net/{netx,memnet},all: add netx.DialFunc, move memnet Network impl

This adds netx.DialFunc, unifying a type we have a bazillion other
places, giving it now a nice short name that's clickable in
editors, etc.

That highlighted that my earlier move (03b47a55c7956) of stuff from
nettest into netx moved too much: it also dragged along the memnet
impl, meaning all users of netx.DialFunc who just wanted netx for the
type definition were instead also pulling in all of memnet.

So move the memnet implementation netx.Network into memnet, a package
we already had.

Then use netx.DialFunc in a bunch of places. I'm sure I missed some.
And plenty remain in other repos, to be updated later.

Updates tailscale/corp#27636

Change-Id: I7296cd4591218e8624e214f8c70dab05fb884e95
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/derper/depaware.txt

@@ -111,6 +111,7 @@ tailscale.com/cmd/derper dependencies: (generated by github.com/tailscale/depawa
      💣 tailscale.com/net/netmon                                     from tailscale.com/derp/derphttp+
      💣 tailscale.com/net/netns                                      from tailscale.com/derp/derphttp
         tailscale.com/net/netutil                                    from tailscale.com/client/local
+        tailscale.com/net/netx                                       from tailscale.com/net/dnscache+
         tailscale.com/net/sockstats                                  from tailscale.com/derp/derphttp
         tailscale.com/net/stun                                       from tailscale.com/net/stunserver
         tailscale.com/net/stunserver                                 from tailscale.com/cmd/derper

cmd/k8s-operator/depaware.txt

@@ -866,6 +866,7 @@ tailscale.com/cmd/k8s-operator dependencies: (generated by github.com/tailscale/
      💣 tailscale.com/net/netns                                      from tailscale.com/derp/derphttp+
    W 💣 tailscale.com/net/netstat                                    from tailscale.com/portlist
         tailscale.com/net/netutil                                    from tailscale.com/client/local+
+        tailscale.com/net/netx                                       from tailscale.com/control/controlclient+
         tailscale.com/net/packet                                     from tailscale.com/net/connstats+
         tailscale.com/net/packet/checksum                            from tailscale.com/net/tstun
         tailscale.com/net/ping                                       from tailscale.com/net/netcheck+

cmd/sniproxy/handlers.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/inetaf/tcpproxy"
 	"tailscale.com/net/netutil"
+	"tailscale.com/net/netx"
 )
 
 type tcpRoundRobinHandler struct {
@@ -22,7 +23,7 @@ type tcpRoundRobinHandler struct {
 	To []string
 
 	// DialContext is used to make the outgoing TCP connection.
-	DialContext func(ctx context.Context, network, address string) (net.Conn, error)
+	DialContext netx.DialFunc
 
 	// ReachableIPs enumerates the IP addresses this handler is reachable on.
 	ReachableIPs []netip.Addr

cmd/tailscale/depaware.txt

@@ -112,6 +112,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
      💣 tailscale.com/net/netmon                                     from tailscale.com/cmd/tailscale/cli+
      💣 tailscale.com/net/netns                                      from tailscale.com/derp/derphttp+
         tailscale.com/net/netutil                                    from tailscale.com/client/local+
+        tailscale.com/net/netx                                       from tailscale.com/control/controlhttp+
         tailscale.com/net/ping                                       from tailscale.com/net/netcheck
         tailscale.com/net/portmapper                                 from tailscale.com/cmd/tailscale/cli+
         tailscale.com/net/sockstats                                  from tailscale.com/control/controlhttp+

cmd/tailscaled/depaware.txt

@@ -316,6 +316,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
      💣 tailscale.com/net/netns                                      from tailscale.com/cmd/tailscaled+
    W 💣 tailscale.com/net/netstat                                    from tailscale.com/portlist
         tailscale.com/net/netutil                                    from tailscale.com/client/local+
+        tailscale.com/net/netx                                       from tailscale.com/control/controlclient+
         tailscale.com/net/packet                                     from tailscale.com/net/connstats+
         tailscale.com/net/packet/checksum                            from tailscale.com/net/tstun
         tailscale.com/net/ping                                       from tailscale.com/net/netcheck+

