I have a view in Django which streams a response. (Think of a web-based chat circa 1999, or the comet technique.)
def events(request):
def generate_events():
for i in range(10):
time.sleep(2)
yield " " * 1024
yield "This is some text.\n"
return HttpResponse(generate_events())
Now, I'd like to detect when the user cancels the loading of the page, since there is no point in sending more data. Ideally, there would be something like:
if not request.is_alive():
return
Is there a way to achieve this in Django?
I really don't think you can do that from the server-side. But I'm sure you could use JavaScript to get some decent results. The "stream" will die when the JS stops asking for stuff from the server like in the case of a cancelled request.
Related
I'm programming an App for the Aldebaran's Pepper robot. I'm using Choregraphe and I made an html for displaying in robots tablet. I have made the boxes for displaying the web and I need to pass a variable from Python to the web Javascript.
Is there any way to do it?
The Python code is the same as the default of a Raise Event box, it receives a string "IMAGE" on his onStart input:
class MyClass(GeneratedClass):
def __init__(self):
GeneratedClass.__init__(self)
pass
def onLoad(self):
self.memory = ALProxy("ALMemory")
def onUnload(self):
self.memory = None
def onInput_onStart(self, p):
self.memory.raiseEvent(self.getParameter("key"), p)
self.onStopped(p)
def onInput_onStop(self):
self.onUnload() #~ it is recommended to call onUnload of this box in a onStop method, as the code written in onUnload is used to stop the box as well
pass
And the Javascript code is this:
$('document').ready(function(){
var session = new QiSession();
session.service("ALMemory").done(function (ALMemory) {
ALMemory.subscriber("PepperQiMessaging/totablet").done(function(subscriber) {
$("#log").text("AAA");
subscriber.signal.connect(toTabletHandler);
});
});
function toTabletHandler(value) {
$("#log").text("-> ");
}
});
It enters the first #log but not the second of JS.
yes, I think the webpage is loading too late to catch your event. One quick solution would be to send an event from Javascript when the page is ready, and wait for this event in your Python script. Once this event is received, then you know that the webpage is ready and you can send the "sendImage" event.
I solved the problem. I put a delay box of 2 seconds between the show HTML box and the sendImage box like in the image below:
I think the problem was that the string that is send to tabled was sent before the web was prepared to receive it, and the delay of 2 seconds (with 1 it doesn't work) the page have time to prepare for receiving data.
I am developing a django app with a large amount of views. But every time I write a view I have to cater the possibility of params being not provided.. I am writing the same code again and again. I was wondering if there was a django shortcut that could do the job and return a standard error message if a param was not provided.. I want to do something like..
#required_params({'get': ['param1', 'param2'], 'post': ['param3', 'param4']})
def my_view(request):
# Do my stuff
A possible solution for this would be to make use of the 'decorator_from_middleware' functionality: https://docs.djangoproject.com/en/dev/ref/utils/#django.utils.decorators.decorator_from_middleware
It would allow you to process the request on a per view basis and assert that the parameters from the requet meet your criteria and if not return a standard error response.
I've been trying this for a couple of days now but I can't seem to wrap my head around this. My problem essentially lies with the fact if I have 2 browsers requesting at the same time, my server-side socketio response will return the wrong results to the wrong browser requesting (the results get swapped). I think my problem is that I don't know how does socket.io determines which browser to return the results to. The current code has lotsa moving parts and it'll be a pain to strip to manner that people can find meaningful so instead, I think I will be able to resolve my bug if someone can help me work through and understand the django_chat example found at https://github.com/abourget/gevent-socketio/tree/master/examples/django_chat. So here goes:
So sequentially, when a user enters something into chat, this code fires
$('#send-message').submit(function () {
message('me', $('#message').val());
socket.emit('user message', $('#message').val());
clear();
$('#lines').get(0).scrollTop = 10000000;
return false;
});
The socket.emit function then triggers this function in the ChatNameSpace class:
def on_user_message(self, msg):
self.log('User message: {0}'.format(msg))
self.emit_to_room(self.room, 'msg_to_room',
self.socket.session['nickname'], msg)
return True
Which in turn calls this emit_to_room function found in the RoomsMixin class
def emit_to_room(self, room, event, *args):
"""This is sent to all in the room (in this particular Namespace)"""
pkt = dict(type="event",
name=event,
args=args,
endpoint=self.ns_name)
room_name = self._get_room_name(room)
for sessid, socket in self.socket.server.sockets.iteritems():
if 'rooms' not in socket.session:
continue
if room_name in socket.session['rooms'] and self.socket != socket:
socket.send_packet(pkt)
I understand that when a user joins a chat room, the [rooms] session gets updated with the chatroom he belongs to. It looks something like ['/chat_1', '/chat_2'] where the numbers signify the primary key of the room object.
