Reduce AJAX request size. Simple chat with Polling system

Why not use the plain javascript AJAX Request? Maybe your AJAX data is too long, that's why it has a large size: and the only thing you can do for it is to make the AJAX data have a few data.

What do you want? like Facebook AJAX Polling? Do it like this on the server PHP:

$chat_data = "(this is the chat data variable if there is no chat data it will idle)";while (!$chat_data) {     // when there's no chat data let's idle the request without disconnecting     // the client from the AJAX request.     sleep(1);}exit(json_encode($chat_data));

On JavaScript Client Side:

function repoll () {     chat_poll = new XMLHttpRequest();     // the chat_req variable is for sending POST data to the server.     chat_req = new FormData();     chat_req.append("do", "chatpoll");     chat_poll.open("POST", "post.php");     chat_poll.send(chat_req);     chat_poll.onload = function () {     // do something here with the chat data     // repoll the server     repoll();}repoll();

By doing this, your implementing the Facebook like server polling.

For the websocket example in JavaScript client side:

web_socket = new WebSocket("ws://[thesocket]:[theport]");web_socket.onmessage = function (w) {     // do something here. this will fire if messages is received from the websocket.     // you will get the message from w.data variable.     alert("Data Received: " + w.data);}// to send data to the web socket do this:web_socket.send("the data you want. I prefer JSON for sending configuration and chat data or XML if you want");

Here's my take on your questions, even though you'd better of using a library like socket.io with fallback support for older browsers (simulating websockets via long-polling or such).

Why all my AJAX requests have ever the same size (343 B) even though I change the SHA1 (20 B) hash to MD5 (16 B)?

Most HTTP communication between browser and server by default is compressed with gzip. The bulk of your request/response stream consists of HTTP headers where 4 bytes of difference in your hashing algorithm's output may not make a difference effectively due to the gzip compression.

My checksum variable (SHA1) occuppies 20 B: Where do the remaining 323 B?

See above, and to see for yourself, you could use a http monitor, tcpdump or developer tools to see the raw data transferred.

Could I reduce more the AJAX request size? How?

WebSocket has a lot less footprint compared to HTTP requests, so using it seems the best option here (and polling in intervals is almost never a good idea, even without WebSocket you would be better off implementing long-polling in your server).

I have assembled a simple page with a jQuery $.post request. It produces a request header that's in the form:

   POST /post_.js HTTP/1.1   Host: localhost   User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Firefox/38.0   Accept: */*   Accept-Language: it-IT,it;q=0.8,en-US;q=0.5,en;q=0.3   Accept-Encoding: gzip, deflate   Content-Type: application/x-www-form-urlencoded; charset=UTF-8   X-Requested-With: XMLHttpRequest   Referer: http://localhost/test.html   Content-Length: 49   Connection: keep-alive   Pragma: no-cache   Cache-Control: no-cache

You can see the response and request headers by using Firebug on Firefox or F12 on Chrome.In my opinion the extra bytes are those involved in the Http request.