Keith Devens .com

Conditional get

In the spirit of Simon's, I created my own conditional get function. My RSS feed finally does conditional get


<?php
function httpConditionalGet($timestamp, $is_timestamp = true){
    if($is_timestamp) $last_modified = gmdate('r', $timestamp);
    if((isset($_SERVER['HTTP_IF_NONE_MATCH']) and $_SERVER['HTTP_IF_NONE_MATCH'] == $timestamp) or
        ($is_timestamp and
        isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) and
        $_SERVER['HTTP_IF_MODIFIED_SINCE'] == $last_modified)
    ){
        header('HTTP/1.1 304 Not Modified');
        exit;
    }
    if($is_timestamp) header("Last-modified: $last_modified");
    header('ETag: '.($is_timestamp ? $timestamp : md5($timestamp)));
}
?>

So, you can pass it a timestamp and it'll use Last-modified headers, but if you explicitly tell it it's not a timestamp then it won't and will just use an ETag instead.

Update (5/7): Note that this code is kind of broken. It was just a quick hack that worked for me, but I didn't test it well because I was (and still am) in the middle of finals. Once I get a chance I'll revise it and fix what's broken. Thanks to Bob Congdon for pointing me to what I did wrong. I explain some of the things in the comments on his post about this.

Update (12/11): I figured I'd post the updated, correct version of this code:


<?php
function httpConditionalGet($thing, $is_timestamp = true){
    #thing can be either a timestamp or anything else you want to serve as an etag
    #if it's not a timestamp, it's the caller's responsibility to md5 it or whatever
    if($is_timestamp) header('Last-modified: '.($lm = gmdate('r', $thing)));
    header('ETag: "'.$thing.'"');
    $client_etag = isset($_SERVER['HTTP_IF_NONE_MATCH'])     ? $_SERVER['HTTP_IF_NONE_MATCH']     : NULL;
    $client_lm   = isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) ? $_SERVER['HTTP_IF_MODIFIED_SINCE'] : NULL;

    if(($client_etag and $client_etag == '"'.$thing.'"') #etag
       or
       ($is_timestamp and $client_lm and ($client_lm == $lm or $thing == strtotime($client_lm))) #last-modified
    ) header('HTTP/1.1 304 Not Modified') and exit;
}
?>