tailscale/cmd/tsconnect/wasm/wasm_js.go

// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause

// The wasm package builds a WebAssembly module that provides a subset of
// Tailscale APIs to JavaScript.
//
// When run in the browser, a newIPN(config) function is added to the global JS
// namespace. When called it returns an ipn object with the methods
// run(callbacks), login(), logout(), and ssh(...).
package main

import (
	"bytes"
	"context"
	"crypto/tls"
	"crypto/x509"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"math/rand/v2"
	"net"
	"net/http"
	"net/http/httptest"
	"net/netip"
	"strconv"
	"strings"
	"sync"
	"syscall/js"
	"time"

	"golang.org/x/crypto/ssh"
	"golang.org/x/net/dns/dnsmessage"
	"gvisor.dev/gvisor/pkg/tcpip"
	"gvisor.dev/gvisor/pkg/tcpip/adapters/gonet"
	"gvisor.dev/gvisor/pkg/tcpip/network/ipv4"
	"gvisor.dev/gvisor/pkg/tcpip/network/ipv6"
	"gvisor.dev/gvisor/pkg/tcpip/transport/icmp"
	"gvisor.dev/gvisor/pkg/waiter"
	"tailscale.com/control/controlclient"
	"tailscale.com/ipn"
	"tailscale.com/ipn/ipnauth"
	"tailscale.com/ipn/ipnlocal"
	"tailscale.com/ipn/ipnserver"
	"tailscale.com/ipn/localapi"
	"tailscale.com/ipn/store/mem"
	"tailscale.com/logpolicy"
	"tailscale.com/logtail"
	"tailscale.com/net/bakedroots"
	"tailscale.com/net/netns"
	"tailscale.com/net/tsaddr"
	"tailscale.com/net/tsdial"
	"tailscale.com/safesocket"
	"tailscale.com/tailcfg"
	"tailscale.com/tsd"
	"tailscale.com/types/logid"
	"tailscale.com/types/views"
	"tailscale.com/wgengine"
	"tailscale.com/wgengine/netstack"
	"tailscale.com/words"
)

// ControlURL defines the URL to be used for connection to Control.
var ControlURL = ipn.DefaultControlURL

func main() {
	js.Global().Set("newIPN", js.FuncOf(func(this js.Value, args []js.Value) any {
		if len(args) != 1 {
			log.Fatal("Usage: newIPN(config)")
			return nil
		}
		return newIPN(args[0])
	}))
	// Keep Go runtime alive, otherwise it will be shut down before newIPN gets
	// called.
	<-make(chan bool)
}

func newIPN(jsConfig js.Value) map[string]any {
	netns.SetEnabled(false)

	var store ipn.StateStore
	if jsStateStorage := jsConfig.Get("stateStorage"); !jsStateStorage.IsUndefined() {
		store = &jsStateStore{jsStateStorage}
	} else {
		store = new(mem.Store)
	}

	controlURL := ControlURL
	if jsControlURL := jsConfig.Get("controlURL"); jsControlURL.Type() == js.TypeString {
		controlURL = jsControlURL.String()
	}

	var authKey string
	if jsAuthKey := jsConfig.Get("authKey"); jsAuthKey.Type() == js.TypeString {
		authKey = jsAuthKey.String()
	}

	var hostname string
	if jsHostname := jsConfig.Get("hostname"); jsHostname.Type() == js.TypeString {
		hostname = jsHostname.String()
	} else {
		hostname = generateHostname()
	}

	lpc := getOrCreateLogPolicyConfig(store)
	c := logtail.Config{
		Collection: lpc.Collection,
		PrivateID:  lpc.PrivateID,

		// Compressed requests set HTTP headers that are not supported by the
		// no-cors fetching mode:
		CompressLogs: false,

		HTTPC: &http.Client{Transport: &noCORSTransport{http.DefaultTransport}},
	}
	logtail := logtail.NewLogger(c, log.Printf)
	logf := logtail.Logf

	sys := tsd.NewSystem()
	sys.Set(store)
	dialer := &tsdial.Dialer{Logf: logf}
	dialer.SetBus(sys.Bus.Get())
	eng, err := wgengine.NewUserspaceEngine(logf, wgengine.Config{
		Dialer:        dialer,
		SetSubsystem:  sys.Set,
		ControlKnobs:  sys.ControlKnobs(),
		HealthTracker: sys.HealthTracker.Get(),
		ExtraRootCAs:  sys.ExtraRootCAs,
		Metrics:       sys.UserMetricsRegistry(),
		EventBus:      sys.Bus.Get(),
	})
	if err != nil {
		log.Fatal(err)
	}
	sys.Set(eng)

	ns, err := netstack.Create(logf, sys.Tun.Get(), eng, sys.MagicSock.Get(), dialer, sys.DNSManager.Get(), sys.ProxyMapper())
	if err != nil {
		log.Fatalf("netstack.Create: %v", err)
	}
	sys.Set(ns)
	ns.ProcessLocalIPs = true
	ns.ProcessSubnets = true

	dialer.UseNetstackForIP = func(ip netip.Addr) bool {
		return true
	}
	dialer.NetstackDialTCP = func(ctx context.Context, dst netip.AddrPort) (net.Conn, error) {
		return ns.DialContextTCP(ctx, dst)
	}
	dialer.NetstackDialUDP = func(ctx context.Context, dst netip.AddrPort) (net.Conn, error) {
		return ns.DialContextUDP(ctx, dst)
	}
	sys.NetstackRouter.Set(true)
	sys.Tun.Get().Start()

	logid := lpc.PublicID
	srv := ipnserver.New(logf, logid, sys.Bus.Get(), sys.NetMon.Get())
	lb, err := ipnlocal.NewLocalBackend(logf, logid, sys, controlclient.LoginEphemeral)
	if err != nil {
		log.Fatalf("ipnlocal.NewLocalBackend: %v", err)
	}
	if err := ns.Start(lb); err != nil {
		log.Fatalf("failed to start netstack: %v", err)
	}
	wireTaildropFileOps(lb, jsConfig.Get("fileOps"))
	srv.SetLocalBackend(lb)

	jsIPN := &jsIPN{
		dialer:      dialer,
		srv:         srv,
		lb:          lb,
		ns:          ns,
		controlURL:  controlURL,
		authKey:     authKey,
		hostname:    hostname,
		logID:       logid,
		funnelPorts: make(map[uint16]*funnelListenerEntry),
	}
	lb.SetTCPHandlerForFunnelFlow(jsIPN.handleFunnelTCP)

	return map[string]any{
		"run": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 1 {
				log.Fatal(`Usage: run({
					notifyState(state: int): void,
					notifyNetMap(netMap: object): void,
					notifyBrowseToURL(url: string): void,
					notifyPanicRecover(err: string): void,
				})`)
				return nil
			}
			jsIPN.run(args[0])
			return nil
		}),
		"login": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 0 {
				log.Printf("Usage: login()")
				return nil
			}
			jsIPN.login()
			return nil
		}),
		"logout": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 0 {
				log.Printf("Usage: logout()")
				return nil
			}
			jsIPN.logout()
			return nil
		}),
		"ssh": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 3 {
				log.Printf("Usage: ssh(hostname, userName, termConfig)")
				return nil
			}
			return jsIPN.ssh(
				args[0].String(),
				args[1].String(),
				args[2])
		}),
		"fetch": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 1 {
				log.Printf("Usage: fetch(url)")
				return nil
			}

