Last-Modified to check feed is updated since last download

Question

i am using PHP to read feed xml in every half an hour, as of now i am always reading whole feed file whether it is updated or not. But i want to check whether feed xml is update since last download, if updated then only read the xml otherwise not.

I am trying to achieve it using below code, but $lastmodifiedRSS is always empty. I am not sure what is going wrong in my code. If i get $lastmodifiedRSS then i can easily compare it with last loaded time and then decide what to do.

If any Expert can share some info that would be great. Thank you in advance.

//get feed information & content
$feed = new feed($rssurl);
$feed->load();

//get the last modified date (web server information)
$lastmodifiedRSS = $feed->http->get_header_value('Last-Modified');

        function http($url)
{
    $this->url($url);
    $this->user_agent = 'posh';
    $this->header = "";
    $this->code = "";
    $this->codeStr = "";
    $this->max_d = 5;
    $this->authorization = "";
    $this->proxy_auth = "";
    $this->url = $url;
    $this->addProxy();
}

    function feed($url)
{
    if ($url) {
        $this->url = $url;
        $this->http = new http($url);
        //$this->addProxy();
    } else {
        $this->http = new http('');      
    }
}
function load()
    {
        $content= $this->http->get();
        if (!$content)
            return false;
        $content = $this->transcode($content);
        return $content;
    }

function get_header_value($name)
    {
        if (preg_match("/$name: ?([^\\r\\n]*)\\r\\n/m",$this->head,$matches) !== false)
        {
            if (count($matches) > 1)
            {
                return $matches[1];
            }
        }
        return false;
    }

Regards, Mona

Answer 1

Make use of stat() in PHP

<?php
print_r(stat('users.json'));

OUTPUT:

Array ( [0] => 2 [1] => 0 [2] => 33206 [3] => 1 [4] => 0 [5] => 0 [6] => 2 [7] => 298 [8] => 1384073940 [9] => 1384073940 [10] => 1368626190 [11] => -1 [12] => -1 [dev] => 2 [ino] => 0 [mode] => 33206 [nlink] => 1 [uid] => 0 [gid] => 0 [rdev] => 2 [size] => 298 [atime] => 1384073940 [mtime] => 1384073940 [ctime] => 1368626190 [blksize] => -1 [blocks] => -1 )

Source

Keeping a track of the variables [atime] , [size] can help you achieve what you are trying to do.

Answer 2

This kind of checking are better handled with HTTP headers itself.

If the server sends Etag header in the response, you could use it with the If-None-Match header on the next request to know if the file has changed.

Similarly, if the server sends Last-Modified header in the response, you could use this timestamp with the If-Modified-Since header on the next request to know if the file got changed.

Just to let you know what you could do, I can't contribute any code cause I don't know which HTTP library you're using here.