This is where I get lost. Where does this distinction of specific chatrooms meet the frontend js code? How does the emit function know where to send the response to which room?
I want to build single page application using Backbone.js and Django.
For checking user is authenticated or not,
I wrote a method get_identity method in django side.
If request.user.is_authenticated is true it returns request.user.id otherwise it returns Http404
In backbone side, I defined a User model and periodically make ajax call to get_identity.
I think it is the most straightforward way to check user is authenticated or not.
For learning single page application, I want to do this operation more sensible and efficient than this way if it is possible.
So what is your advice about this? When I search Django+Backbone.js + User Authentication, I couldn't find any satisfactory result and I really wonder how people do this simple operation.
Any help or idea will be appreciated.
(By the way I tried to read cookie periodically but HttpOnly True flagged cookies are not reacheable in client side.)
Django views.py
def get_identity(request):
if not request.user.is_authenticated():
raise Http404
return HttpResponse(json.dumps({'identity':request.user.id}), mimetype="application/json")
Backbone.js side.
updateUser:function(){
var $self=this;
$.ajaxSetup({async:false});
$.get(
'/get_identity',
function(response){
// update model...
$self.user.id =response.identity;
//check user every five minutes...
$self.user.fetch({success: function() {
$self.user.set('is_authenticated',true);
setTimeout($self.updateUser, 1000*60*1);
}
},this);
}).fail(function(){
//clear model
$self.user.clear().set($self.user.defaults);
setTimeout($self.updateUser, 1000*60*1);
});
$.ajaxSetup({async:true});
}
I had var is_authenticated = {{request.user.is_authenticated}}; in my base.html
and used the global variable to check.
I'm in pursuit of better solution (because this breaks when you start caching).
But you might find it useful.
How can I show a please wait loading message from a django view?
I have a Django view that takes significant time to perform calculations on a large dataset.
While the process loads, I would like to present the user with a feedback message e.g.: spinning loading animated gif or similar.
After trying the two different approaches suggested by Brandon and Murat, Brandon's suggestion proved the most successful.
Create a wrapper template that includes the javascript from http://djangosnippets.org/snippets/679/. The javascript has been modified: (i) to work without a form (ii) to hide the progress bar / display results when a 'done' flag is returned (iii) with the JSON update url pointing to the view described below
Move the slow loading function to a thread. This thread will be passed a cache key and will be responsible for updating the cache with progress status and then its results. The thread renders the original template as a string and saves it to the cache.
Create a view based on upload_progress from http://djangosnippets.org/snippets/678/ modified to (i) instead render the original wrapper template if progress_id='' (ii) generate the cache_key, check if a cache already exists and if not start a new thread (iii) monitor the progress of the thread and when done, pass the results to the wrapper template
The wrapper template displays the results via document.getElementById('main').innerHTML=data.result
(* looking at whether step 4 might be better implemented via a redirect as the rendered template contains javascript that is not currently run by document.getElementById('main').innerHTML=data.result)
Another thing you could do is add a javascript function that displays a loading image before it actually calls the Django View.
function showLoaderOnClick(url) {
showLoader();
window.location=url;
}
function showLoader(){
$('body').append('<div style="" id="loadingDiv"><div class="loader">Loading...</div></div>');
}
And then in your template you can do:
This will take some time...
