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)  2002-2018, University of Amsterdam
    7                              VU University Amsterdam
    8                              CWI, Amsterdam
    9    All rights reserved.
   10
   11    Redistribution and use in source and binary forms, with or without
   12    modification, are permitted provided that the following conditions
   13    are met:
   14
   15    1. Redistributions of source code must retain the above copyright
   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.
   22
   23    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   24    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   25    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   26    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   27    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   28    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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   35*/
   36
   37:- module(thread_httpd,
   38          [ http_current_server/2,      % ?:Goal, ?Port
   39            http_server_property/2,     % ?Port, ?Property
   40            http_server/2,              % :Goal, +Options
   41            http_workers/2,             % +Port, ?WorkerCount
   42            http_add_worker/2,          % +Port, +Options
   43            http_current_worker/2,      % ?Port, ?ThreadID
   44            http_stop_server/2,         % +Port, +Options
   45            http_spawn/2,               % :Goal, +Options
   46
   47            http_requeue/1,             % +Request
   48            http_close_connection/1,    % +Request
   49            http_enough_workers/3       % +Queue, +Why, +Peer
   50          ]).   51:- use_module(library(debug)).   52:- use_module(library(error)).   53:- use_module(library(option)).   54:- use_module(library(socket)).   55:- use_module(library(thread_pool)).   56:- use_module(library(gensym)).   57:- use_module(http_wrapper).   58:- use_module(http_path).   59
   60
   61:- predicate_options(http_server/2, 2,
   62                     [ port(any),
   63                       entry_page(atom),
   64                       tcp_socket(any),
   65                       workers(positive_integer),
   66                       timeout(number),
   67                       keep_alive_timeout(number),
   68                       silent(boolean),
   69                       ssl(list(any)),  % if http/http_ssl_plugin is loaded
   70                       pass_to(system:thread_create/3, 3)
   71                     ]).   72:- predicate_options(http_spawn/2, 2,
   73                     [ pool(atom),
   74                       pass_to(system:thread_create/3, 3),
   75                       pass_to(thread_pool:thread_create_in_pool/4, 4)
   76                     ]).   77:- predicate_options(http_add_worker/2, 2,
   78                     [ timeout(number),
   79                       keep_alive_timeout(number),
   80                       max_idle_time(number),
   81                       pass_to(system:thread_create/3, 3)
   82                     ]).

  106:- meta_predicate
  107    http_server(1, :),
  108    http_current_server(1, ?),
  109    http_spawn(0, +).  110
  111:- dynamic
  112    current_server/6,       % Port, Goal, Thread, Queue, Scheme, StartTime
  113    queue_worker/2,         % Queue, ThreadID
  114    queue_options/2.        % Queue, Options
  115
  116:- multifile
  117    make_socket_hook/3,
  118    accept_hook/2,
  119    close_hook/1,
  120    open_client_hook/6,
  121    http:create_pool/1,
  122    http:schedule_workers/1.

 http_server(:Goal, :Options) is det

Create a server at Port that calls Goal for each parsed request. Options provide a list of options. Defined options are

port(?Address)

Port to bind to. Address is either a port or a term Host:Port. The port may be a variable, causing the system to select a free port. See tcp_bind/2.

entry_page(+URI)

Affects the message printed while the server is started. Interpreted as a URI relative to the server root.

tcp_socket(+Socket)

If provided, use this socket instead of the creating one and binding it to an address. The socket must be bound to an address.

workers(+Count)

Determine the number of worker threads. Default is 5. This is fine for small scale usage. Public servers typically need a higher number.

timeout(+Seconds)

Maximum time of inactivity trying to read the request after a connection has been opened. Default is 60 seconds. See set_stream/1 using the timeout option.

keep_alive_timeout(+Seconds)

Time to keep `Keep alive' connections alive. Default is 2 seconds.

stack_limit(+Bytes)

Stack limit to use for the workers. The default is inherited from the main thread. If you need to control resource usage you may consider the spawn option of http_handler/3 and library(thread_pool).

silent(Bool)

If true (default false), do not print an informational message that the server was started.