control/controlclient/direct.go

@@ -37,6 +37,7 @@ import (
 	"tailscale.com/net/dnsfallback"
 	"tailscale.com/net/netmon"
 	"tailscale.com/net/netutil"
+	"tailscale.com/net/netx"
 	"tailscale.com/net/tlsdial"
 	"tailscale.com/net/tsdial"
 	"tailscale.com/net/tshttpproxy"
@@ -272,7 +273,7 @@ func NewDirect(opts Options) (*Direct, error) {
 		tr.Proxy = tshttpproxy.ProxyFromEnvironment
 		tshttpproxy.SetTransportGetProxyConnectHeader(tr)
 		tr.TLSClientConfig = tlsdial.Config(serverURL.Hostname(), opts.HealthTracker, tr.TLSClientConfig)
-		var dialFunc dialFunc
+		var dialFunc netx.DialFunc
 		dialFunc, interceptedDial = makeScreenTimeDetectingDialFunc(opts.Dialer.SystemDial)
 		tr.DialContext = dnscache.Dialer(dialFunc, dnsCache)
 		tr.DialTLSContext = dnscache.TLSDialer(dialFunc, dnsCache, tr.TLSClientConfig)
@@ -1749,14 +1750,12 @@ func addLBHeader(req *http.Request, nodeKey key.NodePublic) {
 	}
 }
 
-type dialFunc = func(ctx context.Context, network, addr string) (net.Conn, error)
-
 // makeScreenTimeDetectingDialFunc returns dialFunc, optionally wrapped (on
 // Apple systems) with a func that sets the returned atomic.Bool for whether
 // Screen Time seemed to intercept the connection.
 //
 // The returned *atomic.Bool is nil on non-Apple systems.
-func makeScreenTimeDetectingDialFunc(dial dialFunc) (dialFunc, *atomic.Bool) {
+func makeScreenTimeDetectingDialFunc(dial netx.DialFunc) (netx.DialFunc, *atomic.Bool) {
 	switch runtime.GOOS {
 	case "darwin", "ios":
 		// Continue below.

control/controlhttp/client.go

@@ -44,6 +44,7 @@ import (
 	"tailscale.com/net/dnscache"
 	"tailscale.com/net/dnsfallback"
 	"tailscale.com/net/netutil"
+	"tailscale.com/net/netx"
 	"tailscale.com/net/sockstats"
 	"tailscale.com/net/tlsdial"
 	"tailscale.com/net/tshttpproxy"
@@ -494,7 +495,7 @@ func (a *Dialer) tryURLUpgrade(ctx context.Context, u *url.URL, optAddr netip.Ad
 		dns = a.resolver()
 	}
 
-	var dialer dnscache.DialContextFunc
+	var dialer netx.DialFunc
 	if a.Dialer != nil {
 		dialer = a.Dialer
 	} else {

control/controlhttp/constants.go

@@ -12,6 +12,7 @@ import (
 	"tailscale.com/health"
 	"tailscale.com/net/dnscache"
 	"tailscale.com/net/netmon"
+	"tailscale.com/net/netx"
 	"tailscale.com/tailcfg"
 	"tailscale.com/tstime"
 	"tailscale.com/types/key"
@@ -66,7 +67,7 @@ type Dialer struct {
 	// Dialer is the dialer used to make outbound connections.
 	//
 	// If not specified, this defaults to net.Dialer.DialContext.
-	Dialer dnscache.DialContextFunc
+	Dialer netx.DialFunc
 
 	// DNSCache is the caching Resolver used by this Dialer.
 	//

control/controlhttp/http_test.go

@@ -26,8 +26,8 @@ import (
 	"tailscale.com/control/controlhttp/controlhttpcommon"
 	"tailscale.com/control/controlhttp/controlhttpserver"
 	"tailscale.com/health"
-	"tailscale.com/net/dnscache"
 	"tailscale.com/net/netmon"
+	"tailscale.com/net/netx"
 	"tailscale.com/net/socks5"
 	"tailscale.com/net/tsdial"
 	"tailscale.com/tailcfg"
@@ -760,7 +760,7 @@ func TestDialPlan(t *testing.T) {
 
 type closeTrackDialer struct {
 	t     testing.TB
-	inner dnscache.DialContextFunc
+	inner netx.DialFunc
 	mu    sync.Mutex
 	conns map[*closeTrackConn]bool
 }

