1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2007-2020, University of Amsterdam
    7                              VU University Amsterdam
    8                              CWI, Amsterdam
    9    All rights reserved.
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   11    Redistribution and use in source and binary forms, with or without
   12    modification, are permitted provided that the following conditions
   13    are met:
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   16       notice, this list of conditions and the following disclaimer.
   17
   18    2. Redistributions in binary form must reproduce the above copyright
   19       notice, this list of conditions and the following disclaimer in
   20       the documentation and/or other materials provided with the
   21       distribution.
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   24    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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   35*/
   36
   37:- module(http_dispatch,
   38          [ http_dispatch/1,            % +Request
   39            http_handler/3,             % +Path, +Predicate, +Options
   40            http_delete_handler/1,      % +Path
   41            http_request_expansion/2,   % :Goal, +Rank
   42            http_reply_file/3,          % +File, +Options, +Request
   43            http_redirect/3,            % +How, +Path, +Request
   44            http_404/2,                 % +Options, +Request
   45            http_switch_protocol/2,     % :Goal, +Options
   46            http_current_handler/2,     % ?Path, ?Pred
   47            http_current_handler/3,     % ?Path, ?Pred, -Options
   48            http_location_by_id/2,      % +ID, -Location
   49            http_link_to_id/3,          % +ID, +Parameters, -HREF
   50            http_reload_with_parameters/3, % +Request, +Parameters, -HREF
   51            http_safe_file/2            % +Spec, +Options
   52          ]).   53:- use_module(library(lists),
   54              [ select/3, append/3, append/2, same_length/2, member/2,
   55                last/2, delete/3
   56              ]).   57:- autoload(library(apply),
   58	    [partition/4,maplist/3,maplist/2,include/3,exclude/3]).   59:- autoload(library(broadcast),[listen/2]).   60:- autoload(library(error),
   61	    [ must_be/2,
   62	      domain_error/2,
   63	      type_error/2,
   64	      instantiation_error/1,
   65	      existence_error/2,
   66	      permission_error/3
   67	    ]).   68:- autoload(library(filesex),[directory_file_path/3]).   69:- autoload(library(option),[option/3,option/2,merge_options/3]).   70:- autoload(library(pairs),[pairs_values/2]).   71:- if(exists_source(library(time))).   72:- autoload(library(time),[call_with_time_limit/2]).   73:- endif.   74:- autoload(library(uri),
   75	    [ uri_encoded/3,
   76	      uri_data/3,
   77	      uri_components/2,
   78	      uri_query_components/2
   79	    ]).   80:- autoload(library(http/http_header),[http_timestamp/2]).   81:- autoload(library(http/http_path),[http_absolute_location/3]).   82:- autoload(library(http/mimetype),
   83	    [file_content_type/2,file_content_type/3]).   84:- if(exists_source(library(http/thread_httpd))).   85:- autoload(library(http/thread_httpd),[http_spawn/2]).   86:- endif.   87:- use_module(library(settings),[setting/4,setting/2]).   88
   89:- predicate_options(http_404/2, 1, [index(any)]).   90:- predicate_options(http_reply_file/3, 2,
   91                     [ cache(boolean),
   92                       mime_type(any),
   93                       static_gzip(boolean),
   94                       cached_gzip(boolean),
   95                       pass_to(http_safe_file/2, 2),
   96                       headers(list)
   97                     ]).   98:- predicate_options(http_safe_file/2, 2, [unsafe(boolean)]).   99:- predicate_options(http_switch_protocol/2, 2, []).

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

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

write_index(Request) :-
        ...

  126:- setting(http:time_limit, nonneg, 300,
  127           'Time limit handling a single query (0=infinite)').

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

Register Closure as a handler for HTTP requests. Path is either an absolute path such as '/home.html' or a term Alias(Relative). Where Alias is associated with a concrete path using http:location/3 and resolved using http_absolute_location/3. Relative can be a single atom or a term `Segment1/Segment2/...`, where each element is either an atom or a variable. If a segment is a variable it matches any segment and the binding may be passed to the closure. If the last segment is a variable it may match multiple segments. This allows registering REST paths, for example:

:- http_handler(root(user/User), user(Method, User),
                [ method(Method),
                  methods([get,post,put])
                ]).

user(get, User, Request) :-
    ...
user(post, User, Request) :-
    ...

If an HTTP request arrives at the server that matches Path, Closure is called as below, where Request is the parsed HTTP request.

call(Closure, 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(+Atom)

Identifier of the handler. The default identifier is the predicate name. Used by http_location_by_id/2 and http_link_to_id/3.

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 separate 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.

Errors

- existence_error(http_location, Location)

- permission_error(http_method, Method, Location)

See also

- http_reply_file/3 and http_redirect/3 are generic handlers to serve files and achieve redirects.

  234:- dynamic handler/4.                   % Path, Action, IsPrefix, Options
  235:- multifile handler/4.  236:- dynamic generation/1.  237
  238:- meta_predicate
  239    http_handler(+, :, +),
  240    http_current_handler(?, :),
  241    http_current_handler(?, :, ?),
  242    http_request_expansion(3, +),
  243    http_switch_protocol(2, +).  244
  245http_handler(Path, Pred, Options) :-
  246    compile_handler(Path, Pred, Options, Clause),
  247    next_generation,
  248    assert(Clause).
  249
  250:- multifile
  251    system:term_expansion/2.  252
  253system:term_expansion((:- http_handler(Path, Pred, Options)), Clause) :-
  254    \+ current_prolog_flag(xref, true),
  255    prolog_load_context(module, M),
  256    compile_handler(Path, M:Pred, Options, Clause),
  257    next_generation.

 http_delete_handler(+Spec) is det

Delete handler for Spec. Typically, this should only be used for handlers that are registered dynamically. Spec is one of:

id(Id)

Delete a handler with the given id. The default id is the handler-predicate-name.

path(Path)

Delete handler that serves the given path.

  272http_delete_handler(id(Id)) :-
  273    !,
  274    clause(handler(_Path, _:Pred, _, Options), true, Ref),
  275    functor(Pred, DefID, _),
  276    option(id(Id0), Options, DefID),
  277    Id == Id0,
  278    erase(Ref),
  279    next_generation.
  280http_delete_handler(path(Path)) :-
  281    !,
  282    retractall(handler(Path, _Pred, _, _Options)),
  283    next_generation.
  284http_delete_handler(Path) :-
  285    http_delete_handler(path(Path)).

 next_generation is det

 current_generation(-G) is det

Increment the generation count.

