PHP cURL error: "Empty reply from server"

I have a class function to interface with the RESTful API for Last.FM - its purpose is to grab the most recent tracks for my user. Here it is:

private static $base_url = 'http://ws.audioscrobbler.com/2.0/';

public static function getTopTracks($options = array())
{
  $options = array_merge(array(
    'user' => 'bachya',
    'period' => NULL,
    'api_key' => 'xxxxx...', // obfuscated, obviously
  ), $options);

  $options['method'] = 'user.getTopTracks';

  // Initialize cURL request and set parameters
  $ch = curl_init();
  curl_setopt_array($ch, array(
    CURLOPT_URL            => self::$base_url,
    CURLOPT_POST           => TRUE,
    CURLOPT_POSTFIELDS     => $options,
    CURLOPT_RETURNTRANSFER => TRUE,
    CURLOPT_TIMEOUT        => 30,
    CURLOPT_USERAGENT      => 'Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)'
  ));

  $results = curl_exec($ch);
  return $results;
}

This returns "Empty reply from server". I know that some have suggested that this error comes from some fault in network infrastructure; I do not believe this to be true in my case. If I run a cURL request through the command line, I get my data; the Last.FM service is up and accessible.

Before I go to those folks and see if anything has changed, I wanted to check with you fine folks and see if there's some issue in my code that would be causing this.

Thanks!

ANSWER: @Jan Kuboschek helped me stumble onto what is (maybe) going on here. By giving CURLOPT_POSTFIELDS an associative array, a particular content-type is specified that may not work with certain RESTful services. A smarter solution is to manually create a URL-encoded version of that data and pass that as the CURLOPT_POSTFIELDS.

For more info, check out: http://www.brandonchecketts.com/archives/array-versus-string-in-curlopt_postfields

Solution

A common issue are spaces in the URL - beginning, in the middle, or trailing. Did you check that out?

Edit - per comments below, spacing is not the issue.

I ran your code and had the same problem - no output whatsoever. I tried the URL and with a GET request, the server talks to me. I would do the following:

Use the following as $base_url: $base_url = 'http://ws.audioscrobbler.com/2.0/?user=bachya&period=&api_key=xxx&method=user.getTopTracks';
Remove the post fields from your request.

Edit I moved your code out of the class since I didn't have the rest and modified it. The following code runs perfect for me. If these changes don't work for you, I suggest that your error is in a different function.

<?php


function getTopTracks()
{
  $base_url = 'http://ws.audioscrobbler.com/2.0/?user=bachya&period=&api_key=8066d2ebfbf1e1a8d1c32c84cf65c91c&method=user.getTopTracks';
  $options = array_merge(array(
    'user' => 'bachya',
    'period' => NULL,
    'api_key' => 'xxxxx...', // obfuscated, obviously
  ));

  $options['method'] = 'user.getTopTracks';

  // Initialize cURL request and set parameters
  $ch = curl_init($base_url);
  curl_setopt_array($ch, array(
    CURLOPT_URL            => $base_url,
    CURLOPT_RETURNTRANSFER => TRUE,
    CURLOPT_TIMEOUT        => 30,
    CURLOPT_USERAGENT      => 'Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)'
  ));

  $results = curl_exec($ch);
  return $results;
}

echo getTopTracks();

?>