1 files changed, 167 insertions, 0 deletions
diff --git a/extensions/broadcast_channel/01_broadcast_channel.js b/extensions/broadcast_channel/01_broadcast_channel.js
new file mode 100644
index 000000000..7670b0cfd
--- /dev/null
+++ b/extensions/broadcast_channel/01_broadcast_channel.js
@@ -0,0 +1,167 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+"use strict";
+
+((window) => {
+  const core = window.Deno.core;
+  const webidl = window.__bootstrap.webidl;
+  const { setTarget } = window.__bootstrap.event;
+
+  const handlerSymbol = Symbol("eventHandlers");
+  function makeWrappedHandler(handler) {
+    function wrappedHandler(...args) {
+      if (typeof wrappedHandler.handler !== "function") {
+        return;
+      }
+      return wrappedHandler.handler.call(this, ...args);
+    }
+    wrappedHandler.handler = handler;
+    return wrappedHandler;
+  }
+  // TODO(lucacasonato) reuse when we can reuse code between web crates
+  function defineEventHandler(emitter, name) {
+    // HTML specification section 8.1.5.1
+    Object.defineProperty(emitter, `on${name}`, {
+      get() {
+        // TODO(bnoordhuis) The "BroadcastChannel should have an onmessage
+        // event" WPT test expects that .onmessage !== undefined. Returning
+        // null makes it pass but is perhaps not exactly in the spirit.
+        return this[handlerSymbol]?.get(name)?.handler ?? null;
+      },
+      set(value) {
+        if (!this[handlerSymbol]) {
+          this[handlerSymbol] = new Map();
+        }
+        let handlerWrapper = this[handlerSymbol]?.get(name);
+        if (handlerWrapper) {
+          handlerWrapper.handler = value;
+        } else {
+          handlerWrapper = makeWrappedHandler(value);
+          this.addEventListener(name, handlerWrapper);
+        }
+        this[handlerSymbol].set(name, handlerWrapper);
+      },
+      configurable: true,
+      enumerable: true,
+    });
+  }
+
+  const _name = Symbol("[[name]]");
+  const _closed = Symbol("[[closed]]");
+
+  const channels = [];
+  let rid = null;
+
+  async function recv() {
+    while (channels.length > 0) {
+      const message = await core.opAsync("op_broadcast_recv", rid);
+
+      if (message === null) {
+        break;
+      }
+
+      const [name, data] = message;
+      dispatch(null, name, new Uint8Array(data));
+    }
+
+    core.close(rid);
+    rid = null;
+  }
+
+  function dispatch(source, name, data) {
+    for (const channel of channels) {
+      if (channel === source) continue; // Don't self-send.
+      if (channel[_name] !== name) continue;
+      if (channel[_closed]) continue;
+
+      const go = () => {
+        if (channel[_closed]) return;
+        const event = new MessageEvent("message", {
+          data: core.deserialize(data), // TODO(bnoordhuis) Cache immutables.
+          origin: "http://127.0.0.1",
+        });
+        setTarget(event, channel);
+        channel.dispatchEvent(event);
+      };
+
+      defer(go);
+    }
+  }
+
+  // Defer to avoid starving the event loop. Not using queueMicrotask()
+  // for that reason: it lets promises make forward progress but can
+  // still starve other parts of the event loop.
+  function defer(go) {
+    setTimeout(go, 1);
+  }
+
+  class BroadcastChannel extends EventTarget {
+    [_name];
+    [_closed] = false;
+
+    get name() {
+      return this[_name];
+    }
+
+    constructor(name) {
+      super();
+
+      const prefix = "Failed to construct 'broadcastChannel'";
+      webidl.requiredArguments(arguments.length, 1, { prefix });
+
+      this[_name] = webidl.converters["DOMString"](name, {
+        prefix,
+        context: "Argument 1",
+      });
+
+      this[webidl.brand] = webidl.brand;
+
+      channels.push(this);
+
+      if (rid === null) {
+        // Create the rid immediately, otherwise there is a time window (and a
+        // race condition) where messages can get lost, because recv() is async.
+        rid = core.opSync("op_broadcast_subscribe");
+        recv();
+      }
+    }
+
+    postMessage(message) {
+      webidl.assertBranded(this, BroadcastChannel);
+
+      const prefix = "Failed to execute 'postMessage' on 'BroadcastChannel'";
+      webidl.requiredArguments(arguments.length, 1, { prefix });
+
+      if (this[_closed]) {
+        throw new DOMException("Already closed", "InvalidStateError");
+      }
+
+      if (typeof message === "function" || typeof message === "symbol") {
+        throw new DOMException("Uncloneable value", "DataCloneError");
+      }
+
+      const data = core.serialize(message);
+
+      // Send to other listeners in this VM.
+      dispatch(this, this[_name], new Uint8Array(data));
+
+      // Send to listeners in other VMs.
+      defer(() => core.opAsync("op_broadcast_send", [rid, this[_name]], data));
+    }
+
+    close() {
+      webidl.assertBranded(this, BroadcastChannel);
+      this[_closed] = true;
+
+      const index = channels.indexOf(this);
+      if (index === -1) return;
+
+      channels.splice(index, 1);
+      if (channels.length === 0) core.opSync("op_broadcast_unsubscribe", rid);
+    }
+  }
+
+  defineEventHandler(BroadcastChannel.prototype, "message");
+  defineEventHandler(BroadcastChannel.prototype, "messageerror");
+
+  window.__bootstrap.broadcastChannel = { BroadcastChannel };
+})(this);