swarm: fix selection of transport for dialing (#1653)

With WebTransport's /webtransport/certhash/xyz addresses, the assumption that
the last component of a multiaddr identifies the transport to use for dialing
doesn't hold any more.
Note that WebRTC will probably also use the certhash multiaddr component to
encode its certificate hashes.

p2p/net/swarm/swarm_addr_test.go

@@ -2,13 +2,25 @@ package swarm_test
 
 import (
 	"context"
+	"fmt"
 	"testing"
 
+	"github.com/libp2p/go-libp2p/core/peer"
+
+	ic "github.com/libp2p/go-libp2p/core/crypto"
 	"github.com/libp2p/go-libp2p/core/peerstore"
 	"github.com/libp2p/go-libp2p/core/test"
+	"github.com/libp2p/go-libp2p/p2p/net/swarm"
 	swarmt "github.com/libp2p/go-libp2p/p2p/net/swarm/testing"
+	circuitv2 "github.com/libp2p/go-libp2p/p2p/protocol/circuitv2/client"
+	quic "github.com/libp2p/go-libp2p/p2p/transport/quic"
+	"github.com/libp2p/go-libp2p/p2p/transport/tcp"
+	webtransport "github.com/libp2p/go-libp2p/p2p/transport/webtransport"
 
+	"github.com/minio/sha256-simd"
 	ma "github.com/multiformats/go-multiaddr"
+	"github.com/multiformats/go-multibase"
+	"github.com/multiformats/go-multihash"
 	"github.com/stretchr/testify/require"
 )
 
@@ -56,3 +68,37 @@ func TestAddressesWithoutListening(t *testing.T) {
 	require.NoError(t, err)
 	require.Empty(t, a1, "expected to be listening on no addresses")
 }
+
+func TestDialAddressSelection(t *testing.T) {
+	priv, _, err := test.RandTestKeyPair(ic.Ed25519, 256)
+	require.NoError(t, err)
+	id, err := peer.IDFromPrivateKey(priv)
+	require.NoError(t, err)
+	s, err := swarm.NewSwarm("local", nil)
+	require.NoError(t, err)
+
+	tcpTr, err := tcp.NewTCPTransport(nil, nil)
+	require.NoError(t, err)
+	require.NoError(t, s.AddTransport(tcpTr))
+	quicTr, err := quic.NewTransport(priv, nil, nil, nil)
+	require.NoError(t, err)
+	require.NoError(t, s.AddTransport(quicTr))
+	webtransportTr, err := webtransport.New(priv, nil, nil)
+	require.NoError(t, err)
+	require.NoError(t, s.AddTransport(webtransportTr))
+	h := sha256.Sum256([]byte("foo"))
+	hash, err := multihash.Encode(h[:], multihash.SHA2_256)
+	require.NoError(t, err)
+	certHash, err := multibase.Encode(multibase.Base58BTC, hash)
+	require.NoError(t, err)
+	circuitTr, err := circuitv2.New(nil, nil)
+	require.NoError(t, err)
+	require.NoError(t, s.AddTransport(circuitTr))
+
+	require.Equal(t, tcpTr, s.TransportForDialing(ma.StringCast("/ip4/127.0.0.1/tcp/1234")))
+	require.Equal(t, quicTr, s.TransportForDialing(ma.StringCast("/ip4/127.0.0.1/udp/1234/quic")))
+	require.Equal(t, circuitTr, s.TransportForDialing(ma.StringCast(fmt.Sprintf("/ip4/127.0.0.1/udp/1234/quic/p2p-circuit/p2p/%s", id))))
+	require.Equal(t, webtransportTr, s.TransportForDialing(ma.StringCast(fmt.Sprintf("/ip4/127.0.0.1/udp/1234/quic/webtransport/certhash/%s", certHash))))
+	require.Nil(t, s.TransportForDialing(ma.StringCast("/ip4/1.2.3.4")))
+	require.Nil(t, s.TransportForDialing(ma.StringCast("/ip4/1.2.3.4/tcp/443/ws")))
+}

p2p/net/swarm/swarm_transport.go

@@ -19,25 +19,23 @@ func (s *Swarm) TransportForDialing(a ma.Multiaddr) transport.Transport {
 
 	s.transports.RLock()
 	defer s.transports.RUnlock()
+
 	if len(s.transports.m) == 0 {
 		// make sure we're not just shutting down.
 		if s.transports.m != nil {
 			log.Error("you have no transports configured")
 		}
 		return nil
 	}
-
-	for _, p := range protocols {
-		transport, ok := s.transports.m[p.Code]
-		if !ok {
-			continue
-		}
-		if transport.Proxy() {
-			return transport
+	if isRelayAddr(a) {
+		return s.transports.m[ma.P_CIRCUIT]
+	}
+	for _, t := range s.transports.m {
+		if t.CanDial(a) {
+			return t
 		}
 	}
-
-	return s.transports.m[protocols[len(protocols)-1].Code]
+	return nil
 }
 
 // TransportForListening retrieves the appropriate transport for listening on