http_dispatch.pl -- Dispatch requests in the HTTP server

This module can be placed between http_wrapper.pl and the application code to associate HTTP locations to predicates that serve the pages. In addition, it associates parameters with locations that deal with timeout handling and user authentication. The typical setup is:

server(Port, Options) :-
        http_server(http_dispatch,
                    [ port(Port)
                    | Options
                    ]).

:- http_handler('/index.html', write_index, []).

write_index(Request) :-
        ...

http_handler(+Path, :Closure, +Options) is det

Register Closure as a handler for HTTP requests. Path is a specification as provided by http_path.pl. If an HTTP request arrives at the server that matches Path, Closure is called with one extra argument: the parsed HTTP request. Options is a list containing the following options:

authentication(+Type)

Demand authentication. Authentication methods are pluggable. The library http_authenticate.pl provides a plugin for user/password based Basic HTTP authentication.

chunked

Use Transfer-encoding: chunked if the client allows for it.

condition(:Goal)

If present, the handler is ignored if Goal does not succeed.

content_type(+Term)

Specifies the content-type of the reply. This value is currently not used by this library. It enhances the reflexive capabilities of this library through http_current_handler/3.

id(+Term)

Identifier of the handler. The default identifier is the predicate name. Used by http_location_by_id/2.

hide_children(+Bool)

If true on a prefix-handler (see prefix), possible children are masked. This can be used to (temporary) overrule part of the tree.

method(+Method)

Declare that the handler processes Method. This is equivalent to methods([Method]). Using method(*) allows for all methods.

methods(+ListOfMethods)

Declare that the handler processes all of the given methods. If this option appears multiple times, the methods are combined.

prefix

Call Pred on any location that is a specialisation of Path. If multiple handlers match, the one with the longest path is used. Options defined with a prefix handler are the default options for paths that start with this prefix. Note that the handler acts as a fallback handler for the tree below it:

:- http_handler(/, http_404([index('index.html')]),
                [spawn(my_pool),prefix]).

priority(+Integer)

If two handlers handle the same path, the one with the highest priority is used. If equal, the last registered is used. Please be aware that the order of clauses in multifile predicates can change due to reloading files. The default priority is 0 (zero).

spawn(+SpawnOptions)

Run the handler in a seperate thread. If SpawnOptions is an atom, it is interpreted as a thread pool name (see create_thread_pool/3). Otherwise the options are passed to http_spawn/2 and from there to thread_create/3. These options are typically used to set the stack limits.

time_limit(+Spec)

One of infinite, default or a positive number (seconds). If default, the value from the setting http:time_limit is taken. The default of this setting is 300 (5 minutes). See setting/2.

Note that http_handler/3 is normally invoked as a directive and processed using term-expansion. Using term-expansion ensures proper update through make/0 when the specification is modified. We do not expand when the cross-referencer is running to ensure proper handling of the meta-call.

Errors: - existence_error(http_location, Location)
See also: - http_reply_file/3 and http_redirect/3 are generic handlers to serve files and achieve redirects.

Undocumented predicates

The following predicates are exported, but not or incorrectly documented.