Merge pull request #233 from edx/db/ajax-server-error

Make server errors return JSON if requested via AJAX

cms/djangoapps/contentstore/views/error.py

-from django.http import HttpResponseServerError, HttpResponseNotFound
+from django.http import (HttpResponse, HttpResponseServerError,
+                         HttpResponseNotFound)
 from mitxmako.shortcuts import render_to_string, render_to_response
+import functools
+import json
 
 __all__ = ['not_found', 'server_error', 'render_404', 'render_500']
 
 
+def jsonable_error(status=500, message="The Studio servers encountered an error"):
+    """
+    A decorator to make an error view return an JSON-formatted message if
+    it was requested via AJAX.
+    """
+    def outer(func):
+        @functools.wraps(func)
+        def inner(request, *args, **kwargs):
+            if request.is_ajax():
+                content = json.dumps({"error": message})
+                return HttpResponse(content, content_type="application/json",
+                                    status=status)
+            else:
+                return func(request, *args, **kwargs)
+        return inner
+    return outer
+
+
+@jsonable_error(404, "Resource not found")
 def not_found(request):
     return render_to_response('error.html', {'error': '404'})
 
 
+@jsonable_error(500, "The Studio servers encountered an error")
 def server_error(request):
     return render_to_response('error.html', {'error': '500'})
 
 
+@jsonable_error(404, "Resource not found")
 def render_404(request):
     return HttpResponseNotFound(render_to_string('404.html', {}))
 
 
+@jsonable_error(500, "The Studio servers encountered an error")
 def render_500(request):
     return HttpResponseServerError(render_to_string('500.html', {}))

cms/static/coffee/src/main.coffee

@@ -19,6 +19,9 @@ $ ->
     if ajaxSettings.notifyOnError is false
       return
     if jqXHR.responseText
+      try
+        message = JSON.parse(jqXHR.responseText).error
+      catch error
         message = _.str.truncate(jqXHR.responseText, 300)
     else
       message = gettext("This may be happening because of an error with our server or your internet connection. Try refreshing the page or making sure you are online.")

common/djangoapps/util/views.py

@@ -4,7 +4,10 @@ import sys
 
 from django.conf import settings
 from django.core.validators import ValidationError, validate_email
-from django.http import Http404, HttpResponse, HttpResponseNotAllowed
+from django.views.decorators.csrf import requires_csrf_token
+from django.views.defaults import server_error
+from django.http import (Http404, HttpResponse, HttpResponseNotAllowed,
+                         HttpResponseServerError)
 from dogapi import dog_stats_api
 from mitxmako.shortcuts import render_to_response
 import zendesk
@@ -16,6 +19,19 @@ import track.views
 log = logging.getLogger(__name__)
 
 
+@requires_csrf_token
+def jsonable_server_error(request, template_name='500.html'):
+    """
+    500 error handler that serves JSON on an AJAX request, and proxies
+    to the Django default `server_error` view otherwise.
+    """
+    if request.is_ajax():
+        msg = {"error": "The edX servers encountered an error"}
+        return HttpResponseServerError(json.dumps(msg))
+    else:
+        return server_error(request, template_name=template_name)
+
+
 def calculate(request):
     ''' Calculator in footer of every page. '''
     equation = request.GET['equation']
@@ -228,4 +244,3 @@ def accepts(request, media_type):
     """Return whether this request has an Accept header that matches type"""
     accept = parse_accept_header(request.META.get("HTTP_ACCEPT", ""))
     return media_type in [t for (t, p, q) in accept]
-