Here's a quick default loadingDiv : https://stackoverflow.com/a/41730965/13476073
Note that this requires jQuery.
a more straightforward approach is to generate a wait page with your gif etc. and then use the javascript
window.location.href = 'insert results view here';
to switch to the results view which starts your lengthy calculation. The page wont change until the calculation is finished. When it finishes, then the results page will be rendered.
Here's an oldie, but might get you going in the right direction: http://djangosnippets.org/snippets/679/
A workaround that I chose was to use beforunload and unload events to show the loading image. This can be used with or without window.load. In my case, it's the view that is taking a great amount of time and not the page loading, hence I am not using window.load (because it's already a lot of time by the time window.load comes into picture, and at that point of time, I do not need the loading icon to be shown anymore).
The downside is that there is a false message that goes out to the user that the page is loading even when when the request has not even reached the server or it's taking much time. Also, it doesn't work for requests coming from outside my website. But I'm living with this for now.
Update: Sorry for not adding code snippet earlier, thanks #blockhead. The following is a quick and dirty mix of normal JS and JQuery that I have in the master template.
Update 2: I later moved to making my view(s) lightweight which send the crucial part of the page quickly, and then using ajax to get the remaining content while showing the loading icon. It needed quite some work, but the end result is worth it.
window.onload=function(){
$("#load-icon").hide(); // I needed the loading icon to hide once the page loads
}
var onBeforeUnLoadEvent = false;
window.onunload = window.onbeforeunload= function(){
if(!onBeforeUnLoadEvent){ // for avoiding dual calls in browsers that support both events
onBeforeUnLoadEvent = true;
$("#load-icon").show();
setTimeout(function(){
$("#load-icon").hide();},5000); // hiding the loading icon in any case after
// 5 seconds (remove if you do not want it)
}
};
P.S. I cannot comment yet hence posted this as an answer.
Iterating HttpResponse
https://stackoverflow.com/a/1371061/198062
Edit:
I found an example to sending big files with django: http://djangosnippets.org/snippets/365/ Then I look at FileWrapper class(django.core.servers.basehttp):
class FileWrapper(object):
"""Wrapper to convert file-like objects to iterables"""
def __init__(self, filelike, blksize=8192):
self.filelike = filelike
self.blksize = blksize
if hasattr(filelike,'close'):
self.close = filelike.close
def __getitem__(self,key):
data = self.filelike.read(self.blksize)
if data:
return data
raise IndexError
def __iter__(self):
return self
def next(self):
data = self.filelike.read(self.blksize)
if data:
return data
raise StopIteration
I think we can make a iterable class like this
class FlushContent(object):
def __init__(self):
# some initialization code
def __getitem__(self,key):
# send a part of html
def __iter__(self):
return self
def next(self):
# do some work
# return some html code
if finished:
raise StopIteration
then in views.py
def long_work(request):
flushcontent = FlushContent()
return HttpResponse(flushcontent)
Edit:
Example code, still not working:
class FlushContent(object):
def __init__(self):
self.stop_index=2
self.index=0
def __getitem__(self,key):
pass
def __iter__(self):
return self
def next(self):
if self.index==0:
html="loading"
elif self.index==1:
import time
time.sleep(5)
html="finished loading"
self.index+=1
if self.index>self.stop_index:
raise StopIteration
return html
Here is another explanation on how to get a loading message for long loading Django views
Views that do a lot of processing (e.g. complex queries with many objects, accessing 3rd party APIs) can take quite some time before the page is loaded and shown to the user in the browser. What happens is that all that processing is done on the server and Django is not able to serve the page before it is completed.
The only way to show a show a loading message (e.g. a spinner gif) during the processing is to break up the current view into two views:
First view renders the page with no processing and with the loading message
The page includes a AJAX call to the 2nd view that does the actual processing. The result of the processing is displayed on the page once its done with AJAX / JavaScript