# Blosxom Plugin: slashredir
# Author(s): Frank Hecker <hecker@hecker.org>
# Version: 0.4
# Documentation: See the bottom of this file or type: perldoc slashredir

package slashredir;

use strict;

use CGI qw/:standard :netscape/; 


# --- Configurable variables -----

my $debug = 1;                          # set to 1 to print debug messages

# --------------------------------


use vars qw!$redirecting!;              # 1 if we are redirecting, 0 if not


sub start {
    warn "slashredir: start\n" if $debug > 1;

    $redirecting = 0;

    # Activate this plugin only when doing dynamic page generation.
    return $blosxom::static_or_dynamic eq 'dynamic' ? 1 : 0;
}


sub filter {
    my ($pkg, $files_ref) = @_;

    warn "slashredir: filter\n" if $debug > 1;

    warn "slashredir: \$path_info: '" . $blosxom::path_info . "'\n"
        if $debug > 0;
    warn "slashredir: path_info(): '" . path_info() . "'\n"
        if $debug > 0;

    # We need a copy of the original PATH_INFO, prior to Blosxom having
    # parsed it, because we need to see the trailing slashes stripped by
    # Blosxom and also want the full path including date information.

    my $path = path_info();

    # We check to see if the URI is for an entry page and redirect if the URI
    # has a trailing slash. Otherwise we check to see if a trailing slash
    #  needs to be added or removed and redirect if needed.
    #
    # Note: We use $blosxom::path_info to check for the presence of a
    # file extension because the extension may not have been present in the
    # original URI but might have been added by the extensionless plugin.
    # (That also implies that this plugin must run after extensionless runs.)

    if ($blosxom::path_info =~ m!\.!) {
	if ($path =~ m!/$!) {
	    $path =~ s!/+$!!;           # strip *all* trailing slashes
	    redirect($path, "Trailing slash(es) not needed");
	}
    } elsif ($path !~ m!/$!) {
	$path .= '/';                   # add one trailing slash
	redirect($path, "Adding trailing slash");
    } elsif ($path =~ m!//+$!) {
	$path =~ s!//+$!/!;             # remove redundant slash(es)
	redirect($path, "Removing redundant trailing slash(es)");
    }
    1;
}


sub skip {
    warn "slashredir: skip\n" if $debug > 1;

    return $redirecting;                # skip story generation if redirecting
}


sub redirect {
    my ($path, $error_msg) = @_;

    my $uri = "$blosxom::url$path";
    $uri .= "?" . $ENV{QUERY_STRING} if $ENV{QUERY_STRING};

    warn "slashredir: redirecting to '$uri', '$error_msg'\n"
	if $debug > 0;

    my $redir_msg = qq!, redirecting to <a href="$uri">$uri</a>.\n!;
    $blosxom::output = $error_msg . $redir_msg;
    print "Status: 301\n";
    print "Location: $uri\n";
    $redirecting = 1;
}

1;

__END__

=head1 NAME

Blosxom plugin: slashredir

=head1 SYNOPSIS

Have Blosxom force a redirect if a URI is not in canonical form with respect
to trailing slashes.

=head1 VERSION

0.4

=head1 AUTHOR

Frank Hecker <hecker@hecker.org>, http://www.hecker.org/

This plugin is now maintained by the Blosxom Sourceforge Team,
<blosxom-devel@lists.sourceforge.net>.

=head1 DESCRIPTION

This plugin checks to see whether the requested URI has one or more
trailing slashes and if necessary does a browser redirect to the
canonical form of the URI. More specifically, URIs for the blog root,
categories, and date-based archives should have one (and only one)
trailing slash, while URIs for individual entry pages should not have
a trailing slash.

For example, if you request the URI

  http://www.example.com/blog/foo

where "foo" is a category, this plugin will force a redirect to the
URI

  http://www.example.com/blog/foo/

This plugin essentially causes Blosxom to emulate the default behavior
of the Apache web server. The underlying idea is that URIs for Blosxom
pages should have trailing slashes if and only if there are (or could
be) other URIs for other pages "underneath" the URI in question.

Thus an individual entry page with a URI of the form
".../entry.flavour" (or ".../entry" if using the extensionless plugin)
should not have a trailing slash, because URIs of the form
".../entry.html/foo" (or ".../entry/foo" with extensionless) don't and
won't return anything meaningful. However a category page with a URI
of the form ".../category" could refer to additional pages with URIs
of the form ".../category/foo.html (or ".../category/foo/entry"), and
hence the canocical form of the category's URI should be
".../category/".

Similarly, date-based archive pages with URIs like ".../2004" or
".../2004/10" could have subsidiary URIs for months or days
respectively; while days are not subdivided further, per-day archive
pages could be requested in non-default flavours, e.g.,
".../2004/10/14/index.rss" (as could per-year and per-month pages as
well, of course). Hence for date-based archive pages the canonical
form of the URI should also include a trailing slash if the default
flavour is being requested.

Note that using this plugin makes most sense if you are also using URI
rewriting rules to hide use of "/cgi-bin/blosxom.cgi" and support URIs
similar to those traditionally used to access normal directories and
files. This plugin can be used in conjunction with the extensionless
plugin, but does not assume or require its use. (See also below.)

This plugin was inspired by the redirect plugin by Fletcher T. Penny
http://www.blosxom.com/plugins/general/redirect.htm and adapts a bit
of its code.

=head1 INSTALLATION AND CONFIGURATION

Copy this plugin into your Blosxom plugin directory. You do not
normally need to rename the plugin; however see the discussion below.

You can change the value of the variable C<$debug> to 1 if you need to
debug the plugin's operation; the plugin will print to the web
server's error log the original path component of the URI and the new
URI if redirection is to be done.

This plugin supplies a filter and skip subroutine and can normally
coexist with other plugins with filter subroutines. However this
plugin needs to be run after the extensionless plugin, since it needs
the file extension (provided by extensionless if not already present)
to distinguish between individual entry pages and other pages.

Finally, note that this plugin is sensitive to the exact URI rewriting
rules you might have configured (e.g., in an Apache configuration file
or in a .htaccess file). In particular, when rewriting URIs to add the
name of the Blosxom CGI script (e.g., "/cgi-bin/blosxom.cgi") you need
to ensure that such rules preserve any trailing slash on the end of
the URI and pass it on to Blosxom.

=head1 SEE ALSO

Blosxom Home/Docs/Licensing: http://blosxom.sourceforge.net/

Blosxom Plugin Docs: http://blosxom.sourceforge.net/documentation/users/plugins.html

=head1 BUGS

None known; please send bug reports and feedback to the Blosxom
development mailing list <blosxom-devel@lists.sourceforge.net>.

=head1 LICENSE

slashredir Blosxom plugin Copyright 2004 Frank Hecker

Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the "Software"),
to deal in the Software without restriction, including without limitation
the rights to use, copy, modify, merge, publish, distribute, sublicense,
and/or sell copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.