			url := args[0].String()
			return jsIPN.fetch(url)
		}),
		"dial": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 2 {
				log.Printf("Usage: dial(network, addr)")
				return nil
			}
			return jsIPN.dial(args[0].String(), args[1].String())
		}),
		"listen": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 2 {
				log.Printf("Usage: listen(network, addr)")
				return nil
			}
			return jsIPN.listen(args[0].String(), args[1].String())
		}),
		"listenICMP": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 1 {
				log.Printf("Usage: listenICMP(network)")
				return nil
			}
			return jsIPN.listenICMP(args[0].String())
		}),
		"dialTLS": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) < 1 || len(args) > 2 {
				log.Printf("Usage: dialTLS(addr, opts?)")
				return nil
			}
			var opts js.Value
			if len(args) == 2 {
				opts = args[1]
			}
			return jsIPN.dialTLS(args[0].String(), opts)
		}),
		"setExitNode": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 1 {
				log.Printf("Usage: setExitNode(stableNodeID)")
				return nil
			}
			return jsIPN.setExitNode(args[0].String())
		}),
		"setExitNodeEnabled": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 1 {
				log.Printf("Usage: setExitNodeEnabled(enabled)")
				return nil
			}
			return jsIPN.setExitNodeEnabled(args[0].Bool())
		}),
		"listFileTargets": js.FuncOf(func(this js.Value, args []js.Value) any {
			return jsIPN.listFileTargets()
		}),
		"sendFile": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 3 {
				log.Printf("Usage: sendFile(stableNodeID, filename, data)")
				return nil
			}
			return jsIPN.sendFile(args[0].String(), args[1].String(), args[2])
		}),
		"waitingFiles": js.FuncOf(func(this js.Value, args []js.Value) any {
			return jsIPN.waitingFiles()
		}),
		"openWaitingFile": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 1 {
				log.Printf("Usage: openWaitingFile(name)")
				return nil
			}
			return jsIPN.openWaitingFile(args[0].String())
		}),
		"deleteWaitingFile": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 1 {
				log.Printf("Usage: deleteWaitingFile(name)")
				return nil
			}
			return jsIPN.deleteWaitingFile(args[0].String())
		}),
		"getCert": js.FuncOf(func(this js.Value, args []js.Value) any {
			return jsIPN.getCert()
		}),
		"listenTLS": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 3 {
				log.Printf("Usage: listenTLS(addr, certPEM, keyPEM)")
				return nil
			}
			return jsIPN.listenTLS(args[0].String(), args[1].String(), args[2].String())
		}),
		"setFunnel": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) != 3 {
				log.Printf("Usage: setFunnel(hostname, port, enabled)")
				return nil
			}
			return jsIPN.setFunnel(args[0].String(), uint16(args[1].Int()), args[2].Bool())
		}),
		"whoIs": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) < 1 {
				log.Printf("Usage: whoIs(addrPort[, proto])")
				return nil
			}
			proto := ""
			if len(args) >= 2 {
				proto = args[1].String()
			}
			return jsIPN.whoIs(args[0].String(), proto)
		}),
		"queryDNS": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) < 1 {
				log.Printf("Usage: queryDNS(name[, type])")
				return nil
			}
			qtype := 1 // TypeA
			if len(args) >= 2 {
				qtype = args[1].Int()
			}
			return jsIPN.queryDNS(args[0].String(), qtype)
		}),
		"ping": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) < 1 {
				log.Printf("Usage: ping(ip[, type[, size]])")
				return nil
			}
			pingType := "TSMP"
			if len(args) >= 2 {
				pingType = args[1].String()
			}
			size := 0
			if len(args) >= 3 {
				size = args[2].Int()
			}
			return jsIPN.ping(args[0].String(), pingType, size)
		}),
		"suggestExitNode": js.FuncOf(func(this js.Value, args []js.Value) any {
			return jsIPN.suggestExitNode()
		}),
		"localAPI": js.FuncOf(func(this js.Value, args []js.Value) any {
			if len(args) < 2 {
				log.Printf("Usage: localAPI(method, path[, body])")
				return nil
			}
			body := ""
			if len(args) >= 3 {
				body = args[2].String()
			}
			return jsIPN.localAPI(args[0].String(), args[1].String(), body)
		}),
	}
}

type jsIPN struct {
	dialer     *tsdial.Dialer
	srv        *ipnserver.Server
	lb         *ipnlocal.LocalBackend
	ns         *netstack.Impl
	controlURL string
	authKey    string
	hostname   string
	logID      logid.PublicID

	funnelMu    sync.Mutex
	funnelPorts map[uint16]*funnelListenerEntry
}

// funnelListenerEntry is the per-port state for routing Funnel connections to a listenTLS listener.
type funnelListenerEntry struct {
	ch     chan net.Conn
	tlsCfg *tls.Config
}

var jsIPNState = map[ipn.State]string{
	ipn.NoState:          "NoState",
	ipn.InUseOtherUser:   "InUseOtherUser",
	ipn.NeedsLogin:       "NeedsLogin",
	ipn.NeedsMachineAuth: "NeedsMachineAuth",
	ipn.Stopped:          "Stopped",
	ipn.Starting:         "Starting",
	ipn.Running:          "Running",
}

var jsMachineStatus = map[tailcfg.MachineStatus]string{
	tailcfg.MachineUnknown:      "MachineUnknown",
	tailcfg.MachineUnauthorized: "MachineUnauthorized",
	tailcfg.MachineAuthorized:   "MachineAuthorized",
	tailcfg.MachineInvalid:      "MachineInvalid",
}

func (i *jsIPN) run(jsCallbacks js.Value) {
	notifyState := func(state ipn.State) {
		jsCallbacks.Call("notifyState", jsIPNState[state])
	}
	notifyState(ipn.NoState)

	i.lb.SetNotifyCallback(func(n ipn.Notify) {
		// Panics in the notify callback are likely due to be due to bugs in
		// this bridging module (as opposed to actual bugs in Tailscale) and
		// thus may be recoverable. Let the UI know, and allow the user to
		// choose if they want to reload the page.
		defer func() {
			if r := recover(); r != nil {
				fmt.Println("Panic recovered:", r)
				jsCallbacks.Call("notifyPanicRecover", fmt.Sprint(r))
			}
		}()
		log.Printf("NOTIFY: %+v", n)
		if n.State != nil {
			notifyState(*n.State)
		}
		if nm := n.NetMap; nm != nil {
			// Determine which address families we have, for peer peerAPI URL selection.
			var selfHave4, selfHave6 bool
			for _, a := range nm.GetAddresses().All() {
				if !a.IsSingleIP() {
					continue
				}
				if a.Addr().Is4() {
					selfHave4 = true
				} else if a.Addr().Is6() {
					selfHave6 = true
				}
			}

