ssh/tailssh: handle session recording when running in userspace mode

Previously it would dial out using the http.DefaultClient, however that doesn't work
when tailscaled is running in userspace mode (e.g. when testing).

Updates tailscale/corp#9967

Signed-off-by: Maisem Ali <maisem@tailscale.com>

ssh/tailssh/tailssh.go

@@ -35,6 +35,7 @@ import (
 	"tailscale.com/ipn/ipnlocal"
 	"tailscale.com/logtail/backoff"
 	"tailscale.com/net/tsaddr"
+	"tailscale.com/net/tsdial"
 	"tailscale.com/tailcfg"
 	"tailscale.com/tempfork/gliderlabs/ssh"
 	"tailscale.com/types/logger"
@@ -62,6 +63,7 @@ type ipnLocalBackend interface {
 	NetMap() *netmap.NetworkMap
 	WhoIs(ipp netip.AddrPort) (n *tailcfg.Node, u tailcfg.UserProfile, ok bool)
 	DoNoiseRequest(req *http.Request) (*http.Response, error)
+	Dialer() *tsdial.Dialer
 }
 
 type server struct {
@@ -76,11 +78,33 @@ type server struct {
 
 	// mu protects the following
 	mu                   sync.Mutex
+	httpc                *http.Client                // for calling out to peers.
 	activeConns          map[*conn]bool              // set; value is always true
 	fetchPublicKeysCache map[string]pubKeyCacheEntry // by https URL
 	shutdownCalled       bool
 }
 
+// sessionRecordingClient returns an http.Client that uses srv.lb.Dialer() to
+// dial connections. This is used to make requests to the session recording
+// server to upload session recordings.
+func (srv *server) sessionRecordingClient() *http.Client {
+	srv.mu.Lock()
+	defer srv.mu.Unlock()
+	if srv.httpc != nil {
+		return srv.httpc
+	}
+	tr := http.DefaultTransport.(*http.Transport).Clone()
+	tr.DialContext = func(ctx context.Context, network, addr string) (net.Conn, error) {
+		ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
+		defer cancel()
+		return srv.lb.Dialer().UserDial(ctx, network, addr)
+	}
+	srv.httpc = &http.Client{
+		Transport: tr,
+	}
+	return srv.httpc
+}
+
 func (srv *server) now() time.Time {
 	if srv != nil && srv.timeNow != nil {
 		return srv.timeNow()
@@ -1404,9 +1428,8 @@ func (ss *sshSession) startNewRecording() (_ *recording, err error) {
 	go func() {
 		defer pw.Close()
 		ss.logf("starting asciinema recording to %s", recorder)
-
-		// We just use the default client here, which has a 30s dial timeout.
-		resp, err := http.DefaultClient.Do(req)
+		hc := ss.conn.srv.sessionRecordingClient()
+		resp, err := hc.Do(req)
 		if err != nil {
 			ss.cancelCtx(err)
 			ss.logf("recording: error sending recording to %s: %v", recorder, err)

ssh/tailssh/tailssh_test.go

@@ -237,6 +237,10 @@ var (
 	testSignerOnce sync.Once
 )
 
+func (ts *localState) Dialer() *tsdial.Dialer {
+	return nil
+}
+
 func (ts *localState) GetSSH_HostKeys() ([]gossh.Signer, error) {
 	testSignerOnce.Do(func() {
 		_, priv, err := ed25519.GenerateKey(rand.Reader)