  293next_generation :-
  294    retractall(id_location_cache(_,_,_,_)),
  295    with_mutex(http_dispatch, next_generation_unlocked).
  296
  297next_generation_unlocked :-
  298    retract(generation(G0)),
  299    !,
  300    G is G0 + 1,
  301    assert(generation(G)).
  302next_generation_unlocked :-
  303    assert(generation(1)).
  304
  305current_generation(G) :-
  306    with_mutex(http_dispatch, generation(G)),
  307    !.
  308current_generation(0).

 compile_handler(+Path, :Pred, +Options, -Clause) is det

Compile a handler specification.

  315compile_handler(Path, Pred, Options0,
  316                http_dispatch:handler(Path1, Pred, IsPrefix, Options)) :-
  317    check_path(Path, Path1, PathOptions),
  318    check_id(Options0),
  319    (   memberchk(segment_pattern(_), PathOptions)
  320    ->  IsPrefix = true,
  321        Options1 = Options0
  322    ;   select(prefix, Options0, Options1)
  323    ->  IsPrefix = true
  324    ;   IsPrefix = false,
  325        Options1 = Options0
  326    ),
  327    partition(ground, Options1, Options2, QueryOptions),
  328    Pred = M:_,
  329    maplist(qualify_option(M), Options2, Options3),
  330    combine_methods(Options3, Options4),
  331    (   QueryOptions == []
  332    ->  append(PathOptions, Options4, Options)
  333    ;   append(PathOptions, ['$extract'(QueryOptions)|Options4], Options)
  334    ).
  335
  336qualify_option(M, condition(Pred), condition(M:Pred)) :-
  337    Pred \= _:_, !.
  338qualify_option(_, Option, Option).

 combine_methods(+OptionsIn, -Options) is det

Combine method(M) and methods(MList) options into a single methods(MList) option.

  345combine_methods(Options0, Options) :-
  346    collect_methods(Options0, Options1, Methods),
  347    (   Methods == []
  348    ->  Options = Options0
  349    ;   append(Methods, Flat),
  350        sort(Flat, Unique),
  351        (   memberchk('*', Unique)
  352        ->  Final = '*'
  353        ;   Final = Unique
  354        ),
  355        Options = [methods(Final)|Options1]
  356    ).
  357
  358collect_methods([], [], []).
  359collect_methods([method(M)|T0], T, [[M]|TM]) :-
  360    !,
  361    (   M == '*'
  362    ->  true
  363    ;   must_be_method(M)
  364    ),
  365    collect_methods(T0, T, TM).
  366collect_methods([methods(M)|T0], T, [M|TM]) :-
  367    !,
  368    must_be(list, M),
  369    maplist(must_be_method, M),
  370    collect_methods(T0, T, TM).
  371collect_methods([H|T0], [H|T], TM) :-
  372    !,
  373    collect_methods(T0, T, TM).
  374
  375must_be_method(M) :-
  376    must_be(atom, M),
  377    (   method(M)
  378    ->  true
  379    ;   domain_error(http_method, M)
  380    ).
  381
  382method(get).
  383method(put).
  384method(head).
  385method(post).
  386method(delete).
  387method(patch).
  388method(options).
  389method(trace).

 check_path(+PathSpecIn, -PathSpecOut, -Options) is det

Validate the given path specification. We want one of

• AbsoluteLocation
• Alias(Relative)

Similar to absolute_file_name/3, Relative can be a term Component/Component/.... Relative may be a / separated list of path segments, some of which may be variables. A variable patches any segment and its binding can be passed to the handler. If such a pattern is found Options is unified with [segment_pattern(SegmentList)].

Errors

- domain_error, type_error

See also

- http_absolute_location/3

  409check_path(Path, Path, []) :-
  410    atom(Path),
  411    !,
  412    (   sub_atom(Path, 0, _, _, /)
  413    ->  true
  414    ;   domain_error(absolute_http_location, Path)
  415    ).
  416check_path(Alias, AliasOut, Options) :-
  417    compound(Alias),
  418    Alias =.. [Name, Relative],
  419    !,
  420    local_path(Relative, Local, Options),
  421    (   sub_atom(Local, 0, _, _, /)
  422    ->  domain_error(relative_location, Relative)
  423    ;   AliasOut =.. [Name, Local]
  424    ).
  425check_path(PathSpec, _, _) :-
  426    type_error(path_or_alias, PathSpec).
  427
  428local_path(Atom, Atom, []) :-
  429    atom(Atom),
  430    !.
  431local_path(Path, Atom, Options) :-
  432    phrase(path_to_list(Path), Components),
  433    !,
  434    (   maplist(atom, Components)
  435    ->  atomic_list_concat(Components, '/', Atom),
  436        Options = []
  437    ;   append(Pre, [Var|Rest], Components),
  438        var(Var)
  439    ->  append(Pre, [''], PreSep),
  440        atomic_list_concat(PreSep, '/', Atom),
  441        Options = [segment_pattern([Var|Rest])]
  442    ).
  443local_path(Path, _, _) :-
  444    ground(Path),
  445    !,
  446    type_error(relative_location, Path).
  447local_path(Path, _, _) :-
  448    instantiation_error(Path).
  449
  450path_to_list(Var) -->
  451    { var(Var) },
  452    !,
  453    [Var].
  454path_to_list(A/B) -->
  455    !,
  456    path_to_list(A),
  457    path_to_list(B).
  458path_to_list(Atom) -->
  459    { atom(Atom) },
  460    !,
  461    [Atom].
  462path_to_list(Value) -->
  463    { must_be(atom, Value) }.
  464
  465check_id(Options) :-
  466    memberchk(id(Id), Options),
  467    !,
  468    must_be(atom, Id).
  469check_id(_).

 http_dispatch(Request) is det

Dispatch a Request using http_handler/3 registrations. It performs the following steps:

1. Find a matching handler based on the path member of Request. If multiple handlers match due to the prefix option or variables in path segments (see http_handler/3), the longest specification is used. If multiple specifications of equal length match the one with the highest priority is used.
2. Check that the handler matches the method member of the Request or throw permission_error(http_method, Method, Location)
3. Expand the request using expansion hooks registered by http_request_expansion/3. This may add fields to the request, such the authenticated user, parsed parameters, etc. The hooks may also throw exceptions, notably using http_redirect/3 or by throwing http_reply(Term, ExtraHeader, Context) exceptions.
4. Extract possible fields from the Request using e.g. method(Method) as one of the options.
5. Call the registered closure, optionally spawning the request to a new thread or enforcing a time limit.

