Merge pull request #3941 from edx/gprice/handle-invalid-json

Improve handling of bad JSON from comments service

lms/lib/comment_client/utils.py

@@ -104,7 +104,15 @@ def perform_request(method, url, data_or_params=None, raw=False,
         if raw:
             return response.text
         else:
-            data = response.json()
+            try:
+                data = response.json()
+            except ValueError:
+                raise CommentClientError(
+                    u"Comments service returned invalid JSON for request {request_id}; first 100 characters: '{content}'".format(
+                        request_id=request_id,
+                        content=response.text[:100]
+                    )
+                )
             if paged_results:
                 dog_stats_api.histogram(
                     'comment_client.request.paged.result_count',