This may be added in PHP 5.1.

In the mean time you may be able to acheive this behavior using a combination of the header context parameter for the http:// wrapper and the zlib_filter found in PECL.  This stop-gap solution will only work in PHP5 however.

I get the desired result like this:
(lest I didn't get the point...)

<?php

  //  my server sends gzipped data if client allows
  $url = "www.byteshift.de";

  function gzdecode($string){
    $string = substr($string, 10);
    return gzinflate($string);
  }

  function get_gzipped_data($url){
    $http_response = '';
    $fp = fsockopen($url, 80);
    fputs($fp, "GET / HTTP/1.1\r\n");
    fputs($fp, "Accept-Encoding: gzip\r\n");
  
    fputs($fp, "Host: $url\r\n\r\n");
    while (!feof($fp))
      $http_response .= fgets($fp, 128);
    fclose($fp);
    return $http_response;
  }

  preg_match("/^(.+)\r?\n\r?\n\w+\r?\n(.+)$/s",
             get_gzipped_data($url),
             $matches);
  $header = $matches[1];
  $body   = $matches[2];
  $html   = gzdecode($body);
	$strlen_uncomp = strlen(file_get_contents("http://$url/"));
	$strlen_decomp = strlen($body);

  echo "
  strlen_uncomp: $strlen_uncomp Kb
  strlen_decomp: $strlen_decomp Kb
  =============================
  $html
  ";
?>

Marek Moehling
byteshift.de
i4n3fo@byte45shift.de
(del numbers to despam)

> (lest I didn't get the point...)

The point is gzip suppport in file_get_contents().