feat(net): Default to port 0 (OS assigned port) if no port was specified

Validation is also stricter for client ports, which now has to be in
range 1-65535, as connecting to “port 0” is invalid.

Author: ntninja

ext/net/01_net.js

@@ -601,7 +601,7 @@ const listenOptionApiName = Symbol("listenOptionApiName");
 function listen(args) {
   switch (args.transport ?? "tcp") {
     case "tcp": {
-      const port = validatePort(args.port);
+      const port = validatePort(args.port || 0, true);
       const { 0: rid, 1: addr } = op_net_listen_tcp(
         {
           hostname: args.hostname ?? "0.0.0.0",
@@ -646,7 +646,7 @@ function listen(args) {
   }
 }
 
-function validatePort(maybePort) {
+function validatePort(maybePort, isServer = false) {
   if (typeof maybePort !== "number" && typeof maybePort !== "string") {
     throw new TypeError(`Invalid port (expected number): ${maybePort}`);
   }
@@ -658,6 +658,8 @@ function validatePort(maybePort) {
     } else {
       throw new TypeError(`Invalid port: ${maybePort}`);
     }
+  } else if (!isServer && (port < 1 || port > 65535)) {
+    throw new RangeError(`Invalid port (out of range): ${maybePort}`);
   } else if (port < 0 || port > 65535) {
     throw new RangeError(`Invalid port (out of range): ${maybePort}`);
   }
@@ -668,7 +670,7 @@ function createListenDatagram(udpOpFn, unixOpFn) {
   return function listenDatagram(args) {
     switch (args.transport) {
       case "udp": {
-        const port = validatePort(args.port);
+        const port = validatePort(args.port || 0, true);
         const { 0: rid, 1: addr } = udpOpFn(
           {
             hostname: args.hostname ?? "127.0.0.1",

tests/unit/net_test.ts

@@ -2,6 +2,7 @@
 import {
   assert,
   assertEquals,
+  assertGreaterOrEqual,
   assertRejects,
   assertThrows,
   delay,
@@ -46,6 +47,24 @@ Deno.test(
   },
 );
 
+Deno.test(
+  {
+    permissions: { net: true },
+  },
+  function netUdpListenEphermalClose() {
+    const socket = Deno.listenDatagram({
+      hostname: "127.0.0.1",
+      transport: "udp",
+    });
+    assert(socket.addr.transport === "udp");
+    assertEquals(socket.addr.hostname, "127.0.0.1");
+    // Ephermal port range starts at 49152 according to RFC 6335 / IANA, but
+    // many OSes use the lower number below (old OSes also started at 1024)
+    assertGreaterOrEqual(socket.addr.port, 32768);
+    socket.close();
+  },
+);
+
 Deno.test(
   {
     ignore: Deno.build.os === "windows",

tests/unit/test_util.ts

@@ -8,6 +8,7 @@ export {
   assert,
   assertEquals,
   assertFalse,
+  assertGreaterOrEqual,
   AssertionError,
   assertIsError,
   assertMatch,