Code Igniter 3 Last modified and E-tag Library

Last_modified.php

<?php

// Tested by Code Igniter 3.1.7

if (!defined('BASEPATH')) {
    exit('No direct script access allowed');
}

class Last_modified
{
    protected $ci;

    public function __construct()
    {
        $this->ci = get_instance();
    }

    public function set($etag, $timestamp)
    {
        $gmt_mtime = gmdate('r', $timestamp);

        $this->ci->output->set_header('ETag: "'.md5($timestamp.$etag).'"');
        $this->ci->output->set_header('Last-Modified: '.$gmt_mtime);
        $this->ci->output->set_header('Cache-Control: public');

        $et = trim($this->ci->input->server('HTTP_IF_NONE_MATCH'));
        $f = strpos($et, '"');
        $e = strrpos($et, '"');

        if (null != $this->ci->input->server('HTTP_IF_MODIFIED_SINCE') || null != $this->ci->input->server('HTTP_IF_NONE_MATCH')) {
            if ($this->ci->input->server('HTTP_IF_MODIFIED_SINCE') == $gmt_mtime || substr($et, $f + 1, -1) == md5($timestamp.$etag)) {
                $this->ci->output->set_status_header(304);
            }
        }
    }
}