  495http_dispatch(Request) :-
  496    memberchk(path(Path), Request),
  497    find_handler(Path, Closure, Options),
  498    supports_method(Request, Options),
  499    expand_request(Request, Request1, Options),
  500    extract_from_request(Request1, Options),
  501    action(Closure, Request1, Options).
  502
  503extract_from_request(Request, Options) :-
  504    memberchk('$extract'(Fields), Options),
  505    !,
  506    extract_fields(Fields, Request).
  507extract_from_request(_, _).
  508
  509extract_fields([], _).
  510extract_fields([H|T], Request) :-
  511    memberchk(H, Request),
  512    extract_fields(T, Request).

 http_request_expansion(:Goal, +Rank:number)

Register Goal for expanding the HTTP request handler. Goal is called as below. If Goal fail the request is passed to the next expansion unmodified.

call(Goal, Request0, Request, Options)

If multiple goals are registered they expand the request in a pipeline starting with the expansion hook with the lowest rank.

Besides rewriting the request, for example by validating the user identity based on HTTP authentication or cookies and adding this to the request, the hook may raise HTTP exceptions to indicate a bad request, permission error, etc. See http_status_reply/4.

Initially, auth_expansion/3 is registered with rank 100 to deal with the older http:authenticate/3 hook.

  534http_request_expansion(Goal, Rank) :-
  535    throw(error(context_error(nodirective, http_request_expansion(Goal, Rank)), _)).
  536
  537:- multifile
  538    request_expansion/2.  539
  540system:term_expansion((:- http_request_expansion(Goal, Rank)),
  541                      http_dispatch:request_expansion(M:Callable, Rank)) :-
  542    must_be(number, Rank),
  543    prolog_load_context(module, M0),
  544    strip_module(M0:Goal, M, Callable),
  545    must_be(callable, Callable).
  546
  547request_expanders(Closures) :-
  548    findall(Rank-Closure, request_expansion(Closure, Rank), Pairs),
  549    keysort(Pairs, Sorted),
  550    pairs_values(Sorted, Closures).

 expand_request(+Request0, -Request, +Options)

Expand an HTTP request. Options is a list of combined options provided with the handler registration (see http_handler/3).

  557expand_request(Request0, Request, Options) :-
  558    request_expanders(Closures),
  559    expand_request(Closures, Request0, Request, Options).
  560
  561expand_request([], Request, Request, _).
  562expand_request([H|T], Request0, Request, Options) :-
  563    expand_request1(H, Request0, Request1, Options),
  564    expand_request(T, Request1, Request, Options).
  565
  566expand_request1(Closure, Request0, Request, Options) :-
  567    call(Closure, Request0, Request, Options),
  568    !.
  569expand_request1(_, Request, Request, _).

 http_current_handler(+Location, :Closure) is semidet

http_current_handler(-Location, :Closure) is nondet

True if Location is handled by Closure.

  577http_current_handler(Path, Closure) :-
  578    atom(Path),
  579    !,
  580    path_tree(Tree),
  581    find_handler(Tree, Path, Closure, _).
  582http_current_handler(Path, M:C) :-
  583    handler(Spec, M:C, _, _),
  584    http_absolute_location(Spec, Path, []).

 http_current_handler(+Location, :Closure, -Options) is semidet

http_current_handler(?Location, :Closure, ?Options) is nondet

Resolve the current handler and options to execute it.

  591http_current_handler(Path, Closure, Options) :-
  592    atom(Path),
  593    !,
  594    path_tree(Tree),
  595    find_handler(Tree, Path, Closure, Options).
  596http_current_handler(Path, M:C, Options) :-
  597    handler(Spec, M:C, _, _),
  598    http_absolute_location(Spec, Path, []),
  599    path_tree(Tree),
  600    find_handler(Tree, Path, _, Options).

 http_location_by_id(+ID, -Location) is det

True when Location represents the HTTP path to which the handler with identifier ID is bound. Handler identifiers are deduced from the http_handler/3 declaration as follows:

Explicit id

If a term id(ID) appears in the option list of the handler, ID it is used and takes preference over using the predicate.

Using the handler predicate

ID matches a handler if the predicate name matches ID. The ID may have a module qualification, e.g., Module:Pred

If the handler is declared with a pattern, e.g., root(user/User), the location to access a particular user may be accessed using e.g., user('Bob'). The number of arguments to the compound term must match the number of variables in the path pattern.

A plain atom ID can be used to find a handler with a pattern. The returned location is the path up to the first variable, e.g., /user/ in the example above.

User code is adviced to use http_link_to_id/3 which can also add query parameters to the URL. This predicate is a helper for http_link_to_id/3.

Errors

- existence_error(http_handler_id, Id).

See also

- http_link_to_id/3 and the library(http/html_write) construct location_by_id(ID) or its abbreviation #(ID)

