WebReference.com - The WebReference/internet.com Multi-Feed RSS Sidebar Tab (4/6)

The Perl

Our Perl code is just short of 350 lines long and has a bunch of comments, so we won't display the whole listing here (feel free to download the zipped package and have a look for yourself, though). We will however touch on some key points and discuss a few code snippets. The basic task of the Perl code is as follows:

Define and retrieve the locations and titles of local RSS feeds that will be used in your tab. Note that to save time we retrieve only the names of the files here, and not their individual contents.

Retrieve the appropriate HTML template file, and replace the variables within it with information from either the feed listing above (the default action) or the actual RSS file (if one was so designated by the user).

Several global variables are defined near the top of the feedtab script:

$maxInArrays will be the maximum number of links that will be displayed (rotated) within a single page. Generally you will set this to be a pretty high number; of course, a higher number here means more bytes for the user.

$thisURL is the URL of the actual feedtab.cgi script.

$home is typically your document root. It will be prepended to the feed locations requested by the user, so that the user doesn't have to see your directory structure in their links. For example, if you have two feeds that are located in /websites/mysite/mydocroot/myfeeddir1/feed.rss and /websites/mysite/mydocroot/myfeeddir2/feed.rss, the home directory could be set to /websites/mysite/mydocroot/, and the two feed locations would be set to myfeeddir1/feed.rss and myfeeddir2/feed.rss. In this way, when the user views the link used to get to a particular feed, they would see http://yourdomain.com/cgi-bin/feedtab.cgi?feed=myfeeddir1/feed.rss instead of the full path to the selected RSS file.

%defHash is a hash of default data entries to be used in feeds. By assigning values here, you can provide default values for key display parameters, while still allowing each variable to be overridden by the specific feed, if necessary. The defaults currently available as of this writing are:

dark = color for the outer (dark) div
light = color for the inner (light) div
bg = color for the page background
li, al, vl = link, active link, and visited link colors
hbg = hover background color
totlinks = total number of links to display at a time
template_all = HTML template to use for master feed listing
template_one = HTML template to use for a single feed listing

Remember that you do not have to use these values in your HTML display; how you define your HTML output (and which of these values you actually incorporate) is up to you. In the provided example templates included with the download, for example, the li, al, and vl are not used.

Retrieving your feed listing is the purpose of the &getFeeds function; it is discussed next.

sub getFeeds { # # Example initial feed array. Modify/expand this; or # retrieve the structure via your own mechanism (DB, external # configuration file, etc.) # my @NEWSFEEDS = ( { location => 'webreference.rdf', title => 'WebReference.com', shortTitle => 'WebReference Features', dark => '#fc0', light => '#ffed9a', bg => '#fff', hbg => '#fd3', }, { location => 'js/tips/channels/last1512.rdf', title => 'JavaScript Tip of the Day', dark => '#fc6', light => '#ffd', bg => '#fff', hbg => '#fd3', }, ); my %retHash=(); foreach my $feed (@NEWSFEEDS) { my %feedHash=(); # assign all properties from provided feeds foreach my $key (keys %$feed) { $feedHash{$key} =$feed->{$key}; } # check for/assign default # info if not initially present foreach my $key (keys %defHash) { $feedHash{$key} = $defHash{$key} unless (defined($feedHash{$key})); } $retHash{$feed->{'location'}}=\%feedHash; } return %retHash; } # # end sub getFeeds ###############################################

We left &getFeeds purposely fairly bare, since how you retrieve your feeds for listing will depend entirely on what structure you have them in already. In the worse case, you can simply modify and extend the hashes in the @NEWSFEEDS array to accommodate all of your RSS feed listings. The location and title fields are the only required fields; all others will serve as overrides for the defaults for this particular feed (any of the defaults discussed in the earlier %defHash discussion can be used). The shortTitle field, in particular, can be used as a specifically formatted feed title in the event that you don't like the title included within the selected RSS file (which will otherwise be used as the default).

Two other main routines are used in the Perl code; depending on whether the user has chosen to view a specific feed or to view the feed listing for further selection. Since both routines are very similar, we'll focus on a few details of the specific feed display and leave the &showAll routine for your own examination. As a security precaution, feedtab.cgi checks to see that any feed requested by the user matches a feed as listed in the &getFeeds() hash. This prevents a malicous end user from crafting a feedtab request that will attempt to read other files on our system; i.e., only those feeds that we explicitly allow may be read using feedtab. All other requests are shuttled off to the main feed display, &showAll.