3.10 Custom Error Pages

It is possible to create arbitrary error pages for responses generated when a http_reply term is thrown. Currently this is only supported for status 403 (authentication required). To do this, instead of throwing http_reply(authorise(Term)) throw http_reply(authorise(Term), [], Key), where Key is an arbitrary term relating to the page you want to generate. You must then also define a clause of the multifile predicate http:status_page_hook/3:

http:status_page_hook(+TermOrCode, +Context, -CustomHTML)

TermOrCode is either the first argument of the http_reply exception or the HTTP status code, i.e., the hook is called twice. New code should using the Term. Context is the third argument of the http_reply exception which was thrown, and CustomHTML is a list of HTML tokens. A page equivalent to the default page for 401 is generated by the example below.

:- multifile http:status_page_hook/3.

http:status_page_hook(authorise(Term), _Context, HTML) :-
    phrase(page([ title('401 Authorization Required')
                ],
                [ h1('Authorization Required'),
                  p(['This server could not verify that you ',
                     'are authorized to access the document ',
                     'requested.  Either you supplied the wrong ',
                     'credentials (e.g., bad password), or your ',
                     'browser doesn\'t understand how to supply ',
                     'the credentials required.'
                     ]),
                  \address
                ]),
           HTML).