reference basis

.travis.yml

+os:
+  - linux
+
+language: go
+
+go:
+  - 1.13.x
+
+env:
+  global:
+    - GOTFLAGS="-race"
+  matrix:
+    - BUILD_DEPTYPE=gomod
+
+
+# disable travis install
+install:
+  - true
+
+script:
+  - bash <(curl -s https://raw.githubusercontent.com/ipfs/ci-helpers/master/travis-ci/run-standard-tests.sh)
+
+
+cache:
+  directories:
+    - $GOPATH/pkg/mod
+    - $HOME/.cache/go-build
+
+notifications:
+  email: false

LICENSE

+The MIT License (MIT)
+
+Copyright (c) 2016 Jeromy Johnson
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

README.md

 # go-reuseport-transport
 
-dms3 p2p go-reuseport-transport
\ No newline at end of file
+[![](https://img.shields.io/badge/made%20by-Protocol%20Labs-blue.svg?style=flat-square)](https://protocol.ai)
+[![](https://img.shields.io/badge/project-libp2p-yellow.svg?style=flat-square)](https://libp2p.io/)
+[![](https://img.shields.io/badge/freenode-%23libp2p-yellow.svg?style=flat-square)](http://webchat.freenode.net/?channels=%23libp2p)
+[![Discourse posts](https://img.shields.io/discourse/https/discuss.libp2p.io/posts.svg)](https://discuss.libp2p.io)
+[![GoDoc](https://godoc.org/github.com/libp2p/go-reuseport-transport?status.svg)](https://godoc.org/github.com/libp2p/go-reuseport-transport)
+[![Build Status](https://travis-ci.org/libp2p/go-reuseport-transport.svg?branch=master)](https://travis-ci.org/libp2p/go-reuseport-transport)
+
+> Basic reuseport TCP transport
+
+This package provides a basic transport for automatically (and intelligently) reusing TCP ports.
+
+To use, construct a new `Transport` (the zero value is safe to use) and configure any listeners (`tr.Listen(...)`).
+
+Then, when dialing (`tr.Dial(...)`), the transport will attempt to reuse the ports it's currently listening on, choosing the best one depending on the destination address.
+
+
+NOTE: Currently, we don't make any attempts to prevent two reusport transports from interfering with each other (reusing each other's ports). However, we reserve the right to fix this in the future.
+
+## Install
+
+`go-reuseport-transport` is a standard Go module which can be installed with:
+
+```sh
+go get github.com/libp2p/go-reuseport-transport
+```
+
+This repo is [gomod](https://github.com/golang/go/wiki/Modules)-compatible, and users of
+go 1.11 and later with modules enabled will automatically pull the latest tagged release
+by referencing this package. Upgrades to future releases can be managed using `go get`,
+or by editing your `go.mod` file as [described by the gomod documentation](https://github.com/golang/go/wiki/Modules#how-to-upgrade-and-downgrade-dependencies).
+
+## Current use in libp2p
+
+This package is *currently* used by the [go-tcp-transport](https://github.com/libp2p/go-tcp-transport) libp2p transport and will likely be used by more libp2p transports in the future.
+
+## Contribute
+
+Feel free to join in. All welcome. Open an [issue](https://github.com/libp2p/go-reuseport-transport/issues)!
+
+This repository falls under the libp2p [Code of Conduct](https://github.com/libp2p/community/blob/master/code-of-conduct.md).
+
+### Want to hack on libp2p?
+
+[![](https://cdn.rawgit.com/libp2p/community/master/img/contribute.gif)](https://github.com/libp2p/community/blob/master/CONTRIBUTE.md)
+
+## License
+
+MIT
+
+---
+
+The last gx published version of this module was: 0.2.3: QmTmbamDjDWgHe8qeMt7ZpaeNpTj349JpFKuwTF321XavT

