Need to get the Content-Encoding header before headers are sent.

[BinkyBlue]

Hi - when a text document is sent, depending upon the capabilities of the requesting client and the server configuration, it is either sent un-compressed, gzip compressed, or deflate compressed.

I need to detect what is going to happen.

The reason - to be cache friendly I am generating Etag header and evaluating the if-none-match header if a client sends it with a request.

Because of proxy servers, even if the content is identical, the Etag header needs to be different for no-compression, gzip, and deflate.

If my code knows for a fact the server is using zlib.output_compression I can accurately guess based upon the Accept-Encoding header from the client but zlib.output_compression isn’t the only scheme out there.

Using headers_list() unfortunately does not show what Content-Encoding will be sent until after the headers are sent, at which point it is too late to adjust the Etag header.

Is there a reliable way to ask php what it is going to use for the Content-Encoding ??

I’m guessing the reason why headers_list() doesn’t show it before sending headers is because until the point, the code can do things like enable/disable compression that would change what is going to get used - but surely there must be some way to ask php what it is planning to use for the request before the headers are sent.

Thanks for suggestions.

[scottlpool2003]

Maybe this will help:

[PHP]

<?php /****************************** * HTTP Compression Self-Test * Source: http://sammitch.ca * Version: 1.0 * Date: Jan 24, 2013 ******************************/ // make sure cURL is available if( ! function_exists('curl_init') ) { die('You must have the cURL extension installed/enabled.'); // make sure the script isn't being called via command line } else if( php_sapi_name() == 'cli' ) { die('This script must be invoked via a web browser.'); } // use a $_GET var to prevent infinite looping through HTTP requests if( ! isset($_GET['self']) ) { // common compression encodings we want to check for in order of desirability // 'identity' means uncompressed $encodings = array( 'gzip' => '1.0', 'deflate' => '0.5', 'compress' => '0.5', 'identity' => '0.1' ); // create the header string $temp = array(); foreach( $encodings as $key => $value ) { $temp[] = sprintf('%s;q=%s', $key, $value); } $accept_header = 'Accept-Encoding: ' . implode(', ', $temp); echo "

Requesting the following encodings:\n\t" . $accept_header . "

"; } else { // if $_GET['self'] is present print out an itty-bitty test page echo <<<_EOF_ Test page

Test Page

_EOF_; } [/PHP] Source: http://sammitch.ca/2013/01/http-compression-self-test-in-php/ Tested output: [QUOTE] Requesting the following encodings: Accept-Encoding: gzip;q=1.0, deflate;q=0.5, compress;q=0.5, identity;q=0.1 [/QUOTE]