Description:
------------
Redhat/7.3 php/4.3.2 libcurl/7.10.5 OpenSSL/0.9.6b zlib/1.1.4
MS Win php/4.3.2 libcurl/7.10.5 OpenSSL/0.9.7b
MS Win php/4.3.3RC1 libcurl/7.10.5 OpenSSL/0.9.7b

See also:
http://bugs.php.net/bug.php?id=23048
http://bugs.php.net/bug.php?id=21995
http://bugs.php.net/bug.php?id=23702

According to the libcurl docuentation, 
  curl_setopt ($ch, CURLOPT_ENCODING,"");
should generate a header 
  HTTP_ACCEPT_ENCODING: gzip,deflate 
And then autodecode the returned data if the remote server supports compression. However in the above three PHP releases it never does. Reading the three bug reports above, it appears that support for this option call may have been added to php 4.3.2 and so the problem is currently viewed as a documentation problem. However after repeated tests, it still appears to be missing from either php and/or libcurl and hence this bug report. The libcurl crew deny responsibility(!) and point at the php implementation. Using curl from the command line with the --compressed option I can see the header and auto-decoding working but I don't have the facilities to check the libcurl library except from inside php.

The libcurl readme
http://cvs.php.net/co.php/curl/lib/README.encoding?r=1.3
says that "The library zlib is required for this feature." but as can be seen above from the version report, php_curl.dll for windows does not appear to bind the zlib library, so even if the parameter option is being passed to libcurl, it probably wouldn't work anyway.

Reproduce code:
---------------
  $ch = curl_init("http://www.voidstar.com/temp/accept.php");
  curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1);
  curl_setopt ($ch, CURLOPT_ENCODING,"");
  curl_setopt ($ch, CURLOPT_HEADER, 1);

  $data = curl_exec($ch);

  curl_close ($ch);

  print "<pre>" . htmlentities($data) . "</pre>";


Expected result:
----------------
http://www.voidstar.com/temp/accept.php prints the headers it receives. It's running on a server with zlib support compiled into php and zlib.output_compression = on This can be seen by using a browser that supports gzip to navigate to the url above. In this case the header can be seen.

The reproduce code above should generate the accept_encoding header which should then result in it being mirrored back to curl which then displays it.

 HTTP_ACCEPT_ENCODING: gzip,deflate

Actual result:
--------------
Missing header
 HTTP_ACCEPT_ENCODING: gzip,deflate