条件付きGET

cget.class.inc.php

<?php
class CGET {
  
    function __construct($timestamp=0, $content='') {
        
        if(!$timestamp) return;
        
        $last_mod = gmdate('D, d M Y H:i:s T', $timestamp);
        if(!$content) $content = $last_mod;
        $etag = md5($content);
        
        header('Last-Modified: '.$last_mod);
        header(sprintf('ETag: "%s"', $etag));
        if(!$this->isNotModified($last_mod) || !$this->isMatchContent($etag)) return;
        
        header('HTTP/1.1 304 Not Modified');
        header('Content-Length: 0');
        exit;
    }
    
    function isNotModified($last_mod) {
        if (!isset($_SERVER['HTTP_IF_MODIFIED_SINCE']))      return false;
        if ($_SERVER['HTTP_IF_MODIFIED_SINCE'] == $last_mod) return true;
        return false;
    }
    
    function isMatchContent($etag) {
        $_ = $_SERVER;
        if (!isset($_['HTTP_IF_NONE_MATCH']))                return false;
        if (trim($_['HTTP_IF_NONE_MATCH'],'"') === $etag)    return true;
        return false;
    }
}