A typical initialization for an HTTP server that uses http_dispatch/1 to relay requests to predicates is:

:- use_module(library(http/thread_httpd)).
:- use_module(library(http/http_dispatch)).

start_server(Port) :-
    http_server(http_dispatch, [port(Port)]).

Note that multiple servers can coexist in the same Prolog process. A notable application of this is to have both an HTTP and HTTPS server, where the HTTP server redirects to the HTTPS server for handling sensitive requests.

  183http_server(Goal, M:Options0) :-
  184    option(port(Port), Options0),
  185    !,
  186    make_socket(Port, M:Options0, Options),
  187    create_workers(Options),
  188    create_server(Goal, Port, Options),
  189    (   option(silent(true), Options0)
  190    ->  true
  191    ;   print_message(informational,
  192                      httpd_started_server(Port, Options0))
  193    ).
  194http_server(_Goal, _Options) :-
  195    existence_error(option, port).

 make_socket(?Port, :OptionsIn, -OptionsOut) is det

Create the HTTP server socket and worker pool queue. OptionsOut is quaranteed to hold the option queue(QueueId).

Arguments:

OptionsIn

- is qualified to allow passing the module-sensitive ssl option argument.

  206make_socket(Port, Options0, Options) :-
  207    make_socket_hook(Port, Options0, Options),
  208    !.
  209make_socket(Port, _:Options0, Options) :-
  210    option(tcp_socket(_), Options0),
  211    !,
  212    make_addr_atom('httpd', Port, Queue),
  213    Options = [ queue(Queue)
  214              | Options0
  215              ].
  216make_socket(Port, _:Options0, Options) :-
  217    tcp_socket(Socket),
  218    tcp_setopt(Socket, reuseaddr),
  219    tcp_bind(Socket, Port),
  220    tcp_listen(Socket, 5),
  221    make_addr_atom('httpd', Port, Queue),
  222    Options = [ queue(Queue),
  223                tcp_socket(Socket)
  224              | Options0
  225              ].

 make_addr_atom(+Scheme, +Address, -Atom) is det

Create an atom that identifies the server's queue and thread resources.

  232make_addr_atom(Scheme, Address, Atom) :-
  233    phrase(address_parts(Address), Parts),
  234    atomic_list_concat([Scheme,@|Parts], Atom).
  235
  236address_parts(Atomic) -->
  237    { atomic(Atomic) },
  238    !,
  239    [Atomic].
  240address_parts(Host:Port) -->
  241    !,
  242    address_parts(Host), [:], address_parts(Port).
  243address_parts(ip(A,B,C,D)) -->
  244    !,
  245    [ A, '.', B, '.', C, '.', D ].

 create_server(:Goal, +Address, +Options) is det

Create the main server thread that runs accept_server/2 to listen to new requests.

  252create_server(Goal, Address, Options) :-
  253    get_time(StartTime),
  254    memberchk(queue(Queue), Options),
  255    scheme(Scheme, Options),
  256    address_port(Address, Port),
  257    make_addr_atom(Scheme, Port, Alias),
  258    thread_self(Initiator),
  259    thread_create(accept_server(Goal, Initiator, Options), _,
  260                  [ alias(Alias)
  261                  ]),
  262    thread_get_message(server_started),
  263    assert(current_server(Port, Goal, Alias, Queue, Scheme, StartTime)).
  264
  265scheme(Scheme, Options) :-
  266    option(scheme(Scheme), Options),
  267    !.
  268scheme(Scheme, Options) :-
  269    (   option(ssl(_), Options)
  270    ;   option(ssl_instance(_), Options)
  271    ),
  272    !,
  273    Scheme = https.
  274scheme(http, _).
  275
  276address_port(_Host:Port, Port) :- !.
  277address_port(Port, Port).

 http_current_server(:Goal, ?Port) is nondet

True if Goal is the goal of a server at Port.

deprecated

- Use http_server_property(Port, goal(Goal))

  286http_current_server(Goal, Port) :-
  287    current_server(Port, Goal, _, _, _, _).

 http_server_property(?Port, ?Property) is nondet

True if Property is a property of the HTTP server running at Port. Defined properties are:

goal(:Goal)

Goal used to start the server. This is often http_dispatch/1.

scheme(-Scheme)

Scheme is one of http or https.

start_time(?Time)

Time-stamp when the server was created.