derp/derphttp/derphttp_client.go

@@ -35,6 +35,7 @@ import (
 	"tailscale.com/net/dnscache"
 	"tailscale.com/net/netmon"
 	"tailscale.com/net/netns"
+	"tailscale.com/net/netx"
 	"tailscale.com/net/sockstats"
 	"tailscale.com/net/tlsdial"
 	"tailscale.com/net/tshttpproxy"
@@ -587,7 +588,7 @@ func (c *Client) connect(ctx context.Context, caller string) (client *derp.Clien
 //
 // The primary use for this is the derper mesh mode to connect to each
 // other over a VPC network.
-func (c *Client) SetURLDialer(dialer func(ctx context.Context, network, addr string) (net.Conn, error)) {
+func (c *Client) SetURLDialer(dialer netx.DialFunc) {
 	c.dialer = dialer
 }
 

k8s-operator/sessionrecording/hijacker.go

@@ -25,6 +25,7 @@ import (
 	"tailscale.com/k8s-operator/sessionrecording/spdy"
 	"tailscale.com/k8s-operator/sessionrecording/tsrecorder"
 	"tailscale.com/k8s-operator/sessionrecording/ws"
+	"tailscale.com/net/netx"
 	"tailscale.com/sessionrecording"
 	"tailscale.com/tailcfg"
 	"tailscale.com/tsnet"
@@ -102,7 +103,7 @@ type Hijacker struct {
 // connection succeeds. In case of success, returns a list with a single
 // successful recording attempt and an error channel. If the connection errors
 // after having been established, an error is sent down the channel.
-type RecorderDialFn func(context.Context, []netip.AddrPort, sessionrecording.DialFunc) (io.WriteCloser, []*tailcfg.SSHRecordingAttempt, <-chan error, error)
+type RecorderDialFn func(context.Context, []netip.AddrPort, netx.DialFunc) (io.WriteCloser, []*tailcfg.SSHRecordingAttempt, <-chan error, error)
 
 // Hijack hijacks a 'kubectl exec' session and configures for the session
 // contents to be sent to a recorder.

k8s-operator/sessionrecording/hijacker_test.go

@@ -19,7 +19,7 @@ import (
 	"go.uber.org/zap"
 	"tailscale.com/client/tailscale/apitype"
 	"tailscale.com/k8s-operator/sessionrecording/fakes"
-	"tailscale.com/sessionrecording"
+	"tailscale.com/net/netx"
 	"tailscale.com/tailcfg"
 	"tailscale.com/tsnet"
 	"tailscale.com/tstest"
@@ -80,7 +80,7 @@ func Test_Hijacker(t *testing.T) {
 			h := &Hijacker{
 				connectToRecorder: func(context.Context,
 					[]netip.AddrPort,
-					sessionrecording.DialFunc,
+					netx.DialFunc,
 				) (wc io.WriteCloser, rec []*tailcfg.SSHRecordingAttempt, _ <-chan error, err error) {
 					if tt.failRecorderConnect {
 						err = errors.New("test")

logpolicy/logpolicy.go

@@ -42,6 +42,7 @@ import (
 	"tailscale.com/net/netknob"
 	"tailscale.com/net/netmon"
 	"tailscale.com/net/netns"
+	"tailscale.com/net/netx"
 	"tailscale.com/net/tlsdial"
 	"tailscale.com/net/tshttpproxy"
 	"tailscale.com/paths"
@@ -769,7 +770,7 @@ func (p *Policy) Shutdown(ctx context.Context) error {
 //
 // The netMon parameter is optional. It should be specified in environments where
 // Tailscaled is manipulating the routing table.
-func MakeDialFunc(netMon *netmon.Monitor, logf logger.Logf) func(ctx context.Context, netw, addr string) (net.Conn, error) {
+func MakeDialFunc(netMon *netmon.Monitor, logf logger.Logf) netx.DialFunc {
 	if netMon == nil {
 		netMon = netmon.NewStatic()
 	}

net/dns/resolver/forwarder.go

@@ -31,6 +31,7 @@ import (
 	"tailscale.com/net/dnscache"
 	"tailscale.com/net/neterror"
 	"tailscale.com/net/netmon"
+	"tailscale.com/net/netx"
 	"tailscale.com/net/sockstats"
 	"tailscale.com/net/tsdial"
 	"tailscale.com/types/dnstype"
@@ -739,7 +740,7 @@ func (f *forwarder) sendUDP(ctx context.Context, fq *forwardQuery, rr resolverAn
 	return out, nil
 }
 
