The edit page CGI defines a `base` tag with an URL which is not
absolute, which can break the preview function in some circumstances
(with e.g. images not showing). The trivial [[patch]] that fixes
it can be found [[here|http://sprunge.us/EPHT]] as well as on [[my
git|http://git.oblomov.eu/ikiwiki]].

> That patch does mean that if you're accessing the CGI via HTTPS but your
> $config{url} and $config{cgiurl} are HTTP, you'll get preview images loaded
> via HTTP, causing the browser to complain. See
> [[todo/want_to_avoid_ikiwiki_using_http_or_https_in_urls_to_allow_serving_both]]
> for background.
>
> Perhaps the CGI could form its `<base>` URL by using
> `URI->new_abs(urlto(...), $cgi->url)` instead?
>
> You'd also need to change `IkiWiki/Wrapper.pm` to pass at least the
> SERVER_NAME and SERVER_PORT through the environment, probably.
>
> Joey's last comment on
> [[todo/want_to_avoid_ikiwiki_using_http_or_https_in_urls_to_allow_serving_both]]
> suggests that this might already work, but I'm not quite sure how - I'd
> expect it to need more environment variables? --[[smcv]]
>
>> `CGI::url` uses `REQUEST_URI`. So it could be used, but I don't see
>> how to get from the `CGI::url` to an url to the page that is being
>> edited. --[[Joey]]
>>> (The right rune seems to be: `URI->new_abs(urlto($params{page}), $cgi->url))` --[[Joey]] 

---

Update: This bug is worse than it first appeared, and does not only affect
previewing. The cgi always has a `<base>` url, and it's always relative,
and that can break various links etc. For example, when the 404 plugin
displays a missing page, it has a Recentchanges link, which would be broken
if the cgi was in an unusual place.

`misctemplate` needs to *always* set an absolute baseurl. Which is a problem,
since `misctemplate` is not currently passed a cgi object from which to
construct one. --[[Joey]]

Update: Worse and worse. `baseurl(undef)` can be a relative url, but
nearly every use of it I can find actually needs to be absolute. 
the numerous `redirect($q, baseurl(undef))` all need to be absolute
according to `CGI` documentation.

So, I'm seriously thinking about reverting the part of
[[todo/want_to_avoid_ikiwiki_using_http_or_https_in_urls_to_allow_serving_both]]
that made `baseurl(undef)` relative. 
And I suppose, re-opening that todo. :( --[[Joey]]