TLDR;
I managed to simplify my question after a good night's sleep. Here's the simpler question.
I want to upload N files to a server, which would process them together and return a single response (e.g. Total foobars in all files combined = XYZ).
What's the best way to send this single response back to the client?
Thanks.
&
Below is the old question, left behind as a lesson for me.
I'm using Dropzone.js to build D&D functionality into my app.
Please note: I know there are a couple of questions already that discuss multifile uploads. But they are different from my question. They talk about how to get a single callback call instead of multiple ones.
My issue is related to the situation where I drag and drop multiple files into the dropzone, but am seeing the single server response being duplicated multiple times. Here is my config:
Dropzone.options.inner = {
init: function() {
this.on("dragenter", function(e) {
$('#inner').addClass('drag-over');
//// TODO - find out WTF this isn't working (low priority)
}),
this.on("completemultiple", function(file, resp) {
//// TODO
})
},
url: "php/...upload...php",
timeout: 120000, // 2m
uploadMultiple: true,
autoProcessQueue: false,
clickable: false,
};
//// ... Some other stuff
//// ...
$(document).ready(function() {
$('#inner').click(function() {
Dropzone.forElement('.dropzone').processQueue();
});
In the beginning I intercepted the "complete" event, rather than "completemultiple". That resulted in its handler being invoked multiple separate times (once for each file), even though the server-side php was only being invoked once. Each invocation returned a duplicate copy of the same server-side message.
I didn't want that, so I changed it to "completemultiple", and now I can confirm that the handler only gets called once with an array of files, but the single server response is now buried within each file object returned - each has a duplicate copy of the exact same response.
It doesn't matter ultimately because it is the same message, after all. But the whole esthetics of the thing now seems off which indicates to me I'm doing something wrong - the response seems to indicate two independent uploads, but they were part of a single invocation of the server side php. Why make the client "believe" there were two separate upload requests when the server-side script only has one opportunity to respond (i.e. The php is not sending back different messages for each file - should it? And if so, what's the best way to do it?)
How can I make it so that if I have a scenario in which it's all-or-none, I get a single response back from the php script?
This is especially important to me because my server response will contain the status and some other data. The script does more than simply receiving the uploaded files (hence the longer timeout).
I thought maybe that's a sign that I should separate the uploading part from the processing part and trigger the processing once the upload is complete.
But that means that the server side upload script can't clean up after itself. It needs to persist data beyond its own life. Also it now needs to return a handle to this data back to the client, which would dispatch the server-side processor in a different ajax call passing it this handle - and the subsequent call needs to clean up the files left by the uploader after it is done processing them.
This seems the less elegant solution. Is this something I just need to get used to? Or is there a better way of accomplishing what I want?
Also, any other free tips and hints from the front-end gurus in my network will be gratefully accepted.
Thanks.
&
The following approach works. Until something better can be found.
Dropzone.options.inner = {
// . . .
init: function() {
this.on("completemultiple", function(file) {
var code = JSON.parse(file[0].xhr.response).code;
var data = { "code" : code };
$.post('php/......php', data, function(res) {
// TODO - surface the res back to the user
});
})
},
};
&
I have a web-page (Django 1.9 on back-end, Apache server) with an endless-paginated table with large data set and column filters. When a user activates one filter (let's denote it CHOICE 1), and then instantly changes his mind resetting the filter (let's refer to it as CHOICE 2), I would like to tell Ajax to give up waiting for back-end response to CHOICE 1 and go on to posting and waiting for CHOICE 2 request. For this purpose, I had the following JS code:
// AJAX_GET_REQUEST is a global variable
AJAX_GET_REQUEST= $.ajax(
{
type:'GET',
url:"/my_url/",
beforeSend : function()
{
if (AJAX_GET_REQUEST!= null)
AJAX_GET_REQUEST.abort();
},
data:data,
success: function(response)
{
// Do something
}
});
Fine. I used to think that I achieved the goal of successfully canceling irrelevant requests, But I found out that AJAX_GET_REQUEST.abort(); leads to Django error [Errno 10053] An established connection was aborted by the software in your host machine. The interesting think is that this is not a 'fatal error' in that the app does not terminate, but rather it takes years for my paginated table to load. Django seems to reactivate connection itself and go on to handle last request. Finally after waiting for long time I see the correct result on front-end. If I remove the AJAX_GET_REQUEST.abort(); line, everything is fine, but I have to wait until Django is through with irrelevant requests until it goes on to handle the last relevant request.
Is there any way out? Is it possible to abort previous requests avoiding this annoying 10053 error ?
I want to call 1 million different URLs with AJAX.
What I did is (Javascript, jQuery used):
var numbers = [1, 2, 3...1000000]; // numbers.length = 1000000
$(function () {
$.each(numbers, function(key, val) {
$.ajax({
url: '/getter.php',
data: { id: val},
success: function () {
console.info(id);
}
});
});
});
I loop over 1 million integers, and passing them to my getter.php (which is doing something cool with that numbers).
The problem is after ~1,5k of requests I get Google Chrome dead.
