This is a plugin that prompts the user for a title for a post, and then redirects the user to post in a hierarchically organized directory structure. It supports limiting blog posts only to certain users, and this applies to creating new as well as editing old ones. It's a little clumsy so far:

• Although Joey said specifically not to, I export the printheader function so that the plugin can create a form.
• The form doesn't invoke the formbuilder hooks; I couldn't figure out a way to do that easily from inside the plugin (unless I exported run_hooks and that didn't seem right).
• This invokes a new hook, authcgi, although Joey said that "the best approach was adding a flag that makes a cgi hook get postponed and called after a session is set up". I don't know if this is a good idea; authenticated CGI plugins need sessions, and unauthenticated CGI plugins don't, so it seems like a new hook is a better idea.
• This creates a lot of broken parents unless you use something like missingparents.pm.

I don't expect that this will be applied; it's more like a first draft. I would like to hear good ideas on how to solve the first two problems. Maybe make the hook return a form, which is printed by CGI.pm? --Ethan

Index: IkiWiki/CGI.pm
===================================================================
--- IkiWiki/CGI.pm  (revision 3968)
+++ IkiWiki/CGI.pm  (working copy)
@@ -684,6 +684,9 @@
        }
    }
    
+   run_hooks(authcgi => sub { shift->($q, $session); });
+   my $do=$q->param('do'); # in case the hook changed it
+
    if (defined $session->param("name") &&
        userinfo_get($session->param("name"), "banned")) {
        print $q->header(-status => "403 Forbidden");
Index: IkiWiki/Plugin/blogpost.pm
===================================================================
--- IkiWiki/Plugin/blogpost.pm  (revision 0)
+++ IkiWiki/Plugin/blogpost.pm  (revision 0)
@@ -0,0 +1,97 @@
+#!/usr/bin/perl
+# blogpost plugin: interprets cgi "blogpost" commands as create commands.
+package IkiWiki::Plugin::blogpost;
+
+use warnings;
+use strict;
+use POSIX;
+use IkiWiki 2.00;
+
+sub import {
+   hook(type => "checkconfig", id => "blogpost", call => \&checkconfig);
+   hook(type => "authcgi", id => "blogpost", call => \&authcgi);
+   hook(type => "canedit", id => "blogpost", call => \&canedit);
+}
+
+sub checkconfig () {
+   if (! defined $config{blogformat}){
+       $config{blogformat} = 'posts/%Y/%m/%d/$title';
+   }
+
+   if (! defined $config{blogpagespec}){
+       my $spec = $config{blogformat};
+       $spec =~ s/%./\*/g;
+       $spec =~ s/\$title/*/;
+       $config{blogpagespec} = "$spec and ! $spec/*";
+   }
+   
+   if (! defined $config{blogusers}) {
+       $config{blogusers} = (); # disallow all posting by default
+   }
+}
+
+sub authcgi ($$) {
+   my $cgi=shift;
+   my $session=shift;
+
+   return unless (defined $cgi->param('do') && $cgi->param('do') eq "blogpost");
+   my $user=$session->param("name");
+   error ("not allowed to blog, $user") unless
+       $config{blogusers} eq "*" ||
+       grep {$_ eq $user} $config{blogusers};
+   eval q{use CGI::FormBuilder};
+   error($@) if $@;
+   my @fields=qw(title);
+   my $form = CGI::FormBuilder->new(
+       fields => \@fields,
+       title => "post title",
+       name => "post title",
+       header => 1,
+       charset => "utf-8",
+       method => 'POST',
+       required => 'NONE',
+       javascript => 0,
+       params => $cgi,
+       action => $config{cgiurl},
+       header => 0,
+       template => {type => 'div'},
+       stylesheet => $config{url}."/style.css",
+   );
+   my $buttons=["Blog!"];
+   $form->field(name => "do", type => "hidden", value => "blogpost",
+       force => 1);
+   if (! $form->submitted){
+       printheader($session);
+       print misctemplate($form->title, $form->render(submit => $buttons));
+       exit;
+   }
+   else {
+       my $page = blogpage($form->field("title"));
+       $cgi->param("do", "create");
+       $cgi->param("page", $page);
+   }
+
+}
+
+sub blogpage ($) {
+   my $title=shift;
+   my $page=POSIX::strftime $config{blogformat}, localtime;
+   $page =~ s/\$title/$title/;
+   return $page;
+}
+
+sub canedit ($$$) {
+   my $page=shift;
+   my $cgi=shift;
+   my $session=shift;
+
+   return undef unless pagespec_match($page, $config{blogpagespec});
+   my $user=$session->param("name");
+   IkiWiki::needsignin($cgi, $session) unless defined $user;
+
+   return "" if ($config{blogusers} eq "*" ||
+             grep {$_ eq $user} $config{blogusers});
+   return ("not allowed to blog, $user");
+}
+
+1
Index: IkiWiki.pm
===================================================================
--- IkiWiki.pm  (revision 3968)
+++ IkiWiki.pm  (working copy)
@@ -17,6 +17,7 @@
 our @EXPORT = qw(hook debug error template htmlpage add_depends pagespec_match
                  bestlink htmllink readfile writefile pagetype srcfile pagename
                  displaytime will_render gettext urlto targetpage
+                 misctemplate printheader
                  %config %links %renderedfiles %pagesources %destsources);
 our $VERSION = 2.00; # plugin interface version, next is ikiwiki version
 our $version='unknown'; # VERSION_AUTOREPLACE done by Makefile, DNE