WebSocketHandler.drain method | Bun module | Bun

Called when a connection was previously under backpressure, meaning it had too many queued messages, but is now ready to receive more data.

The websocket that is ready for more data

A fast WebSocket designed for servers.

Features:

This is slightly different than the browser WebSocket which Bun supports for clients.

Powered by uWebSockets.

Bun.serve({
websocket: {
open(ws) {
console.log("Connected", ws.remoteAddress);
},
message(ws, data) {
console.log("Received", data);
ws.send(data);
},
close(ws, code, reason) {
console.log("Disconnected", code, reason);
},
}
});

Sets how binary data is returned in events.

let ws: WebSocket;
ws.binaryType = "uint8array";
ws.addEventListener("message", ({ data }) => {
console.log(data instanceof Uint8Array); // true
});

Custom data that you can assign to a client, can be read and written at any time.

import { serve } from "bun";

serve({
fetch(request, server) {
const data = {
accessToken: request.headers.get("Authorization"),
};
if (server.upgrade(request, { data })) {
return;
}
return new Response();
},
websocket: {
data: {} as {accessToken: string | null},
message(ws) {
console.log(ws.data.accessToken);
}
}
});

The ready state of the client.

console.log(socket.readyState); // 1

The IP address of the client.

console.log(socket.remoteAddress); // "127.0.0.1"

Returns an array of all topics the client is currently subscribed to.

ws.subscribe("chat");
ws.subscribe("notifications");
console.log(ws.subscriptions); // ["chat", "notifications"]

Closes the connection.

Here is a list of close codes:

To close the connection abruptly, use terminate().

The close code to send

The close reason to send

Batches send() and publish() operations, which makes it faster to send data.

The message, open, and drain callbacks are automatically corked, so you only need to call this if you are sending messages outside of those callbacks or in async functions.

The callback to run.

ws.cork((ctx) => {
ctx.send("These messages");
ctx.sendText("are sent");
ctx.sendBinary(new TextEncoder().encode("together!"));
});

Is the client subscribed to a topic?

The topic name.

ws.subscribe("chat");
console.log(ws.isSubscribed("chat")); // true

Sends a ping.

The data to send

Sends a pong.

The data to send

Sends a message to subscribers of the topic.

The topic name.

The data to send.

Should the data be compressed? If the client does not support compression, this is ignored.

ws.publish("chat", "Hello!");
ws.publish("chat", "Compress this.", true);
ws.publish("chat", new Uint8Array([1, 2, 3, 4]));

Sends a binary message to subscribers of the topic.

The topic name.

The data to send.

Should the data be compressed? If the client does not support compression, this is ignored.

ws.publish("chat", new TextEncoder().encode("Hello!"));
ws.publish("chat", new Uint8Array([1, 2, 3, 4]), true);

Sends a text message to subscribers of the topic.

The topic name.

The data to send.

Should the data be compressed? If the client does not support compression, this is ignored.

ws.publish("chat", "Hello!");
ws.publish("chat", "Compress this.", true);

Sends a message to the client.

The data to send.

Should the data be compressed? If the client does not support compression, this is ignored.

ws.send("Hello!");
ws.send("Compress this.", true);
ws.send(new Uint8Array([1, 2, 3, 4]));

Sends a binary message to the client.

The data to send.

Should the data be compressed? If the client does not support compression, this is ignored.

ws.send(new TextEncoder().encode("Hello!"));
ws.send(new Uint8Array([1, 2, 3, 4]), true);

Sends a text message to the client.

The data to send.

Should the data be compressed? If the client does not support compression, this is ignored.

ws.send("Hello!");
ws.send("Compress this.", true);

Subscribes a client to the topic.

The topic name.

ws.subscribe("chat");

Abruptly close the connection.

To gracefully close the connection, use close().

Unsubscribes a client to the topic.

The topic name.

ws.unsubscribe("chat");