  633:- dynamic
  634    id_location_cache/4.                        % Id, Argv, Location, Segments
  635
  636http_location_by_id(ID, _) :-
  637    \+ ground(ID),
  638    !,
  639    instantiation_error(ID).
  640http_location_by_id(M:ID, Location) :-
  641    compound(ID),
  642    !,
  643    compound_name_arguments(ID, Name, Argv),
  644    http_location_by_id(M:Name, Argv, Location).
  645http_location_by_id(M:ID, Location) :-
  646    atom(ID),
  647    must_be(atom, M),
  648    !,
  649    http_location_by_id(M:ID, -, Location).
  650http_location_by_id(ID, Location) :-
  651    compound(ID),
  652    !,
  653    compound_name_arguments(ID, Name, Argv),
  654    http_location_by_id(Name, Argv, Location).
  655http_location_by_id(ID, Location) :-
  656    atom(ID),
  657    !,
  658    http_location_by_id(ID, -, Location).
  659http_location_by_id(ID, _) :-
  660    type_error(location_id, ID).
  661
  662http_location_by_id(ID, Argv, Location) :-
  663    id_location_cache(ID, Argv, Segments, Path),
  664    !,
  665    add_segments(Path, Segments, Location).
  666http_location_by_id(ID, Argv, Location) :-
  667    findall(t(Priority, ArgvP, Segments, Prefix),
  668            location_by_id(ID, Argv, ArgvP, Segments, Prefix, Priority),
  669            List),
  670    sort(1, >=, List, Sorted),
  671    (   Sorted = [t(_,ArgvP,Segments,Path)]
  672    ->  assert(id_location_cache(ID,ArgvP,Segments,Path)),
  673        Argv = ArgvP
  674    ;   List == []
  675    ->  existence_error(http_handler_id, ID)
  676    ;   List = [t(P0,ArgvP,Segments,Path),t(P1,_,_,_)|_]
  677    ->  (   P0 =:= P1
  678        ->  print_message(warning,
  679                          http_dispatch(ambiguous_id(ID, Sorted, Path)))
  680        ;   true
  681        ),
  682        assert(id_location_cache(ID,Argv,Segments,Path)),
  683        Argv = ArgvP
  684    ),
  685    add_segments(Path, Segments, Location).
  686
  687add_segments(Path0, [], Path) :-
  688    !,
  689    Path = Path0.
  690add_segments(Path0, Segments, Path) :-
  691    maplist(uri_encoded(path), Segments, Encoded),
  692    atomic_list_concat(Encoded, '/', Rest),
  693    atom_concat(Path0, Rest, Path).
  694
  695location_by_id(ID, -, _, [], Location, Priority) :-
  696    !,
  697    location_by_id_raw(ID, L0, _Segments, Priority),
  698    to_path(L0, Location).
  699location_by_id(ID, Argv, ArgvP, Segments, Location, Priority) :-
  700    location_by_id_raw(ID, L0, Segments, Priority),
  701    include(var, Segments, ArgvP),
  702    same_length(Argv, ArgvP),
  703    to_path(L0, Location).
  704
  705to_path(prefix(Path0), Path) :-         % old style prefix notation
  706    !,
  707    add_prefix(Path0, Path).
  708to_path(Path0, Path) :-
  709    atomic(Path0),                      % old style notation
  710    !,
  711    add_prefix(Path0, Path).
  712to_path(Spec, Path) :-                  % new style notation
  713    http_absolute_location(Spec, Path, []).
  714
  715add_prefix(P0, P) :-
  716    (   catch(setting(http:prefix, Prefix), _, fail),
  717        Prefix \== ''
  718    ->  atom_concat(Prefix, P0, P)
  719    ;   P = P0
  720    ).
  721
  722location_by_id_raw(ID, Location, Pattern, Priority) :-
  723    handler(Location, _, _, Options),
  724    option(id(ID), Options),
  725    option(priority(P0), Options, 0),
  726    option(segment_pattern(Pattern), Options, []),
  727    Priority is P0+1000.            % id(ID) takes preference over predicate
  728location_by_id_raw(ID, Location, Pattern, Priority) :-
  729    handler(Location, M:C, _, Options),
  730    option(priority(Priority), Options, 0),
  731    functor(C, PN, _),
  732    (   ID = M:PN
  733    ->  true
  734    ;   ID = PN
  735    ),
  736    option(segment_pattern(Pattern), Options, []).

 http_link_to_id(+HandleID, +Parameters, -HREF)

HREF is a link on the local server to a handler with given ID, passing the given Parameters. This predicate is typically used to formulate a HREF that resolves to a handler implementing a particular predicate. The code below provides a typical example. The predicate user_details/1 returns a page with details about a user from a given id. This predicate is registered as a handler. The DCG user_link//1 renders a link to a user, displaying the name and calling user_details/1 when clicked. Note that the location (root(user_details)) is irrelevant in this equation and HTTP locations can thus be moved freely without breaking this code fragment.

:- http_handler(root(user_details), user_details, []).

user_details(Request) :-
    http_parameters(Request,
                    [ user_id(ID)
                    ]),
    ...

user_link(ID) -->
    { user_name(ID, Name),
      http_link_to_id(user_details, [id(ID)], HREF)
    },
    html(a([class(user), href(HREF)], Name)).

Arguments:

HandleID	- is either an atom, possibly module qualified predicate or a compound term if the hander is defined using a pattern. See http_handler/3 and http_location_by_id/2.
Parameters	- is one of path_postfix(File) to pass a single value as the last segment of the HTTP location (path). This way of passing a parameter is commonly used in REST APIs. New code should use a path pattern in the handler declaration and a term `HandleID(Arg, ...)` A list of search parameters for a GET request.

See also

- http_location_by_id/2 and http_handler/3 for defining and specifying handler IDs.

  786http_link_to_id(HandleID, path_postfix(File), HREF) :-
  787    !,
  788    http_location_by_id(HandleID, HandlerLocation),
  789    uri_encoded(path, File, EncFile),
  790    directory_file_path(HandlerLocation, EncFile, Location),
  791    uri_data(path, Components, Location),
  792    uri_components(HREF, Components).
  793http_link_to_id(HandleID, Parameters, HREF) :-
  794    must_be(list, Parameters),
  795    http_location_by_id(HandleID, Location),
  796    (   Parameters == []
  797    ->  HREF = Location
  798    ;   uri_data(path, Components, Location),
  799        uri_query_components(String, Parameters),
  800        uri_data(search, Components, String),
  801        uri_components(HREF, Components)
  802    ).

 http_reload_with_parameters(+Request, +Parameters, -HREF) is det

Create a request on the current handler with replaced search parameters.

  809http_reload_with_parameters(Request, NewParams, HREF) :-
  810    memberchk(path(Path), Request),
  811    (   memberchk(search(Params), Request)
  812    ->  true
  813    ;   Params = []
  814    ),
  815    merge_options(NewParams, Params, AllParams),
  816    uri_query_components(Search, AllParams),
  817    uri_data(path, Data, Path),
  818    uri_data(search, Data, Search),
  819    uri_components(HREF, Data).
  820
  821
  822%       hook into html_write:attribute_value//1.
  823
  824:- multifile
  825    html_write:expand_attribute_value//1.  826
  827html_write:expand_attribute_value(location_by_id(ID)) -->
  828    { http_location_by_id(ID, Location) },
  829    html_write:html_quoted_attribute(Location).
  830html_write:expand_attribute_value(#(ID)) -->
  831    { http_location_by_id(ID, Location) },
  832    html_write:html_quoted_attribute(Location).

 authentication(+Options, +Request, -Fields) is det

Verify authentication information. If authentication is requested through Options, demand it. The actual verification is done by the multifile predicate http:authenticate/3. The library http_authenticate.pl provides an implementation thereof.

Errors

- permission_error(access, http_location, Location)

deprecated

- This hook predates the extensible request expansion provided by http_request_expansion/2. New hooks should use http_request_expansion/2 instead of http:authenticate/3.