			// Self peerAPI URL: own port as reported by LocalBackend.
			selfPeerAPIURL := ""
			for _, a := range nm.GetAddresses().All() {
				if !a.IsSingleIP() {
					continue
				}
				if port, ok := i.lb.GetPeerAPIPort(a.Addr()); ok && port != 0 {
					selfPeerAPIURL = fmt.Sprintf("http://%v", netip.AddrPortFrom(a.Addr(), port))
					break
				}
			}

			jsNetMap := jsNetMap{
				Self: jsNetMapSelfNode{
					jsNetMapNode: jsNetMapNode{
						Name:       nm.SelfName(),
						Addresses:  mapSliceView(nm.GetAddresses(), func(a netip.Prefix) string { return a.Addr().String() }),
						NodeKey:    nm.NodeKey.String(),
						MachineKey: nm.MachineKey.String(),
						PeerAPIURL: selfPeerAPIURL,
					},
					MachineStatus: jsMachineStatus[nm.GetMachineStatus()],
				},
				Peers: mapSlice(nm.Peers, func(p tailcfg.NodeView) jsNetMapPeerNode {
					name := p.Name()
					if name == "" {
						// In practice this should only happen for Hello.
						name = p.Hostinfo().Hostname()
					}
					addrs := make([]string, p.Addresses().Len())
					for idx, ap := range p.Addresses().All() {
						addrs[idx] = ap.Addr().String()
					}

					// Peer peerAPI URL from the peer's advertised Services.
					peerURL := ""
					var pp4, pp6 uint16
					for _, s := range p.Hostinfo().Services().All() {
						switch s.Proto {
						case tailcfg.PeerAPI4:
							pp4 = s.Port
						case tailcfg.PeerAPI6:
							pp6 = s.Port
						}
					}
					if selfHave4 && pp4 != 0 {
						for _, a := range p.Addresses().All() {
							if a.IsSingleIP() && a.Addr().Is4() {
								peerURL = fmt.Sprintf("http://%v", netip.AddrPortFrom(a.Addr(), pp4))
								break
							}
						}
					}
					if peerURL == "" && selfHave6 && pp6 != 0 {
						for _, a := range p.Addresses().All() {
							if a.IsSingleIP() && a.Addr().Is6() {
								peerURL = fmt.Sprintf("http://%v", netip.AddrPortFrom(a.Addr(), pp6))
								break
							}
						}
					}

					return jsNetMapPeerNode{
						jsNetMapNode: jsNetMapNode{
							Name:       name,
							Addresses:  addrs,
							MachineKey: p.Machine().String(),
							NodeKey:    p.Key().String(),
							PeerAPIURL: peerURL,
						},
						Online:              p.Online().Clone(),
						TailscaleSSHEnabled: p.Hostinfo().TailscaleSSHEnabled(),
						ExitNodeOption:      tsaddr.ContainsExitRoutes(p.AllowedIPs()),
						StableNodeID:        string(p.StableID()),
					}
				}),
				LockedOut: nm.TKAEnabled && nm.SelfNode.KeySignature().Len() == 0,
			}
			if jsonNetMap, err := json.Marshal(jsNetMap); err == nil {
				jsCallbacks.Call("notifyNetMap", string(jsonNetMap))
			} else {
				log.Printf("Could not generate JSON netmap: %v", err)
			}
		}
		if n.Prefs != nil && n.Prefs.Valid() {
			jsCallbacks.Call("notifyExitNode", string(n.Prefs.ExitNodeID()))
		}
		if n.BrowseToURL != nil {
			jsCallbacks.Call("notifyBrowseToURL", *n.BrowseToURL)
		}
		if n.FilesWaiting != nil {
			jsCallbacks.Call("notifyFilesWaiting")
		}
		if n.IncomingFiles != nil {
			files := make([]jsIncomingFile, len(n.IncomingFiles))
			for i, f := range n.IncomingFiles {
				files[i] = jsIncomingFile{
					Name:         f.Name,
					Started:      f.Started.UnixMilli(),
					DeclaredSize: f.DeclaredSize,
					Received:     f.Received,
					Done:         f.Done,
				}
			}
			if b, err := json.Marshal(files); err == nil {
				jsCallbacks.Call("notifyIncomingFiles", string(b))
			} else {
				log.Printf("could not marshal IncomingFiles: %v", err)
			}
		}
		if n.OutgoingFiles != nil {
			files := make([]jsOutgoingFile, len(n.OutgoingFiles))
			for i, f := range n.OutgoingFiles {
				files[i] = jsOutgoingFile{
					ID:           f.ID,
					PeerID:       string(f.PeerID),
					Name:         f.Name,
					Started:      f.Started.UnixMilli(),
					DeclaredSize: f.DeclaredSize,
					Sent:         f.Sent,
					Finished:     f.Finished,
					Succeeded:    f.Succeeded,
				}
			}
			if b, err := json.Marshal(files); err == nil {
				jsCallbacks.Call("notifyOutgoingFiles", string(b))
			} else {
				log.Printf("could not marshal OutgoingFiles: %v", err)
			}
		}
	})

	go func() {
		err := i.lb.Start(ipn.Options{
			UpdatePrefs: &ipn.Prefs{
				ControlURL:  i.controlURL,
				RouteAll:    false,
				WantRunning: true,
				Hostname:    i.hostname,
			},
			AuthKey: i.authKey,
		})
		if err != nil {
			log.Printf("Start error: %v", err)
		}
	}()

	go func() {
		ln, err := safesocket.Listen("")
		if err != nil {
			log.Fatalf("safesocket.Listen: %v", err)
		}

		err = i.srv.Run(context.Background(), ln)
		log.Fatalf("ipnserver.Run exited: %v", err)
	}()
}

func (i *jsIPN) login() {
	go i.lb.StartLoginInteractive(context.Background())
}

func (i *jsIPN) logout() {
	if i.lb.State() == ipn.NoState {
		log.Printf("Backend not running")
	}
	go func() {
		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()
		i.lb.Logout(ctx, ipnauth.Self)
	}()
}

func (i *jsIPN) ssh(host, username string, termConfig js.Value) map[string]any {
	jsSSHSession := &jsSSHSession{
		jsIPN:      i,
		host:       host,
		username:   username,
		termConfig: termConfig,
	}

	go jsSSHSession.Run()

	return map[string]any{
		"close": js.FuncOf(func(this js.Value, args []js.Value) any {
			return jsSSHSession.Close() != nil
		}),
		"resize": js.FuncOf(func(this js.Value, args []js.Value) any {
			rows := args[0].Int()
			cols := args[1].Int()
			return jsSSHSession.Resize(rows, cols) != nil
		}),
	}
}

type jsSSHSession struct {
	jsIPN      *jsIPN
	host       string
	username   string
	termConfig js.Value
	session    *ssh.Session

