PHP Manual GZip Encoding

Question

I was testing my website with Page Speed and the result was around 70/100. Enable Compression was the first and most important factor in slowing it down.

I know that I can do that by modifying the php.ini to automatically do that but I was more interested in the manual method (gzencode).

The problem is either all browsers fail in opening the website (Firefox: "The page you are trying to view cannot be shown because it uses an invalid or unsupported form of compression.", Chrome: "303, ERR Content Encoding", etc.) or they display the encoded string.

Live Headers shows that the browser accepts the encoding, and the response has the content type set, but it still fails.

GET / HTTP/1.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Encoding: gzip,deflate

HTTP/1.1 200 OK
Content-Encoding: gzip
Content-Length: 5827
Vary: Accept-Encoding

private function _compress($data) {
    //return trim(preg_replace(array('/\>[^\S ]+/s','/[^\S ]+\</s','/(\s)+/s'), array('>','<','\\1'), $data));
    $supportsGzip = strpos($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip') !== false;

    ob_start();
    if ($supportsGzip) {
        echo gzencode(trim(preg_replace('/\s+/', ' ', $data)), 9);
    } else {
        echo $data;
    }

    $content = ob_get_contents();
    header("content-type: text/html; charset: UTF-8");
    header("cache-control: must-revalidate");
    $offset = 60 * 60;
    $expire = "expires: " . gmdate("D, d M Y H:i:s", time() + $offset) . " GMT";
    header($expire);
    header('Content-Length: ' . strlen($content));
    header('Vary: Accept-Encoding');
    ob_end_clean();
    echo $content;
}

If I change the Content-Encoding to zlib, I get the encoded string:

‹������ÕZÿsÛ¶ÿW^‘¥²o‘¨/–-Ë–ÚØ‰_Ôµ•õÚ_v I°I‚!A©j–Öºnçÿb·»%ÍÚë²nëå?‘þ›=€¤L)’,ÛIw>ŸEâxïáƒ÷°ùÞ½O¶Ÿïß‡ŽtlØ¼µ·» $kŸ•¶ ã^ã<Üƒ•\¾� Ÿº—\¸Ô6ŒûŽ”^Õ0z½^®WÊ ¿m4ÅjÅ°…XÎ’©Ã¦ænS·]#ÌÕF-|8LRPL²ìIÈ»5²-\É\™mô=FÀŒJ5"Ù—RóÝ�³Cý€ÉZ([ÙŠb%¹´YýÑãáîcx}±iD´˜¿KV#4”á§x>¬°à®íÒ ãpÅËæî1øÌ®‘@öm

I don’t really care anymore about getting the compression as much as I want to know why its not working.

Cheers,

If it `$supportsGzip` shouldn't `Content-Length` be the length of the gzipped content instead? — Fanis Hatzidakis, Apr 18 '11 at 06:18
@Fanis, contents holds the content of the buffer, either the encoded or the plain depending on the $supportsGzip. — M.Alnashmi, Apr 18 '11 at 06:51
Strange, do you get the same behaviour if you use ob_gzhandler() instead of rolling your own compression wrapper? — symcbean, Apr 18 '11 at 10:28
@user687976 you're absolutely right, I managed to miss that line while looking for $data. Actually, as @Craig Sefton mentions in his answer, could this be the issue? $data vs $content — Fanis Hatzidakis, Apr 18 '11 at 18:44

Craig Sefton · Answer 1 · 2015-12-24T09:08:59.487

Well, I think it's because you're trying to compress an empty string.

I took your script as you gave it, and ran it in FF and IE.

Both failed, and FF said that there was an issue (like you described).

However, I then noticed $data is an empty string.

When I set $data = "Some test data."; at the top of the file it worked immediately (browser displayed "Some test data."), and checking in Firebug, I can see the correct headers.