-func (f *forwarder) getDialerType() dnscache.DialContextFunc {
+func (f *forwarder) getDialerType() netx.DialFunc {
 	if f.controlKnobs != nil && f.controlKnobs.UserDialUseRoutes.Load() {
 		// It is safe to use UserDial as it dials external servers without going through Tailscale
 		// and closes connections on interface change in the same way as SystemDial does,

net/dnscache/dnscache.go

@@ -19,6 +19,7 @@ import (
 	"time"
 
 	"tailscale.com/envknob"
+	"tailscale.com/net/netx"
 	"tailscale.com/types/logger"
 	"tailscale.com/util/cloudenv"
 	"tailscale.com/util/singleflight"
@@ -355,10 +356,8 @@ func (r *Resolver) addIPCache(host string, ip, ip6 netip.Addr, allIPs []netip.Ad
 	}
 }
 
-type DialContextFunc func(ctx context.Context, network, address string) (net.Conn, error)
-
 // Dialer returns a wrapped DialContext func that uses the provided dnsCache.
-func Dialer(fwd DialContextFunc, dnsCache *Resolver) DialContextFunc {
+func Dialer(fwd netx.DialFunc, dnsCache *Resolver) netx.DialFunc {
 	d := &dialer{
 		fwd:         fwd,
 		dnsCache:    dnsCache,
@@ -369,7 +368,7 @@ func Dialer(fwd DialContextFunc, dnsCache *Resolver) DialContextFunc {
 
 // dialer is the config and accumulated state for a dial func returned by Dialer.
 type dialer struct {
-	fwd      DialContextFunc
+	fwd      netx.DialFunc
 	dnsCache *Resolver
 
 	mu          sync.Mutex
@@ -653,7 +652,7 @@ func v6addrs(aa []netip.Addr) (ret []netip.Addr) {
 // TLSDialer is like Dialer but returns a func suitable for using with net/http.Transport.DialTLSContext.
 // It returns a *tls.Conn type on success.
 // On TLS cert validation failure, it can invoke a backup DNS resolution strategy.
-func TLSDialer(fwd DialContextFunc, dnsCache *Resolver, tlsConfigBase *tls.Config) DialContextFunc {
+func TLSDialer(fwd netx.DialFunc, dnsCache *Resolver, tlsConfigBase *tls.Config) netx.DialFunc {
 	tcpDialer := Dialer(fwd, dnsCache)
 	return func(ctx context.Context, network, address string) (net.Conn, error) {
 		host, _, err := net.SplitHostPort(address)

net/memnet/memnet.go

@@ -6,3 +6,82 @@
 // in tests and other situations where you don't want to use the
 // network.
 package memnet
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/netip"
+	"sync"
+
+	"tailscale.com/net/netx"
+)
+
+var _ netx.Network = (*Network)(nil)
+
+// Network implements [Network] using an in-memory network, usually
+// used for testing.
+//
+// As of 2025-04-08, it only supports TCP.
+//
+// Its zero value is a valid [netx.Network] implementation.
+type Network struct {
+	mu  sync.Mutex
+	lns map[string]*Listener // address -> listener
+}
+
+func (m *Network) Listen(network, address string) (net.Listener, error) {
+	if network != "tcp" && network != "tcp4" && network != "tcp6" {
+		return nil, fmt.Errorf("memNetwork: Listen called with unsupported network %q", network)
+	}
+	ap, err := netip.ParseAddrPort(address)
+	if err != nil {
+		return nil, fmt.Errorf("memNetwork: Listen called with invalid address %q: %w", address, err)
+	}
+
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if m.lns == nil {
+		m.lns = make(map[string]*Listener)
+	}
+	port := ap.Port()
+	for {
+		if port == 0 {
+			port = 33000
+		}
+		key := net.JoinHostPort(ap.Addr().String(), fmt.Sprint(port))
+		_, ok := m.lns[key]
+		if ok {
+			if ap.Port() != 0 {
+				return nil, fmt.Errorf("memNetwork: Listen called with duplicate address %q", address)
+			}
+			port++
+			continue
+		}
+		ln := Listen(key)
+		m.lns[key] = ln
+		return ln, nil
+	}
+}
+
+func (m *Network) NewLocalTCPListener() net.Listener {
+	ln, err := m.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		panic(fmt.Sprintf("memNetwork: failed to create local TCP listener: %v", err))
+	}
+	return ln
+}
+
+func (m *Network) Dial(ctx context.Context, network, address string) (net.Conn, error) {
+	if network != "tcp" && network != "tcp4" && network != "tcp6" {
+		return nil, fmt.Errorf("memNetwork: Dial called with unsupported network %q", network)
+	}
+	m.mu.Lock()
+	ln, ok := m.lns[address]
+	m.mu.Unlock()
+	if !ok {
+		return nil, fmt.Errorf("memNetwork: Dial called on unknown address %q", address)
+	}
+	return ln.Dial(ctx, network, address)
+}