  303http_server_property(_:Port, Property) :-
  304    integer(Port),
  305    !,
  306    server_property(Property, Port).
  307http_server_property(Port, Property) :-
  308    server_property(Property, Port).
  309
  310server_property(goal(Goal), Port) :-
  311    current_server(Port, Goal, _, _, _, _).
  312server_property(scheme(Scheme), Port) :-
  313    current_server(Port, _, _, _, Scheme, _).
  314server_property(start_time(Time), Port) :-
  315    current_server(Port, _, _, _, _, Time).

 http_workers(+Port, -Workers) is det

http_workers(+Port, +Workers:int) is det

Query or set the number of workers for the server at this port. The number of workers is dynamically modified. Setting it to 1 (one) can be used to profile the worker using tprofile/1.

  325http_workers(Port, Workers) :-
  326    must_be(ground, Port),
  327    current_server(Port, _, _, Queue, _, _),
  328    !,
  329    (   integer(Workers)
  330    ->  resize_pool(Queue, Workers)
  331    ;   findall(W, queue_worker(Queue, W), WorkerIDs),
  332        length(WorkerIDs, Workers)
  333    ).
  334http_workers(Port, _) :-
  335    existence_error(http_server, Port).

 http_add_worker(+Port, +Options) is det

Add a new worker to the HTTP server for port Port. Options overrule the default queue options. The following additional options are processed:

max_idle_time(+Seconds)

The created worker will automatically terminate if there is no new work within Seconds.

  348http_add_worker(Port, Options) :-
  349    must_be(ground, Port),
  350    current_server(Port, _, _, Queue, _, _),
  351    !,
  352    queue_options(Queue, QueueOptions),
  353    merge_options(Options, QueueOptions, WorkerOptions),
  354    atom_concat(Queue, '_', AliasBase),
  355    create_workers(1, 1, Queue, AliasBase, WorkerOptions).
  356http_add_worker(Port, _) :-
  357    existence_error(http_server, Port).

 http_current_worker(?Port, ?ThreadID) is nondet

True if ThreadID is the identifier of a Prolog thread serving Port. This predicate is motivated to allow for the use of arbitrary interaction with the worker thread for development and statistics.

  367http_current_worker(Port, ThreadID) :-
  368    current_server(Port, _, _, Queue, _, _),
  369    queue_worker(Queue, ThreadID).

 accept_server(:Goal, +Initiator, +Options)

The goal of a small server-thread accepting new requests and posting them to the queue of workers.

  377accept_server(Goal, Initiator, Options) :-
  378    catch(accept_server2(Goal, Initiator, Options), http_stop, true),
  379    thread_self(Thread),
  380    retract(current_server(_Port, _, Thread, _Queue, _Scheme, _StartTime)),
  381    close_server_socket(Options).
  382
  383accept_server2(Goal, Initiator, Options) :-
  384    thread_send_message(Initiator, server_started),
  385    repeat,
  386      (   catch(accept_server3(Goal, Options), E, true)
  387      ->  (   var(E)
  388          ->  fail
  389          ;   accept_rethrow_error(E)
  390          ->  throw(E)
  391          ;   print_message(error, E),
  392              fail
  393          )
  394      ;   print_message(error,      % internal error
  395                        goal_failed(accept_server3(Goal, Options))),
  396          fail
  397      ).
  398
  399accept_server3(Goal, Options) :-
  400    accept_hook(Goal, Options),
  401    !.
  402accept_server3(Goal, Options) :-
  403    memberchk(tcp_socket(Socket), Options),
  404    memberchk(queue(Queue), Options),
  405    tcp_accept(Socket, Client, Peer),
  406    debug(http(connection), 'New HTTP connection from ~p', [Peer]),
  407    thread_send_message(Queue, tcp_client(Client, Goal, Peer)),
  408    http_enough_workers(Queue, accept, Peer).
  409
  410accept_rethrow_error(http_stop).
  411accept_rethrow_error('$aborted').

