Generating cache file for Twitter rss feed

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.