  847:- multifile
  848    http:authenticate/3.  849
  850authentication([], _, []).
  851authentication([authentication(Type)|Options], Request, Fields) :-
  852    !,
  853    (   http:authenticate(Type, Request, XFields)
  854    ->  append(XFields, More, Fields),
  855        authentication(Options, Request, More)
  856    ;   memberchk(path(Path), Request),
  857        permission_error(access, http_location, Path)
  858    ).
  859authentication([_|Options], Request, Fields) :-
  860    authentication(Options, Request, Fields).
  861
  862:- http_request_expansion(auth_expansion, 100).

 auth_expansion(+Request0, -Request, +Options) is semidet

Connect the HTTP authentication infrastructure by means of http_request_expansion/2.

See also

- http:authenticate/3, http_digest.pl and http_authenticate.pl

  871auth_expansion(Request0, Request, Options) :-
  872    authentication(Options, Request0, Extra),
  873    append(Extra, Request0, Request).

 find_handler(+Path, -Action, -Options) is det

Find the handler to call from Path. Rules:

• If there is a matching handler, use this.
• If there are multiple prefix(Path) handlers, use the longest.

If there is a handler for /dir/ and the requested path is /dir, find_handler/3 throws a http_reply exception, causing the wrapper to generate a 301 (Moved Permanently) reply.

Errors

- existence_error(http_location, Location) @throw http_reply(moved(Dir))

To be done

- Introduce automatic redirection to indexes here?

  891find_handler(Path, Action, Options) :-
  892    path_tree(Tree),
  893    (   find_handler(Tree, Path, Action, Options),
  894        eval_condition(Options)
  895    ->  true
  896    ;   \+ sub_atom(Path, _, _, 0, /),
  897        atom_concat(Path, /, Dir),
  898        find_handler(Tree, Dir, Action, Options),
  899        \+ memberchk(segment_pattern(_), Options) % Variables in pattern
  900    ->  throw(http_reply(moved(Dir)))
  901    ;   throw(error(existence_error(http_location, Path), _))
  902    ).
  903
  904
  905find_handler([node(prefix(Prefix), PAction, POptions, Children)|_],
  906             Path, Action, Options) :-
  907    sub_atom(Path, 0, _, After, Prefix),
  908    !,
  909    (   option(hide_children(false), POptions, false),
  910        find_handler(Children, Path, Action, Options)
  911    ->  true
  912    ;   member(segment_pattern(Pattern, PatAction, PatOptions), POptions),
  913        copy_term(t(Pattern,PatAction,PatOptions), t(Pattern2,Action,Options)),
  914        match_segments(After, Path, Pattern2)
  915    ->  true
  916    ;   PAction \== nop
  917    ->  Action = PAction,
  918        path_info(After, Path, POptions, Options)
  919    ).
  920find_handler([node(Path, Action, Options, _)|_], Path, Action, Options) :- !.
  921find_handler([_|Tree], Path, Action, Options) :-
  922    find_handler(Tree, Path, Action, Options).
  923
  924path_info(0, _, Options,
  925          [prefix(true)|Options]) :- !.
  926path_info(After, Path, Options,
  927          [path_info(PathInfo),prefix(true)|Options]) :-
  928    sub_atom(Path, _, After, 0, PathInfo).
  929
  930match_segments(After, Path, [Var]) :-
  931    !,
  932    sub_atom(Path, _, After, 0, Var).
  933match_segments(After, Path, Pattern) :-
  934    sub_atom(Path, _, After, 0, PathInfo),
  935    split_string(PathInfo, "/", "", Segments),
  936    match_segment_pattern(Pattern, Segments).
  937
  938match_segment_pattern([], []).
  939match_segment_pattern([Var], Segments) :-
  940    !,
  941    atomic_list_concat(Segments, '/', Var).
  942match_segment_pattern([H0|T0], [H|T]) :-
  943    atom_string(H0, H),
  944    match_segment_pattern(T0, T).
  945
  946
  947eval_condition(Options) :-
  948    (   memberchk(condition(Cond), Options)
  949    ->  catch(Cond, E, (print_message(warning, E), fail))
  950    ;   true
  951    ).

 supports_method(+Request, +Options) is det

Verify that the asked http method is supported by the handler. If not, raise an error that will be mapped to a 405 page by the http wrapper.

Errors

- permission_error(http_method, Method, Location).

  962supports_method(Request, Options) :-
  963    (   option(methods(Methods), Options)
  964    ->  (   Methods == '*'
  965        ->  true
  966        ;   memberchk(method(Method), Request),
  967            memberchk(Method, Methods)
  968        )
  969    ;   true
  970    ),
  971    !.
  972supports_method(Request, _Options) :-
  973    memberchk(path(Location), Request),
  974    memberchk(method(Method), Request),
  975    permission_error(http_method, Method, Location).

 action(+Action, +Request, +Options) is det

Execute the action found. Here we take care of the options time_limit, chunked and spawn.

Errors

- goal_failed(Goal)

  985action(Action, Request, Options) :-
  986    memberchk(chunked, Options),
  987    !,
  988    format('Transfer-encoding: chunked~n'),
  989    spawn_action(Action, Request, Options).
  990action(Action, Request, Options) :-
  991    spawn_action(Action, Request, Options).
  992
  993:- if(current_predicate(http_spawn/2)).  994spawn_action(Action, Request, Options) :-
  995    option(spawn(Spawn), Options),
  996    !,
  997    spawn_options(Spawn, SpawnOption),
  998    http_spawn(time_limit_action(Action, Request, Options), SpawnOption).
  999:- endif. 1000spawn_action(Action, Request, Options) :-
 1001    time_limit_action(Action, Request, Options).
 1002
 1003spawn_options([], []) :- !.
 1004spawn_options(Pool, Options) :-
 1005    atom(Pool),
 1006    !,
 1007    Options = [pool(Pool)].
 1008spawn_options(List, List).
 1009
 1010:- if(current_predicate(call_with_time_limit/2)). 1011time_limit_action(Action, Request, Options) :-
 1012    (   option(time_limit(TimeLimit), Options),
 1013        TimeLimit \== default
 1014    ->  true
 1015    ;   setting(http:time_limit, TimeLimit)
 1016    ),
 1017    number(TimeLimit),
 1018    TimeLimit > 0,
 1019    !,
 1020    call_with_time_limit(TimeLimit, call_action(Action, Request, Options)).
 1021:- endif. 1022time_limit_action(Action, Request, Options) :-
 1023    call_action(Action, Request, Options).

 call_action(+Action, +Request, +Options)

To be done

- reply_file is normal call?