 close_server_socket(+Options)

Close the server socket.

  418close_server_socket(Options) :-
  419    close_hook(Options),
  420    !.
  421close_server_socket(Options) :-
  422    memberchk(tcp_socket(Socket), Options),
  423    !,
  424    tcp_close_socket(Socket).

 http_stop_server(+Port, +Options)

Stop the indicated HTTP server gracefully. First stops all workers, then stops the server.

To be done

- Realise non-graceful stop

  434http_stop_server(Host:Port, Options) :-         % e.g., localhost:4000
  435    ground(Host),
  436    !,
  437    http_stop_server(Port, Options).
  438http_stop_server(Port, _Options) :-
  439    http_workers(Port, 0),                  % checks Port is ground
  440    current_server(Port, _, Thread, Queue, _Scheme, _Start),
  441    retractall(queue_options(Queue, _)),
  442    thread_signal(Thread, throw(http_stop)),
  443    catch(connect(localhost:Port), _, true),
  444    thread_join(Thread, _),
  445    message_queue_destroy(Queue).
  446
  447connect(Address) :-
  448    setup_call_cleanup(
  449        tcp_socket(Socket),
  450        tcp_connect(Socket, Address),
  451        tcp_close_socket(Socket)).

 http_enough_workers(+Queue, +Why, +Peer) is det

Check that we have enough workers in our queue. If not, call the hook http:schedule_workers/1 to extend the worker pool. This predicate can be used by accept_hook/2.

  459http_enough_workers(Queue, Why, Peer) :-
  460    message_queue_property(Queue, size(Size)),
  461    (   enough(Size, Why)
  462    ->  true
  463    ;   current_server(Port, _, _, Queue, _, _),
  464        catch(http:schedule_workers(_{port:Port,
  465                                      reason:Why,
  466                                      peer:Peer,
  467                                      waiting:Size,
  468                                      queue:Queue
  469                                     }),
  470              Error,
  471              print_message(error, Error))
  472    ->  true
  473    ;   true
  474    ).
  475
  476enough(0, _).
  477enough(1, keep_alive).                  % I will be ready myself

 http:schedule_workers(+Data:dict) is semidet

Hook called if a new connection or a keep-alive connection cannot be scheduled immediately to a worker. Dict contains the following keys:

port:Port

Port number that identifies the server.

reason:Reason

One of accept for a new connection or keep_alive if a worker tries to reschedule itself.

peer:Peer

Identify the other end of the connection

waiting:Size

Number of messages waiting in the queue.

queue:Queue

Message queue used to dispatch accepted messages.

Note that, when called with reason:accept, we are called in the time critical main accept loop. An implementation of this hook shall typically send the event to thread dedicated to dynamic worker-pool management.

See also

- http_add_worker/2 may be used to create (temporary) extra workers.

  507                 /*******************************
  508                 *    WORKER QUEUE OPERATIONS   *
  509                 *******************************/

 create_workers(+Options)

Create the pool of HTTP worker-threads. Each worker has the alias http_worker_N.

