php - How to determine the Content-Length of a gzipped file?

Question

Right now I'm trying to serve CSS and JS files from a server that won't let me enable mod_gzip or mod_deflate. So I wrote a small PHP script to compress with GZIP and return to the user.

Example Code:

$filename = "style.css";

if (!file_exists($filename) || !($info = stat($filename))) {
  header("HTTP/1.1 404 Not Found");
  die();
}

header("Date: ".gmdate("D, j M Y H:i:s e", time()));
header("Cache-Control: max-age=2592000");
header("Last-Modified: ".gmdate("D, j M Y H:i:s e", $info['mtime']));
header("Etag: ".sprintf(""%x-%x-%x"", $info['ino'], $info['size'], $info['mtime']));
header("Accept-Ranges: bytes");
header("Cache-Control: Expires ".gmdate("D, j M Y H:i:s e", $info['mtime']+2592000));
header("Content-Type: text/html");

ob_start("ob_gzhandler");
echo file_get_contents($filename);
ob_end_flush();

I'm having two problems right now. The first is, I'm having trouble determining the resulting size of the compressed file to inform the browser of the content-length. Normally, I would include this line:

header("Content-Length: ".$info["size"]);

But, if I do, the browser hangs while trying to wait for more data. Is there a way to calculate the total size? Or should I ignore this header directive.

The other issue is, whenever I view this PHP file in Firefox, it tries to have me download the result. In Chrome, it just displays it like I would expect. Any suggestions?

Edit: Thanks to SoapBox, I replaced the end of the code with this:

header("Content-Encoding: gzip");
$compressed = gzencode(file_get_contents($filename), 5);
header("Content-Length: ".strlen($compressed));
die($compressed);

This works great for the content-length! But I'm still getting Firefox to download the file instead of display it. :(

Edit Again: Here is the modified end-of-code code, courtesy of Cletus.

// Start buffered output
ob_start();
// Check for gzip capability
if (stripos($_SERVER['HTTP_ACCEPT_ENCODING'], "gzip") !== false) {
  ob_start("ob_gzhandler");
  echo file_get_contents($filename);
  ob_end_flush();
} else
  echo file_get_contents($filename);

// Write the content length
header('Content-Length: '.ob_get_length());
ob_end_flush();

I'm going to start a new question to figure out why Firefox keeps trying to download the file.

Answer 1

The problem here is that to know the content length you need to know whether or not the client supports gzip encoding and you've delegated that decision by using ob_gzhandler. From HTTP Headers:

ob_start();
ob_start('ob_gzhandler');

  ... output the page content...

ob_end_flush();  // The ob_gzhandler one

header('Content-Length: '.ob_get_length());

ob_end_flush();  // The main one

Complete version:

$filename = "style.css";

if (!file_exists($filename) || !($info = stat($filename))) {
  header("HTTP/1.1 404 Not Found");
  die();
}

header("Date: ".gmdate("D, j M Y H:i:s e", time()));
header("Cache-Control: max-age=2592000");
header("Last-Modified: ".gmdate("D, j M Y H:i:s e", $info['mtime']));
header("ETag: ".sprintf(""%x-%x-%x"", $info['ino'], $info['size'], $info['mtime']));
header("Accept-Ranges: bytes");
header("Expires: ".gmdate("D, j M Y H:i:s e", $info['mtime']+2592000));
header("Content-Type: text/css"); // note: this was text/html for some reason?

ob_start();
ob_start("ob_gzhandler");
echo file_get_contents($filename);
ob_end_flush();
header('Content-Length: '.ob_get_length());
ob_end_flush();

This is much better than taking on the gzip encoding issue yourself.