 1030call_action(reply_file(File, FileOptions), Request, _Options) :-
 1031    !,
 1032    http_reply_file(File, FileOptions, Request).
 1033call_action(Pred, Request, Options) :-
 1034    memberchk(path_info(PathInfo), Options),
 1035    !,
 1036    call_action(Pred, [path_info(PathInfo)|Request]).
 1037call_action(Pred, Request, _Options) :-
 1038    call_action(Pred, Request).
 1039
 1040call_action(Pred, Request) :-
 1041    (   call(Pred, Request)
 1042    ->  true
 1043    ;   extend(Pred, [Request], Goal),
 1044        throw(error(goal_failed(Goal), _))
 1045    ).
 1046
 1047extend(Var, _, Var) :-
 1048    var(Var),
 1049    !.
 1050extend(M:G0, Extra, M:G) :-
 1051    extend(G0, Extra, G).
 1052extend(G0, Extra, G) :-
 1053    G0 =.. List,
 1054    append(List, Extra, List2),
 1055    G =.. List2.

 http_reply_file(+FileSpec, +Options, +Request) is det

Options is a list of

cache(+Boolean)

If true (default), handle If-modified-since and send modification time.

mime_type(+Type)

Overrule mime-type guessing from the filename as provided by file_mime_type/2.

static_gzip(+Boolean)

If true (default false) and, in addition to the plain file, there is a .gz file that is not older than the plain file and the client acceps gzip encoding, send the compressed file with Transfer-encoding: gzip.

cached_gzip(+Boolean)

If true (default false) the system maintains cached gzipped files in a directory accessible using the file search path http_gzip_cache and serves these similar to the static_gzip(true) option. If the gzip file does not exist or is older than the input the file is recreated.

unsafe(+Boolean)

If false (default), validate that FileSpec does not contain references to parent directories. E.g., specifications such as www('../../etc/passwd') are not allowed.

headers(+List)

Provides additional reply-header fields, encoded as a list of Field(Value).

If caching is not disabled, it processes the request headers If-modified-since and Range.

throws

- http_reply(not_modified)

- http_reply(file(MimeType, Path))

 1099http_reply_file(File, Options, Request) :-
 1100    http_safe_file(File, Options),
 1101    absolute_file_name(File, Path,
 1102                       [ access(read)
 1103                       ]),
 1104    (   option(cache(true), Options, true)
 1105    ->  (   memberchk(if_modified_since(Since), Request),
 1106            time_file(Path, Time),
 1107            catch(http_timestamp(Time, Since), _, fail)
 1108        ->  throw(http_reply(not_modified))
 1109        ;   true
 1110        ),
 1111        (   memberchk(range(Range), Request)
 1112        ->  Reply = file(Type, Path, Range)
 1113        ;   option(static_gzip(true), Options),
 1114            accepts_encoding(Request, gzip),
 1115            file_name_extension(Path, gz, PathGZ),
 1116            access_file(PathGZ, read),
 1117            time_file(PathGZ, TimeGZ),
 1118            time_file(Path, Time),
 1119            TimeGZ >= Time
 1120        ->  Reply = gzip_file(Type, PathGZ)
 1121        ;   option(cached_gzip(true), Options),
 1122            accepts_encoding(Request, gzip),
 1123            gzip_cached(Path, PathGZ)
 1124        ->  Reply = gzip_file(Type, PathGZ)
 1125        ;   Reply = file(Type, Path)
 1126        )
 1127    ;   Reply = tmp_file(Type, Path)
 1128    ),
 1129    (   option(mime_type(MediaType), Options)
 1130    ->  file_content_type(Path, MediaType, Type)
 1131    ;   file_content_type(Path, Type)
 1132    ->  true
 1133    ;   Type = text/plain           % fallback type
 1134    ),
 1135    option(headers(Headers), Options, []),
 1136    throw(http_reply(Reply, Headers)).
 1137
 1138accepts_encoding(Request, Enc) :-
 1139    memberchk(accept_encoding(Accept), Request),
 1140    split_string(Accept, ",", " ", Parts),
 1141    member(Part, Parts),
 1142    split_string(Part, ";", " ", [EncS|_]),
 1143    atom_string(Enc, EncS).
 1144
 1145gzip_cached(Path, PathGZ) :-
 1146    with_mutex(http_reply_file, gzip_cached_sync(Path, PathGZ)).
 1147
 1148gzip_cached_sync(Path, PathGZ) :-
 1149    time_file(Path, Time),
 1150    variant_sha1(Path, SHA1),
 1151    (   absolute_file_name(http_gzip_cache(SHA1),
 1152                           PathGZ,
 1153                           [ access(read),
 1154                             file_errors(fail)
 1155                           ]),
 1156        time_file(PathGZ, TimeGZ),
 1157        TimeGZ >= Time
 1158    ->  true
 1159    ;   absolute_file_name(http_gzip_cache(SHA1),
 1160                           PathGZ,
 1161                           [ access(write),
 1162                             file_errors(fail)
 1163                           ])
 1164    ->  setup_call_cleanup(
 1165            gzopen(PathGZ, write, Out, [type(binary)]),
 1166            setup_call_cleanup(
 1167                open(Path, read, In, [type(binary)]),
 1168                copy_stream_data(In, Out),
 1169                close(In)),
 1170            close(Out))
 1171    ).

 http_safe_file(+FileSpec, +Options) is det

True if FileSpec is considered safe. If it is an atom, it cannot be absolute and cannot have references to parent directories. If it is of the form alias(Sub), than Sub cannot have references to parent directories.

Errors

- instantiation_error

- permission_error(read, file, FileSpec)

 1183http_safe_file(File, _) :-
 1184    var(File),
 1185    !,
 1186    instantiation_error(File).
 1187http_safe_file(_, Options) :-
 1188    option(unsafe(true), Options, false),
 1189    !.
 1190http_safe_file(File, _) :-
 1191    http_safe_file(File).
 1192
 1193http_safe_file(File) :-
 1194    compound(File),
 1195    functor(File, _, 1),
 1196    !,
 1197    arg(1, File, Name),
 1198    safe_name(Name, File).
 1199http_safe_file(Name) :-
 1200    (   is_absolute_file_name(Name)
 1201    ->  permission_error(read, file, Name)
 1202    ;   true
 1203    ),
 1204    safe_name(Name, Name).
 1205
 1206safe_name(Name, _) :-
 1207    must_be(atom, Name),
 1208    prolog_to_os_filename(FileName, Name),
 1209    \+ unsafe_name(FileName),
 1210    !.
 1211safe_name(_, Spec) :-
 1212    permission_error(read, file, Spec).
 1213
 1214unsafe_name(Name) :- Name == '..'.
 1215unsafe_name(Name) :- sub_atom(Name, 0, _, _, '../').
 1216unsafe_name(Name) :- sub_atom(Name, _, _, _, '/../').
 1217unsafe_name(Name) :- sub_atom(Name, _, _, 0, '/..').

 http_redirect(+How, +To, +Request) is det

Redirect to a new location. The argument order, using the Request as last argument, allows for calling this directly from the handler declaration:

:- http_handler(root(.),
                http_redirect(moved, myapp('index.html')),
                []).