codecov.yml

+coverage:
+  range: "50...100"
+comment: off

dial.go

+package tcpreuse
+
+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.
+//
+// Dial attempts to be smart about choosing the source port. For example, If
+// we're dialing a loopback address and we're listening on one or more loopback
+// ports, Dial will randomly choose one of the loopback ports and addresses and
+// reuse it.
+func (t *Transport) Dial(raddr ma.Multiaddr) (manet.Conn, error) {
+	return t.DialContext(context.Background(), raddr)
+}
+
+// DialContext is like Dial but takes a context.
+func (t *Transport) DialContext(ctx context.Context, raddr ma.Multiaddr) (manet.Conn, error) {
+	network, addr, err := manet.DialArgs(raddr)
+	if err != nil {
+		return nil, err
+	}
+	var d dialer
+	switch network {
+	case "tcp4":
+		d = t.v4.getDialer(network)
+	case "tcp6":
+		d = t.v6.getDialer(network)
+	default:
+		return nil, ErrWrongProto
+	}
+	conn, err := d.DialContext(ctx, network, addr)
+	if err != nil {
+		return nil, err
+	}
+	maconn, err := manet.WrapNetConn(conn)
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+	return maconn, nil
+}
+
+func (n *network) getDialer(network string) dialer {
+	n.mu.RLock()
+	d := n.dialer
+	n.mu.RUnlock()
+	if d == nil {
+		n.mu.Lock()
+		defer n.mu.Unlock()
+
+		if n.dialer == nil {
+			n.dialer = n.makeDialer(network)
+		}
+		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)
+}

go.mod

+module github.com/libp2p/go-reuseport-transport
+
+go 1.15
+
+require (
+	github.com/ipfs/go-log v0.0.1
+	github.com/libp2p/go-netroute v0.1.3
+	github.com/libp2p/go-reuseport v0.0.2
+	github.com/multiformats/go-multiaddr v0.3.3
+)

go.sum

+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/gogo/protobuf v1.2.1 h1:/s5zKNz0uPFCZ5hddgPdo2TK2TVrUNMn0OOX8/aZMTE=
+github.com/gogo/protobuf v1.2.1/go.mod h1:hp+jE20tsWTFYpLwKvXlhS1hjn+gTNwPg2I6zVXpSg4=
+github.com/google/gopacket v1.1.17 h1:rMrlX2ZY2UbvT+sdz3+6J+pp2z+msCq9MxTU6ymxbBY=
+github.com/google/gopacket v1.1.17/go.mod h1:UdDNZ1OO62aGYVnPhxT1U6aI7ukYtA/kB8vaU0diBUM=
+github.com/ipfs/go-cid v0.0.7 h1:ysQJVJA3fNDF1qigJbsSQOdjhVLsOEoPdh0+R97k3jY=
+github.com/ipfs/go-cid v0.0.7/go.mod h1:6Ux9z5e+HpkQdckYoX1PG/6xqKspzlEIR5SDmgqgC/I=
+github.com/ipfs/go-log v0.0.1 h1:9XTUN/rW64BCG1YhPK9Hoy3q8nr4gOmHHBpgFdfw6Lc=
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+github.com/kisielk/errcheck v1.1.0/go.mod h1:EZBBE59ingxPouuu3KfxchcWSUPOHkagtvWXihfKN4Q=
+github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
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+github.com/libp2p/go-netroute v0.1.3 h1:1ngWRx61us/EpaKkdqkMjKk/ufr/JlIFYQAxV2XX8Ig=
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+github.com/libp2p/go-reuseport v0.0.2 h1:XSG94b1FJfGA01BUrT82imejHQyTxO4jEWqheyCXYvU=
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listen.go

