I am pulling my hair out over this. I'm developing a webapp in Django 1.3 (recently upgraded from 1.2.5 in a feeble hope that this might solve my error) and I've come across a bizzare bug in one of my views.
The view is called as an AJAX request from the client. If I call the view as a GET request, all is fine and dandy. If I call it as a POST request with no data, all is fine and dandy. But, if I call it as POST and actually include data (no matter what that data is) Django returns a blank page.
Being the kind to tinker, I discovered that I can print from my view and get output in the debug console, so I went to work, and discovered this strange oddity:
c = Character.objects.get(id=int(character))
This is the first line of code in that view that deals with a model. Printing shows that not only is character a sane value (it's the ID passed in by the request) but c is actually ending up with the correct database record. Regardless, if that line is called, Django's output for the request is zilch. Nada. Nothing.
If I return early before doing anything with my Models, Django correctly renders the rest of the request. Doing something with the Models causes a response 200 to be sent, but the content seems to be omitted.
This only seems to happen when POST data is sent, regardless of whether that post data is read or used in any way. I'm completely and utterly baffled by this. I'm going to post my code here and hope that someone here has some clue as to what black magic might be going on behind the scenes.
This is the view itself, which is called straight from urls.py:
@csrf_exempt
def ajax_update(request, character):
#determine the timestamp to send the client *before* polling
#the database
update_time = int(time.time())
#grab each update... thingy as json, and put it all together
output = {
"events": current_events(request, character, "default"),
"character": character,
"update_time": update_time,
}
return HttpResponse(json.dumps(output), mimetype = "application/json")
This is the current_events code, which contains the mentioned line:
def current_events(request, character, type = "default", timestamp = 0):
'''
purpose: grab the last 3 days worth of events, or the last 10 events,
whichever is a larger list.
'''
#TODO: actually do something with timestamp
c = Character.objects.get(id=int(character))
#DEBUG: What on earth is going on here?
print c
#TODO: See if this can be optimized into a single query
event_links = EventLink.objects.filter(viewer=c)
events = Event.objects.filter(id__in=event_links.values('event')).order_by('timestamp')
t = loader.get_template('ajax/world-events.html')
output = []
for event in events:
revisions = Event.objects.filter(original_event=event.id).order_by('timestamp')
display_message = event.message
history = []
if len(revisions):
history.append(event) #first item in the history is the original event
history.extend(revisions)
display_message = history[-1].message
output.append({
"id": event.id,
"writer": event.writer.id,
"type": event.type,
"timestamp": int(time.mktime(event.timestamp.timetuple())),
"message": t.render(RequestContext(request, {"event_text": display_message, "event": event, "history": history}))
})
return output
And finally, this is the CoffeeScript which calls the code, using jQuery, from the client:
auto_refresh_abort = 0
last_server_timestamp = 0
window.update_display = ->
#ajax call to grab events from the server
$.ajax
type: 'POST'
url: "/ajax/update/"+window.active_character
data:
"last_update": last_server_timestamp
dataType: "json"
success: (output) ->
auto_refresh_abort = 0
update_character_log output.events
error: (XMLHttpRequest, textStatus, errorThrown) ->
auto_refresh_abort += 1
console.log XMLHttpRequest
return null
If you think it would help (this is a LOT already) I can post any other code samples needed, like the model code itself. I can confirm that the Character which is being looked up in my test cases does exist, and it's just a standard Django ID, I'm not doing anything weird with it.
Thanks in advance.
Update: As requested, here is a sample of what output should contain:
{'update_time': 1305984080, 'character': u'1', 'events': /*snip*/}
I've verified that code execution is making it all the way through, and that the output passed to HttpResponse does contain this data. For giggles, I inserted a return "TASTY" after the line where I poll Character, so that output's data should be:
{'update_time': 1305984080, 'character': u'1', 'events': 'TASTY'}
and confirmed that this is working. I can "print output" to the debug console right before HttpRequest and this is displayed.
If I comment out the line dealing with Character, my browser receives this data as the content of the request. Also, if I leave the code as-is and simply do not send POST data, the browser receives the correct data. The specific case where it fails is when I manipulate models after having sent in POST data from the client-- in this case the browser receives exactly the same HTTP headers, but no content. The headers that it receives are:
Content-Type:application/json
Date:Sat, 21 May 2011 13:29:38 GMT
Server:WSGIServer/0.1 Python/2.6
but no actual content is delivered.
