chat: Plumb message object end to end

This will make it possible for future commits to add hooks that allow
plugins to augment chat messages with arbitrary metadata.

src/static/js/ChatMessage.js

@@ -0,0 +1,50 @@
+'use strict';
+
+/**
+ * Represents a chat message stored in the database and transmitted among users. Plugins can extend
+ * the object with additional properties.
+ *
+ * Supports serialization to JSON.
+ */
+class ChatMessage {
+  static fromObject(obj) {
+    return Object.assign(new ChatMessage(), obj);
+  }
+
+  /**
+   * @param {?string} [text] - Initial value of the `text` property.
+   * @param {?string} [userId] - Initial value of the `userId` property.
+   * @param {?number} [time] - Initial value of the `time` property.
+   */
+  constructor(text = null, userId = null, time = null) {
+    /**
+     * The raw text of the user's chat message (before any rendering or processing).
+     *
+     * @type {?string}
+     */
+    this.text = text;
+
+    /**
+     * The user's author ID.
+     *
+     * @type {?string}
+     */
+    this.userId = userId;
+
+    /**
+     * The message's timestamp, as milliseconds since epoch.
+     *
+     * @type {?number}
+     */
+    this.time = time;
+
+    /**
+     * The user's display name.
+     *
+     * @type {?string}
+     */
+    this.userName = null;
+  }
+}
+
+module.exports = ChatMessage;

src/static/js/chat.js

@@ -15,6 +15,7 @@
  * limitations under the License.
  */
 
+const ChatMessage = require('./ChatMessage');
 const padutils = require('./pad_utils').padutils;
 const padcookie = require('./pad_cookie').padcookie;
 const Tinycon = require('tinycon/tinycon');
@@ -102,10 +103,11 @@ exports.chat = (() => {
     send() {
       const text = $('#chatinput').val();
       if (text.replace(/\s+/, '').length === 0) return;
-      this._pad.collabClient.sendMessage({type: 'CHAT_MESSAGE', text});
+      this._pad.collabClient.sendMessage({type: 'CHAT_MESSAGE', message: new ChatMessage(text)});
       $('#chatinput').val('');
     },
     async addMessage(msg, increment, isHistoryAdd) {
+      msg = ChatMessage.fromObject(msg);
       // correct the time
       msg.time += this._pad.clientTimeOffset;
 

src/static/js/collab_client.js

@@ -272,7 +272,7 @@ const getCollabClient = (ace2editor, serverVars, initialUserInfo, options, _pad)
     } else if (msg.type === 'CLIENT_MESSAGE') {
       callbacks.onClientMessage(msg.payload);
     } else if (msg.type === 'CHAT_MESSAGE') {
-      chat.addMessage(msg, true, false);
+      chat.addMessage(msg.message, true, false);
     } else if (msg.type === 'CHAT_MESSAGES') {
       for (let i = msg.messages.length - 1; i >= 0; i--) {
         chat.addMessage(msg.messages[i], true, true);