external_api: add ability to send a text message through datachannels

conference.js

 
 import { openConnection } from './connection';
 
+import { ENDPOINT_TEXT_MESSAGE_NAME } from './modules/API/constants';
 import AuthHandler from './modules/UI/authentication/AuthHandler';
 import Recorder from './modules/recorder/Recorder';
 
 
         room.on(
             JitsiConferenceEvents.ENDPOINT_MESSAGE_RECEIVED,
-            (...args) => APP.store.dispatch(endpointMessageReceived(...args)));
+            (...args) => {
+                APP.store.dispatch(endpointMessageReceived(...args));
+                if (args && args.length >= 2) {
+                    const [ sender, eventData ] = args;
+
+                    if (eventData.name === ENDPOINT_TEXT_MESSAGE_NAME) {
+                        APP.API.notifyEndpointTextMessageReceived({
+                            senderInfo: {
+                                jid: sender._jid,
+                                id: sender._id
+                            },
+                            eventData
+                        });
+                    }
+                }
+            });
 
         room.on(
             JitsiConferenceEvents.LOCK_STATE_CHANGED,

doc/api.md

 api.executeCommand('avatarUrl', 'https://avatars0.githubusercontent.com/u/3671647');
 ```
 
+* **sendEndpointTextMessage** - Sends a text message to another participant through the datachannels.
+```javascript
+api.executeCommand('receiverParticipantId', 'text');
+```
+
 You can also execute multiple commands using the `executeCommands` method:
 ```javascript
 api.executeCommands(commands);
 }
 ```
 
+* **endpointTextMessageReceived** - event notifications about a text message received through datachannels.
+The listener will receive an object with the following structure:
+```javascript
+{
+    senderInfo: {
+        jid: string, // the jid of the sender
+        id: string // the participant id of the sender
+    },
+    eventData: {
+        name: string // the name of the datachannel event: `endpoint-text-message`
+        text: string // the received text from the sender
+    }
+}
+```
+
 * **micError** - event notifications about Jitsi-Meet having failed to access the mic. The listener will receive an object with the following structure:
 ```javascript
 {

modules/API/API.js

 import { toggleTileView } from '../../react/features/video-layout';
 import { getJitsiMeetTransport } from '../transport';
 
-import { API_ID } from './constants';
+import { API_ID, ENDPOINT_TEXT_MESSAGE_NAME } from './constants';
 import {
     processExternalDeviceRequest
 } from '../../react/features/device-selection/functions';
         'avatar-url': avatarUrl => {
             sendAnalytics(createApiEvent('avatar.url.changed'));
             APP.conference.changeLocalAvatarUrl(avatarUrl);
+        },
+        'send-endpoint-text-message': (to, text) => {
+            logger.debug('Send endpoint message command received');
+            try {
+                APP.conference.sendEndpointMessage(to, {
+                    name: ENDPOINT_TEXT_MESSAGE_NAME,
+                    text
+                });
+            } catch (err) {
+                logger.error('Failed sending endpoint text message', err);
+            }
         }
     };
     transport.on('event', ({ data, name }) => {
         });
     }
 
+    /**
+     * Notify external application (if API is enabled) that user received
+     * a text message through datachannels.
+     *
+     * @param {Object} data - The event data.
+     * @returns {void}
+     */
+    notifyEndpointTextMessageReceived(data: Object) {
+        this._sendEvent({
+            name: 'endpoint-text-message-received',
+            data
+        });
+    }
+
     /**
      * Notify external application (if API is enabled) that the device list has
      * changed.

modules/API/constants.js

 /**
  * JitsiMeetExternalAPI id - unique for a webpage.
  */
-export const API_ID
-    = parseURLParams(window.location).jitsi_meet_external_api_id;
+export const API_ID = parseURLParams(window.location).jitsi_meet_external_api_id;
+
+/**
+ * The payload name for the datachannel/endpoint text message event
+ */
+export const ENDPOINT_TEXT_MESSAGE_NAME = 'endpoint-text-message';

modules/API/external/external_api.js

     email: 'email',
     hangup: 'video-hangup',
     password: 'password',
+    sendEndpointTextMessage: 'send-endpoint-text-message',
     sendTones: 'send-tones',
     subject: 'subject',
     submitFeedback: 'submit-feedback',
     'device-list-changed': 'deviceListChanged',
     'display-name-change': 'displayNameChange',
     'email-change': 'emailChange',
+    'endpoint-text-message-received': 'endpointTextMessageReceived',
     'feedback-submitted': 'feedbackSubmitted',
     'feedback-prompt-displayed': 'feedbackPromptDisplayed',
     'filmstrip-display-changed': 'filmstripDisplayChanged',