feat(tsconnect): add TCPListener and tighten dial/listen network types

Type the new TCP listening surface from the tailscale submodule:

- listen() is now overloaded: tcp/tcp4/tcp6 returns a TCPListener,
  udp/udp4/udp6 returns a PacketConn. The network parameter is a
  literal union instead of a bare string so callers get completion
  and typo protection.
- TCPListener extends AsyncIterable<Conn>, so consumers can write
  `for await (const conn of listener)`.
- dial() drops "udp" from its accepted networks. Connected UDP
  through a stream-shaped Conn was confusing; UDP belongs in
  listen(), and ICMP in listenICMP(). The Go side still accepts
  whatever string for callers who really want to bypass the type.

Bumps the TS lib/target to ES2018 for AsyncIterable, bumps the
tailscale submodule, and updates the test-app inline example to
demonstrate `for await` over a TCP listener.

packages/test-app/index.html

@@ -46,7 +46,14 @@ ipn.login()
 // Once running, try the networking APIs:
 const conn = await ipn.dial("tcp", "some-peer:22")
 const pc = await ipn.listenICMP("icmp4")
-const tls = await ipn.dialTLS("some-peer.tail-scale.ts.net:443")</code></pre>
+const tls = await ipn.dialTLS("some-peer.tail-scale.ts.net:443")
+
+// Accept incoming TCP connections via async iteration:
+const ln = await ipn.listen("tcp", "0.0.0.0:8080")
+for await (const c of ln) {
+  console.log("got conn from", c.remoteAddr())
+  c.close()
+}</code></pre>
     <p id="status">Loading…</p>
     <script type="module" src="/src/main.ts"></script>
   </body>

packages/tsconnect/src/index.ts

@@ -5,6 +5,7 @@ import type { IPN, IPNConfig } from "./types"
 export type {
   Conn,
   PacketConn,
+  TCPListener,
   TLSDialOptions,
   IPN,
   IPNConfig,

packages/tsconnect/src/types.ts

@@ -83,6 +83,24 @@ export interface PacketConn {
   localAddr(): string
 }
 
+/**
+ * A TCP listener accepting incoming connections from the Tailscale network.
+ *
+ * Implements `AsyncIterable<Conn>` so callers can write:
+ *
+ *     for await (const conn of listener) { ... }
+ *
+ * The iterator finishes cleanly when `close()` is called; any other accept
+ * error rejects the iterator's pending `next()`.
+ */
+export interface TCPListener extends AsyncIterable<Conn> {
+  /** Accept a single incoming connection. */
+  accept(): Promise<Conn>
+  close(): boolean
+  /** The local listening address, e.g. "100.64.0.1:8080". */
+  addr(): string
+}
+
 export interface IPN {
   run(callbacks: IPNCallbacks): void
   login(): void
@@ -109,18 +127,30 @@ export interface IPN {
   }>
 
   /**
-   * Dial a TCP or UDP connection to a Tailscale peer.
-   * @param network - "tcp" or "udp"
+   * Dial a TCP connection to a Tailscale peer.
+   * @param network - "tcp", "tcp4", or "tcp6"
    * @param addr - "host:port" (host can be a Tailscale IP or MagicDNS name)
    */
-  dial(network: "tcp" | "udp", addr: string): Promise<Conn>
+  dial(network: "tcp" | "tcp4" | "tcp6", addr: string): Promise<Conn>
 
+  /**
+   * Listen for incoming TCP connections on the Tailscale network.
+   * @param network - "tcp", "tcp4", or "tcp6"
+   * @param addr - "host:port" to bind to (e.g. "0.0.0.0:0" for any address and port)
+   */
+  listen(
+    network: "tcp" | "tcp4" | "tcp6",
+    addr: string
+  ): Promise<TCPListener>
   /**
    * Listen for incoming UDP packets on the Tailscale network.
    * @param network - "udp", "udp4", or "udp6"
-   * @param addr - "host:port" to bind to (e.g. "0.0.0.0:0" for any)
+   * @param addr - "host:port" to bind to (e.g. "0.0.0.0:0" for any address and port)
    */
-  listen(network: string, addr: string): Promise<PacketConn>
+  listen(
+    network: "udp" | "udp4" | "udp6",
+    addr: string
+  ): Promise<PacketConn>
 
   /**
    * Open an ICMP endpoint on the Tailscale network stack.

packages/tsconnect/tsconfig.json

@@ -1,6 +1,6 @@
 {
   "compilerOptions": {
-    "target": "ES2017",
+    "target": "ES2018",
     "module": "ES2020",
     "moduleResolution": "node",
     "strict": true,
@@ -8,7 +8,7 @@
     "outDir": "out",
     "rootDir": "src",
     "sourceMap": true,
-    "lib": ["ES2017", "DOM"]
+    "lib": ["ES2018", "DOM"]
   },
   "include": ["src/**/*"]
 }