	pendingResizeRows int
	pendingResizeCols int
}

func (s *jsSSHSession) Run() {
	writeFn := s.termConfig.Get("writeFn")
	writeErrorFn := s.termConfig.Get("writeErrorFn")
	setReadFn := s.termConfig.Get("setReadFn")
	rows := s.termConfig.Get("rows").Int()
	cols := s.termConfig.Get("cols").Int()
	timeoutSeconds := 5.0
	if jsTimeoutSeconds := s.termConfig.Get("timeoutSeconds"); jsTimeoutSeconds.Type() == js.TypeNumber {
		timeoutSeconds = jsTimeoutSeconds.Float()
	}
	onConnectionProgress := s.termConfig.Get("onConnectionProgress")
	onConnected := s.termConfig.Get("onConnected")
	onDone := s.termConfig.Get("onDone")
	defer onDone.Invoke()

	writeError := func(label string, err error) {
		writeErrorFn.Invoke(fmt.Sprintf("%s Error: %v\r\n", label, err))
	}
	reportProgress := func(message string) {
		onConnectionProgress.Invoke(message)
	}

	ctx, cancel := context.WithTimeout(context.Background(), time.Duration(timeoutSeconds*float64(time.Second)))
	defer cancel()
	reportProgress(fmt.Sprintf("Connecting to %s…", strings.Split(s.host, ".")[0]))
	c, err := s.jsIPN.dialer.UserDial(ctx, "tcp", net.JoinHostPort(s.host, "22"))
	if err != nil {
		writeError("Dial", err)
		return
	}
	defer c.Close()

	config := &ssh.ClientConfig{
		HostKeyCallback: func(hostname string, remote net.Addr, key ssh.PublicKey) error {
			// Host keys are not used with Tailscale SSH, but we can use this
			// callback to know that the connection has been established.
			reportProgress("SSH connection established…")
			return nil
		},
		User: s.username,
	}

	reportProgress("Starting SSH client…")
	sshConn, _, _, err := ssh.NewClientConn(c, s.host, config)
	if err != nil {
		writeError("SSH Connection", err)
		return
	}
	defer sshConn.Close()

	sshClient := ssh.NewClient(sshConn, nil, nil)
	defer sshClient.Close()

	session, err := sshClient.NewSession()
	if err != nil {
		writeError("SSH Session", err)
		return
	}
	s.session = session
	defer session.Close()

	stdin, err := session.StdinPipe()
	if err != nil {
		writeError("SSH Stdin", err)
		return
	}

	session.Stdout = termWriter{writeFn}
	session.Stderr = termWriter{writeFn}

	setReadFn.Invoke(js.FuncOf(func(this js.Value, args []js.Value) any {
		input := args[0].String()
		_, err := stdin.Write([]byte(input))
		if err != nil {
			writeError("Write Input", err)
		}
		return nil
	}))

	// We might have gotten a resize notification since we started opening the
	// session, pick up the latest size.
	if s.pendingResizeRows != 0 {
		rows = s.pendingResizeRows
	}
	if s.pendingResizeCols != 0 {
		cols = s.pendingResizeCols
	}
	err = session.RequestPty("xterm", rows, cols, ssh.TerminalModes{})
	if err != nil {
		writeError("Pseudo Terminal", err)
		return
	}

	err = session.Shell()
	if err != nil {
		writeError("Shell", err)
		return
	}

	onConnected.Invoke()
	err = session.Wait()
	if err != nil {
		writeError("Wait", err)
		return
	}
}

func (s *jsSSHSession) Close() error {
	if s.session == nil {
		// We never had a chance to open the session, ignore the close request.
		return nil
	}
	return s.session.Close()
}

func (s *jsSSHSession) Resize(rows, cols int) error {
	if s.session == nil {
		s.pendingResizeRows = rows
		s.pendingResizeCols = cols
		return nil
	}
	return s.session.WindowChange(rows, cols)
}

func (i *jsIPN) fetch(url string) js.Value {
	return makePromise(func() (any, error) {
		c := &http.Client{
			Transport: &http.Transport{
				DialContext: i.dialer.UserDial,
			},
		}
		res, err := c.Get(url)
		if err != nil {
			return nil, err
		}

		return map[string]any{
			"status":     res.StatusCode,
			"statusText": res.Status,
			"text": js.FuncOf(func(this js.Value, args []js.Value) any {
				return makePromise(func() (any, error) {
					defer res.Body.Close()
					buf := new(bytes.Buffer)
					if _, err := buf.ReadFrom(res.Body); err != nil {
						return nil, err
					}
					return buf.String(), nil
				})
			}),
			// TODO: populate a more complete JS Response object
		}, nil
	})
}

func (i *jsIPN) setExitNode(stableNodeID string) js.Value {
	return makePromise(func() (any, error) {
		mp := &ipn.MaskedPrefs{
			ExitNodeIDSet: true,
			Prefs:         ipn.Prefs{ExitNodeID: tailcfg.StableNodeID(stableNodeID)},
		}
		_, err := i.lb.EditPrefs(mp)
		return nil, err
	})
}

func (i *jsIPN) setExitNodeEnabled(enabled bool) js.Value {
	return makePromise(func() (any, error) {
		_, err := i.lb.SetUseExitNodeEnabled(ipnauth.Self, enabled)
		return nil, err
	})
}

func (i *jsIPN) dial(network, addr string) js.Value {
	return makePromise(func() (any, error) {
		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
		defer cancel()
		conn, err := i.dialer.UserDial(ctx, network, addr)
		if err != nil {
			return nil, err
		}
		return wrapConn(conn), nil
	})
}

func (i *jsIPN) listen(network, addr string) js.Value {
	return makePromise(func() (any, error) {
		switch network {
		case "tcp", "tcp4", "tcp6":
			// netstack.ListenTCP only accepts tcp4/tcp6; bare "tcp"
			// defaults to IPv4 to match net.Listen's typical behavior
			// when given an unspecified address.
			n := network
			if n == "tcp" {
				n = "tcp4"
			}
			ln, err := i.ns.ListenTCP(n, addr)
			if err != nil {
				return nil, err
			}
			return wrapTCPListener(ln), nil
		case "udp", "udp4", "udp6":
			pc, err := i.ns.ListenPacket(network, addr)
			if err != nil {
				return nil, err
			}
			return wrapPacketConn(pc), nil
		default:
			return nil, fmt.Errorf("unsupported network %q", network)
		}
	})
}

func (i *jsIPN) dialTLS(addr string, opts js.Value) js.Value {
	return makePromise(func() (any, error) {
		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
		defer cancel()

		host, _, err := net.SplitHostPort(addr)
		if err != nil {
			return nil, fmt.Errorf("invalid address %q: %w", addr, err)
		}

