CodeResponse does basic error handling from xqueue submission

common/lib/capa/capa/responsetypes.py

@@ -881,12 +881,15 @@ class CodeResponse(LoncapaResponse):
                     'edX_student_response': submission}
         
         # Submit request
-        xqueue_interface.send_to_queue(header=xheader,
-                                       body=json.dumps(contents))
+        success = xqueue_interface.send_to_queue(header=xheader,
+                                                 body=json.dumps(contents))
 
-        # Non-null CorrectMap['queuekey'] indicates that the problem has been queued 
-        cmap = CorrectMap()
-        cmap.set(self.answer_id, queuekey=queuekey, msg='Submitted to queue')
+        cmap = CorrectMap() 
+        if success:
+            # Non-null CorrectMap['queuekey'] indicates that the problem has been queued 
+            cmap.set(self.answer_id, queuekey=queuekey, msg='Submitted to grader')
+        else:
+            cmap.set(self.answer_id, msg='Unable to deliver submission to grader! Please try again later')
 
         return cmap
 
@@ -908,7 +911,7 @@ class CodeResponse(LoncapaResponse):
             self.context['correct'][0] = admap[ad]
 
         # Replace 'oldcmap' with new grading results if queuekey matches.
-        #   If queuekey does not match, we keep waiting for the score_msg whose key actually matchs
+        #   If queuekey does not match, we keep waiting for the score_msg whose key actually matches
         if oldcmap.is_right_queuekey(self.answer_id, queuekey):
             msg = rxml.find('message').text.replace(' ', ' ')
             oldcmap.set(self.answer_id, correctness=self.context['correct'][0], msg=msg, queuekey=None)  # Queuekey is consumed

lms/djangoapps/courseware/xqueue_interface.py

@@ -35,6 +35,7 @@ def send_to_queue(header, body, xqueue_url=None):
     body: Serialized data for the receipient behind the queueing service. The operation of
             xqueue is agnostic to the contents of 'body'
 
+    Returns a 'success' flag indicating successful submission
     '''
     if xqueue_url is None:
         xqueue_url = XQUEUE_SUBMIT_URL
@@ -48,4 +49,7 @@ def send_to_queue(header, body, xqueue_url=None):
         msg = 'Error in xqueue_interface.send_to_queue %s: Cannot connect to server url=%s' % (err, xqueue_url)
         raise Exception(msg)
 
-    #print r.text
+    # Xqueue responses are JSON-serialized dicts
+    xreply = json.loads(r.text)
+
+    return xreply['return_code'] == 0 # return_code == 0 from xqueue indicates successful submission