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We're accumulating a significant number of bugs related to cross-linking
between the content and the CGI not being as relative as we would like.
This is an attempt to design a solution for them all in a unified way,
rather than solving one bug at the cost of exacerbating another.
--[[smcv]]
# Terminology
* Absolute: starts with a scheme, like
`http://example.com/ikiwiki.cgi`, `https://www.example.org/`
* Protocol-relative: starts with `//` like `//example.com/ikiwiki.cgi`
* Host-relative: starts with `/` like `/ikiwiki.cgi`
* Relative: starts with neither `/` nor a scheme, like `../ikiwiki.cgi`
# What we need
* Static content must be able to link to other static content
* Static content must be able to link to the CGI
* CGI-generated content must be able to link to arbitrary
static content (it is sufficient for it to be able to link
to the "root" of the `destdir`)
* CGI-generated content must be able to link to the CGI
# Constraints
* URIs in RSS feeds must be absolute, because feed readers do not have
any consistent semantics for the base of relative links
* If we have a `<base href>` then HTML 4.01 says it must be
absolute, although HTML 5 does relax this by defining semantics
for a relative `<base href>` - it is interpreted relative to the
"fallback base URL" which is the URL of the page being viewed
([[bugs/trouble_with_base_in_search]],
[[bugs/preview_base_url_should_be_absolute]])
* It is currently possible for the static content and the CGI
to be on different domains, e.g. `www.example.com`
vs. `cgi.example.com`; this should be preserved
* It is currently possible to serve static content "mostly over
HTTP" (i.e. advertise a http URI to readers, and use a http
URI in RSS feeds etc.) but use HTTPS for the CGI
* If the static content is served over HTTPS, it must refer
to other static content and the CGI via HTTPS (to avoid
mixed content, which is a vulnerability); this may be
either absolute, protocol-relative, host-relative or relative
* If the CGI is served over HTTPS, it must refer to static
content and the CGI via HTTPS; again, this may be either
either absolute, protocol-relative, host-relative or relative
([[todo/Protocol_relative_urls_for_stylesheet_linking]])
* Because reverse proxies and `w3mmode` exist, it must be
possible to configure ikiwiki to not believe the `HTTPS`, etc.,
CGI variables, and force a particular scheme or host
([[bugs/W3MMode_still_uses_http:__47____47__localhost__63__]],
[[forum/Using_reverse_proxy__59___base_URL_is_http_instead_of_https]],
[[forum/Dot_CGI_pointing_to_localhost._What_happened__63__]])
* For relative links in page-previews to work correctly without
having to have global state or thread state through every use of
`htmllink` etc., `cgitemplate` needs to make links in the page body
work as if we were on the page being previewed.
# "Would be nice"
* In general, the more relative the better
* [[schmonz]] wants to direct all CGI pageviews to https
even if the visitor comes from http (but this can be done
at the webserver level by making http://example.com/ikiwiki.cgi
a redirect to https://example.com/ikiwiki.cgi, so is not
necessarily mandatory)
* [[smcv]] has some sites that have non-CA-cartel-approved
certificates, with a limited number of editors who can be taught
to add SSL policy exceptions and log in via https;
anonymous/read-only actions like `do=goto` should
not go via HTTPS, since random readers would get scary SSL
warnings
([[todo/want_to_avoid_ikiwiki_using_http_or_https_in_urls_to_allow_serving_both]],
[[forum/CGI_script_and_HTTPS]])
* It would be nice if the CGI did not need to use a `<base>` so that
we could use host-relative URI references (`/sandbox/`) or scheme-relative
URI references (`//static.example.com/sandbox/`)
(see [[bugs/trouble_with_base_in_search]])
As a consequence of the "no mixed content" constraint, I think we can
make some assumptions:
* if the `cgiurl` is http but the CGI discovers at runtime that it has
been reached via https, we can assume that the https equivalent,
or a host- or protocol-relative URI reference to itself, would work;
* if the `url` is http but the CGI discovers at runtime that it has been
reached via https, we can assume that the https equivalent of the `url`
would work
In other words, best-practice would be to list your `url` and `cgiurl`
in the setup file as http if you intend that they will most commonly
be accessed via http (e.g. the "my cert is not CA-cartel approved"
use-case), or as https if you intend to force accesses into
being via https (the "my wiki is secret" use-case).
# Regression test
I've added a regression test in `t/relativity.t`. We might want to
consider dropping some of it or skipping it unless a special environment
variable is set once this is all working, since it's a bit slow.
--[[smcv]]
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