cURL not sending POST data in some requests - php

Question

I've been stuck on this problem for several hours: I'm using PHP and cURL to write a sort of PHP proxy. Almost everything works fine, setting cookies, handling redirects, and submitting forms using POST.
Basically, I'm trying to mirror a remote website with my local proxy. To do so, I redirect every request to http://localhost/resource to http://localhost/proxy.php?url=http://remotesite.com/resource that will fetch the resource on the remote website. The redirect is handled by a 404 error page on .htaccess but I guess that using mod_rewrite would not change things.
I'm testing my proxy on a complex application (the latest version of WordPress) deployed on a remote server. The WordPress login works fine and uses POST. However, I found a page where updating a form does not work, and for which all the POST data is not sent at all to the server.
Here is what I see with wireshark listening on the loopback interface:
POST /proxy/wp-admin/media.php?attachment_id=691&action=edit HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.23) Gecko/20110921 Ubuntu/10.04 (lucid) Firefox/3.6.23
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 115
Connection: keep-alive
Referer: http://localhost/proxy/wp-admin/media.php?attachment_id=691&action=edit
Cookie: [snip]
Cache-Control: max-age=0
Content-Type: application/x-www-form-urlencoded
Content-Length: 501
attachments%5B691%5D%5Bmenu_order%5D=0&attachments%5B691%5D%5Bpost_title%5D=fb&attachments%5B691%5D%5Bimage_alt%5D=&attachments%5B691%5D%5Bpost_excerpt%5D=&attachments%5B691%5D%5Bpost_content%5D=foobar&attachments%5B691%5D%5Burl%5D=http%3A%2F%2Flocalhost%2Fproxy%2Fwp-content%2Fuploads%2F2009%2F04%2Ffb.gif&save=Aggiorna+media&post_id=&attachment_id=691&action=editattachment&_wp_original_http_referer=&_wpnonce=02caf30462&_wp_http_referer=%2Fwp-admin%2Fmedia.php%3Fattachment_id%3D691%26action%3Dedit
HTTP/1.1 200 OK
Date: Wed, 19 Oct 2011 16:18:56 GMT
Server: Apache/2.2.14 (Ubuntu)
X-Powered-By: PHP/5.3.2-1ubuntu4.10
Vary: Accept-Encoding
Content-Encoding: gzip
Content-Length: 5441
Keep-Alive: timeout=15, max=100
Connection: Keep-Alive
Content-Type: text/html; charset=UTF-8
[content]
While, what I see if listening on the interface connected to the internet is:
POST /wp-admin/media.php?attachment_id=691&action=edit HTTP/1.1
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.23) Gecko/20110921 Ubuntu/10.04 (lucid) Firefox/3.6.23
Host: www.remotesite.com
Accept: */*
Referer: http://www.remotesite.com/wp-admin/media.php?attachment_id=691&action=edit
Cookie: [snip]
X-Forwarded-For: 127.0.0.1
Content-Length: 0
Content-Type: application/x-www-form-urlencoded
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Date: Wed, 19 Oct 2011 16:25:13 GMT
Server: LiteSpeed
Connection: close
X-Powered-By: PHP/5.2.17
Expires: Wed, 11 Jan 1984 05:00:00 GMT
Last-Modified: Wed, 19 Oct 2011 16:25:13 GMT
Cache-Control: no-cache, must-revalidate, max-age=0
Pragma: no-cache
X-Frame-Options: SAMEORIGIN
Content-Type: text/html; charset=UTF-8
[content]
As you see my proxy is not transmitting the post data to the remote server.
I expect the problem to be related to the encoding of the POSTDATA, as POST variables in this case are in an array (attachments[691][menu_order]=0; attachments[691][post_content]=foobar and so on...).
I tried several changes as suggested by similar posts but haven't managed to change the behavior of the script at all. All this because apparently the first (local) POST sends the data to localhost, but cURL is unable to fetch the POST data (indeed, file_get_contents("php://input") in the code below reads 0 bytes).
I paste here part of my code hoping somebody can help me:
$ch = curl_init( $url );
$headers = array();
if ( isset($_SERVER['CONTENT_TYPE']) ) {
// commenting this out or changing to multipart/form-data does not change anything
array_push($headers, "Content-Type: ".$_SERVER['CONTENT_TYPE'] );
}
if ( count($headers) > 0 ) {
curl_setopt( $ch, CURLOPT_HTTPHEADER, $headers );
}
$postdata = file_get_contents("php://input"); //this turns out to be empty - and so is $_POST
//REQUEST METHOD: since pages are redirected from a 404 error page, we have to handle
//a redirect, so the real method is specified in REDIRECT_REQUEST_METHOD
if ( isset($_SERVER['REDIRECT_REQUEST_METHOD']) && isset($postdata) ){
if ($_SERVER['REDIRECT_REQUEST_METHOD'] == 'POST'){
curl_setopt( $ch, CURLOPT_POST, true );
}
}
else{
if (isset($_SERVER['REQUEST_METHOD']) && $_SERVER['REQUEST_METHOD'] == 'POST' ){
curl_setopt( $ch, CURLOPT_POST, true );
}
}
if ( isset($_SERVER['CONTENT_LENGTH'] ) && $_SERVER['CONTENT_LENGTH'] > 0 ) {
curl_setopt( $ch, CURLOPT_POSTFIELDS, $postdata );
}
//set cookies
curl_setopt($ch, CURLOPT_COOKIEJAR, '/tmp/cookietofwd');
curl_setopt($ch, CURLOPT_COOKIEFILE,'/tmp/cookietofwd');
curl_setopt( $ch, CURLOPT_FOLLOWLOCATION, true );
curl_setopt( $ch, CURLOPT_HEADER, true );
curl_setopt( $ch, CURLOPT_RETURNTRANSFER, true );
$out=curl_exec( $ch );
[...]

Answer 1

Why don't you get your POST data from $_POST? The application/x-www-form-urlencoded header appears to be an AJAX request instead of a regular POST, which I am not sure how it is handled by php://input.
You could so something like:
curl_setopt( $ch, CURLOPT_POSTFIELDS, http_build_query($_POST) );
Is there a specific reason why you want this in PHP? Why don't you just use nginx? (http://nginx.org/en/)
It will probably do a better job (and faster).