Can't make Curl POST request from web app - php

Question

A server I am working on appears to be denying outbound HTTP requests. The reason I think this is because I've tried both Guzzle and curl requests to the API.
The API lives on the same domain as the web server (this is temporary at clients request). I can make requests to the API server via Postman (Chrome plugin), but when I run that same request on the server, it doesn't return anything.
Here are the headers from the 'Postman' request:
POST /api2/user/session HTTP/1.1
Host: example.com
Connection: keep-alive
Content-Length: 49
Cache-Control: no-cache
Origin: chrome-extension://fdmmgilgnpjigdojojpjoooidkmcomcm
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.76 Safari/537.36
Content-Type: application/x-www-form-urlencoded
Accept: */*
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.8
Cookie: PHPSESSID=d9ad79c4c0822fc5c86f4d8799307f1b; _ga=GA1.2.1674422587.1425409444
Post data:
token=a559d5bba5a9e9517d5c3ed7aeb62db6&user=30972
This works. It returns the data. But when I call the same endpoint from within my web app, I get nothing.
$data = urlencode("token=a559d5bba5a9e9517d5c3ed7aeb62db6&user=30972");
$ch = curl_init('http://example.com/api2/user/session');
curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
'Content-Type: application/x-www-form-urlencoded',
'Content-Length: ' . strlen($data))
);
$result = curl_exec($ch);
What I don't understand is I can run the following, and it returns the content:
print file_get_contents("http://www.google.com");
When I var_dump the $_POST fields on the endpoint user/session it returns the array of postdata using Postman but $_POST fields are blank when sending via the web app. Even before it makes any request to the database, the post fields should be set right?
Via SSH this also works:
curl -F token=a559d5bba5a9e9517d5c3ed7aeb62db6 -F user=30972 http://example.com/api2/user/session
As suggested in comments I've tried:
var_dump(function_exists('curl_version'));
// bool(true)
I can't figure out what's going on.
Edit: This works ... but I don't want to use sockets. Must be a curl issue.
$fp = fsockopen('example.com', 80);
$vars = array(
'token' => 'a559d5bba5a9e9517d5c3ed7aeb62db6',
'user' => '30972'
);
$content = http_build_query($vars);
fwrite($fp, "POST /api2/user/session HTTP/1.1\r\n");
fwrite($fp, "Host: example.com\r\n");
fwrite($fp, "Content-Type: application/x-www-form-urlencoded\r\n");
fwrite($fp, "Content-Length: ".strlen($content)."\r\n");
fwrite($fp, "Connection: close\r\n");
fwrite($fp, "\r\n");
fwrite($fp, $content);
header('Content-type: text/plain');
while (!feof($fp)) {
echo fgets($fp, 1024);
}
Edit:
curl_error() also returns no error.

Answer 1

To better understand the differences between the PHP code and cURL, I created a RequestBin instance and tried both on it. They yielded drastically different results:
It seemed like the POST data from the PHP script yielded an incorrect result for what was sent. This can be fixed by using a built-in PHP function http_build_query.
It will yield a more apt result:

Answer 2

This can be caused by a session lock... If you use curl to access the same server, the same session is used. While the script is running, the session is locked by default, this means that the current request has to finish before another is handled for the same session. This would explain a timeout of the request in curl, as your first request is not completed and another is made...
Using session_write_close() before the curl_exec will unlock the session and correct the problem.

Answer 3

It turns out I needed to use http_build_query.
$vars = array(
'token' => 'a559d5bba5a9e9517d5c3ed7aeb62db6',
'user' => '30972'
);
$content = http_build_query($vars);
$ch = curl_init('http://example.com/api2/user/session');
curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
'Content-Type: application/x-www-form-urlencoded',
'Content-Length: ' . strlen($content))
);
$result = curl_exec($ch);