		// On wasm there's no system root pool, so default to the
		// baked-in LetsEncrypt roots (which is what `tailscale cert`
		// uses for tailnet HTTPS endpoints). Callers can override with
		// caCerts (PEM) or bypass entirely with insecureSkipVerify.
		cfg := &tls.Config{
			ServerName: host,
			RootCAs:    bakedroots.Get(),
		}
		if !opts.IsUndefined() && !opts.IsNull() {
			if sn := opts.Get("serverName"); sn.Type() == js.TypeString {
				cfg.ServerName = sn.String()
			}
			if iv := opts.Get("insecureSkipVerify"); iv.Type() == js.TypeBoolean {
				cfg.InsecureSkipVerify = iv.Bool()
			}
			if ca := opts.Get("caCerts"); ca.Type() == js.TypeString {
				pool := x509.NewCertPool()
				if !pool.AppendCertsFromPEM([]byte(ca.String())) {
					return nil, fmt.Errorf("caCerts: no valid PEM certificates found")
				}
				cfg.RootCAs = pool
			}
		}

		rawConn, err := i.dialer.UserDial(ctx, "tcp", addr)
		if err != nil {
			return nil, err
		}
		tlsConn := tls.Client(rawConn, cfg)
		if err := tlsConn.HandshakeContext(ctx); err != nil {
			rawConn.Close()
			return nil, err
		}
		return wrapConn(tlsConn), nil
	})
}

func (i *jsIPN) listenICMP(network string) js.Value {
	return makePromise(func() (any, error) {
		var transportProto tcpip.TransportProtocolNumber
		var networkProto tcpip.NetworkProtocolNumber

		switch network {
		case "icmp4", "icmp":
			transportProto = icmp.ProtocolNumber4
			networkProto = ipv4.ProtocolNumber
		case "icmp6":
			transportProto = icmp.ProtocolNumber6
			networkProto = ipv6.ProtocolNumber
		default:
			return nil, fmt.Errorf("unsupported network %q (use \"icmp4\" or \"icmp6\")", network)
		}

		st := i.ns.Stack()
		var wq waiter.Queue
		ep, nserr := st.NewEndpoint(transportProto, networkProto, &wq)
		if nserr != nil {
			return nil, fmt.Errorf("creating ICMP endpoint: %v", nserr)
		}

		pc := gonet.NewUDPConn(&wq, ep)
		return wrapPacketConn(pc), nil
	})
}

func (i *jsIPN) getCert() js.Value {
	return makePromise(func() (any, error) {
		nm := i.lb.NetMap()
		if nm == nil {
			return nil, errors.New("getCert: no network map available")
		}
		certDomains := nm.DNS.CertDomains
		if len(certDomains) == 0 {
			return nil, errors.New("getCert: this tailnet does not support TLS certificates")
		}
		pair, err := i.lb.GetCertPEM(context.Background(), certDomains[0])
		if err != nil {
			return nil, err
		}
		return map[string]any{
			"certPEM": string(pair.CertPEM),
			"keyPEM":  string(pair.KeyPEM),
		}, nil
	})
}

func (i *jsIPN) listenTLS(addr, certPEM, keyPEM string) js.Value {
	return makePromise(func() (any, error) {
		cert, err := tls.X509KeyPair([]byte(certPEM), []byte(keyPEM))
		if err != nil {
			return nil, fmt.Errorf("listenTLS: parsing cert/key: %w", err)
		}
		tlsCfg := &tls.Config{Certificates: []tls.Certificate{cert}}

		tcpLn, err := i.ns.ListenTCP("tcp4", addr)
		if err != nil {
			return nil, err
		}

		// Determine the actual port (handles ":0" ephemeral assignment).
		// Use SplitHostPort rather than netip.ParseAddrPort because gVisor
		// may return ":443" (empty host) which ParseAddrPort rejects.
		_, portStr, err := net.SplitHostPort(tcpLn.Addr().String())
		if err != nil {
			tcpLn.Close()
			return nil, fmt.Errorf("listenTLS: getting port from listener addr: %w", err)
		}
		portNum, err := strconv.ParseUint(portStr, 10, 16)
		if err != nil {
			tcpLn.Close()
			return nil, fmt.Errorf("listenTLS: parsing port %q: %w", portStr, err)
		}
		port := uint16(portNum)

		// Register a Funnel entry so handleFunnelTCP can route to this listener.
		entry := &funnelListenerEntry{
			ch:     make(chan net.Conn, 8),
			tlsCfg: tlsCfg,
		}
		i.funnelMu.Lock()
		i.funnelPorts[port] = entry
		i.funnelMu.Unlock()

		ln := newCombinedTLSListener(tcpLn, tlsCfg, entry.ch, port, i)
		return wrapTCPListener(ln), nil
	})
}

// handleFunnelTCP is registered with LocalBackend.SetTCPHandlerForFunnelFlow.
// It routes incoming Funnel connections to the matching listenTLS listener.
func (i *jsIPN) handleFunnelTCP(src netip.AddrPort, dstPort uint16) func(net.Conn) {
	i.funnelMu.Lock()
	entry := i.funnelPorts[dstPort]
	i.funnelMu.Unlock()
	if entry == nil {
		return nil
	}
	return func(conn net.Conn) {
		tlsConn := tls.Server(conn, entry.tlsCfg)
		select {
		case entry.ch <- tlsConn:
		default:
			// Channel full; drop the connection rather than block.
			conn.Close()
		}
	}
}

// combinedTLSListener merges TLS connections from the local netstack (direct
// tailnet access) and from Funnel ingress into a single net.Listener.
type combinedTLSListener struct {
	tcpLn      net.Listener
	tlsCfg     *tls.Config
	funnelCh   <-chan net.Conn
	port       uint16
	ipn        *jsIPN
	netstackCh chan net.Conn
	errCh      chan error
	done       chan struct{}
	closeOnce  sync.Once
}

func newCombinedTLSListener(tcpLn net.Listener, tlsCfg *tls.Config, funnelCh <-chan net.Conn, port uint16, ipn *jsIPN) *combinedTLSListener {
	l := &combinedTLSListener{
		tcpLn:      tcpLn,
		tlsCfg:     tlsCfg,
		funnelCh:   funnelCh,
		port:       port,
		ipn:        ipn,
		netstackCh: make(chan net.Conn, 8),
		errCh:      make(chan error, 1),
		done:       make(chan struct{}),
	}
	go l.drainNetstack()
	return l
}

func (l *combinedTLSListener) drainNetstack() {
	for {
		conn, err := l.tcpLn.Accept()
		if err != nil {
			select {
			case l.errCh <- err:
			default:
			}
			return
		}
		tlsConn := tls.Server(conn, l.tlsCfg)
		select {
		case l.netstackCh <- tlsConn:
		case <-l.done:
			conn.Close()
			return
		}
	}
}

func (l *combinedTLSListener) Accept() (net.Conn, error) {
	select {
	case conn := <-l.funnelCh:
		return conn, nil
	case conn := <-l.netstackCh:
		return conn, nil
	case err := <-l.errCh:
		return nil, err
	case <-l.done:
		return nil, net.ErrClosed
	}
}

func (l *combinedTLSListener) Close() error {
	l.closeOnce.Do(func() {
		close(l.done)
		l.tcpLn.Close()
		l.ipn.funnelMu.Lock()
		delete(l.ipn.funnelPorts, l.port)
		l.ipn.funnelMu.Unlock()
	})
	return nil
}

