {
 	}
 
 	BeforeEach(func() {
-		var err error
-		serverKey = createPeer()
-		serverID, err = peer.IDFromPrivateKey(serverKey)
-		Expect(err).ToNot(HaveOccurred())
-		clientKey = createPeer()
-		clientID, err = peer.IDFromPrivateKey(clientKey)
-		Expect(err).ToNot(HaveOccurred())
+		serverID, serverKey = createPeer()
+		clientID, clientKey = createPeer()
 	})
 
 	It("handshakes", func() {
@@ -107,8 +106,7 @@ var _ = Describe("Connection", func() {
 	})
 
 	It("fails if the peer ID doesn't match", func() {
-		thirdPartyID, err := peer.IDFromPrivateKey(createPeer())
-		Expect(err).ToNot(HaveOccurred())
+		thirdPartyID, _ := createPeer()
 
 		serverTransport, err := NewTransport(serverKey)
 		Expect(err).ToNot(HaveOccurred())
@@ -171,4 +169,57 @@ var _ = Describe("Connection", func() {
 		Expect(err).ToNot(HaveOccurred())
 		Eventually(serverConnChan).Should(Receive())
 	})
+
+	It("dials to two servers at the same time", func() {
+		serverID2, serverKey2 := createPeer()
+
+		serverTransport, err := NewTransport(serverKey)
+		Expect(err).ToNot(HaveOccurred())
+		serverAddr, serverConnChan := runServer(serverTransport)
+		serverTransport2, err := NewTransport(serverKey2)
+		Expect(err).ToNot(HaveOccurred())
+		serverAddr2, serverConnChan2 := runServer(serverTransport2)
+
+		data := bytes.Repeat([]byte{'a'}, 5*1<<20) // 5 MB
+		// wait for both servers to accept a connection
+		// then send some data
+		go func() {
+			for _, c := range []tpt.Conn{<-serverConnChan, <-serverConnChan2} {
+				go func(conn tpt.Conn) {
+					defer GinkgoRecover()
+					str, err := conn.OpenStream()
+					Expect(err).ToNot(HaveOccurred())
+					defer str.Close()
+					_, err = str.Write(data)
+					Expect(err).ToNot(HaveOccurred())
+				}(c)
+			}
+		}()
+
+		clientTransport, err := NewTransport(clientKey)
+		Expect(err).ToNot(HaveOccurred())
+		c1, err := clientTransport.Dial(context.Background(), serverAddr, serverID)
+		Expect(err).ToNot(HaveOccurred())
+		c2, err := clientTransport.Dial(context.Background(), serverAddr2, serverID2)
+		Expect(err).ToNot(HaveOccurred())
+
+		done := make(chan struct{}, 2)
+		// receive the data on both connections at the same time
+		for _, c := range []tpt.Conn{c1, c2} {
+			go func(conn tpt.Conn) {
+				defer GinkgoRecover()
+				str, err := conn.AcceptStream()
+				Expect(err).ToNot(HaveOccurred())
+				str.Close()
+				d, err := ioutil.ReadAll(str)
+				Expect(err).ToNot(HaveOccurred())
+				Expect(d).To(Equal(data))
+				conn.Close()
+				done <- struct{}{}
+			}(c)
+		}
+
+		Eventually(done, 5*time.Second).Should(Receive())
+		Eventually(done, 5*time.Second).Should(Receive())
+	})
 })

transport.go

@@ -31,6 +31,7 @@ type transport struct {
 	privKey   ic.PrivKey
 	localPeer peer.ID
 	tlsConf   *tls.Config
+	pconn     net.PacketConn
 }
 
 var _ tpt.Transport = &transport{}
@@ -45,10 +46,22 @@ func NewTransport(key ic.PrivKey) (tpt.Transport, error) {
 	if err != nil {
 		return nil, err
 	}
+
+	// create a packet conn for outgoing connections
+	addr, err := net.ResolveUDPAddr("udp", "localhost:0")
+	if err != nil {
+		return nil, err
+	}
+	conn, err := net.ListenUDP("udp", addr)
+	if err != nil {
+		return nil, err
+	}
+
 	return &transport{
 		privKey:   key,
 		localPeer: localPeer,
 		tlsConf:   tlsConf,
+		pconn:     conn,
 	}, nil
 }
 
@@ -58,6 +71,10 @@ func (t *transport) Dial(ctx context.Context, raddr ma.Multiaddr, p peer.ID) (tp
 	if err != nil {
 		return nil, err
 	}
+	addr, err := fromQuicMultiaddr(raddr)
+	if err != nil {
+		return nil, err
+	}
 	var remotePubKey ic.PubKey
 	tlsConf := t.tlsConf.Clone()
 	// We need to check the peer ID in the VerifyPeerCertificate callback.
@@ -82,7 +99,7 @@ func (t *transport) Dial(ctx context.Context, raddr ma.Multiaddr, p peer.ID) (tp
 		}
 		return nil
 	}
-	sess, err := quic.DialAddrContext(ctx, host, tlsConf, quicConfig)
+	sess, err := quic.DialContext(ctx, t.pconn, addr, host, tlsConf, quicConfig)
 	if err != nil {
 		return nil, err
 	}