fix: don't prefer local ports from other addresses when dialing

This address may already be in-use (on that other address) somewhere
else.

Thanks to @schomatis for figuring this out.

fixes #1611

p2p/net/reuseport/dial.go

@@ -2,18 +2,11 @@ package reuseport
 
 import (
 	"context"
-	"net"
 
-	"github.com/libp2p/go-reuseport"
 	ma "github.com/multiformats/go-multiaddr"
 	manet "github.com/multiformats/go-multiaddr/net"
 )
 
-type dialer interface {
-	Dial(network, addr string) (net.Conn, error)
-	DialContext(ctx context.Context, network, addr string) (net.Conn, error)
-}
-
 // Dial dials the given multiaddr, reusing ports we're currently listening on if
 // possible.
 //
@@ -31,7 +24,7 @@ func (t *Transport) DialContext(ctx context.Context, raddr ma.Multiaddr) (manet.
 	if err != nil {
 		return nil, err
 	}
-	var d dialer
+	var d *dialer
 	switch network {
 	case "tcp4":
 		d = t.v4.getDialer(network)
@@ -52,7 +45,7 @@ func (t *Transport) DialContext(ctx context.Context, raddr ma.Multiaddr) (manet.
 	return maconn, nil
 }
 
-func (n *network) getDialer(network string) dialer {
+func (n *network) getDialer(network string) *dialer {
 	n.mu.RLock()
 	d := n.dialer
 	n.mu.RUnlock()
@@ -61,53 +54,9 @@ func (n *network) getDialer(network string) dialer {
 		defer n.mu.Unlock()
 
 		if n.dialer == nil {
-			n.dialer = n.makeDialer(network)
+			n.dialer = newDialer(n.listeners)
 		}
 		d = n.dialer
 	}
 	return d
 }
-
-func (n *network) makeDialer(network string) dialer {
-	if !reuseport.Available() {
-		log.Debug("reuseport not available")
-		return &net.Dialer{}
-	}
-
-	var unspec net.IP
-	switch network {
-	case "tcp4":
-		unspec = net.IPv4zero
-	case "tcp6":
-		unspec = net.IPv6unspecified
-	default:
-		panic("invalid network: must be either tcp4 or tcp6")
-	}
-
-	// How many ports are we listening on.
-	var port = 0
-	for l := range n.listeners {
-		newPort := l.Addr().(*net.TCPAddr).Port
-		switch {
-		case newPort == 0: // Any port, ignore (really, we shouldn't get this case...).
-		case port == 0: // Haven't selected a port yet, choose this one.
-			port = newPort
-		case newPort == port: // Same as the selected port, continue...
-		default: // Multiple ports, use the multi dialer
-			return newMultiDialer(unspec, n.listeners)
-		}
-	}
-
-	// None.
-	if port == 0 {
-		return &net.Dialer{}
-	}
-
-	// One. Always dial from the single port we're listening on.
-	laddr := &net.TCPAddr{
-		IP:   unspec,
-		Port: port,
-	}
-
-	return (*singleDialer)(laddr)
-}