+package tcpreuse
+
+import (
+	"net"
+
+	"github.com/libp2p/go-reuseport"
+	ma "github.com/multiformats/go-multiaddr"
+	manet "github.com/multiformats/go-multiaddr/net"
+)
+
+type listener struct {
+	manet.Listener
+	network *network
+}
+
+func (l *listener) Close() error {
+	l.network.mu.Lock()
+	delete(l.network.listeners, l)
+	l.network.dialer = nil
+	l.network.mu.Unlock()
+	return l.Listener.Close()
+}
+
+// Listen listens on the given multiaddr.
+//
+// If reuseport is supported, it will be enabled for this listener and future
+// dials from this transport may reuse the port.
+//
+// Note: You can listen on the same multiaddr as many times as you want
+// (although only *one* listener will end up handling the inbound connection).
+func (t *Transport) Listen(laddr ma.Multiaddr) (manet.Listener, error) {
+	nw, naddr, err := manet.DialArgs(laddr)
+	if err != nil {
+		return nil, err
+	}
+	var n *network
+	switch nw {
+	case "tcp4":
+		n = &t.v4
+	case "tcp6":
+		n = &t.v6
+	default:
+		return nil, ErrWrongProto
+	}
+
+	if !reuseport.Available() {
+		return manet.Listen(laddr)
+	}
+	nl, err := reuseport.Listen(nw, naddr)
+	if err != nil {
+		return manet.Listen(laddr)
+	}
+
+	if _, ok := nl.Addr().(*net.TCPAddr); !ok {
+		nl.Close()
+		return nil, ErrWrongProto
+	}
+
+	malist, err := manet.WrapNetListener(nl)
+	if err != nil {
+		nl.Close()
+		return nil, err
+	}
+
+	list := &listener{
+		Listener: malist,
+		network:  n,
+	}
+
+	n.mu.Lock()
+	defer n.mu.Unlock()
+
+	if n.listeners == nil {
+		n.listeners = make(map[*listener]struct{})
+	}
+	n.listeners[list] = struct{}{}
+	n.dialer = nil
+
+	return list, nil
+}

multidialer.go

+package tcpreuse
+
+import (
+	"context"
+	"fmt"
+	"math/rand"
+	"net"
+
+	"github.com/libp2p/go-netroute"
+)
+
+type multiDialer struct {
+	listeningAddresses []*net.TCPAddr
+	loopback           []*net.TCPAddr
+	unspecified        []*net.TCPAddr
+	fallback           net.TCPAddr
+}
+
+func (d *multiDialer) 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.
+// * Use the fallback IP specified during construction, with a port that's already being listened on, if one exists.
+func (d *multiDialer) DialContext(ctx context.Context, network, addr string) (net.Conn, error) {
+	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 router, err := netroute.New(); err == nil {
+		if _, _, preferredSrc, err := router.Route(ip); err == nil {
+			for _, optAddr := range d.listeningAddresses {
+				if optAddr.IP.Equal(preferredSrc) {
+					return reuseDial(ctx, optAddr, network, addr)
+				}
+			}
+		}
+	}
+
+	if ip.IsLoopback() && len(d.loopback) > 0 {
+		return reuseDial(ctx, randAddr(d.loopback), network, addr)
+	}
+	if len(d.unspecified) == 0 {
+		return reuseDial(ctx, &d.fallback, network, addr)
+	}
+
+	return reuseDial(ctx, randAddr(d.unspecified), network, addr)
+}
+
+func newMultiDialer(unspec net.IP, listeners map[*listener]struct{}) (m dialer) {
+	addrs := make([]*net.TCPAddr, 0)
+	loopback := make([]*net.TCPAddr, 0)
+	unspecified := make([]*net.TCPAddr, 0)
+	existingPort := 0
+
+	for l := range listeners {
+		addr := l.Addr().(*net.TCPAddr)
+		addrs = append(addrs, addr)
+		if addr.IP.IsLoopback() {
+			loopback = append(loopback, addr)
+		} else if addr.IP.IsGlobalUnicast() && existingPort == 0 {
+			existingPort = addr.Port
+		} else if addr.IP.IsUnspecified() {
+			unspecified = append(unspecified, addr)
+		}
+	}
+	m = &multiDialer{
+		listeningAddresses: addrs,
+		loopback:           loopback,
+		unspecified:        unspecified,
+		fallback:           net.TCPAddr{IP: unspec, Port: existingPort},
+	}
+	return
+}

