[[!template id=plugin name=postcomment author="[[Simon_McVittie|smcv]]"]]
[[!tag type/useful]]

This plugin adds "blog-style" comments. The intention is that on a non-wiki site
(like a blog) you can lock all pages for admin-only access, then allow otherwise
unprivileged (or perhaps even anonymous) users to comment on posts.

Comments are saved as internal pages, so they can never be edited through the CGI,
only by direct committers. Currently, comments are always in [[ikiwiki/markdown]].

> So, why do it this way, instead of using regular wiki pages in a
> namespace, such as `$page/comments/*`? Then you could use [[plugins/lockedit]] to
> limit editing of comments in more powerful ways. --[[Joey]]

>> Er... I suppose so. I'd assumed that these pages ought to only exist as inlines
>> rather than as individual pages (same reasoning as aggregated posts), though.
>>
>> lockedit is actually somewhat insufficient, since `check_canedit()`
>> doesn't distinguish between creation and editing; I'd have to continue to use
>> some sort of odd hack to allow creation but not editing.
>>
>> I also can't think of any circumstance where you'd want a user other than
>> admins (~= git committers) and possibly the commenter (who we can't check for
>> at the moment anyway, I don't think?) to be able to edit comments - I think
>> user expectations for something that looks like ordinary blog comments are
>> likely to include "others can't put words into my mouth". --[[smcv]]

Directives and raw HTML are filtered out by default, and comment authorship should
hopefully be unforgeable by CGI users.

> I'm not sure that raw html should be a problem, as long as the
> htmlsanitizer and htmlbalanced plugins are enabled. I can see filtering
> out directives, as a special case. --[[Joey]]

>> Right, if I sanitize each post individually, with htmlscrubber and either htmltidy
>> or htmlbalance turned on, then there should be no way the user can forge a comment;
>> I was initially wary of allowing meta directives, but I think those are OK, as long
>> as the comment template puts the \[[!meta author]] at the *end*. Disallowing
>> directives is more a way to avoid commenters causing expensive processing than
>> anything else, at this point. --[[smcv]]

When comments have been enabled generally, you still need to mark which pages
can have comments, by including the `\[[!postcomment]]` directive in them. By default,
this directive expands to a "post a comment" link plus an `\[[!inline]]` with
the comments.

> I don't like this, because it's hard to explain to someone why they have
> to insert this into every post to their blog. Seems that the model used
> for discussion pages could work -- if comments are enabled, automatically
> add the comment posting form and comments to the end of each page.
> --[[Joey]]

>> I don't think I'd want comments on *every* page (particularly, not the
>> front page). Perhaps a pagespec in the setup file, where the default is "*"?
>> Then control freaks like me could use "link(tags/comments)" and tag pages
>> as allowing comments.
>>
>> The model used for discussion pages does require patching the existing
>> page template, which I was trying to avoid - I'm not convinced that having
>> every possible feature hard-coded there really scales (and obviously it's
>> rather annoying while this plugin is on a branch). --[[smcv]]

The plugin adds a new [[ikiwiki/PageSpec]] match type, `postcomment`, for use
with `anonok_pagespec` from the [[plugins/anonok]] plugin or `locked_pages` from
the [[plugins/lockedit]] plugin. Typical usage would be something like:

    locked_pages => "!postcomment(*)"

to allow non-admin users to comment on pages, but not edit anything. You can also do

    anonok_pages => "postcomment(*)"

to allow anonymous comments (the IP address will be used as the "author").

Optional parameters to the postcomment directive:

* `commit=no`: by default, comments are committed to version control. Use this to
  disable commits.
* `allowhtml=yes`: by default, raw HTML is filtered out. Use this to allow HTML
  (you should enable [[plugins/htmlscrubber]] and either [[plugins/htmltidy]] or
  [[plugins/contrib/htmlbalance]] if you do this).
* `allowdirectives=yes`: by default, IkiWiki directives are filtered out. Use this
  to allow directives (avoid enabling any [[plugins/type/slow]] directives if you
  do this).
* `closed=yes`: use this to prevent new comments while still displaying existing ones.
* `atom`, `rss`, `feeds`, `feedshow`, `timeformat`, `feedonly`: the same as for [[plugins/inline]]

This plugin aims to close the [[todo]] item "[[todo/supporting_comments_via_disussion_pages]]",
and is currently available from [[smcv]]'s git repository on git.pseudorandom.co.uk.

Known issues:

* Needs code review
* The access control via postcomment() is rather strange
* There is some common code cargo-culted from other plugins (notably inline and editpage) which
  should probably be shared
* If the postcomment directive is removed from a page, comments can still be made on that page,
  and will be committed but not displayed; to disable comments properly you have to set the
  closed="yes" directive parameter (and refresh the wiki), *then* remove the directive if
  desired

> I haven't done a detailed code review, but I will say I'm pleased you
> avoided re-implementing inline! --[[Joey]]