Make an HTTP POST request with PHP curl.

<?php

// Request Yahoo! REST Web Service using HTTP POST with curl.
// requires PHP4/PHP5.
// Allows retrieval of HTTP status code for error reporting
// Author: Jason Levitt
// February 1, 2006

error_reporting(E_ALL);

// The POST URL and parameters
$request = 'http://search.yahooapis.com/ContentAnalysisService/V1/termExtraction';
$appid = 'YahooDemo';
$context = 'Italian sculptors and painters of the renaissance favored the Virgin Mary for inspiration';
$query = 'madonna';

$postargs = 'appid=' . $appid . '&context=' . urlencode($context) . '&query=' . urlencode($query);

// Get the curl session object
$session = curl_init($request);

// Set the POST options.
curl_setopt($session, CURLOPT_POST, true);
curl_setopt($session, CURLOPT_POSTFIELDS, $postargs);
curl_setopt($session, CURLOPT_HEADER, true);
curl_setopt($session, CURLOPT_RETURNTRANSFER, true);

// Do the POST and then close the session
$response = curl_exec($session);
curl_close($session);

// Get HTTP Status code from the response
$status_code = array();
preg_match('/\d\d\d/', $response, $status_code);

// Check for errors
switch($status_code[0]) {
  case 200:
    // Success
    break;
  case 503:
    die('Your call to Yahoo Web Services failed and returned an HTTP status of 503. That means: Service unavailable. An internal problem prevented us from returning data to you.');
    break;
  case 403:
    die('Your call to Yahoo Web Services failed and returned an HTTP status of 403. That means: Forbidden. You do not have permission to access this resource, or are over your rate limit.');
    break;
  case 400:
    // You may want to fall through here and read the specific XML error
    die('Your call to Yahoo Web Services failed and returned an HTTP status of 400. That means:  Bad request. The parameters passed to the service did not match as expected. The exact error is returned in the XML response.');
    break;
  default:
    die('Your call to Yahoo Web Services returned an unexpected HTTP status of:' . $status_code[0]);
}

// Get the XML from the response, bypassing the header
if (!($xml = strstr($response, '<?xml'))) {
  $xml = null;
}

// Output the XML
echo htmlspecialchars($xml, ENT_QUOTES);
?>