WebSocket BroadcastChannel

import { createBroadcastChannel } from "https://deno.land/x/websocket_broadcastchannel/mod.ts";

const channel = createBroadcastChannel("my-channel");
// Now use the channel as usual.

import { createBroadcastChannel } from "https://deno.land/x/websocket_broadcastchannel/mod.ts";

const pid = Deno.pid;
const pidLastDigit = pid % 10;
const delay = pidLastDigit * 1000;

const log = (s: string, ...args: unknown[]) => {
  console.log(`[broadcast.ts#${pid}] ${s}`, ...args);
};

log("run this in multiple terminals on the same host, to see it work");

log("starting...");
const testChannel = createBroadcastChannel("test");
log("testChannel.constructor.name", testChannel.constructor.name);

testChannel.onmessage = (event: MessageEvent<unknown>) => {
  log("onmessage event.data =", event.data);
};

testChannel.onmessageerror = (event: Event) => {
  log("onmessageerror event =", event);
};

setInterval(() => {
  log("posting...");
  testChannel.postMessage(`hello from ${pid}`);
  log("posted");
  log(`waiting ${delay / 1000}s...`);
}, delay);

import { serve } from "https://deno.land/std@0.194.0/http/server.ts";
import { createBroadcastChannel } from "https://deno.land/x/websocket_broadcastchannel/mod.ts";

const messages: string[] = [];
// Create a new broadcast channel named earth.
const channel = createBroadcastChannel("earth");
// Set onmessage event handler.
channel.onmessage = (event: MessageEvent) => {
  // Update the local state when other instances
  // send us a new message.
  messages.push(event.data);
};

function handler(req: Request): Response {
  const { pathname, searchParams } = new URL(req.url);

  // Handle /send?message=<message> endpoint.
  if (pathname.startsWith("/send")) {
    const message = searchParams.get("message");
    if (!message) {
      return new Response("?message not provided", { status: 400 });
    }

    // Update local state.
    messages.push(message);
    // Inform all other active instances of the deployment
    // about the new message.
    channel.postMessage(message);
    return new Response("message sent");
  }

  // Handle /messages request.
  if (pathname.startsWith("/messages")) {
    return new Response(
      JSON.stringify(messages),
      {
        headers: { "content-type": "application/json" },
      },
    );
  }

  return new Response("not found", { status: 404 });
}

serve(handler, { port: parseInt(Deno.env.get("PORT") ?? "8080", 10) });

import {
  BroadcastChannelIsh,
  createBroadcastChannel,
  Logger,
  logger,
  WebSocketBroadcastChannel,
} from "https://deno.land/x/websocket_broadcastchannel/mod.ts";

const log: Logger = logger(import.meta.url);

/**
 * The application's main entry point.
 */
async function main() {
  log("Starting...");
  const chat: BroadcastChannelIsh = createBroadcastChannel(
    "chat",
  );

  if (chat instanceof WebSocketBroadcastChannel) {
    console.error(`
===============================================================================
Welcome to the chat example of WebSocketBroadcastChannel!

You are not running on Deno Deploy. This means that you are not guaranteed to
have application-wide BroadcastChannel available. This example uses a WebSocket
to provide a host-wide one.

Do start several processes of this example in different terminals on the same
computer. Then type messages in one, and see them appear in them all.

To exit a process, press ctrl-d on a separate line. Remaining processes will
continue to run. If you exit the one that happened to act as server, one of
the others will take over that duty, and the rest will reconnect to it.
-------------------------------------------------------------------------------
    `.trim());
  } else {
    console.error(`
===============================================================================
Running on Deno Deploy. Application-wide BroadcastChannel is fully supported,
so you don't need WebSocketBroadcastChannel!

(However, it makes little sense to read from stdin on Deno Deploy, so this
example CLI-based chat app is only useful on Deno Deploy, for seeing this
detection in your logs :)
===============================================================================
`);
  }

  chat.addEventListener("message", handleIncoming);

  try {
    log("continuously reading from stdin");
    const decoder = new TextDecoder();
    for await (const chunk of Deno.stdin.readable) {
      const text = decoder.decode(chunk).trimEnd();
      log("stdin text =", text);
      chat.postMessage(text);
    }

    log("stdin closed, closing chat");
  } finally {
    chat.removeEventListener("message", handleIncoming);
    chat.close();
  }

  log("Done.");
}

/**
 * Prints an incoming chat message to stdout.
 * @param event
 */
function handleIncoming(event: Event): void {
  if (!(event instanceof MessageEvent)) {
    log.sub(handleIncoming.name)("not a MessageEvent");
    return;
  }

  console.log(event.data);
}

if (import.meta.main) {
  await main();
}