feat(ext/net): enable sending to broadcast address (#12860)

You can now send UDP datagrams to the broadcast address.

cli/tests/unit/net_test.ts

@@ -306,6 +306,44 @@ Deno.test(
   },
 );
 
+Deno.test(
+  { permissions: { net: true } },
+  async function netUdpSendReceiveBroadcast() {
+    // Must bind sender to an address that can send to the broadcast address on MacOS.
+    // Macos will give us error 49 when sending the broadcast packet if we omit hostname here.
+    const alice = Deno.listenDatagram({
+      port: 3500,
+      transport: "udp",
+      hostname: "0.0.0.0",
+    });
+
+    const bob = Deno.listenDatagram({
+      port: 4501,
+      transport: "udp",
+      hostname: "0.0.0.0",
+    });
+    assert(bob.addr.transport === "udp");
+    assertEquals(bob.addr.port, 4501);
+    assertEquals(bob.addr.hostname, "0.0.0.0");
+
+    const broadcastAddr = { ...bob.addr, hostname: "255.255.255.255" };
+
+    const sent = new Uint8Array([1, 2, 3]);
+    const byteLength = await alice.send(sent, broadcastAddr);
+
+    assertEquals(byteLength, 3);
+    const [recvd, remote] = await bob.receive();
+    assert(remote.transport === "udp");
+    assertEquals(remote.port, 3500);
+    assertEquals(recvd.length, 3);
+    assertEquals(1, recvd[0]);
+    assertEquals(2, recvd[1]);
+    assertEquals(3, recvd[2]);
+    alice.close();
+    bob.close();
+  },
+);
+
 Deno.test(
   { permissions: { net: true } },
   async function netUdpConcurrentSendReceive() {

ext/net/ops.rs

@@ -440,6 +440,8 @@ fn listen_udp(
 ) -> Result<(u32, SocketAddr), AnyError> {
   let std_socket = std::net::UdpSocket::bind(&addr)?;
   std_socket.set_nonblocking(true)?;
+  // Enable messages to be sent to the broadcast address (255.255.255.255) by default
+  std_socket.set_broadcast(true)?;
   let socket = UdpSocket::from_std(std_socket)?;
   let local_addr = socket.local_addr()?;
   let socket_resource = UdpSocketResource {