Adds utility functions to httpd.c for checking the request headers for
either an "If-None-Match" or an "If-Not-Modified-Since" headers. If the
header value is found and it matches the current value for the requested
resource, we return early with a http response code 403 (Not Modified).
If the request header value is not present or does not match we add the
current ETag/Last-Modified values to the response headers and process
the request normally.
Some clients aren't really capable of authenticating + some users probably
don't want to enter a password for the web interface. This option allows
clients on for instance the local network to connect without authentication.
Make it easier to add new parameters later, get rid of redundant code, clean
up, align between httpd_xxx modules and introduce new bugs. Yes, the refactor
got a bit out of hand.
In preparation for the new endpoints the following refactorings where
done in lastfm.c:
- Initialize lastfm.c in main.c instead of on first scrobble attempt
(necessary to retrieve the correct lastfm status)
- Return error messages if login attempt failed
- Add api function for status and logout
- Notify about Last.fm status changes
Unrelated changes in lastfm.c are:
- Refactoring of request_post
- Add request parameters sorted alphabetically and remove calling the
sort method in request_post
