fix: robustify the STT streaming results handling (#768)

* fix: robustify the STT streaming results handling

In the STT recognize_listener, the clause that handles 'results' or 'speaker_labels'
was prone to index errors when the 'results' object returned by the service was
empty. This can happen, so this change makes that logic safe to empty (or otherwise
malformed) results.

* Remove buggy extra call to on_hypothesis

Co-authored-by: Mamoon Raja <mamoonraja1@gmail.com>
Co-authored-by: Angelo Paparazzi <angelo.paparazzi@ibm.com>

Author: 3 people

ibm_watson/websocket/recognize_listener.py

@@ -194,18 +194,21 @@ def on_data(self, ws, message, message_type, fin):
 
         # if in streaming
         elif 'results' in json_object or 'speaker_labels' in json_object:
-            hypothesis = ''
-            if 'results' in json_object:
-                hypothesis = json_object['results'][0]['alternatives'][0][
-                    'transcript']
-                b_final = (json_object['results'][0]['final'] is True)
-                transcripts = self.extract_transcripts(
-                    json_object['results'][0]['alternatives'])
-
-                if b_final:
-                    self.callback.on_transcription(transcripts)
-
-                self.callback.on_hypothesis(hypothesis)
+            # If results are present, extract the hypothesis and, if finalized, the full
+            # set of transcriptions and send them to the appropriate callbacks.
+            results = json_object.get('results')
+            if results:
+                b_final = (results[0].get('final') is True)
+                alternatives = results[0].get('alternatives')
+                if alternatives:
+                    hypothesis = alternatives[0].get('transcript')
+                    transcripts = self.extract_transcripts(alternatives)
+                    if b_final:
+                        self.callback.on_transcription(transcripts)
+                    if hypothesis:
+                        self.callback.on_hypothesis(hypothesis)
+
+            # Always call the on_data callback if 'results' or 'speaker_labels' are present
             self.callback.on_data(json_object)
 
     def on_error(self, ws, error):