Content-Encoding    gzip
Content-Length  68
Vary    Accept-Encoding
Content-Type    text/html

Edit: Also, just to point out, your if ($supportsGzip) { is a bit odd, because your else condition should actually echo out $data, not $content.

Edit: Okay, based on your revised function above, there are two key problems.

The primary problem has to do with the fact that you're wiping out your headers by calling ob_end_clean(). A comment on the PHP Docs states that "ob_end_clean() does discard headers".

This means any headers you set before calling ob_end_clean() will get wiped. Also, your revised function doesn't send a gzip encoding header, either.

I must say that there is probably no need to even use ob_start and related functions here, either. Try the following:

function _compress( $data ) {

    $supportsGzip = strpos( $_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip' ) !== false;


    if ( $supportsGzip ) {
        $content = gzencode( trim( preg_replace( '/\s+/', ' ', $data ) ), 9);
        header('Content-Encoding: gzip');
    } else {
        $content = $data;
    }

    $offset = 60 * 60;
    $expire = "expires: " . gmdate("D, d M Y H:i:s", time() + $offset) . " GMT";

    header("content-type: text/html; charset: UTF-8");
    header("cache-control: must-revalidate");
    header( $expire );
    header( 'Content-Length: ' . strlen( $content ) );
    header('Vary: Accept-Encoding');

    echo $content;

}

_compress( "Some test data" );

This works in IE and FF, but I didn't have time to test other browsers.

If you really must use ob_start and related functions, make sure you set your headers after you call ob_end_clean().

GZIP is not an encryption algorithm but a compression algorithm. — Gumbo, Apr 18 '11 at 10:47
the data string is a function parameter, the code was a snippet. i even tried the `data= "Some string"` and still failed the test. — M.Alnashmi, Apr 19 '11 at 05:18
@user687976 - Just updated my answer with further info. Hope that helps. — Craig Sefton, Apr 19 '11 at 08:10
no need to invoke `header('Content-Encoding: gzip');` if not `$supportGzip`. — lazycommit, Dec 23 '15 at 21:42

score 8 · Answer 2 · answered Apr 18 '11 at 13:00

8

I'd suggest to use http://php.net/manual/de/function.ob-gzhandler.php, this works out of the box for me:

In my index.php I just place this before some output:

    /**
     * Enable GZIP-Compression for Browser that support it.
     */
    ob_start("ob_gzhandler");

And it encodes it!

answered Apr 18 '11 at 13:00

daschl

1,124
6
11

1

`if ($supportsGzip) { ob_start("ob_gzhandler"); echo trim(preg_replace('/\s+/', ' ', $data)); }` tried that but still wont open. No output is being displayed before this function is being called. – M.Alnashmi Apr 19 '11 at 05:24
you don't need the if() in front of it, because php checks for you (from the docs): ob_gzhandler() is intended to be used as a callback function for ob_start() to help facilitate sending gz-encoded data to web browsers that support compressed web pages. Before ob_gzhandler() actually sends compressed data, it determines what type of content encoding the browser will accept ("gzip", "deflate" or none at all) and will return its output accordingly. ... If a browser doesn't support compressed pages this function returns FALSE. – daschl Apr 19 '11 at 06:10
There is a way to check if user supports encoding following code should be at the very beginning of document: if (substr_count($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip')) ob_start("ob_gzhandler"); else ob_start(); there's no need using ob_flush (it's added automaticly in this case) – Zydnar Nov 20 '16 at 10:36

Jens Roland · Answer 3 · 2011-04-20T21:28:32.863

A few things:

You probably want to add another header: header('Content-Encoding: gzip');
You are using ob_end_clean, which deletes all echoed/printed content without sending it to the browser. Depending on what you're trying to do, you may want to use ob_flush instead.
To make sure your output is buffered and handled (and compressed if you use PHP's output buffering compression), make sure all echo/print statements are placed BETWEEN the ob_start and ob_flush sttements.

--and then try it again :)

PHP Manual GZip Encoding

3 Answers3

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