net/netx/netx.go

@@ -1,23 +1,25 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
-// Package netx contains the Network type to abstract over either a real
+// Package netx contains types to describe and abstract over how dialing and
-// network or a virtual network for testing.
+// listening are performed.
 package netx
 
 import (
 	"context"
 	"fmt"
 	"net"
-	"net/netip"
-	"sync"
-
-	"tailscale.com/net/memnet"
 )
 
+// DialFunc is a function that dials a network address.
+//
+// It's the type implemented by net.Dialer.DialContext or required
+// by net/http.Transport.DialContext, etc.
+type DialFunc func(ctx context.Context, network, address string) (net.Conn, error)
+
 // Network describes a network that can listen and dial. The two common
 // implementations are [RealNetwork], using the net package to use the real
-// network, or [MemNetwork], using an in-memory network (typically for testing)
+// network, or [memnet.Network], using an in-memory network (typically for testing)
 type Network interface {
 	NewLocalTCPListener() net.Listener
 	Listen(network, address string) (net.Listener, error)
@@ -44,77 +46,8 @@ func (realNetwork) NewLocalTCPListener() net.Listener {
 	ln, err := net.Listen("tcp", "127.0.0.1:0")
 	if err != nil {
 		if ln, err = net.Listen("tcp6", "[::1]:0"); err != nil {
-			panic(fmt.Sprintf("httptest: failed to listen on a port: %v", err))
+			panic(fmt.Sprintf("failed to listen on either IPv4 or IPv6 localhost port: %v", err))
 		}
 	}
 	return ln
 }
-
-// MemNetwork returns a Network implementation that uses an in-memory
-// network for testing. It is only suitable for tests that do not
-// require real network access.
-//
-// As of 2025-04-08, it only supports TCP.
-func MemNetwork() Network { return &memNetwork{} }
-
-// memNetwork implements [Network] using an in-memory network.
-type memNetwork struct {
-	mu  sync.Mutex
-	lns map[string]*memnet.Listener // address -> listener
-}
-
-func (m *memNetwork) Listen(network, address string) (net.Listener, error) {
-	if network != "tcp" && network != "tcp4" && network != "tcp6" {
-		return nil, fmt.Errorf("memNetwork: Listen called with unsupported network %q", network)
-	}
-	ap, err := netip.ParseAddrPort(address)
-	if err != nil {
-		return nil, fmt.Errorf("memNetwork: Listen called with invalid address %q: %w", address, err)
-	}
-
-	m.mu.Lock()
-	defer m.mu.Unlock()
-
-	if m.lns == nil {
-		m.lns = make(map[string]*memnet.Listener)
-	}
-	port := ap.Port()
-	for {
-		if port == 0 {
-			port = 33000
-		}
-		key := net.JoinHostPort(ap.Addr().String(), fmt.Sprint(port))
-		_, ok := m.lns[key]
-		if ok {
-			if ap.Port() != 0 {
-				return nil, fmt.Errorf("memNetwork: Listen called with duplicate address %q", address)
-			}
-			port++
-			continue
-		}
-		ln := memnet.Listen(key)
-		m.lns[key] = ln
-		return ln, nil
-	}
-}
-
-func (m *memNetwork) NewLocalTCPListener() net.Listener {
-	ln, err := m.Listen("tcp", "127.0.0.1:0")
-	if err != nil {
-		panic(fmt.Sprintf("memNetwork: failed to create local TCP listener: %v", err))
-	}
-	return ln
-}
-
-func (m *memNetwork) Dial(ctx context.Context, network, address string) (net.Conn, error) {
-	if network != "tcp" && network != "tcp4" && network != "tcp6" {
-		return nil, fmt.Errorf("memNetwork: Dial called with unsupported network %q", network)
-	}
-	m.mu.Lock()
-	ln, ok := m.lns[address]
-	m.mu.Unlock()
-	if !ok {
-		return nil, fmt.Errorf("memNetwork: Dial called on unknown address %q", address)
-	}
-	return ln.Dial(ctx, network, address)
-}

