MagpieRSS Recipes: Cooking with Corbies

"Four and twenty blackbirds baked in a pie."

  1. Limit the Number of Headlines(aka Items) Returned
  2. Display a Custom Error Message if Something Goes Wrong
  3. Generate a New RSS Feed
  4. Display Headlines More Recent then X Date
  5. Parse a Local File Containing RSS

1. Limit the Number of Headlines(aka Items) Returned.

Problem:

You want to display the 10 (or 3 or whatever) most recent headlines, but the RSS feed contains 15.

Solution:

$num_items = 10;
$rss = fetch_rss($url);

$items = array_slice($rss->items, 0, $num_items);

foreach ( $items as $item ) {

Discussion:

Rather then trying to limit the number of items Magpie parses, a much simpler, and more flexible approach is to take a "slice" of the array of items. And array_slice() is smart enough to do the right thing if the feed has less items then $num_items.

See:

http://www.php.net/array_slice

2. Display a Custom Error Message if Something Goes Wrong

Problem:

You don't want Magpie's error messages showing up if something goes wrong.

Solution:

# Magpie throws USER_WARNINGS only
# so you can cloak these, by only showing ERRORs
error_reporting(E_ERROR);

# check the return value of fetch_rss()

$rss = fetch_rss($url);

if ( $rss ) {
...display rss feed...
}
else {
   echo "An error occured!  " .
        "Consider donating more $$$ for restoration of services." .
        "<br>Error Message: " . magpie_error();
}

Discussion:

MagpieRSS triggers a warning in a number of circumstances. The 2 most common circumstances are: if the specified RSS file isn't properly formed (usually because it includes illegal HTML), or if Magpie can't download the remote RSS file, and there is no cached version. If you don't want your users to see these warnings change your error_reporting settings to only display ERRORs.
Another option is to turn off display_error, so that WARNINGs, and NOTICEs still go to the error_log but not to the webpages. You can do this with: 
# you can also do this in your php.ini file
ini_set('display_errors', 0);

See:

http://www.php.net/error_reporting,
http://www.php.net/ini_set,
http://www.php.net/manual/en/ref.errorfunc.php

3. Generate a New RSS Feed

Problem:

Create an RSS feed for other people to use.

Solution:

Use Useful Inc's RSSWriter.

Discussion:

An example of turning a Magpie parsed RSS object back into an RSS file is forthcoming. In the meantime RSSWriter is well documented.

4. Display Headlines More Recent then X Date

Problem:

You only want to display headlines that were published on, or after a certain date.

Solution:

require_once('rss_utils.inc');

# get all headlines published today
$today = getdate();

# today, 12AM
$date = mktime(0,0,0,$today['mon'], $today['mday'], $today['year']);

$rss = fetch_rss($url);

foreach ( $rss->items as $item ) {
   $published = parse_w3cdtf($item['dc']['date']);
   if ( $published >= $date ) {
        echo "Title: " . $item['title'];
        echo "Published: " . date("h:i:s A", $published);
        echo "<p>";
    }
}

Discussion:

This recipe only works for RSS 1.0 feeds that include the field. (which is very good RSS style)
parse_w3cdtf() is defined in rss_utils.inc, and parses RSS style dates into Unix epoch seconds.

See:

http://www.php.net/manual/en/ref.datetime.php

5. Parse a Local File Containing RSS

Problem:

MagpieRSS provides fetch_rss() which takes a URL and returns a parsed RSS object, but what if you want to parse a file stored locally that doesn't have a URL?

Solution

require_once('rss_parse.inc');

$rss_file = 'some_rss_file.rdf';
$rss_string = read_file($rss_file);
$rss = new MagpieRSS( $rss_string );

if ( $rss and !$rss->ERROR) {
...display rss...
}
else {
    echo "Error: " . $rss->ERROR;
}

# efficiently read a file into a string
# in php >= 4.3.0 you can simply use file_get_contents()
#
function read_file($filename) {
    $fh = fopen($filename, 'r') or die($php_errormsg);
    $rss_string = fread($fh, filesize($filename) );
    fclose($fh);
    return $rss_string;
}

Discussion

Here we are using MagpieRSS's RSS parser directly without the convience wrapper of fetch_rss(). We read the contents of the RSS file into a string, and pass it to the parser constructor. Notice also that error handling is subtly different.

See:

http://www.php.net/manual/en/ref.filesystem.php,
http://www.php.net/manual/en/language.oop.php