Generating cache file for Twitter rss feed - php

Question

I'm working on a site with a simple php-generated twitter box with user timeline tweets pulled from the user_timeline rss feed, and cached to a local file to cut down on loads, and as backup for when twitter goes down. I based the caching on this: http://snipplr.com/view/8156/twitter-cache/. It all seemed to be working well yesterday, but today I discovered the cache file was blank. Deleting it then loading again generated a fresh file.
The code I'm using is below. I've edited it to try to get it to work with what I was already using to display the feed and probably messed something crucial up.
The changes I made are the following (and I strongly believe that any of these could be the cause):
- Revised the time difference code (the linked example seemed to use a custom function that wasn't included in the code)
Removed the "serialize" function from the "fwrites". This is purely because I couldn't figure out how to unserialize once I loaded it in the display code. I truthfully don't understand the role that serialize plays or how it works, so I'm sure I should have kept it in. If that's the case I just need to understand where/how to deserialize in the second part of the code so that it can be parsed.
Removed the $rss variable in favor of just loading up the cache file in my original tweet display code.
So, here are the relevant parts of the code I used:
<?php
$feedURL = "http://twitter.com/statuses/user_timeline/#######.rss";
// START CACHING
$cache_file = dirname(__FILE__).'/cache/twitter_cache.rss';
// Start with the cache
if(file_exists($cache_file)){
$mtime = (strtotime("now") - filemtime($cache_file));
if($mtime > 600) {
$cache_rss = file_get_contents('http://twitter.com/statuses/user_timeline/75168146.rss');
$cache_static = fopen($cache_file, 'wb');
fwrite($cache_static, $cache_rss);
fclose($cache_static);
}
echo "<!-- twitter cache generated ".date('Y-m-d h:i:s', filemtime($cache_file))." -->";
}
else {
$cache_rss = file_get_contents('http://twitter.com/statuses/user_timeline/#######.rss');
$cache_static = fopen($cache_file, 'wb');
fwrite($cache_static, $cache_rss);
fclose($cache_static);
}
//END CACHING
//START DISPLAY
$doc = new DOMDocument();
$doc->load($cache_file);
$arrFeeds = array();
foreach ($doc->getElementsByTagName('item') as $node) {
$itemRSS = array (
'title' => $node->getElementsByTagName('title')->item(0)->nodeValue,
'date' => $node->getElementsByTagName('pubDate')->item(0)->nodeValue
);
array_push($arrFeeds, $itemRSS);
}
// the rest of the formatting and display code....
}
?>
ETA 6/17 Nobody can help…?
I'm thinking it has something to do with writing a blank cache file over a good one when twitter is down, because otherwise I imagine that this should be happening every ten minutes when the cache file is overwritten again, but it doesn't happen that frequently.
I made the following change to the part where it checks how old the file is to overwrite it:
$cache_rss = file_get_contents('http://twitter.com/statuses/user_timeline/75168146.rss');
if($mtime > 600 && $cache_rss != ''){
$cache_static = fopen($cache_file, 'wb');
fwrite($cache_static, $cache_rss);
fclose($cache_static);
}
…so now, it will only write the file if it's over ten minutes old and there's actual content retrieved from the rss page. Do you think this will work?

Answer 1

Yes your code is problematic, because whatever Twitter sends you, you write it.
You should test the file you get from Twitter like this:
if (($mtime > 600) && ($cache_rss = file_get_contents($feedURL)))
{
file_put_contents($cache_rss);
}
file_get_contents() return false if there is an error, check it before caching some new content.