Arguments:

How	- is one of moved, moved_temporary or see_other
To	- is an atom, a aliased path as defined by http_absolute_location/3. or a term location_by_id(Id) or its abbreviations #(Id) or #(Id)+Parameters. If To is not absolute, it is resolved relative to the current location.

 1238http_redirect(How, To, Request) :-
 1239    must_be(oneof([moved, moved_temporary, see_other]), How),
 1240    must_be(ground, To),
 1241    (   id_location(To, URL)
 1242    ->  true
 1243    ;   memberchk(path(Base), Request),
 1244        http_absolute_location(To, URL, [relative_to(Base)])
 1245    ),
 1246    Term =.. [How,URL],
 1247    throw(http_reply(Term)).
 1248
 1249id_location(location_by_id(Id), URL) :-
 1250    http_location_by_id(Id, URL).
 1251id_location(#(Id), URL) :-
 1252    http_location_by_id(Id, URL).
 1253id_location(#(Id)+Parameters, URL) :-
 1254    http_link_to_id(Id, Parameters, URL).

 http_404(+Options, +Request) is det

Reply using an "HTTP 404 not found" page. This handler is intended as fallback handler for prefix handlers. Options processed are:

index(Location)

If there is no path-info, redirect the request to Location using http_redirect/3.

Errors

- http_reply(not_found(Path))

 1269http_404(Options, Request) :-
 1270    option(index(Index), Options),
 1271    \+ ( option(path_info(PathInfo), Request),
 1272         PathInfo \== ''
 1273       ),
 1274    !,
 1275    http_redirect(moved, Index, Request).
 1276http_404(_Options, Request) :-
 1277    option(path(Path), Request),
 1278    !,
 1279    throw(http_reply(not_found(Path))).
 1280http_404(_Options, Request) :-
 1281    domain_error(http_request, Request).

 http_switch_protocol(:Goal, +Options)

Send an "HTTP 101 Switching Protocols" reply. After sending the reply, the HTTP library calls call(Goal, InStream, OutStream), where InStream and OutStream are the raw streams to the HTTP client. This allows the communication to continue using an an alternative protocol.

If Goal fails or throws an exception, the streams are closed by the server. Otherwise Goal is responsible for closing the streams. Note that Goal runs in the HTTP handler thread. Typically, the handler should be registered using the spawn option if http_handler/3 or Goal must call thread_create/3 to allow the HTTP worker to return to the worker pool.

The streams use binary (octet) encoding and have their I/O timeout set to the server timeout (default 60 seconds). The predicate set_stream/2 can be used to change the encoding, change or cancel the timeout.

This predicate interacts with the server library by throwing an exception.

The following options are supported:

header(+Headers)

Backward compatible. Use headers(+Headers).

headers(+Headers)

Additional headers send with the reply. Each header takes the form Name(Value).

 1315%       @throws http_reply(switch_protocol(Goal, Options))
 1316
 1317http_switch_protocol(Goal, Options) :-
 1318    throw(http_reply(switching_protocols(Goal, Options))).
 1319
 1320
 1321                 /*******************************
 1322                 *        PATH COMPILATION      *
 1323                 *******************************/

 path_tree(-Tree) is det

Compile paths into a tree. The treee is multi-rooted and represented as a list of nodes, where each node has the form:

node(PathOrPrefix, Action, Options, Children)

The tree is a potentially complicated structure. It is cached in a global variable. Note that this cache is per-thread, so each worker thread holds a copy of the tree. If handler facts are changed the generation is incremented using next_generation/0 and each worker thread will re-compute the tree on the next ocasion.

 1339path_tree(Tree) :-
 1340    current_generation(G),
 1341    nb_current(http_dispatch_tree, G-Tree),
 1342    !. % Avoid existence error
 1343path_tree(Tree) :-
 1344    path_tree_nocache(Tree),
 1345    current_generation(G),
 1346    nb_setval(http_dispatch_tree, G-Tree).
 1347
 1348path_tree_nocache(Tree) :-
 1349    findall(Prefix, prefix_handler(Prefix, _, _, _), Prefixes0),
 1350    sort(Prefixes0, Prefixes),
 1351    prefix_tree(Prefixes, [], PTree),
 1352    prefix_options(PTree, [], OPTree),
 1353    add_paths_tree(OPTree, Tree).
 1354
 1355prefix_handler(Prefix, Action, Options, Priority-PLen) :-
 1356    handler(Spec, Action, true, Options),
 1357    (   memberchk(priority(Priority), Options)
 1358    ->  true
 1359    ;   Priority = 0
 1360    ),
 1361    (   memberchk(segment_pattern(Pattern), Options)
 1362    ->  length(Pattern, PLen)
 1363    ;   PLen = 0
 1364    ),
 1365    Error = error(existence_error(http_alias,_),_),
 1366    catch(http_absolute_location(Spec, Prefix, []), Error,
 1367          (   print_message(warning, Error),
 1368              fail
 1369          )).

 prefix_tree(PrefixList, +Tree0, -Tree)

Arguments:

Tree	- list(Prefix-list(Children))

 1375prefix_tree([], Tree, Tree).
 1376prefix_tree([H|T], Tree0, Tree) :-
 1377    insert_prefix(H, Tree0, Tree1),
 1378    prefix_tree(T, Tree1, Tree).
 1379
 1380insert_prefix(Prefix, Tree0, Tree) :-
 1381    select(P-T, Tree0, Tree1),
 1382    sub_atom(Prefix, 0, _, _, P),
 1383    !,
 1384    insert_prefix(Prefix, T, T1),
 1385    Tree = [P-T1|Tree1].
 1386insert_prefix(Prefix, Tree, [Prefix-[]|Tree]).

 prefix_options(+PrefixTree, +DefOptions, -OptionTree)

Generate the option-tree for all prefix declarations.

