PHP cURL error: "Empty reply from server"

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:

1. Use the following as $base_url: $base_url = 'http://ws.audioscrobbler.com/2.0/?user=bachya&period=&api_key=xxx&method=user.getTopTracks';

2. 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();

?>

The server received your request, but sent an empty response. Check the result of curl_getinfo($ch, CURLINFO_HTTP_CODE) to find out if the server responded with an HTTP error code.

Update: Ok so the server responds with the 100 Continue HTTP status code. In that case, this should solve your problem:

curl_setopt($ch, CURLOPT_HTTPHEADER, array('Expect:'));

I found this here: PHP and cURL: Disabling 100-continue header. Hope it works!