Getting a file via CURL Posting Data - php

Question

I have a web service which you post data to and it returns you a txt.gz file. I'm trying to use cURL to post up the information, however I'm not sure how to be ready and handle the file which comes back at me to download.
I'm getting a successful response; but the file is 0 KB, and obviously isn't downloading. Any help would be greatly appreciated!
Here is currently what I'm doing:
$url = 'http://www.mywonderfulurl.com';
$fields = array('id'=>'123');
$fields_string = 'id=123';
$useragent="Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.1) Gecko/20061204 Firefox/2.0.0.1";
$ch = curl_init();
// set user agent
curl_setopt($ch, CURLOPT_USERAGENT, $useragent);
//set the url, number of POST vars, POST data
curl_setopt($ch,CURLOPT_URL,$url);
curl_setopt($ch,CURLOPT_POST,count($fields));
curl_setopt($ch,CURLOPT_POSTFIELDS,$fields_string);
curl_setopt($ch, CURLOPT_TIMEOUT, 250);
curl_setopt($ch, CURLOPT_FILE, 'download.txt.gz');
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
if (file_put_contents('download.txt.gz', curl_exec($ch)) === false) {
// Handle unable to write to file error.
echo('you failed');
exit;
}
echo curl_getinfo( $ch, CURLINFO_HTTP_CODE );
//close connection
curl_close($ch);

Answer 1

You are never writing to the file.
You need to write the result to file.
fwrite($fp, $result);
You are probably better off using file_put_contents, then you don't need to open/close the file.
http://php.net/manual/en/function.file-put-contents.php
if ($file_put_contents('download.txt.gz', curl_exec($ch)) === false) {
// Handle unable to write to file error.
}
But maybe using the $result in between to check the request was actually ok before saving it to file.
You should check the return from curl_exec()
$result = curl_exec($ch);
if ($result === false) {
echo 'Curl error: ' . curl_error($ch);
}
Writing false to a file would result in an empty file, so this could be whats happening.