reuseport.go

+package tcpreuse
+
+import (
+	"context"
+	"net"
+
+	reuseport "github.com/libp2p/go-reuseport"
+)
+
+var fallbackDialer net.Dialer
+
+// Dials using reuseport and then redials normally if that fails.
+func reuseDial(ctx context.Context, laddr *net.TCPAddr, network, raddr string) (con net.Conn, err error) {
+	if laddr == nil {
+		return fallbackDialer.DialContext(ctx, network, raddr)
+	}
+
+	d := net.Dialer{
+		LocalAddr: laddr,
+		Control:   reuseport.Control,
+	}
+
+	con, err = d.DialContext(ctx, network, raddr)
+	if err == nil {
+		return con, nil
+	}
+
+	if reuseErrShouldRetry(err) && ctx.Err() == nil {
+		// We could have an existing socket open or we could have one
+		// stuck in TIME-WAIT.
+		log.Debugf("failed to reuse port, will try again with a random port: %s", err)
+		con, err = fallbackDialer.DialContext(ctx, network, raddr)
+	}
+	return con, err
+}

reuseport_plan9.go

+package tcpreuse
+
+import (
+	"net"
+	"os"
+)
+
+const (
+	EADDRINUSE   = "address in use"
+	ECONNREFUSED = "connection refused"
+)
+
+// reuseErrShouldRetry diagnoses whether to retry after a reuse error.
+// if we failed to bind, we should retry. if bind worked and this is a
+// real dial error (remote end didnt answer) then we should not retry.
+func reuseErrShouldRetry(err error) bool {
+	if err == nil {
+		return false // hey, it worked! no need to retry.
+	}
+
+	// if it's a network timeout error, it's a legitimate failure.
+	if nerr, ok := err.(net.Error); ok && nerr.Timeout() {
+		return false
+	}
+
+	e, ok := err.(*net.OpError)
+	if !ok {
+		return true
+	}
+
+	e1, ok := e.Err.(*os.PathError)
+	if !ok {
+		return true
+	}
+
+	switch e1.Err.Error() {
+	case EADDRINUSE:
+		return true
+	case ECONNREFUSED:
+		return false
+	default:
+		return true // optimistically default to retry.
+	}
+}

reuseport_posix.go

+// +build !plan9
+
+package tcpreuse
+
+import (
+	"net"
+	"syscall"
+)
+
+// reuseErrShouldRetry diagnoses whether to retry after a reuse error.
+// if we failed to bind, we should retry. if bind worked and this is a
+// real dial error (remote end didnt answer) then we should not retry.
+func reuseErrShouldRetry(err error) bool {
+	if err == nil {
+		return false // hey, it worked! no need to retry.
+	}
+
+	// if it's a network timeout error, it's a legitimate failure.
+	if nerr, ok := err.(net.Error); ok && nerr.Timeout() {
+		return false
+	}
+
+	errno, ok := err.(syscall.Errno)
+	if !ok { // not an errno? who knows what this is. retry.
+		return true
+	}
+
+	switch errno {
+	case syscall.EADDRINUSE, syscall.EADDRNOTAVAIL:
+		return true // failure to bind. retry.
+	case syscall.ECONNREFUSED:
+		return false // real dial error
+	default:
+		return true // optimistically default to retry.
+	}
+}

reuseport_test.go

+// +build !plan9
+
+package tcpreuse
+
+import (
+	"net"
+	"syscall"
+	"testing"
+)
+
+type netTimeoutErr struct {
+	timeout bool
+}
+
+func (e netTimeoutErr) Error() string {
+	return ""
+}
+
+func (e netTimeoutErr) Timeout() bool {
+	return e.timeout
+}
+
+func (e netTimeoutErr) Temporary() bool {
+	panic("not checked")
+}
+
+func TestReuseError(t *testing.T) {
+	var nte1 net.Error = &netTimeoutErr{true}
+	var nte2 net.Error = &netTimeoutErr{false}
+
+	cases := map[error]bool{
+		nil:                   false,
+		syscall.EADDRINUSE:    true,
+		syscall.EADDRNOTAVAIL: true,
+		syscall.ECONNREFUSED:  false,
+
+		nte1: false,
+		nte2: true, // this ones a little weird... we should check neterror.Temporary() too
+
+		// test 'default' to true
+		syscall.EBUSY: true,
+	}
+
+	for k, v := range cases {
+		if reuseErrShouldRetry(k) != v {
+			t.Fatalf("expected %t for %#v", v, k)
+		}
+	}
+
+}

