http_path.pl -- Abstract specification of HTTP server locations

This module provides an abstract specification of HTTP server locations that is inspired on absolute_file_name/3. The specification is done by adding rules to the dynamic multifile predicate http:location/3. The speficiation is very similar to file_search_path/2, but takes an additional argument with options. Currently only one option is defined:

priority(+Integer): If two rules match, take the one with highest priority. Using priorities is needed because we want to be able to overrule paths, but we do not want to become dependent on clause ordering.
The default priority is 0. Note however that notably libraries may decide to provide a fall-back using a negative priority. We suggest -100 for such cases.

This library predefines a single location at priority -100:

root: The root of the server. Default is /, but this may be overruled using the setting (see setting/2) http:prefix

To serve additional resource files such as CSS, JavaScript and icons, see library(http/http_server_files).

Here is an example that binds /login to login/1. The user can reuse this application while moving all locations using a new rule for the admin location with the option [priority(10)].

:- multifile http:location/3.
:- dynamic   http:location/3.

http:location(admin, /, []).

:- http_handler(admin(login), login, []).

login(Request) :-
        ...

http:location(+Alias, -Expansion, -Options) is nondet[multifile]

Multifile hook used to specify new HTTP locations. Alias is the name of the abstract path. Expansion is either a term Alias2(Relative), telling http_absolute_location/3 to translate Alias by first translating Alias2 and then applying the relative path Relative or, Expansion is an absolute location, i.e., one that starts with a /. Options currently only supports the priority of the path. If http:location/3 returns multiple solutions the one with the highest priority is selected. The default priority is 0.

This library provides a default for the abstract location root. This defaults to the setting http:prefix or, when not available to the path /. It is adviced to define all locations (ultimately) relative to root. For example, use root('home.html') rather than '/home.html'.

http_absolute_uri(+Spec, -URI) is det

URI is the absolute (i.e., starting with http://) URI for the abstract specification Spec. Use http_absolute_location/3 to create references to locations on the same server.

To be done: - Distinguish http from https

http_absolute_location(+Spec, -Path, +Options) is det

Path is the HTTP location for the abstract specification Spec. Options:

relative_to(Base): Path is made relative to Base. Default is to generate absolute URLs.

See also: - http_absolute_uri/2 to create a reference that can be used on another server.

http_location_path(+Alias, -Expansion) is det[private]

Expansion is the expanded HTTP location for Alias. As we have no condition search, we demand a single expansion for an alias. An ambiguous alias results in a printed warning. A lacking alias results in an exception.

Errors: - existence_error(http_alias, Alias)

http_location_path(+Alias, -Path, -Priority) is nondet[private]

To be done: - prefix(Path) is discouraged; use root(Path)

relative_to(+Base, +Path, -AbsPath) is det[private]

AbsPath is an absolute URL location created from Base and Path. The result is cleaned

clean_segments(+SegmentsIn, -SegmentsOut) is det[private]

Clean a path represented as a segment list, removing empty segments and resolving .. based on syntax.

path_list(+Spec, -List) is det[private]

Translate seg1/seg2/... into [seg1,seg2,...].

Errors: - instantiation_error; - type_error(atomic, X)

http_clean_location_cache

HTTP locations resolved through http_absolute_location/3 are cached. This predicate wipes the cache. The cache is automatically wiped by make/0 and if the setting http:prefix is changed.