feat fast recognition (#461)

* feat fast recognition

* don't use buffer transcript for fast recognition

* update verb specification

* fix merge conflict

---------

Co-authored-by: Dave Horton <daveh@beachdognet.com>

lib/tasks/gather.js

@@ -59,6 +59,9 @@ class TaskGather extends SttTask {
         logger.debug('Gather: an empty hints array was supplied, so we will mask global hints');
         this.maskGlobalSttHints = true;
       }
+      // fast Recognition, fire event after a specified time after the last hypothesis.
+      this.fastRecognitionTimeout =  typeof this.data.recognizer.fastRecognitionTimeout === 'number' ?
+        this.data.recognizer.fastRecognitionTimeout * 1000 : 0;
     }
 
     this.digitBuffer = '';
@@ -520,6 +523,22 @@ class TaskGather extends SttTask {
     this._asrTimer = null;
   }
 
+  _startFastRecognitionTimer(evt) {
+    assert(this.fastRecognitionTimeout > 0);
+    this._clearFastRecognitionTimer();
+    this._fastRecognitionTimer = setTimeout(() => {
+      evt.is_final = true;
+      this._resolve('speech', evt);
+    }, this.fastRecognitionTimeout);
+  }
+
+  _clearFastRecognitionTimer() {
+    if (this._fastRecognitionTimer) {
+      clearTimeout(this._fastRecognitionTimer);
+    }
+    this._fastRecognitionTimer = null;
+  }
+
   _startFinalAsrTimer() {
     this._clearFinalAsrTimer();
     this._finalAsrTimer = setTimeout(() => {
@@ -657,6 +676,9 @@ class TaskGather extends SttTask {
         }
         this._killAudio(cs);
       }
+      if (this.fastRecognitionTimeout) {
+        this._startFastRecognitionTimer(evt);
+      }
       if (this.partialResultHook) {
         const b3 = this.getTracingPropagation();
         const httpHeaders = b3 && {b3};
@@ -821,6 +843,7 @@ class TaskGather extends SttTask {
     }
     clearTimeout(this.interDigitTimer);
     this._clearTimer();
+    this._clearFastRecognitionTimer();
 
     if (this.isContinuousAsr && reason.startsWith('speech')) {
       evt = {