fix(RTC): cache and send pinned endpoint

Do the same which was done for the selected endpoint. That is if
an endpoint is pinned, before data channels are available then the value
should be cached and sent as soon as they are opened.

modules/RTC/RTC.js

@@ -98,11 +98,30 @@ export default class RTC extends Listenable {
          */
         this._lastN = null;
 
-        // Defines the last N endpoints list. It can be null or an array once
-        // initialised with a datachannel last N event.
-        // @type {Array<string>|null}
+        /**
+         * Defines the last N endpoints list. It can be null or an array once
+         * initialised with a datachannel last N event.
+         * @type {Array<string>|null}
+         * @private
+         */
         this._lastNEndpoints = null;
 
+        /**
+         * The endpoint ID of currently pinned participant or <tt>null</tt> if
+         * no user is pinned.
+         * @type {string|null}
+         * @private
+         */
+        this._pinnedEndpoint = null;
+
+        /**
+         * The endpoint ID of currently selected participant or <tt>null</tt> if
+         * no user is selected.
+         * @type {string|null}
+         * @private
+         */
+        this._selectedEndpoint = null;
+
         // The last N change listener.
         this._lastNChangeListener = this._onLastNChanged.bind(this);
 
@@ -165,14 +184,17 @@ export default class RTC extends Listenable {
                 // about video selections so that it can do adaptive simulcast,
                 // we want the notification to trigger even if userJid
                 // is undefined, or null.
-                // XXX why do we not do the same for pinned endpoints?
                 try {
+                    this.dataChannels.sendPinnedEndpointMessage(
+                        this._pinnedEndpoint);
                     this.dataChannels.sendSelectedEndpointMessage(
-                        this.selectedEndpoint);
+                        this._selectedEndpoint);
                 } catch (error) {
                     GlobalOnErrorHandler.callErrorHandler(error);
-                    logger.error('Cannot sendSelectedEndpointMessage ',
-                        this.selectedEndpoint, '. Error: ', error);
+                    logger.error(
+                        `Cannot send selected(${this._selectedEndpoint})`
+                        + `pinned(${this._pinnedEndpoint}) endpoint message.`,
+                        error);
                 }
 
                 this.removeListener(RTCEvents.DATA_CHANNEL_OPEN,
@@ -247,7 +269,7 @@ export default class RTC extends Listenable {
      */
     selectEndpoint(id) {
         // cache the value if channel is missing, till we open it
-        this.selectedEndpoint = id;
+        this._selectedEndpoint = id;
         if (this.dataChannels && this.dataChannelsOpen) {
             this.dataChannels.sendSelectedEndpointMessage(id);
         }
@@ -262,12 +284,10 @@ export default class RTC extends Listenable {
      * fails.
      */
     pinEndpoint(id) {
-        if (this.dataChannels) {
+        // cache the value if channel is missing, till we open it
+        this._pinnedEndpoint = id;
+        if (this.dataChannels && this.dataChannelsOpen) {
             this.dataChannels.sendPinnedEndpointMessage(id);
-        } else {
-            // FIXME: cache value while there is no data channel created
-            // and send the cached state once channel is created
-            throw new Error('Data channels support is disabled!');
         }
     }