  516create_workers(Options) :-
  517    option(workers(N), Options, 5),
  518    option(queue(Queue), Options),
  519    catch(message_queue_create(Queue), _, true),
  520    atom_concat(Queue, '_', AliasBase),
  521    create_workers(1, N, Queue, AliasBase, Options),
  522    assert(queue_options(Queue, Options)).
  523
  524create_workers(I, N, _, _, _) :-
  525    I > N,
  526    !.
  527create_workers(I, N, Queue, AliasBase, Options) :-
  528    gensym(AliasBase, Alias),
  529    thread_create(http_worker(Options), Id,
  530                  [ alias(Alias)
  531                  | Options
  532                  ]),
  533    assertz(queue_worker(Queue, Id)),
  534    I2 is I + 1,
  535    create_workers(I2, N, Queue, AliasBase, Options).

 resize_pool(+Queue, +Workers) is det

Create or destroy workers. If workers are destroyed, the call waits until the desired number of waiters is reached.

  543resize_pool(Queue, Size) :-
  544    findall(W, queue_worker(Queue, W), Workers),
  545    length(Workers, Now),
  546    (   Now < Size
  547    ->  queue_options(Queue, Options),
  548        atom_concat(Queue, '_', AliasBase),
  549        I0 is Now+1,
  550        create_workers(I0, Size, Queue, AliasBase, Options)
  551    ;   Now == Size
  552    ->  true
  553    ;   Now > Size
  554    ->  Excess is Now - Size,
  555        thread_self(Me),
  556        forall(between(1, Excess, _), thread_send_message(Queue, quit(Me))),
  557        forall(between(1, Excess, _), thread_get_message(quitted(_)))
  558    ).

 http_worker(+Options)

Run HTTP worker main loop. Workers simply wait until they are passed an accepted socket to process a client.

If the message quit(Sender) is read from the queue, the worker stops.

  569http_worker(Options) :-
  570    thread_at_exit(done_worker),
  571    option(queue(Queue), Options),
  572    option(max_idle_time(MaxIdle), Options, infinite),
  573    repeat,
  574      garbage_collect,
  575      trim_stacks,
  576      debug(http(worker), 'Waiting for a job ...', []),
  577      (   MaxIdle == infinite
  578      ->  thread_get_message(Queue, Message)
  579      ;   thread_get_message(Queue, Message, [timeout(MaxIdle)])
  580      ->  true
  581      ;   Message = quit(idle)
  582      ),
  583      debug(http(worker), 'Got job ~p', [Message]),
  584      (   Message = quit(Sender)
  585      ->  !,
  586          thread_self(Self),
  587          thread_detach(Self),
  588          (   Sender == idle
  589          ->  true
  590          ;   retract(queue_worker(Queue, Self)),
  591              thread_send_message(Sender, quitted(Self))
  592          )
  593      ;   open_client(Message, Queue, Goal, In, Out,
  594                      Options, ClientOptions),
  595          (   catch(http_process(Goal, In, Out, ClientOptions),
  596                    Error, true)
  597          ->  true
  598          ;   Error = goal_failed(http_process/4)
  599          ),
  600          (   var(Error)
  601          ->  fail
  602          ;   current_message_level(Error, Level),
  603              print_message(Level, Error),
  604              memberchk(peer(Peer), ClientOptions),
  605              close_connection(Peer, In, Out),
  606              fail
  607          )
  608      ).

 open_client(+Message, +Queue, -Goal, -In, -Out, +Options, -ClientOptions) is semidet

Opens the connection to the client in a worker from the message sent to the queue by accept_server/2.

  617open_client(requeue(In, Out, Goal, ClOpts),
  618            _, Goal, In, Out, Opts, ClOpts) :-
  619    !,
  620    memberchk(peer(Peer), ClOpts),
  621    option(keep_alive_timeout(KeepAliveTMO), Opts, 2),
  622    check_keep_alive_connection(In, KeepAliveTMO, Peer, In, Out).
  623open_client(Message, Queue, Goal, In, Out, Opts,
  624            [ pool(client(Queue, Goal, In, Out)),
  625              timeout(Timeout)
  626            | Options
  627            ]) :-
  628    catch(open_client(Message, Goal, In, Out, Options, Opts),
  629          E, report_error(E)),
  630    option(timeout(Timeout), Opts, 60),
  631    (   debugging(http(connection))
  632    ->  memberchk(peer(Peer), Options),
  633        debug(http(connection), 'Opened connection from ~p', [Peer])
  634    ;   true
  635    ).

