simplify handling of reinvites from feature server

lib/call-session.js

@@ -154,10 +154,9 @@ class CallSession extends Emitter {
         this.rtpEngineResource.destroy();
         this.activeCallIds.delete(this.req.get('Call-ID'));
       });
-
-      //re-invite
-      dlg.on('modify', this._onReinvite.bind(this, dlg));
     });
+    uas.on('modify', this._onReinvite.bind(this, uas));
+    uac.on('modify', this._onFeatureServerReinvite.bind(this, uac));
 
     // default forwarding of other request types
     forwardInDialogRequests(uas);
@@ -184,6 +183,21 @@ class CallSession extends Emitter {
     }
   }
 
+  async _onFeatureServerReinvite(dlg, req, res) {
+    try {
+      const opts = Object.assign({sdp: req.body, 'to-tag': res.getParsedHeader('To').params.tag},
+        this.rtpEngineOpts.answer);
+      const response = await this.answer(opts);
+      if ('ok' !== response.result) {
+        res.send(488);
+        throw new Error(`_onFeatureServerReinvite: rtpengine failed: ${JSON.stringify(response)}`);
+      }
+      res.send(200, {body: response.sdp});
+    } catch (err) {
+      this.logger.error(err, 'Error handling reinvite from feature server');
+    }
+  }
+
 }
 
 module.exports = CallSession;