func (l *combinedTLSListener) Addr() net.Addr {
	return l.tcpLn.Addr()
}

func (i *jsIPN) setFunnel(hostname string, port uint16, enabled bool) js.Value {
	return makePromise(func() (any, error) {
		hp := ipn.HostPort(fmt.Sprintf("%s:%d", hostname, port))
		var cfg *ipn.ServeConfig
		if enabled {
			cfg = &ipn.ServeConfig{
				AllowFunnel: map[ipn.HostPort]bool{hp: true},
			}
		} else {
			cfg = &ipn.ServeConfig{}
		}
		return nil, i.lb.SetServeConfig(cfg, "")
	})
}

func (i *jsIPN) whoIs(addr string, proto string) js.Value {
	return makePromise(func() (any, error) {
		// Accept both "ip:port" and bare "ip" (port 0 still resolves by IP).
		var ipp netip.AddrPort
		if ap, err := netip.ParseAddrPort(addr); err == nil {
			ipp = ap
		} else if ip, err := netip.ParseAddr(addr); err == nil {
			ipp = netip.AddrPortFrom(ip, 0)
		} else {
			return nil, fmt.Errorf("whoIs: invalid address %q (want ip:port or ip)", addr)
		}
		n, u, ok := i.lb.WhoIs(proto, ipp)
		if !ok {
			return nil, nil
		}
		addrs := make([]any, n.Addresses().Len())
		for idx, ap := range n.Addresses().All() {
			addrs[idx] = ap.Addr().String()
		}
		return map[string]any{
			"node": map[string]any{
				"id":        string(n.StableID()),
				"name":      n.Name(),
				"addresses": addrs,
			},
			"user": map[string]any{
				"id":            int64(u.ID),
				"loginName":     u.LoginName,
				"displayName":   u.DisplayName,
				"profilePicURL": u.ProfilePicURL,
			},
		}, nil
	})
}

func (i *jsIPN) queryDNS(name string, queryType int) js.Value {
	return makePromise(func() (any, error) {
		res, resolvers, err := i.lb.QueryDNS(name, dnsmessage.Type(queryType))

		// Detect SERVFAIL with no upstream resolvers (common when an exit node is
		// active but the DNS manager forwarder has no configured upstreams). Fall
		// back to querying 8.8.8.8 via the dialer (which routes through the exit
		// node), then as a last resort use the browser's default name resolver.
		needsFallback := err != nil
		if !needsFallback && len(resolvers) == 0 && len(res) > 0 {
			var hdrParser dnsmessage.Parser
			if hdr, hdrErr := hdrParser.Start(res); hdrErr == nil && hdr.RCode == dnsmessage.RCodeServerFailure {
				needsFallback = true
			}
		}
		if needsFallback {
			qt := dnsmessage.Type(queryType)
			if qt != dnsmessage.TypeA && qt != dnsmessage.TypeAAAA {
				if err != nil {
					return nil, fmt.Errorf("queryDNS: %w (no upstream resolver; only A/AAAA queries support fallback)", err)
				}
				return nil, fmt.Errorf("queryDNS: no upstream resolver available; only A/AAAA queries support fallback lookup")
			}
			ctx := context.Background()
			d := i.dialer
			r := &net.Resolver{
				PreferGo: true,
				Dial: func(rctx context.Context, network, address string) (net.Conn, error) {
					return d.UserDial(rctx, "tcp", "8.8.8.8:53")
				},
			}
			ips, rerr := r.LookupIPAddr(ctx, name)
			if rerr != nil {
				// Last resort: browser-native resolution (no exit-node routing).
				ips, rerr = (&net.Resolver{PreferGo: false}).LookupIPAddr(ctx, name)
				if rerr != nil {
					return nil, fmt.Errorf("queryDNS: fallback resolution failed: %w", rerr)
				}
			}
			var answers []any
			for _, ia := range ips {
				ip, ok := netip.AddrFromSlice(ia.IP)
				if !ok {
					continue
				}
				ip = ip.Unmap()
				if qt == dnsmessage.TypeA && ip.Is4() {
					answers = append(answers, ip.String())
				} else if qt == dnsmessage.TypeAAAA && ip.Is6() {
					answers = append(answers, ip.String())
				}
			}
			return map[string]any{
				"answers":   answers,
				"resolvers": []any{},
			}, nil
		}

		var p dnsmessage.Parser
		if _, err := p.Start(res); err != nil {
			return nil, fmt.Errorf("queryDNS: parsing response: %w", err)
		}
		if err := p.SkipAllQuestions(); err != nil {
			return nil, fmt.Errorf("queryDNS: skipping questions: %w", err)
		}
		var answers []any
		for {
			h, err := p.AnswerHeader()
			if err == dnsmessage.ErrSectionDone {
				break
			}
			if err != nil {
				return nil, fmt.Errorf("queryDNS: reading answer: %w", err)
			}
			switch h.Type {
			case dnsmessage.TypeA:
				r, err := p.AResource()
				if err != nil {
					return nil, fmt.Errorf("queryDNS: reading A record: %w", err)
				}
				answers = append(answers, netip.AddrFrom4(r.A).String())
			case dnsmessage.TypeAAAA:
				r, err := p.AAAAResource()
				if err != nil {
					return nil, fmt.Errorf("queryDNS: reading AAAA record: %w", err)
				}
				answers = append(answers, netip.AddrFrom16(r.AAAA).String())
			case dnsmessage.TypeCNAME:
				r, err := p.CNAMEResource()
				if err != nil {
					return nil, fmt.Errorf("queryDNS: reading CNAME record: %w", err)
				}
				answers = append(answers, r.CNAME.String())
			case dnsmessage.TypeTXT:
				r, err := p.TXTResource()
				if err != nil {
					return nil, fmt.Errorf("queryDNS: reading TXT record: %w", err)
				}
				for _, s := range r.TXT {
					answers = append(answers, s)
				}
			default:
				if err := p.SkipAnswer(); err != nil {
					return nil, fmt.Errorf("queryDNS: skipping unknown answer: %w", err)
				}
			}
		}
		resolverAddrs := make([]any, len(resolvers))
		for idx, r := range resolvers {
			resolverAddrs[idx] = r.Addr
		}
		return map[string]any{
			"answers":   answers,
			"resolvers": resolverAddrs,
		}, nil
	})
}

func (i *jsIPN) ping(ip string, pingType string, size int) js.Value {
	return makePromise(func() (any, error) {
		addr, err := netip.ParseAddr(ip)
		if err != nil {
			return nil, fmt.Errorf("ping: invalid IP %q: %w", ip, err)
		}
		switch tailcfg.PingType(pingType) {
		case tailcfg.PingDisco, tailcfg.PingTSMP, tailcfg.PingICMP, tailcfg.PingPeerAPI:
			// valid
		default:
			return nil, fmt.Errorf("ping: unknown type %q, must be one of: disco, TSMP, icmp, peerapi", pingType)
		}
		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
		defer cancel()
		pr, err := i.lb.Ping(ctx, addr, tailcfg.PingType(pingType), size)
		if err != nil {
			return nil, err
		}
		result := map[string]any{
			"ip":             pr.IP,
			"nodeIP":         pr.NodeIP,
			"nodeName":       pr.NodeName,
			"latencySeconds": pr.LatencySeconds,
			"endpoint":       pr.Endpoint,
			"derpRegionID":   pr.DERPRegionID,
			"derpRegionCode": pr.DERPRegionCode,
			"peerAPIURL":     pr.PeerAPIURL,
			"isLocalIP":      pr.IsLocalIP,
		}
		if pr.Err != "" {
			result["err"] = pr.Err
		}
		return result, nil
	})
}