I know I do this ineffective way, that's why am asking for help - how to actually do it right? How to GET request a php script 1 million times (not necessary with JavaScript!)?
You could use a persistent connection between your php script and the client requesting the data.
I think you are bumping into a limitation of the time to live on the single request you are calling. Also the HTTP requests functions as a Request - Response why, when you put it in your foreach statement, each single statement is being processed alone like:
1. iteration: GET /getter.php with value 1 .... wait... Oh theres a response
2. iteration GET /getter.php with value 2 .... wait Oh another response
This is a seemingly long and wrong proces as you might already have figured out.
Another approach would be to set up a persistent socket, which functions like the TCP procotol:
1. open the connection
2. send all the data
3. close the connection
Have you considered trying with a websocket?
Heres a few tutorials:
HTML5websocket
http://www.tutorialspoint.com/html5/html5_websocket.htm
PHP socket:
http://www.phpbuilder.com/articles/application-architecture/optimization/creating-real-time-applications-with-php-and-websockets.html
EDIT:
Also see this article on the difference between AJAX and websocket.
"AJAX is great if you aren’t in a hurry, but if you’re moving a high volume of data then the overhead of creating an HTTP connection every time is going to be a bottleneck. You need a persistent connection instead. In addition, AJAX always has to poll the server for data rather than receive it via push from the server. If you want speed and efficiency you need WebSockets."
http://blog.safe.com/2014/08/websockets-ajax-webhooks-comparison/
I develop some application with "desktop", shortcuts and widget on it. So, I have a lot of AJAX requests when open my application.
They freeze each other, and Firebug shows that response time was about 170-250 ms, but in nginx log all responses have time about 50-60 ms.
How can I to fix it? Need I to build some queue, or some workaround with Web Workers, etc.?
Thank you.
An easy fix is to switch from low level Ajax to Ext.Direct remoting. One of its advantages is request batching, it's built in and automatic. Why not use it?
See the docs: http://docs.sencha.com/ext-js/4-1/#!/guide/direct_grid_pt1
What I have personally played around with is, for inital page load, have 1 ajax call that does the whole lot, and then when that loads, either have a store factory, or figure out which data you loaded, then manually publish that to the store.
Ext.onReady(function(){
Ext.Ajax.request({
url: 'page.php',
params: {
id: 1
},
success: function(response){
var text = response.responseText;
var json = Ext.JSON.decode(text);
var store = Ext.data.StoreManager.lookup('myStore')
store.add(json.myStore.records);
// and do for whatever other stores you need to do
}
});
})
I have read some posts about this topic and the answers are comet, reverse ajax, http streaming, server push, etc.
How does incoming mail notification on Gmail works?
How is GMail Chat able to make AJAX requests without client interaction?
I would like to know if there are any code references that I can follow to write a very simple example. Many posts or websites just talk about the technology. It is hard to find a complete sample code. Also, it seems many methods can be used to implement the comet, e.g. Hidden IFrame, XMLHttpRequest. In my opinion, using XMLHttpRequest is a better choice. What do you think of the pros and cons of different methods? Which one does Gmail use?
I know it needs to do it both in server side and client side.
Is there any PHP and Javascript sample code?
The way Facebook does this is pretty interesting.
A common method of doing such notifications is to poll a script on the server (using AJAX) on a given interval (perhaps every few seconds), to check if something has happened. However, this can be pretty network intensive, and you often make pointless requests, because nothing has happened.
The way Facebook does it is using the comet approach, rather than polling on an interval, as soon as one poll completes, it issues another one. However, each request to the script on the server has an extremely long timeout, and the server only responds to the request once something has happened. You can see this happening if you bring up Firebug's Console tab while on Facebook, with requests to a script possibly taking minutes. It is quite ingenious really, since this method cuts down immediately on both the number of requests, and how often you have to send them. You effectively now have an event framework that allows the server to 'fire' events.
Behind this, in terms of the actual content returned from those polls, it's a JSON response, with what appears to be a list of events, and info about them. It's minified though, so is a bit hard to read.
In terms of the actual technology, AJAX is the way to go here, because you can control request timeouts, and many other things. I'd recommend (Stack overflow cliche here) using jQuery to do the AJAX, it'll take a lot of the cross-compability problems away. In terms of PHP, you could simply poll an event log database table in your PHP script, and only return to the client when something happens? There are, I expect, many ways of implementing this.
Implementing:
Server Side:
There appear to be a few implementations of comet libraries in PHP, but to be honest, it really is very simple, something perhaps like the following pseudocode:
while(!has_event_happened()) {
sleep(5);
}
echo json_encode(get_events());
The has_event_happened function would just check if anything had happened in an events table or something, and then the get_events function would return a list of the new rows in the table? Depends on the context of the problem really.
Don't forget to change your PHP max execution time, otherwise it will timeout early!
Client Side:
Take a look at the jQuery plugin for doing Comet interaction:
Project homepage: http://plugins.jquery.com/project/Comet
Google Code: https://code.google.com/archive/p/jquerycomet/ - Appears to have some sort of example usage in the subversion repository.