net/tsdial/tsdial.go

@@ -23,6 +23,7 @@ import (
 	"tailscale.com/net/netknob"
 	"tailscale.com/net/netmon"
 	"tailscale.com/net/netns"
+	"tailscale.com/net/netx"
 	"tailscale.com/net/tsaddr"
 	"tailscale.com/types/logger"
 	"tailscale.com/types/netmap"
@@ -71,7 +72,7 @@ type Dialer struct {
 
 	netnsDialerOnce sync.Once
 	netnsDialer     netns.Dialer
-	sysDialForTest  func(_ context.Context, network, addr string) (net.Conn, error) // or nil
+	sysDialForTest  netx.DialFunc // or nil
 
 	routes atomic.Pointer[bart.Table[bool]] // or nil if UserDial should not use routes. `true` indicates routes that point into the Tailscale interface
 
@@ -364,7 +365,7 @@ func (d *Dialer) logf(format string, args ...any) {
 
 // SetSystemDialerForTest sets an alternate function to use for SystemDial
 // instead of netns.Dialer. This is intended for use with nettest.MemoryNetwork.
-func (d *Dialer) SetSystemDialerForTest(fn func(ctx context.Context, network, addr string) (net.Conn, error)) {
+func (d *Dialer) SetSystemDialerForTest(fn netx.DialFunc) {
 	testenv.AssertInTest()
 	d.sysDialForTest = fn
 }

sessionrecording/connect.go

@@ -20,6 +20,7 @@ import (
 	"time"
 
 	"golang.org/x/net/http2"
+	"tailscale.com/net/netx"
 	"tailscale.com/tailcfg"
 	"tailscale.com/util/httpm"
 	"tailscale.com/util/multierr"
@@ -40,9 +41,6 @@ const (
 // in tests.
 var uploadAckWindow = 30 * time.Second
 
-// DialFunc is a function for dialing the recorder.
-type DialFunc func(ctx context.Context, network, host string) (net.Conn, error)
-
 // ConnectToRecorder connects to the recorder at any of the provided addresses.
 // It returns the first successful response, or a multierr if all attempts fail.
 //
@@ -55,7 +53,7 @@ type DialFunc func(ctx context.Context, network, host string) (net.Conn, error)
 // attempts are in order the recorder(s) was attempted. If successful a
 // successful connection is made, the last attempt in the slice is the
 // attempt for connected recorder.
-func ConnectToRecorder(ctx context.Context, recs []netip.AddrPort, dial DialFunc) (io.WriteCloser, []*tailcfg.SSHRecordingAttempt, <-chan error, error) {
+func ConnectToRecorder(ctx context.Context, recs []netip.AddrPort, dial netx.DialFunc) (io.WriteCloser, []*tailcfg.SSHRecordingAttempt, <-chan error, error) {
 	if len(recs) == 0 {
 		return nil, nil, nil, errors.New("no recorders configured")
 	}
@@ -293,7 +291,7 @@ func (u *readCounter) Read(buf []byte) (int, error) {
 
 // clientHTTP1 returns a claassic http.Client with a per-dial context. It uses
 // dialCtx and adds a 5s timeout to it.
-func clientHTTP1(dialCtx context.Context, dial DialFunc) *http.Client {
+func clientHTTP1(dialCtx context.Context, dial netx.DialFunc) *http.Client {
 	tr := http.DefaultTransport.(*http.Transport).Clone()
 	tr.DialContext = func(ctx context.Context, network, addr string) (net.Conn, error) {
 		perAttemptCtx, cancel := context.WithTimeout(ctx, perDialAttemptTimeout)
@@ -313,7 +311,7 @@ func clientHTTP1(dialCtx context.Context, dial DialFunc) *http.Client {
 // clientHTTP2 is like clientHTTP1 but returns an http.Client suitable for h2c
 // requests (HTTP/2 over plaintext). Unfortunately the same client does not
 // work for HTTP/1 so we need to split these up.
-func clientHTTP2(dialCtx context.Context, dial DialFunc) *http.Client {
+func clientHTTP2(dialCtx context.Context, dial netx.DialFunc) *http.Client {
 	return &http.Client{
 		Transport: &http2.Transport{
 			// Allow "http://" scheme in URLs.

