浏览器使用PHP输出缓冲区和ETag缓存动态内容

Question

I have been researching some strategies to optimize a web application I am working on particularly related to web browser caching and dynamic data. Since potentially the same dynamic content may be loaded multiple times in a session, I came up with the following method using PHP's output buffer and using a hash of the content as an ETag.

I realize that the only thing I really save with this method is the transfer of data back to the user since the PHP script still has to completely run, but I was curious if anyone has done something similar and if there are any thoughts or concerns I should be aware of or what other methods may be better.

Here is the code I am including at the top of each page:

<?php
function hash_buffer($content) {
    $buffer_hash = crc32($content);
    if ($_SERVER['HTTP_IF_NONE_MATCH'] == $buffer_hash) {
        header('HTTP/1.1 304 Not Modified');
        header("ETag: $buffer_hash");
        return '';
    }
    header('Cache-Control: private, no-cache');
    header("ETag: $buffer_hash");
    return $content;
}

ob_start('hash_buffer');
?>

Answer 1

Use something fast to create the hash crc32 is fast but might give you more collisions than md5 (although filename takes care of some).

<?php
function hash_buffer($content) {
    $buffer_hash = crc32($content);

    // You could add expire time so the check is not made every time.
    // Or force it to happen always
    header('Expires:');//.date('r',strtotime('+1 hour')));

    // Add vary header so client knows to usee ETag
    // Without overwriting existing vary headers
    header('Vary: If-None-Match',false);

    if ($_SERVER['HTTP_IF_NONE_MATCH'] == $buffer_hash) {
        header('HTTP/1.1 304 Not Modified');
        header("ETag: $buffer_hash");
        return '';
    }
    header('Cache-Control: private, no-cache');
    header("ETag: $buffer_hash");
    return $content;
}

ob_start('hash_buffer');
?>

Try to get content faster to the buffer

To get content to be buffered generated faster you could use file caching. For example writing generated navigation/blogroll/newslist into a file and reading it from there if filemtime is within cache lifetime ( 10min - 1h etc.) otherwise write it down on file and handle as usual.

You need write locks to prevent collisions etc. see ZendFramework implementation on that https://github.com/zendframework/zf2/blob/master/library/Zend/Cache/Storage/Adapter/Filesystem.php#L1489

Remember

User rights might play a part on filecaching like with any cache you don't want someone else's shopping cart appear on you checkout page etc. Generally leaving authenticated users out of filecache is playing it safe.

When caching on files cache files must be safeguarded from public read and write access over the web and otherwise.