feat(tsconnect): add TCP listening to ipn.listen

Extend ipn.listen to also accept "tcp"/"tcp4"/"tcp6" and return a
TCPListener bound to a netstack gonet.TCPListener. The listener
exposes accept/close/addr like a Go net.Listener and additionally
implements Symbol.asyncIterator so JS callers can write:

  for await (const conn of listener) { ... }

The async iterator returns done when the listener is closed (via
errors.Is(net.ErrClosed)) and rejects on any other accept error.
Symbol-keyed properties are set via Reflect.set since syscall/js
only exposes string-keyed Set.

cmd/tsconnect/wasm/wasm_js.go

@@ -16,6 +16,7 @@ import (
 	"crypto/x509"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"log"
 	"math/rand/v2"
@@ -589,11 +590,29 @@ func (i *jsIPN) dial(network, addr string) js.Value {
 
 func (i *jsIPN) listen(network, addr string) js.Value {
 	return makePromise(func() (any, error) {
-		pc, err := i.ns.ListenPacket(network, addr)
-		if err != nil {
-			return nil, err
+		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)
 		}
-		return wrapPacketConn(pc), nil
 	})
 }
 
@@ -711,6 +730,54 @@ func wrapConn(conn net.Conn) map[string]any {
 	}
 }
 
+// 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{