prevent dialing addresses that we're listening on

It's impossible to run two nodes on the same IP:port, so we know for
sure that any dial to an address that we're listening on will fail (as
the peer IDs won't match).
In practice, this will be most useful for preventing dials to localhost
for nodes that are listening on the default port.

swarm_dial.go

@@ -440,7 +440,7 @@ func (s *Swarm) filterKnownUndialables(p peer.ID, addrs []ma.Multiaddr) []ma.Mul
 	for _, addr := range lisAddrs {
 		protos := addr.Protocols()
 		// we're only sure about filtering out /ip4 and /ip6 addresses, so far
-		if len(protos) == 2 && (protos[0].Code == ma.P_IP4 || protos[0].Code == ma.P_IP6) {
+		if protos[0].Code == ma.P_IP4 || protos[0].Code == ma.P_IP6 {
 			ourAddrs = append(ourAddrs, addr)
 		}
 	}

swarm_test.go

@@ -3,8 +3,10 @@ package swarm_test
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"io"
+	"strings"
 	"sync"
 	"testing"
 	"time"
@@ -20,6 +22,7 @@ import (
 
 	logging "github.com/ipfs/go-log"
 	ma "github.com/multiformats/go-multiaddr"
+	manet "github.com/multiformats/go-multiaddr/net"
 	"github.com/stretchr/testify/require"
 )
 
@@ -457,3 +460,31 @@ func TestCloseWithOpenStreams(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestPreventDialListenAddr(t *testing.T) {
+	s := GenSwarm(t, context.Background(), OptDialOnly)
+	if err := s.Listen(ma.StringCast("/ip4/0.0.0.0/udp/0/quic")); err != nil {
+		t.Fatal(err)
+	}
+	addrs, err := s.InterfaceListenAddresses()
+	if err != nil {
+		t.Fatal(err)
+	}
+	var addr ma.Multiaddr
+	for _, a := range addrs {
+		_, s, err := manet.DialArgs(a)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if strings.Split(s, ":")[0] == "127.0.0.1" {
+			addr = a
+			break
+		}
+	}
+	remote := peer.ID("foobar")
+	s.Peerstore().AddAddr(remote, addr, time.Hour)
+	_, err = s.DialPeer(context.Background(), remote)
+	if !errors.Is(err, ErrNoGoodAddresses) {
+		t.Fatal("expected dial to fail: %w", err)
+	}
+}