tstest/natlab/vnet/vnet.go

@@ -54,6 +54,7 @@ import (
 	"tailscale.com/derp"
 	"tailscale.com/derp/derphttp"
 	"tailscale.com/net/netutil"
+	"tailscale.com/net/netx"
 	"tailscale.com/net/stun"
 	"tailscale.com/syncs"
 	"tailscale.com/tailcfg"
@@ -649,7 +650,7 @@ type Server struct {
 	mu              sync.Mutex
 	agentConnWaiter map[*node]chan<- struct{} // signaled after added to set
 	agentConns      set.Set[*agentConn]       //  not keyed by node; should be small/cheap enough to scan all
-	agentDialer     map[*node]DialFunc
+	agentDialer     map[*node]netx.DialFunc
 }
 
 func (s *Server) logf(format string, args ...any) {
@@ -664,8 +665,6 @@ func (s *Server) SetLoggerForTest(logf func(format string, args ...any)) {
 	s.optLogf = logf
 }
 
-type DialFunc func(ctx context.Context, network, address string) (net.Conn, error)
-
 var derpMap = &tailcfg.DERPMap{
 	Regions: map[int]*tailcfg.DERPRegion{
 		1: {
@@ -2130,7 +2129,7 @@ type NodeAgentClient struct {
 	HTTPClient *http.Client
 }
 
-func (s *Server) NodeAgentDialer(n *Node) DialFunc {
+func (s *Server) NodeAgentDialer(n *Node) netx.DialFunc {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 

tstest/nettest/nettest.go

@@ -14,6 +14,7 @@ import (
 	"sync"
 	"testing"
 
+	"tailscale.com/net/memnet"
 	"tailscale.com/net/netmon"
 	"tailscale.com/net/netx"
 	"tailscale.com/util/testenv"
@@ -42,7 +43,7 @@ func PreferMemNetwork() bool {
 func GetNetwork(tb testing.TB) netx.Network {
 	var n netx.Network
 	if PreferMemNetwork() {
-		n = netx.MemNetwork()
+		n = &memnet.Network{}
 	} else {
 		n = netx.RealNetwork()
 	}

wgengine/netstack/netstack.go

@@ -38,6 +38,7 @@ import (
 	"tailscale.com/net/dns"
 	"tailscale.com/net/ipset"
 	"tailscale.com/net/netaddr"
+	"tailscale.com/net/netx"
 	"tailscale.com/net/packet"
 	"tailscale.com/net/tsaddr"
 	"tailscale.com/net/tsdial"
@@ -208,7 +209,7 @@ type Impl struct {
 	// TCP connection to another host (e.g. in subnet router mode).
 	//
 	// This is currently only used in tests.
-	forwardDialFunc func(context.Context, string, string) (net.Conn, error)
+	forwardDialFunc netx.DialFunc
 
 	// forwardInFlightPerClientDropped is a metric that tracks how many
 	// in-flight TCP forward requests were dropped due to the per-client
@@ -1457,7 +1458,7 @@ func (ns *Impl) forwardTCP(getClient func(...tcpip.SettableSocketOption) *gonet.
 	}()
 
 	// Attempt to dial the outbound connection before we accept the inbound one.
-	var dialFunc func(context.Context, string, string) (net.Conn, error)
+	var dialFunc netx.DialFunc
 	if ns.forwardDialFunc != nil {
 		dialFunc = ns.forwardDialFunc
 	} else {

wgengine/netstack/netstack_test.go

@@ -22,6 +22,7 @@ import (
 	"tailscale.com/ipn/ipnlocal"
 	"tailscale.com/ipn/store/mem"
 	"tailscale.com/metrics"
+	"tailscale.com/net/netx"
 	"tailscale.com/net/packet"
 	"tailscale.com/net/tsaddr"
 	"tailscale.com/net/tsdial"
@@ -512,7 +513,7 @@ func tcp4syn(tb testing.TB, src, dst netip.Addr, sport, dport uint16) []byte {
 
 // makeHangDialer returns a dialer that notifies the returned channel when a
 // connection is dialed and then hangs until the test finishes.
-func makeHangDialer(tb testing.TB) (func(context.Context, string, string) (net.Conn, error), chan struct{}) {
+func makeHangDialer(tb testing.TB) (netx.DialFunc, chan struct{}) {
 	done := make(chan struct{})
 	tb.Cleanup(func() {
 		close(done)