implement generic broadcastchannel and apply it to websocket provider

lib/binary.js

@@ -1,10 +1,40 @@
+/* eslint-env browser */
+
 /**
  * @module binary
  */
 
+import * as string from './string.js'
+import * as globals from './globals.js'
+
 export const BITS32 = 0xFFFFFFFF
 export const BITS21 = (1 << 21) - 1
 export const BITS16 = (1 << 16) - 1
 
 export const BIT26 = 1 << 26
 export const BIT32 = 1 << 32
+
+/**
+ * @param {Uint8Array} bytes
+ * @return {string}
+ */
+export const toBase64 = bytes => {
+  let s = ''
+  for (let i = 0; i < bytes.byteLength; i++) {
+    s += string.fromCharCode(bytes[i])
+  }
+  return btoa(s)
+}
+
+/**
+ * @param {string} s
+ * @return {Uint8Array}
+ */
+export const fromBase64 = s => {
+  const a = atob(s)
+  const bytes = globals.createUint8ArrayFromLen(a.length)
+  for (let i = 0; i < a.length; i++) {
+    bytes[i] = a.charCodeAt(i)
+  }
+  return bytes
+}

lib/broadcastchannel.js

@@ -0,0 +1,72 @@
+/* eslint-env browser */
+
+import * as binary from './binary.js'
+import * as globals from './globals.js'
+
+/**
+ * @typedef {Object} Channel
+ * @property {Set<Function>} Channel.subs
+ * @property {BC} Channel.bc
+ */
+
+/**
+ * @type {Map<string, Channel>}
+ */
+const channels = new Map()
+
+class LocalStoragePolyfill {
+  constructor (room) {
+    this.room = room
+    this.onmessage = null
+    addEventListener('storage', e => e.key === room && this.onmessage !== null && this.onmessage({ data: binary.fromBase64(e.newValue) }))
+  }
+  /**
+   * @param {ArrayBuffer} data
+   */
+  postMessage (buf) {
+    if (typeof localStorage !== 'undefined') {
+      localStorage.setItem(this.room, binary.toBase64(globals.createUint8ArrayFromArrayBuffer(buf)))
+    }
+  }
+}
+
+// Use BroadcastChannel or Polyfill
+const BC = typeof BroadcastChannel === 'undefined' ? LocalStoragePolyfill : BroadcastChannel
+
+/**
+ * @param {string} room
+ * @return {Channel}
+ */
+const getChannel = room => {
+  let c = channels.get(room)
+  if (c === undefined) {
+    const subs = new Set()
+    const bc = new BC(room)
+    bc.onmessage = e => subs.forEach(sub => sub(e.data))
+    c = {
+      bc, subs
+    }
+    channels.set(room, c)
+  }
+  return c
+}
+
+/**
+ * @function
+ * @param {string} room
+ * @param {Function} f
+ */
+export const subscribe = (room, f) => getChannel(room).subs.add(f)
+
+/**
+ * Publish data to all subscribers (including subscribers on this tab)
+ *
+ * @function
+ * @param {string} room
+ * @param {ArrayBuffer} data
+ */
+export const publish = (room, data) => {
+  const c = getChannel(room)
+  c.bc.postMessage(data)
+  c.subs.forEach(sub => sub(data))
+}