 open_client(+Message, +Goal, -In, -Out, -ClientOptions, +Options) is det

  641open_client(Message, Goal, In, Out, ClientOptions, Options) :-
  642    open_client_hook(Message, Goal, In, Out, ClientOptions, Options),
  643    !.
  644open_client(tcp_client(Socket, Goal, Peer), Goal, In, Out,
  645            [ peer(Peer),
  646              protocol(http)
  647            ], _) :-
  648    tcp_open_socket(Socket, In, Out).
  649
  650report_error(E) :-
  651    print_message(error, E),
  652    fail.

 check_keep_alive_connection(+In, +TimeOut, +Peer, +In, +Out) is semidet

Wait for the client for at most TimeOut seconds. Succeed if the client starts a new request within this time. Otherwise close the connection and fail.

  661check_keep_alive_connection(In, TMO, Peer, In, Out) :-
  662    stream_property(In, timeout(Old)),
  663    set_stream(In, timeout(TMO)),
  664    debug(http(keep_alive), 'Waiting for keep-alive ...', []),
  665    catch(peek_code(In, Code), E, true),
  666    (   var(E),                     % no exception
  667        Code \== -1                 % no end-of-file
  668    ->  set_stream(In, timeout(Old)),
  669        debug(http(keep_alive), '\tre-using keep-alive connection', [])
  670    ;   (   Code == -1
  671        ->  debug(http(keep_alive), '\tRemote closed keep-alive connection', [])
  672        ;   debug(http(keep_alive), '\tTimeout on keep-alive connection', [])
  673        ),
  674        close_connection(Peer, In, Out),
  675        fail
  676    ).

 done_worker

Called when worker is terminated due to http_workers/2 or a (debugging) exception. In the latter case, recreate_worker/2 creates a new worker.

  685done_worker :-
  686    thread_self(Self),
  687    thread_detach(Self),
  688    retract(queue_worker(Queue, Self)),
  689    thread_property(Self, status(Status)),
  690    !,
  691    (   catch(recreate_worker(Status, Queue), _, fail)
  692    ->  print_message(informational,
  693                      httpd_restarted_worker(Self))
  694    ;   done_status_message_level(Status, Level),
  695        print_message(Level,
  696                      httpd_stopped_worker(Self, Status))
  697    ).
  698done_worker :-                                  % received quit(Sender)
  699    thread_self(Self),
  700    thread_property(Self, status(Status)),
  701    done_status_message_level(Status, Level),
  702    print_message(Level,
  703                  httpd_stopped_worker(Self, Status)).
  704
  705done_status_message_level(true, silent) :- !.
  706done_status_message_level(exception('$aborted'), silent) :- !.
  707done_status_message_level(_, informational).

 recreate_worker(+Status, +Queue) is semidet

Deal with the possibility that threads are, during development, killed with abort/0. We recreate the worker to avoid that eventually we run out of workers. If we are aborted due to a halt/0 call, thread_create/3 will raise a permission error.

The first clause deals with the possibility that we cannot write to user_error. This is possible when Prolog is started as a service using some service managers. Would be nice if we could write an error, but where?

  722recreate_worker(exception(error(io_error(write,user_error),_)), _Queue) :-
  723    halt(2).
  724recreate_worker(exception(Error), Queue) :-
  725    recreate_on_error(Error),
  726    queue_options(Queue, Options),
  727    atom_concat(Queue, '_', AliasBase),
  728    create_workers(1, 1, Queue, AliasBase, Options).
  729
  730recreate_on_error('$aborted').
  731recreate_on_error(time_limit_exceeded).

 thread_httpd:message_level(+Exception, -Level)

Determine the message stream used for exceptions that may occur during server_loop/5. Being multifile, clauses can be added by the application to refine error handling. See also message_hook/3 for further programming error handling.