To be done

- What to do if there are more?

 1395prefix_options([], _, []).
 1396prefix_options([Prefix-C|T0], DefOptions,
 1397               [node(prefix(Prefix), Action, PrefixOptions, Children)|T]) :-
 1398    findall(h(A,O,P), prefix_handler(Prefix,A,O,P), Handlers),
 1399    sort(3, >=, Handlers, Handlers1),
 1400    Handlers1 = [h(_,_,P0)|_],
 1401    same_priority_handlers(Handlers1, P0, Same),
 1402    option_patterns(Same, SegmentPatterns, Action),
 1403    last(Same, h(_, Options0, _-_)),
 1404    merge_options(Options0, DefOptions, Options),
 1405    append(SegmentPatterns, Options, PrefixOptions),
 1406    exclude(no_inherit, Options, InheritOpts),
 1407    prefix_options(C, InheritOpts, Children),
 1408    prefix_options(T0, DefOptions, T).
 1409
 1410no_inherit(id(_)).
 1411no_inherit('$extract'(_)).
 1412
 1413same_priority_handlers([H|T0], P, [H|T]) :-
 1414    H = h(_,_,P0-_),
 1415    P = P0-_,
 1416    !,
 1417    same_priority_handlers(T0, P, T).
 1418same_priority_handlers(_, _, []).
 1419
 1420option_patterns([], [], nop).
 1421option_patterns([h(A,_,_-0)|_], [], A) :-
 1422    !.
 1423option_patterns([h(A,O,_)|T0], [segment_pattern(P,A,O)|T], AF) :-
 1424    memberchk(segment_pattern(P), O),
 1425    option_patterns(T0, T, AF).

 add_paths_tree(+OPTree, -Tree) is det

Add the plain paths.

 1432add_paths_tree(OPTree, Tree) :-
 1433    findall(path(Path, Action, Options),
 1434            plain_path(Path, Action, Options),
 1435            Triples),
 1436    add_paths_tree(Triples, OPTree, Tree).
 1437
 1438add_paths_tree([], Tree, Tree).
 1439add_paths_tree([path(Path, Action, Options)|T], Tree0, Tree) :-
 1440    add_path_tree(Path, Action, Options, [], Tree0, Tree1),
 1441    add_paths_tree(T, Tree1, Tree).

 plain_path(-Path, -Action, -Options) is nondet

True if {Path,Action,Options} is registered and Path is a plain (i.e. not prefix) location.

 1449plain_path(Path, Action, Options) :-
 1450    handler(Spec, Action, false, Options),
 1451    catch(http_absolute_location(Spec, Path, []), E,
 1452          (print_message(error, E), fail)).

 add_path_tree(+Path, +Action, +Options, +Tree0, -Tree) is det

Add a path to a tree. If a handler for the same path is already defined, the one with the highest priority or the latest takes precedence.

 1461add_path_tree(Path, Action, Options0, DefOptions, [],
 1462              [node(Path, Action, Options, [])]) :-
 1463    !,
 1464    merge_options(Options0, DefOptions, Options).
 1465add_path_tree(Path, Action, Options, _,
 1466              [node(prefix(Prefix), PA, DefOptions, Children0)|RestTree],
 1467              [node(prefix(Prefix), PA, DefOptions, Children)|RestTree]) :-
 1468    sub_atom(Path, 0, _, _, Prefix),
 1469    !,
 1470    delete(DefOptions, id(_), InheritOpts),
 1471    add_path_tree(Path, Action, Options, InheritOpts, Children0, Children).
 1472add_path_tree(Path, Action, Options1, DefOptions, [H0|T], [H|T]) :-
 1473    H0 = node(Path, _, Options2, _),
 1474    option(priority(P1), Options1, 0),
 1475    option(priority(P2), Options2, 0),
 1476    P1 >= P2,
 1477    !,
 1478    merge_options(Options1, DefOptions, Options),
 1479    H = node(Path, Action, Options, []).
 1480add_path_tree(Path, Action, Options, DefOptions, [H|T0], [H|T]) :-
 1481    add_path_tree(Path, Action, Options, DefOptions, T0, T).
 1482
 1483
 1484                 /*******************************
 1485                 *            MESSAGES          *
 1486                 *******************************/
 1487
 1488:- multifile
 1489    prolog:message/3. 1490
 1491prolog:message(http_dispatch(ambiguous_id(ID, _List, Selected))) -->
 1492    [ 'HTTP dispatch: ambiguous handler ID ~q (selected ~q)'-[ID, Selected]
 1493    ].
 1494
 1495
 1496                 /*******************************
 1497                 *            XREF              *
 1498                 *******************************/
 1499
 1500:- multifile
 1501    prolog:meta_goal/2. 1502:- dynamic
 1503    prolog:meta_goal/2. 1504
 1505prolog:meta_goal(http_handler(_, G, _), [G+1]).
 1506prolog:meta_goal(http_current_handler(_, G), [G+1]).
 1507
 1508
 1509                 /*******************************
 1510                 *             EDIT             *
 1511                 *******************************/
 1512
 1513% Allow edit(Location) to edit the implementation for an HTTP location.
 1514
 1515:- multifile
 1516    prolog_edit:locate/3. 1517
 1518prolog_edit:locate(Path, Spec, Location) :-
 1519    atom(Path),
 1520    sub_atom(Path, 0, _, _, /),
 1521    Pred = _M:_H,
 1522    catch(http_current_handler(Path, Pred), _, fail),
 1523    closure_name_arity(Pred, 1, PI),
 1524    prolog_edit:locate(PI, Spec, Location).
 1525
 1526closure_name_arity(M:Term, Extra, M:Name/Arity) :-
 1527    !,
 1528    callable(Term),
 1529    functor(Term, Name, Arity0),
 1530    Arity is Arity0 + Extra.
 1531closure_name_arity(Term, Extra, Name/Arity) :-
 1532    callable(Term),
 1533    functor(Term, Name, Arity0),
 1534    Arity is Arity0 + Extra.
 1535
 1536
 1537                 /*******************************
 1538                 *        CACHE CLEANUP         *
 1539                 *******************************/
 1540
 1541:- listen(settings(changed(http:prefix, _, _)),
 1542          next_generation). 1543
 1544:- multifile
 1545    user:message_hook/3. 1546:- dynamic
 1547    user:message_hook/3. 1548
 1549user:message_hook(make(done(Reload)), _Level, _Lines) :-
 1550    Reload \== [],
 1551    next_generation,
 1552    fail