How to send and receive JSON data between two servers via php - php

Question

Obviously I am not using the right keywords in my searches or am not understanding what others have written in blogs or forums, et al.
Looking for information on passing data between two servers. The data will be preferably contained within a JSON array.
If you know of someone who has written a blog fully encompassing this I would really like a chance to read it. Otherwise could you offer some thoughts?
More detailed:
As a user visits a page a PHP function will be called and some data will be "packaged up" in a JSON array and then a POST command to the other server. The second server after receiving the POST will do some processing and then "package up" some data and return it in a JSON array. Then the user will be presented with the results.
With the following I am receiving a HTTP 200 response. Just no data.
SITE 1:
$data_string = json_encode(array('user_id'=>123));
$ch = curl_init('http://site2.dev/retrieve');
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
'Content-Type: application/json',
'Content-Length: ' . strlen($data_string)
));
$result = curl_exec($ch);
$status = curl_getinfo($ch);
curl_close($ch);
$result = json_decode($result);
SITE 2:
public function retrieve() {
return json_encode(array('some'=>'456'));
}
The Json array was chosen as it can be encrypted and yes HTTPS will be used in the final environment.
Both servers will have Laravel 4 as the PHP Framework.
Thank you for your thoughts and comments.

Answer 1

Add this:
curl_setopt($ch, CURLOPT_HEADER, 0);
and put quotes on content-length:
curl_setopt($ch, CURLOPT_HTTPHEADER,
array('Content-Type: application/json','"Content-Length: ' . strlen($data_string) . '"'));