func (i *jsIPN) suggestExitNode() js.Value {
	return makePromise(func() (any, error) {
		resp, err := i.lb.SuggestExitNode()
		if err != nil {
			return nil, err
		}
		result := map[string]any{
			"id":   string(resp.ID),
			"name": resp.Name,
		}
		if l := resp.Location; l.Valid() {
			result["location"] = map[string]any{
				"country":     l.Country(),
				"countryCode": l.CountryCode(),
				"city":        l.City(),
				"cityCode":    l.CityCode(),
				"latitude":    l.Latitude(),
				"longitude":   l.Longitude(),
			}
		}
		return result, nil
	})
}

func (i *jsIPN) localAPI(method, path, body string) js.Value {
	return makePromise(func() (any, error) {
		h := localapi.NewHandler(localapi.HandlerConfig{
			Actor: &ipnauth.TestActor{
				Name:       "wasm",
				LocalAdmin: true,
			},
			Backend:  i.lb,
			Logf:     log.Printf,
			LogID:    i.logID,
			EventBus: i.lb.Sys().Bus.Get(),
		})
		h.PermitRead = true
		h.PermitWrite = true
		h.PermitCert = true

		var bodyReader io.Reader
		if body != "" {
			bodyReader = strings.NewReader(body)
		}
		req, err := http.NewRequest(method, "http://local-tailscaled.sock"+path, bodyReader)
		if err != nil {
			return nil, fmt.Errorf("localAPI: %w", err)
		}
		// Empty Host passes the validHost check in the LocalAPI handler.
		req.Host = ""
		if body != "" {
			req.Header.Set("Content-Type", "application/json")
		}
		w := httptest.NewRecorder()
		h.ServeHTTP(w, req)
		resp := w.Result()
		respBody, err := io.ReadAll(resp.Body)
		if err != nil {
			return nil, fmt.Errorf("localAPI: reading response: %w", err)
		}
		return map[string]any{
			"status": resp.StatusCode,
			"body":   string(respBody),
		}, nil
	})
}

// wrapConn exposes a net.Conn to JavaScript with binary (Uint8Array) I/O.
func wrapConn(conn net.Conn) map[string]any {
	return map[string]any{
		"read": js.FuncOf(func(this js.Value, args []js.Value) any {
			return makePromise(func() (any, error) {
				buf := make([]byte, 65536)
				n, err := conn.Read(buf)
				if err != nil {
					return nil, err
				}
				arr := js.Global().Get("Uint8Array").New(n)
				js.CopyBytesToJS(arr, buf[:n])
				return arr, nil
			})
		}),
		"write": js.FuncOf(func(this js.Value, args []js.Value) any {
			return makePromise(func() (any, error) {
				data := args[0]
				buf := make([]byte, data.Get("length").Int())
				js.CopyBytesToGo(buf, data)
				n, err := conn.Write(buf)
				if err != nil {
					return nil, err
				}
				return n, nil
			})
		}),
		"close": js.FuncOf(func(this js.Value, args []js.Value) any {
			return conn.Close() != nil
		}),
		"localAddr": js.FuncOf(func(this js.Value, args []js.Value) any {
			return conn.LocalAddr().String()
		}),
		"remoteAddr": js.FuncOf(func(this js.Value, args []js.Value) any {
			return conn.RemoteAddr().String()
		}),
	}
}

// wrapTCPListener exposes a net.Listener to JavaScript as an object with
// accept/close/addr methods plus a Symbol.asyncIterator implementation, so
// callers can write `for await (const conn of listener)`.
func wrapTCPListener(ln net.Listener) js.Value {
	obj := js.Global().Get("Object").New()
	obj.Set("accept", js.FuncOf(func(this js.Value, args []js.Value) any {
		return makePromise(func() (any, error) {
			conn, err := ln.Accept()
			if err != nil {
				return nil, err
			}
			return wrapConn(conn), nil
		})
	}))
	obj.Set("close", js.FuncOf(func(this js.Value, args []js.Value) any {
		return ln.Close() != nil
	}))
	obj.Set("addr", js.FuncOf(func(this js.Value, args []js.Value) any {
		return ln.Addr().String()
	}))

	asyncIterSym := js.Global().Get("Symbol").Get("asyncIterator")
	iterFactory := js.FuncOf(func(this js.Value, args []js.Value) any {
		iter := js.Global().Get("Object").New()
		iter.Set("next", js.FuncOf(func(this js.Value, args []js.Value) any {
			return makePromise(func() (any, error) {
				conn, err := ln.Accept()
				if err != nil {
					if errors.Is(err, net.ErrClosed) {
						return map[string]any{
							"value": js.Undefined(),
							"done":  true,
						}, nil
					}
					return nil, err
				}
				return map[string]any{
					"value": wrapConn(conn),
					"done":  false,
				}, nil
			})
		}))
		return iter
	})
	js.Global().Get("Reflect").Call("set", obj, asyncIterSym, iterFactory)
	return obj
}

// wrapPacketConn exposes a net.PacketConn to JavaScript with binary (Uint8Array) I/O.
func wrapPacketConn(pc net.PacketConn) map[string]any {
	return map[string]any{
		"readFrom": js.FuncOf(func(this js.Value, args []js.Value) any {
			return makePromise(func() (any, error) {
				buf := make([]byte, 65536)
				n, addr, err := pc.ReadFrom(buf)
				if err != nil {
					return nil, err
				}
				arr := js.Global().Get("Uint8Array").New(n)
				js.CopyBytesToJS(arr, buf[:n])
				return map[string]any{
					"data": arr,
					"addr": addr.String(),
				}, nil
			})
		}),
		"writeTo": js.FuncOf(func(this js.Value, args []js.Value) any {
			return makePromise(func() (any, error) {
				data := args[0]
				addrStr := args[1].String()
				buf := make([]byte, data.Get("length").Int())
				js.CopyBytesToGo(buf, data)
				addr, err := resolveUDPAddr(addrStr)
				if err != nil {
					return nil, err
				}
				n, err := pc.WriteTo(buf, addr)
				if err != nil {
					return nil, err
				}
				return n, nil
			})
		}),
		"close": js.FuncOf(func(this js.Value, args []js.Value) any {
			return pc.Close() != nil
		}),
		"localAddr": js.FuncOf(func(this js.Value, args []js.Value) any {
			return pc.LocalAddr().String()
		}),
	}
}

