Last-Modified to check feed is updated since last download - php

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.