Understanding how XMLHttpRequest sends data to a server - php

Question

I haven't understand data transfer to the server completely. Which ways do I have? When I started learning PHP, I thought there are two ways called GET which encrypts data in the URL and POST which sends data in another way to the server. I didn't know where exactly, though.
Now I want to learn about RESTful server backends, and I learned that GET and POST are just request methods, among others like PUT and DELETE, which doesn't seem to have anything to do with how data is transferred to the server.
Moreover, I read that additional data can be sent in the HTTP header. Is this how POST actually sends its data or is there even a difference?
I would like to either read POST data regardless of the request method using PHP's $_POST array, but this doesn't work. On the other hand, when I try to manually parse the header information from php://input, I cannot see POST data. Could someone please explain to me where data is transferred in the different cases?
My goal is to get parameters from the client regardless of content type, which may be form-data, json or something other, and request method. How can I do this in PHP? Requests will be sent using JQuery's AJAX functionality.

Answer 1

To explain how does http work using nc
http://linux.die.net/man/1/nc
GET
$ nc -l 8888 to start a dummy server listen at 8888
send a GET request using jQuery (impl via XHR)
$.get("http://localhost:8888", { a :1 ,b: 2})
nc would print what XHR sent to server to stdout
$nc -l 8888
GET /?a=1&b=2&_=1383234919249 HTTP/1.1
Host: localhost:8888
Connection: keep-alive
Accept: */*
Origin: http://stackoverflow.com
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/30.0.1599.101 Safari/537.36
DNT: 1
Referer: http://stackoverflow.com/questions/19710815/understanding-how-xmlhttprequest-sends-data-to-a-server
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8,zh-CN;q=0.6,zh;q=0.4
thus, PHP parse GET /?a=1&b=2&_=1383234919249 into $_GET
POST
using nc to recording POST
POST / HTTP/1.1
Host: localhost:8888
Connection: keep-alive
Content-Length: 7
Accept: */*
Origin: http://stackoverflow.com
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/30.0.1599.101 Safari/537.36
Content-Type: application/x-www-form-urlencoded
DNT: 1
Referer: http://stackoverflow.com/questions/19710815/understanding-how-xmlhttprequest-sends-data-to-a-server
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8,zh-CN;q=0.6,zh;q=0.4
a=1&b=2
here you can see Content-Type: application/x-www-form-urlencoded
,which tell the http body sent by browser is form encoded
as a result, PHP parse a=1&b=2 in to array $_POST
WHY php://input can't see POST BODY
according to http://php.net/manual/en/wrappers.php.php
php://input is a stream and can be read only once
below is from php doc
Note: A stream opened with php://input can only be read once; the
stream does not support seek operations. However, depending on the
SAPI implementation, it may be possible to open another php://input
stream and restart reading. This is only possible if the request body
data has been saved. Typically, this is the case for POST requests,
but not other request methods, such as PUT or PROPFIND.