Feat/handle 3pcc invite (#1005)

* wip

* wip

* linting

lib/session/call-session.js

@@ -400,6 +400,13 @@ class CallSession extends Emitter {
     return this.application.transferredCall === true;
   }
 
+  /**
+   * returns true if this session is an inbound call session
+   */
+  get isInboundCallSession() {
+    return this.constructor.name === 'InboundCallSession';
+  }
+
   /**
    * returns true if this session is a ConfirmCallSession
    */
@@ -428,6 +435,10 @@ class CallSession extends Emitter {
     return this.constructor.name === 'SmsCallSession';
   }
 
+  get is3pccInvite() {
+    return this.isInboundCallSession && this.req?.body?.length === 0;
+  }
+
   get webhook_secret() {
     return this.accountInfo?.account?.webhook_secret;
   }
@@ -2098,7 +2109,6 @@ Duration=${duration} `
       //ep.cs = this;
       this.ep = ep;
       this.logger.info(`allocated endpoint ${ep.uuid}`);
-
       this._configMsEndpoint();
 
       this.ep.on('destroy', () => {
@@ -2260,7 +2270,8 @@ Duration=${duration} `
         },
         localSdp: this.ep.local.sdp
       });
-      this.logger.debug('answered call');
+
+      const tidyUp = () => {
         this.dlg.on('destroy', this._callerHungup.bind(this));
         this.wrapDialog(this.dlg);
         this.dlg.callSid = this.callSid;
@@ -2276,6 +2287,26 @@ Duration=${duration} `
           this.dlg.on('message', this._onRequestWithinDialog.bind(this));
         }
         this.logger.debug(`CallSession:propagateAnswer - answered callSid ${this.callSid}`);
+      };
+
+      if (this.is3pccInvite) {
+        return new Promise((resolve, reject) => {
+          this.dlg.once('ack', (ackRequest) => {
+            this.logger.debug({body: ackRequest.body}, 'received ACK for 3pcc invite');
+            this.ep.modify(ackRequest.body)
+              .then(() => {
+                tidyUp();
+                return resolve();
+              })
+              .catch((err) => {
+                this.logger.info({err}, 'Error modifying endpoint with ACK');
+                reject(err);
+              });
+          });
+          this.logger.debug('this is a 3pcc invite');
+        });
+      }
+      tidyUp();
     }
     else {
       this.logger.debug('CallSession:propagateAnswer - call already answered - re-anchor media with a reinvite');