singledialer.go

+package tcpreuse
+
+import (
+	"context"
+	"net"
+)
+
+type singleDialer net.TCPAddr
+
+func (d *singleDialer) Dial(network, address string) (net.Conn, error) {
+	return d.DialContext(context.Background(), network, address)
+}
+
+func (d *singleDialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
+	return reuseDial(ctx, (*net.TCPAddr)(d), network, address)
+}

transport.go

+package tcpreuse
+
+import (
+	"errors"
+	"sync"
+
+	logging "github.com/ipfs/go-log"
+)
+
+var log = logging.Logger("reuseport-transport")
+
+// ErrWrongProto is returned when dialing a protocol other than tcp.
+var ErrWrongProto = errors.New("can only dial TCP over IPv4 or IPv6")
+
+// Transport is a TCP reuse transport that reuses listener ports.
+type Transport struct {
+	v4 network
+	v6 network
+}
+
+type network struct {
+	mu        sync.RWMutex
+	listeners map[*listener]struct{}
+	dialer    dialer
+}

transport_test.go

+package tcpreuse
+
+import (
+	"net"
+	"testing"
+
+	ma "github.com/multiformats/go-multiaddr"
+	manet "github.com/multiformats/go-multiaddr/net"
+)
+
+var loopbackV4, _ = ma.NewMultiaddr("/ip4/127.0.0.1/tcp/0")
+var loopbackV6, _ = ma.NewMultiaddr("/ip6/::1/tcp/0")
+var unspecV6, _ = ma.NewMultiaddr("/ip6/::/tcp/0")
+var unspecV4, _ = ma.NewMultiaddr("/ip4/0.0.0.0/tcp/0")
+
+var globalV4 ma.Multiaddr
+var globalV6 ma.Multiaddr
+
+func init() {
+	addrs, err := manet.InterfaceMultiaddrs()
+	if err != nil {
+		return
+	}
+	for _, addr := range addrs {
+		if !manet.IsIP6LinkLocal(addr) && !manet.IsIPLoopback(addr) {
+			tcp, _ := ma.NewMultiaddr("/tcp/0")
+			switch addr.Protocols()[0].Code {
+			case ma.P_IP4:
+				if globalV4 == nil {
+					globalV4 = addr.Encapsulate(tcp)
+				}
+			case ma.P_IP6:
+				if globalV6 == nil {
+					globalV6 = addr.Encapsulate(tcp)
+				}
+			}
+		}
+	}
+}
+
+func acceptOne(t *testing.T, listener manet.Listener) <-chan interface{} {
+	t.Helper()
+	done := make(chan interface{}, 1)
+	go func() {
+		defer close(done)
+		done <- nil
+		c, err := listener.Accept()
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		c.Close()
+	}()
+	<-done
+	return done
+}
+
+func dialOne(t *testing.T, tr *Transport, listener manet.Listener, expected ...int) int {
+	t.Helper()
+
+	done := acceptOne(t, listener)
+	c, err := tr.Dial(listener.Multiaddr())
+	if err != nil {
+		t.Fatal(err)
+	}
+	port := c.LocalAddr().(*net.TCPAddr).Port
+	<-done
+	c.Close()
+	if len(expected) == 0 {
+		return port
+	}
+	for _, p := range expected {
+		if p == port {
+			return port
+		}
+	}
+	t.Errorf("dialed %s from %v. expected to dial from port %v", listener.Multiaddr(), c.LocalAddr(), expected)
+	return 0
+}
+
+func TestNoneAndSingle(t *testing.T) {
+	var trA Transport
+	var trB Transport
+	listenerA, err := trA.Listen(loopbackV4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listenerA.Close()
+
+	dialOne(t, &trB, listenerA)
+
+	listenerB, err := trB.Listen(loopbackV4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listenerB.Close()
+
+	dialOne(t, &trB, listenerA, listenerB.Addr().(*net.TCPAddr).Port)
+}
+
+func TestTwoLocal(t *testing.T) {
+	var trA Transport
+	var trB Transport
+	listenerA, err := trA.Listen(loopbackV4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listenerA.Close()