// resolveUDPAddr parses an address string that is either "host:port" or just
// an IP (for ICMP, where port defaults to 0).
func resolveUDPAddr(s string) (*net.UDPAddr, error) {
	host, portStr, err := net.SplitHostPort(s)
	if err != nil {
		// Bare IP address without port (used for ICMP).
		ip := net.ParseIP(s)
		if ip == nil {
			return nil, fmt.Errorf("invalid address: %s", s)
		}
		return &net.UDPAddr{IP: ip}, nil
	}
	ip := net.ParseIP(host)
	if ip == nil {
		return nil, fmt.Errorf("invalid IP: %s", host)
	}
	port, err := strconv.Atoi(portStr)
	if err != nil {
		return nil, fmt.Errorf("invalid port: %s", portStr)
	}
	return &net.UDPAddr{IP: ip, Port: port}, nil
}

type termWriter struct {
	f js.Value
}

func (w termWriter) Write(p []byte) (n int, err error) {
	r := bytes.Replace(p, []byte("\n"), []byte("\n\r"), -1)
	w.f.Invoke(string(r))
	return len(p), nil
}

// jsIncomingFile is the JSON representation of an in-progress inbound file
// transfer sent to the notifyIncomingFiles callback.
type jsIncomingFile struct {
	Name         string `json:"name"`
	Started      int64  `json:"started"`      // Unix milliseconds; use new Date(started) in JS
	DeclaredSize int64  `json:"declaredSize"` // -1 if unknown
	Received     int64  `json:"received"`     // bytes received so far
	Done         bool   `json:"done"`         // true once the file has been fully received
}

// jsOutgoingFile is the JSON representation of an outgoing file transfer
// sent to the notifyOutgoingFiles callback.
type jsOutgoingFile struct {
	ID           string `json:"id"`
	PeerID       string `json:"peerID"`
	Name         string `json:"name"`
	Started      int64  `json:"started"`      // Unix milliseconds
	DeclaredSize int64  `json:"declaredSize"` // -1 if unknown
	Sent         int64  `json:"sent"`         // bytes sent so far
	Finished     bool   `json:"finished"`
	Succeeded    bool   `json:"succeeded"` // only meaningful when finished
}

type jsNetMap struct {
	Self      jsNetMapSelfNode   `json:"self"`
	Peers     []jsNetMapPeerNode `json:"peers"`
	LockedOut bool               `json:"lockedOut"`
}

type jsNetMapNode struct {
	Name        string   `json:"name"`
	Addresses   []string `json:"addresses"`
	MachineKey  string   `json:"machineKey"`
	NodeKey     string   `json:"nodeKey"`
	PeerAPIURL  string   `json:"peerAPIURL,omitempty"`
}

type jsNetMapSelfNode struct {
	jsNetMapNode
	MachineStatus string `json:"machineStatus"`
}

type jsNetMapPeerNode struct {
	jsNetMapNode
	Online              *bool  `json:"online,omitempty"`
	TailscaleSSHEnabled bool   `json:"tailscaleSSHEnabled"`
	ExitNodeOption      bool   `json:"exitNodeOption"`
	StableNodeID        string `json:"stableNodeID"`
}

type jsStateStore struct {
	jsStateStorage js.Value
}

func (s *jsStateStore) ReadState(id ipn.StateKey) ([]byte, error) {
	jsValue := s.jsStateStorage.Call("getState", string(id))
	if jsValue.String() == "" {
		return nil, ipn.ErrStateNotExist
	}
	return hex.DecodeString(jsValue.String())
}

func (s *jsStateStore) WriteState(id ipn.StateKey, bs []byte) error {
	s.jsStateStorage.Call("setState", string(id), hex.EncodeToString(bs))
	return nil
}

func mapSlice[T any, M any](a []T, f func(T) M) []M {
	n := make([]M, len(a))
	for i, e := range a {
		n[i] = f(e)
	}
	return n
}

func mapSliceView[T any, M any](a views.Slice[T], f func(T) M) []M {
	n := make([]M, a.Len())
	for i, v := range a.All() {
		n[i] = f(v)
	}
	return n
}

func filterSlice[T any](a []T, f func(T) bool) []T {
	n := make([]T, 0, len(a))
	for _, e := range a {
		if f(e) {
			n = append(n, e)
		}
	}
	return n
}

func generateHostname() string {
	tails := words.Tails()
	scales := words.Scales()
	if rand.IntN(2) == 0 {
		// JavaScript
		tails = filterSlice(tails, func(s string) bool { return strings.HasPrefix(s, "j") })
		scales = filterSlice(scales, func(s string) bool { return strings.HasPrefix(s, "s") })
	} else {
		// WebAssembly
		tails = filterSlice(tails, func(s string) bool { return strings.HasPrefix(s, "w") })
		scales = filterSlice(scales, func(s string) bool { return strings.HasPrefix(s, "a") })
	}

	tail := tails[rand.IntN(len(tails))]
	scale := scales[rand.IntN(len(scales))]
	return fmt.Sprintf("%s-%s", tail, scale)
}

// makePromise handles the boilerplate of wrapping goroutines with JS promises.
// f is run on a goroutine and its return value is used to resolve the promise
// (or reject it if an error is returned).
func makePromise(f func() (any, error)) js.Value {
	handler := js.FuncOf(func(this js.Value, args []js.Value) any {
		resolve := args[0]
		reject := args[1]
		go func() {
			if res, err := f(); err == nil {
				resolve.Invoke(res)
			} else {
				reject.Invoke(err.Error())
			}
		}()
		return nil
	})

	promiseConstructor := js.Global().Get("Promise")
	return promiseConstructor.New(handler)
}

const logPolicyStateKey = "log-policy"

func getOrCreateLogPolicyConfig(state ipn.StateStore) *logpolicy.Config {
	if configBytes, err := state.ReadState(logPolicyStateKey); err == nil {
		if config, err := logpolicy.ConfigFromBytes(configBytes); err == nil {
			return config
		} else {
			log.Printf("Could not parse log policy config: %v", err)
		}
	} else if err != ipn.ErrStateNotExist {
		log.Printf("Could not get log policy config from state store: %v", err)
	}
	config := logpolicy.NewConfig(logtail.CollectionNode)
	if err := state.WriteState(logPolicyStateKey, config.ToBytes()); err != nil {
		log.Printf("Could not save log policy config to state store: %v", err)
	}
	return config
}

// noCORSTransport wraps a RoundTripper and forces the no-cors mode on requests,
// so that we can use it with non-CORS-aware servers.
type noCORSTransport struct {
	http.RoundTripper
}

func (t *noCORSTransport) RoundTrip(req *http.Request) (*http.Response, error) {
	req.Header.Set("js.fetch:mode", "no-cors")
	resp, err := t.RoundTripper.RoundTrip(req)
	if err == nil {
		// In no-cors mode no response properties are returned. Populate just
		// the status so that callers do not think this was an error.
		resp.StatusCode = http.StatusOK
		resp.Status = http.StatusText(http.StatusOK)
	}
	return resp, err
}