Async iterator for listener (#2263)

js/net.ts

@@ -14,7 +14,7 @@ export type Network = "tcp";
 export type Addr = string;
 
 /** A Listener is a generic network listener for stream-oriented protocols. */
-export interface Listener {
+export interface Listener extends AsyncIterator<Conn> {
   /** Waits for and resolves to the next connection to the `Listener`. */
   accept(): Promise<Conn>;
 
@@ -25,6 +25,8 @@ export interface Listener {
 
   /** Return the address of the `Listener`. */
   addr(): Addr;
+
+  [Symbol.asyncIterator](): AsyncIterator<Conn>;
 }
 
 enum ShutdownMode {
@@ -97,6 +99,17 @@ class ListenerImpl implements Listener {
   addr(): Addr {
     return notImplemented();
   }
+
+  async next(): Promise<IteratorResult<Conn>> {
+    return {
+      done: false,
+      value: await this.accept()
+    };
+  }
+
+  [Symbol.asyncIterator](): AsyncIterator<Conn> {
+    return this;
+  }
 }
 
 export interface Conn extends Reader, Writer, Closer {

js/net_test.ts

@@ -72,6 +72,37 @@ testPerm({ net: true }, async function netDialListen(): Promise<void> {
   conn.close();
 });
 
+testPerm({ net: true }, async function netListenAsyncIterator(): Promise<void> {
+  const listener = Deno.listen("tcp", ":4500");
+  const runAsyncIterator = async (): Promise<void> => {
+    for await (let conn of listener) {
+      await conn.write(new Uint8Array([1, 2, 3]));
+      conn.close();
+    }
+  };
+  runAsyncIterator();
+  const conn = await Deno.dial("tcp", "127.0.0.1:4500");
+  const buf = new Uint8Array(1024);
+  const readResult = await conn.read(buf);
+  assertEquals(3, readResult.nread);
+  assertEquals(1, buf[0]);
+  assertEquals(2, buf[1]);
+  assertEquals(3, buf[2]);
+  assert(conn.rid > 0);
+
+  // TODO Currently ReadResult does not properly transmit EOF in the same call.
+  // it requires a second call to get the EOF. Either ReadResult to be an
+  // integer in which 0 signifies EOF or the handler should be modified so that
+  // EOF is properly transmitted.
+  assertEquals(false, readResult.eof);
+
+  const readResult2 = await conn.read(buf);
+  assertEquals(true, readResult2.eof);
+
+  listener.close();
+  conn.close();
+});
+
 /* TODO Fix broken test.
 testPerm({ net: true }, async function netCloseReadSuccess() {
   const addr = "127.0.0.1:4500";