That said, the plugin seems to add a fair bit of complexity, it really is very simple on the client, perhaps (with jQuery) something like:
function doPoll() {
$.get("events.php", {}, function(result) {
$.each(result.events, function(event) { //iterate over the events
//do something with your event
});
doPoll();
//this effectively causes the poll to run again as
//soon as the response comes back
}, 'json');
}
$(document).ready(function() {
$.ajaxSetup({
timeout: 1000*60//set a global AJAX timeout of a minute
});
doPoll(); // do the first poll
});
The whole thing depends a lot on how your existing architecture is put together.
Update
As I continue to recieve upvotes on this, I think it is reasonable to remember that this answer is 4 years old. Web has grown in a really fast pace, so please be mindful about this answer.
I had the same issue recently and researched about the subject.
The solution given is called long polling, and to correctly use it you must be sure that your AJAX request has a "large" timeout and to always make this request after the current ends (timeout, error or success).
Long Polling - Client
Here, to keep code short, I will use jQuery:
function pollTask() {
$.ajax({
url: '/api/Polling',
async: true, // by default, it's async, but...
dataType: 'json', // or the dataType you are working with
timeout: 10000, // IMPORTANT! this is a 10 seconds timeout
cache: false
}).done(function (eventList) {
// Handle your data here
var data;
for (var eventName in eventList) {
data = eventList[eventName];
dispatcher.handle(eventName, data); // handle the `eventName` with `data`
}
}).always(pollTask);
}
It is important to remember that (from jQuery docs):
In jQuery 1.4.x and below, the XMLHttpRequest object will be in an
invalid state if the request times out; accessing any object members
may throw an exception. In Firefox 3.0+ only, script and JSONP
requests cannot be cancelled by a timeout; the script will run even if
it arrives after the timeout period.
Long Polling - Server
It is not in any specific language, but it would be something like this:
function handleRequest () {
while (!anythingHappened() || hasTimedOut()) { sleep(2); }
return events();
}
Here, hasTimedOut will make sure your code does not wait forever, and anythingHappened, will check if any event happend. The sleep is for releasing your thread to do other stuff while nothing happens. The events will return a dictionary of events (or any other data structure you may prefer) in JSON format (or any other you prefer).
It surely solves the problem, but, if you are concerned about scalability and perfomance as I was when researching, you might consider another solution I found.
Solution
Use sockets!
On client side, to avoid any compatibility issues, use socket.io. It tries to use socket directly, and have fallbacks to other solutions when sockets are not available.
On server side, create a server using NodeJS (example here). The client will subscribe to this channel (observer) created with the server. Whenever a notification has to be sent, it is published in this channel and the subscriptor (client) gets notified.
If you don't like this solution, try APE (Ajax Push Engine).
Hope I helped.
According to a slideshow about Facebook's Messaging system, Facebook uses the comet technology to "push" message to web browsers. Facebook's comet server is built on the open sourced Erlang web server mochiweb.
In the picture below, the phrase "channel clusters" means "comet servers".
Many other big web sites build their own comet server, because there are differences between every company's need. But build your own comet server on a open source comet server is a good approach.
You can try icomet, a C1000K C++ comet server built with libevent. icomet also provides a JavaScript library, it is easy to use as simple as:
var comet = new iComet({
sign_url: 'http://' + app_host + '/sign?obj=' + obj,
sub_url: 'http://' + icomet_host + '/sub',
callback: function(msg){
// on server push
alert(msg.content);
}
});
icomet supports a wide range of Browsers and OSes, including Safari(iOS, Mac), IEs(Windows), Firefox, Chrome, etc.
Facebook uses MQTT instead of HTTP. Push is better than polling.
Through HTTP we need to poll the server continuously but via MQTT server pushes the message to clients.
Comparision between MQTT and HTTP: http://www.youtube.com/watch?v=-KNPXPmx88E
Note: my answers best fits for mobile devices.
One important issue with long polling is error handling.
There are two types of errors:
The request might timeout in which case the client should reestablish the connection immediately. This is a normal event in long polling when no messages have arrived.
A network error or an execution error. This is an actual error which the client should gracefully accept and wait for the server to come back on-line.
The main issue is that if your error handler reestablishes the connection immediately also for a type 2 error, the clients would DOS the server.
Both answers with code sample miss this.
function longPoll() {
var shouldDelay = false;
$.ajax({
url: 'poll.php',
async: true, // by default, it's async, but...
dataType: 'json', // or the dataType you are working with
timeout: 10000, // IMPORTANT! this is a 10 seconds timeout
cache: false
}).done(function (data, textStatus, jqXHR) {
// do something with data...
}).fail(function (jqXHR, textStatus, errorThrown ) {
shouldDelay = textStatus !== "timeout";
}).always(function() {
// in case of network error. throttle otherwise we DOS ourselves. If it was a timeout, its normal operation. go again.
var delay = shouldDelay ? 10000: 0;
window.setTimeout(longPoll, delay);
});
}
longPoll(); //fire first handler