p2p/net/reuseport/dialer.go

@@ -0,0 +1,91 @@
+package reuseport
+
+import (
+	"context"
+	"fmt"
+	"math/rand"
+	"net"
+
+	"github.com/libp2p/go-netroute"
+)
+
+type dialer struct {
+	specific    []*net.TCPAddr
+	loopback    []*net.TCPAddr
+	unspecified []*net.TCPAddr
+}
+
+func (d *dialer) Dial(network, addr string) (net.Conn, error) {
+	return d.DialContext(context.Background(), network, addr)
+}
+
+func randAddr(addrs []*net.TCPAddr) *net.TCPAddr {
+	if len(addrs) > 0 {
+		return addrs[rand.Intn(len(addrs))]
+	}
+	return nil
+}
+
+// DialContext dials a target addr.
+// Dialing preference is
+// * If there is a listener on the local interface the OS expects to use to route towards addr, use that.
+// * If there is a listener on a loopback address, addr is loopback, use that.
+// * If there is a listener on an undefined address (0.0.0.0 or ::), use that.
+// * Otherwise, dial with a random port on the unspecified address.
+func (d *dialer) DialContext(ctx context.Context, network, addr string) (net.Conn, error) {
+	if len(d.specific) > 0 || len(d.loopback) > 0 {
+		tcpAddr, err := net.ResolveTCPAddr(network, addr)
+		if err != nil {
+			return nil, err
+		}
+		ip := tcpAddr.IP
+		if !ip.IsLoopback() && !ip.IsGlobalUnicast() {
+			return nil, fmt.Errorf("undialable IP: %s", ip)
+		}
+
+		if len(d.specific) > 0 {
+			if router, err := netroute.New(); err == nil {
+				if _, _, preferredSrc, err := router.Route(ip); err == nil {
+					for _, optAddr := range d.specific {
+						if optAddr.IP.Equal(preferredSrc) {
+							return reuseDial(ctx, optAddr, network, addr)
+						}
+					}
+				}
+			}
+		}
+
+		if len(d.loopback) > 0 && ip.IsLoopback() {
+			return reuseDial(ctx, randAddr(d.loopback), network, addr)
+		}
+	}
+
+	if len(d.unspecified) > 0 {
+		return reuseDial(ctx, randAddr(d.unspecified), network, addr)
+	}
+
+	var dialer net.Dialer
+	return dialer.DialContext(ctx, network, addr)
+}
+
+func newDialer(listeners map[*listener]struct{}) *dialer {
+	specific := make([]*net.TCPAddr, 0)
+	loopback := make([]*net.TCPAddr, 0)
+	unspecified := make([]*net.TCPAddr, 0)
+
+	for l := range listeners {
+		addr := l.Addr().(*net.TCPAddr)
+		if addr.IP.IsLoopback() {
+			loopback = append(loopback, addr)
+		} else if addr.IP.IsUnspecified() {
+			unspecified = append(unspecified, addr)
+		} else {
+			specific = append(specific, addr)
+		}
+	}
+	return &dialer{
+		specific:    specific,
+		loopback:    loopback,
+		unspecified: unspecified,
+	}
+}

p2p/net/reuseport/transport.go

@@ -31,5 +31,5 @@ type Transport struct {
 type network struct {
 	mu        sync.RWMutex
 	listeners map[*listener]struct{}
-	dialer    dialer
+	dialer    *dialer
 }

p2p/net/reuseport/transport_test.go

@@ -141,7 +141,6 @@ func TestGlobalPreferenceV4(t *testing.T) {
 	testPrefer(t, loopbackV4, loopbackV4, globalV4)
 	t.Logf("when listening on %v, should prefer %v over %v", loopbackV4, unspecV4, globalV4)
 	testPrefer(t, loopbackV4, unspecV4, globalV4)
-
 	t.Logf("when listening on %v, should prefer %v over %v", globalV4, unspecV4, loopbackV4)
 	testPrefer(t, globalV4, unspecV4, loopbackV4)
 }
@@ -177,20 +176,13 @@ func testPrefer(t *testing.T, listen, prefer, avoid ma.Multiaddr) {
 	}
 	defer listenerB1.Close()
 
-	dialOne(t, &trB, listenerA, listenerB1.Addr().(*net.TCPAddr).Port)
-
 	listenerB2, err := trB.Listen(prefer)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer listenerB2.Close()
 
 	dialOne(t, &trB, listenerA, listenerB2.Addr().(*net.TCPAddr).Port)
-
-	// Closing the listener should reset the dialer.
-	listenerB2.Close()
-
-	dialOne(t, &trB, listenerA, listenerB1.Addr().(*net.TCPAddr).Port)
 }
 
 func TestV6V4(t *testing.T) {