+
+	listenerB1, err := trB.Listen(loopbackV4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listenerB1.Close()
+
+	listenerB2, err := trB.Listen(loopbackV4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listenerB2.Close()
+
+	dialOne(t, &trB, listenerA,
+		listenerB1.Addr().(*net.TCPAddr).Port,
+		listenerB2.Addr().(*net.TCPAddr).Port)
+}
+
+func TestGlobalPreferenceV4(t *testing.T) {
+	if globalV4 == nil {
+		t.Skip("no global IPv4 addresses configured")
+		return
+	}
+	t.Logf("when listening on %v, should prefer %v over %v", loopbackV4, loopbackV4, globalV4)
+	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)
+}
+
+func TestGlobalPreferenceV6(t *testing.T) {
+	if globalV6 == nil {
+		t.Skip("no global IPv6 addresses configured")
+		return
+	}
+	testPrefer(t, loopbackV6, loopbackV6, globalV6)
+	testPrefer(t, loopbackV6, unspecV6, globalV6)
+
+	testPrefer(t, globalV6, unspecV6, loopbackV6)
+}
+
+func TestLoopbackPreference(t *testing.T) {
+	testPrefer(t, loopbackV4, loopbackV4, unspecV4)
+	testPrefer(t, loopbackV6, loopbackV6, unspecV6)
+}
+
+func testPrefer(t *testing.T, listen, prefer, avoid ma.Multiaddr) {
+	var trA Transport
+	var trB Transport
+	listenerA, err := trA.Listen(listen)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listenerA.Close()
+
+	listenerB1, err := trB.Listen(avoid)
+	if err != nil {
+		t.Fatal(err)
+	}
+	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) {
+	testUseFirst(t, loopbackV4, loopbackV4, loopbackV6)
+	testUseFirst(t, loopbackV6, loopbackV6, loopbackV4)
+}
+
+func TestGlobalToGlobal(t *testing.T) {
+	if globalV4 == nil {
+		t.Skip("no globalV4 addresses configured")
+		return
+	}
+	testUseFirst(t, globalV4, globalV4, loopbackV4)
+	testUseFirst(t, globalV6, globalV6, loopbackV6)
+}
+
+func testUseFirst(t *testing.T, listen, use, never ma.Multiaddr) {
+	var trA Transport
+	var trB Transport
+	listenerA, err := trA.Listen(globalV4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listenerA.Close()
+
+	listenerB1, err := trB.Listen(loopbackV4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listenerB1.Close()
+
+	// It works (random port)
+	dialOne(t, &trB, listenerA)
+
+	listenerB2, err := trB.Listen(globalV4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listenerB2.Close()
+
+	// Uses globalV4 port.
+	dialOne(t, &trB, listenerA, listenerB2.Addr().(*net.TCPAddr).Port)
+
+	// Closing the listener should reset the dialer.
+	listenerB2.Close()
+
+	// It still works.
+	dialOne(t, &trB, listenerA)
+}
+
+func TestDuplicateGlobal(t *testing.T) {
+	if globalV4 == nil {
+		t.Skip("no globalV4 addresses configured")
+		return
+	}
+
+	var trA Transport
+	var trB Transport
+	listenerA, err := trA.Listen(globalV4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listenerA.Close()
+
+	listenerB1, err := trB.Listen(globalV4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listenerB1.Close()
+
+	listenerB2, err := trB.Listen(globalV4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listenerB2.Close()
+
+	// Check which port we're using
+	port := dialOne(t, &trB, listenerA)
+
+	// Check consistency
+	for i := 0; i < 10; i++ {
+		dialOne(t, &trB, listenerA, port)
+	}
+}