PHP handles a zip file as if it's empty - php

Question

Here's a very stripped down version of the code I'm using.
$url = "http://server.com/getDaFile";
//Get the file from the server
$zip_file_contents = file_get_contents($url);
//Write file to disk
file_put_contents("file.zip", $zip_file_contents);
//open zip file
$zip = zip_open("file.zip");
if(is_resource($zip))
{
while($zip_entry = zip_read($zip))
{
if(zip_entry_open($zip, $zip_entry, 'r'))
{
//Read the whole file
$buf = zip_entry_read($zip_entry, zip_entry_filesize($zip_entry));
/*
Do stuff with $buf!!!
*/
zip_entry_close($zip_entry);
}
}
zip_close($zip);
}
else
{
echo "Not a resource. Oh noes!\n";
}
So : get the file, save it to disk, unzip it to extract files it contains, do stuff with files. The problem here is that, for some reason I cannot figure out, zip_read returns FALSE, as if it couldn't read files inside the ZIP archive. $zip does contain a resource, I've checked with var_dump.
What makes this even stranger is that I downloaded the ZIP file on my PC using the URL on top, manually uploaded it to the PHP server, and commented out the calls to file_get_contents and file_put_contents so PHP uses the local version. When I do this, zip_read correctly finds the right amount of files inside the ZIP and processing proceeds as it should.
I also tried doing this : $zip = zip_open($url) but $zip fails the is_resource($zip) check.
Something is obviously wrong with my code since the URL works and returns a valid ZIP archive. What is it?

Answer 1

So I finally found out the problem. Following #diolemo's suggestion, I opened my server's ZIP archive in a hex editor. Here's what I found at the top, followed by the usual ZIP binary data : http://pastebin.com/vQEXJtTN
It turns out there was a PHP error mixed in with the actual content of the ZIP file. Unsure of how to fix this (but knowing it certainly had to do with HTTP headers), I tried this guy's code and, what do you know, my code works perfectly now!
Lessons learned? Never trust your data, even if it seems all right (both 7-Zip and Winrar managed to open the file without problem).