Sockets

For protocols below HTTP — a raw TCP service, a UDP sensor feed, a small on-device server — Kog gives you TCPSocket, UDPSocket, and TCPServer as globals. The API is Kog-native: promises for connect/bind/listen, and onX(cb) callbacks that return an unsubscribe function. It is deliberately not node's net/dgram, and not the browser.

Not in the web playground

A browser has no raw sockets, so new TCPSocket() / UDPSocket() / TCPServer() throw KogNetUnavailableError in the playground. Run these on a device (kog flash) or the desktop simulator (kog dev). fetch and WebSocket cover most needs and work everywhere.

See it for yourself — this runs in the playground, so new TCPSocket() throws the helpful error (on a device or kog dev, it would construct fine):

Binary in, string or binary out

Inbound data is always an ArrayBuffer — never a string or a node Buffer. When you want text, decode it with TextDecoder. When you send, you may pass a string (UTF-8 encoded for you), an ArrayBuffer, or a typed array.

TCP client

const socket = new TCPSocket();
await socket.connect('192.168.1.50', 8080);

const off = socket.onData((chunk) => {
  const text = new TextDecoder().decode(chunk);
  console.log('got', text);
});

socket.onError((err) => console.error(err.code));
socket.onClose(() => console.log('closed'));

socket.send('GET /status\n');
// ...later
off();               // unsubscribe this listener
await socket.close(); // graceful close

connect resolves once the connection is established (after the TLS handshake if you pass { tls: true }), and rejects with a KogNetError on refusal or timeout. Pace large sends with socket.bufferedAmount and socket.onDrain(...).

UDP

const udp = new UDPSocket();
await udp.bind(41234);

udp.onMessage((msg, rinfo) => {
  console.log(`${rinfo.address}:${rinfo.port} sent ${msg.byteLength} bytes`);
});

udp.send('ping', 41234, '192.168.1.255');

onMessage delivers the datagram as an ArrayBuffer plus an rinfo with the sender's address, port, family, and size.

A tiny TCP server (on-device)

Because a Kog device is a real network host, it can listen:

const server = new TCPServer();
await server.listen(8080);

server.onConnection((conn) => {
  conn.onData((chunk) => {
    // echo it back
    conn.send(chunk);
  });
});

Each onConnection callback receives an already-open TCPSocket. await server.close() stops accepting new connections; existing ones keep running.

Errors

Socket failures reject or emit a KogNetError with a stable .code string — branch on the string, never a raw number:

try {
  await socket.connect(host, port);
} catch (err) {
  if (err instanceof KogNetError && err.code === 'NET_CONNREFUSED') {
    // nothing listening there
  }
}

The full code list (NET_TIMEOUT, NET_RESET, NET_TLS, …) is in the API reference.