  740:- multifile
  741    message_level/2.  742
  743message_level(error(io_error(read, _), _),      silent).
  744message_level(error(socket_error(epipe,_), _),	silent).
  745message_level(error(timeout_error(read, _), _), informational).
  746message_level(keep_alive_timeout,               silent).
  747
  748current_message_level(Term, Level) :-
  749    (   message_level(Term, Level)
  750    ->  true
  751    ;   Level = error
  752    ).

 http_requeue(+Header)

Re-queue a connection to the worker pool. This deals with processing additional requests on keep-alive connections.

  760http_requeue(Header) :-
  761    requeue_header(Header, ClientOptions),
  762    memberchk(pool(client(Queue, Goal, In, Out)), ClientOptions),
  763    memberchk(peer(Peer), ClientOptions),
  764    http_enough_workers(Queue, keep_alive, Peer),
  765    thread_send_message(Queue, requeue(In, Out, Goal, ClientOptions)),
  766    !.
  767http_requeue(Header) :-
  768    debug(http(error), 'Re-queue failed: ~p', [Header]),
  769    fail.
  770
  771requeue_header([], []).
  772requeue_header([H|T0], [H|T]) :-
  773    requeue_keep(H),
  774    !,
  775    requeue_header(T0, T).
  776requeue_header([_|T0], T) :-
  777    requeue_header(T0, T).
  778
  779requeue_keep(pool(_)).
  780requeue_keep(peer(_)).
  781requeue_keep(protocol(_)).

 http_process(Message, Queue, +Options)

Handle a single client message on the given stream.

  788http_process(Goal, In, Out, Options) :-
  789    debug(http(server), 'Running server goal ~p on ~p -> ~p',
  790          [Goal, In, Out]),
  791    option(timeout(TMO), Options, 60),
  792    set_stream(In, timeout(TMO)),
  793    set_stream(Out, timeout(TMO)),
  794    http_wrapper(Goal, In, Out, Connection,
  795                 [ request(Request)
  796                 | Options
  797                 ]),
  798    next(Connection, Request).
  799
  800next(switch_protocol(SwitchGoal, _SwitchOptions), Request) :-
  801    !,
  802    memberchk(pool(client(_Queue, _Goal, In, Out)), Request),
  803    (   catch(call(SwitchGoal, In, Out), E,
  804              (   print_message(error, E),
  805                  fail))
  806    ->  true
  807    ;   http_close_connection(Request)
  808    ).
  809next(spawned(ThreadId), _) :-
  810    !,
  811    debug(http(spawn), 'Handler spawned to thread ~w', [ThreadId]).
  812next(Connection, Request) :-
  813    downcase_atom(Connection, 'keep-alive'),
  814    http_requeue(Request),
  815    !.
  816next(_, Request) :-
  817    http_close_connection(Request).

 http_close_connection(+Request)

Close connection associated to Request. See also http_requeue/1.

  824http_close_connection(Request) :-
  825    memberchk(pool(client(_Queue, _Goal, In, Out)), Request),
  826    memberchk(peer(Peer), Request),
  827    close_connection(Peer, In, Out).

 close_connection(+Peer, +In, +Out)

Closes the connection from the server to the client. Errors are currently silently ignored.

  834close_connection(Peer, In, Out) :-
  835    debug(http(connection), 'Closing connection from ~p', [Peer]),
  836    catch(close(In, [force(true)]), _, true),
  837    catch(close(Out, [force(true)]), _, true).

 http_spawn(:Goal, +Options) is det

Continue this connection on a new thread. A handler may call http_spawn/2 to start a new thread that continues processing the current request using Goal. The original thread returns to the worker pool for processing new requests. Options are passed to thread_create/3, except for:

pool(+Pool)

Interfaces to library(thread_pool), starting the thread on the given pool.

