update lcc_dtmf to use media server

backport of https://github.com/jambonz/feature-server/pull/153

lib/session/call-session.js

@@ -458,6 +458,18 @@ class CallSession extends Emitter {
     return this.accountInfo?.account?.service_provider_sid;
   }
 
+  /**
+   * true when we are no longer anchored in the media path (media released to the SBC).
+   * Media release is a feature of the dial verb; when the current task is a dial we consult its
+   * media path, otherwise media is anchored at the media server for the life of the app.
+   */
+  get isMediaReleased() {
+    if (this.currentTask?.name === TaskName.Dial) {
+      return this.currentTask.mediaPath !== MediaPath.FullMedia;
+    }
+    return false;
+  }
+
   /**
    * returns true if this session was transferred from another server
    */
@@ -1784,26 +1796,46 @@ class CallSession extends Emitter {
      * media stream (via send_dtmf), which the SBC/rtpengine simply forwards. This is reliable
      * regardless of whether rtpengine is transcoding the call. Sending SIP INFO to the SBC
      * instead relies on rtpengine 'play DTMF' injection, which silently no-ops on calls that
-     * are not being transcoded (rtpengine has no DSP to synthesize the tone into). We fall back
-     * to SIP INFO only when we have no endpoint in the media path for the targeted leg, e.g. when
-     * media has been released to the SBC.
+     * are not being transcoded (rtpengine has no DSP to synthesize the tone into).
      * this.ep is the endpoint facing the caller (A) leg; this.currentTask.ep is the endpoint
      * facing the dialed (B) leg.
+     *
+     * We choose the path based on the media routing (this.isMediaReleased), not merely on whether
+     * an endpoint object exists. While anchored in the media path we send via send_dtmf, and if
+     * that fails we deliberately do NOT fall back to SIP INFO: the media path is the reliable one,
+     * so a failure here is a real error (falling back risks a silently-dropped or duplicated
+     * digit). We log and raise an alert instead. SIP INFO is used only once media has been
+     * released to the SBC, when there is no endpoint in the media path at all.
      */
-    const ep = callSid === this.callSid ? this.ep : this.currentTask?.ep;
-    if (ep?.connected) {
+    if (!this.isMediaReleased) {
+      const ep = callSid === this.callSid ? this.ep : this.currentTask?.ep;
       try {
+        if (!ep?.connected) throw new Error('no connected media endpoint for the targeted leg');
         this.logger.debug(`CallSession:_lccDtmf - sending ${digit}@${duration} via send_dtmf on ${ep.uuid}`);
         await ep.execute('send_dtmf', `${digit}@${duration}`);
         return;
       } catch (err) {
-        this.logger.error({err},
-          'CallSession:_lccDtmf - error sending DTMF via send_dtmf, falling back to SIP INFO');
+        this.logger.error({err}, 'CallSession:_lccDtmf - error sending DTMF via send_dtmf');
+        const {writeAlerts} = this.srf.locals;
+        if (writeAlerts) {
+          try {
+            writeAlerts({
+              alert_type: 'dtmf-send-failure',
+              account_sid: this.accountSid,
+              service_provider_sid: this.serviceProviderSid,
+              message: `failed to send DTMF digit ${digit} to ${callSid === this.callSid ? 'caller' : 'called party'}`,
+              target_sid: this.callSid
+            });
+          } catch (alertErr) {
+            this.logger.error({err: alertErr}, 'CallSession:_lccDtmf - error writing dtmf-send-failure alert');
+          }
+        }
+        return;
       }
     }
 
-    /* fallback: signal the SBC to inject DTMF via SIP INFO (used when media is released
-     * and we have no endpoint in the media path for the targeted leg)
+    /* no endpoint in the media path (e.g. media released to the SBC): signal the SBC to inject
+     * DTMF via SIP INFO
      */
     try {
       const dlg = callSid === this.callSid ? this.dlg : this.currentTask.dlg;

lib/tasks/dial.js

@@ -176,6 +176,13 @@ class TaskDial extends Task {
     return this.data.exitMediaPath;
   }
 
+  /* current media routing for this dial: MediaPath.FullMedia (anchored at the media server),
+   * PartialMedia or NoMedia (media released to the SBC)
+   */
+  get mediaPath() {
+    return this._mediaPath;
+  }
+
   get summary() {
     if (this.target.length === 1) {
       const target = this.target[0];