If a pool does not exist, this predicate calls the multifile hook create_pool/1 to create it. If this predicate succeeds the operation is retried.

  855http_spawn(Goal, Options) :-
  856    select_option(pool(Pool), Options, ThreadOptions),
  857    !,
  858    current_output(CGI),
  859    catch(thread_create_in_pool(Pool,
  860                                wrap_spawned(CGI, Goal), Id,
  861                                [ detached(true)
  862                                | ThreadOptions
  863                                ]),
  864          Error,
  865          true),
  866    (   var(Error)
  867    ->  http_spawned(Id)
  868    ;   Error = error(resource_error(threads_in_pool(_)), _)
  869    ->  throw(http_reply(busy))
  870    ;   Error = error(existence_error(thread_pool, Pool), _),
  871        create_pool(Pool)
  872    ->  http_spawn(Goal, Options)
  873    ;   throw(Error)
  874    ).
  875http_spawn(Goal, Options) :-
  876    current_output(CGI),
  877    thread_create(wrap_spawned(CGI, Goal), Id,
  878                  [ detached(true)
  879                  | Options
  880                  ]),
  881    http_spawned(Id).
  882
  883wrap_spawned(CGI, Goal) :-
  884    set_output(CGI),
  885    http_wrap_spawned(Goal, Request, Connection),
  886    next(Connection, Request).

 create_pool(+Pool)

Lazy creation of worker-pools for the HTTP server. This predicate calls the hook create_pool/1. If the hook fails it creates a default pool of size 10. This should suffice most typical usecases. Note that we get a permission error if the pool is already created. We can ignore this.

  896create_pool(Pool) :-
  897    E = error(permission_error(create, thread_pool, Pool), _),
  898    catch(http:create_pool(Pool), E, true).
  899create_pool(Pool) :-
  900    print_message(informational, httpd(created_pool(Pool))),
  901    thread_pool_create(Pool, 10, []).
  902
  903
  904
  905                 /*******************************
  906                 *            MESSAGES          *
  907                 *******************************/
  908
  909:- multifile
  910    prolog:message/3.  911
  912prolog:message(httpd_started_server(Port, Options)) -->
  913    [ 'Started server at '-[] ],
  914    http_root(Port, Options).
  915prolog:message(httpd_stopped_worker(Self, Status)) -->
  916    [ 'Stopped worker ~p: ~p'-[Self, Status] ].
  917prolog:message(httpd_restarted_worker(Self)) -->
  918    [ 'Replaced aborted worker ~p'-[Self] ].
  919prolog:message(httpd(created_pool(Pool))) -->
  920    [ 'Created thread-pool ~p of size 10'-[Pool], nl,
  921      'Create this pool at startup-time or define the hook ', nl,
  922      'http:create_pool/1 to avoid this message and create a ', nl,
  923      'pool that fits the usage-profile.'
  924    ].
  925
  926http_root(Address, Options) -->
  927    { landing_page(Address, URI, Options) },
  928    [ '~w'-[URI] ].
  929
  930landing_page(Host:Port, URI, Options) :-
  931    must_be(atom, Host),
  932    http_server_property(Port, scheme(Scheme)),
  933    (   default_port(Scheme, Port)
  934    ->  format(atom(Base), '~w://~w', [Scheme, Host])
  935    ;   format(atom(Base), '~w://~w:~w', [Scheme, Host, Port])
  936    ),
  937    entry_page(Base, URI, Options).
  938landing_page(Port, URI, Options) :-
  939    landing_page(localhost:Port, URI, Options).
  940
  941default_port(http, 80).
  942default_port(https, 443).
  943
  944entry_page(Base, URI, Options) :-
  945    option(entry_page(Entry), Options),
  946    !,
  947    uri_resolve(Entry, Base, URI).
  948entry_page(Base, URI, _) :-
  949    http_absolute_location(root(.), Entry, []),
  950    uri_resolve(Entry, Base, URI)