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)  2002-2024, University of Amsterdam
    7                              VU University Amsterdam
    8                              CWI, Amsterdam
    9                              SWI-Prolog Solutions b.v.
   10    All rights reserved.
   11
   12    Redistribution and use in source and binary forms, with or without
   13    modification, are permitted provided that the following conditions
   14    are met:
   15
   16    1. Redistributions of source code must retain the above copyright
   17       notice, this list of conditions and the following disclaimer.
   18
   19    2. Redistributions in binary form must reproduce the above copyright
   20       notice, this list of conditions and the following disclaimer in
   21       the documentation and/or other materials provided with the
   22       distribution.
   23
   24    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   25    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   26    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   27    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   28    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   29    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   30    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   31    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   32    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   33    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   34    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   35    POSSIBILITY OF SUCH DAMAGE.
   36*/
   37
   38:- module(thread_httpd,
   39          [ http_current_server/2,      % ?:Goal, ?Port
   40            http_server_property/2,     % ?Port, ?Property
   41            http_server/2,              % :Goal, +Options
   42            http_workers/2,             % +Port, ?WorkerCount
   43            http_add_worker/2,          % +Port, +Options
   44            http_current_worker/2,      % ?Port, ?ThreadID
   45            http_stop_server/2,         % +Port, +Options
   46            http_spawn/2,               % :Goal, +Options
   47
   48            http_requeue/1,             % +Request
   49            http_close_connection/1,    % +Request
   50            http_enough_workers/3       % +Queue, +Why, +Peer
   51          ]).   52:- use_module(library(debug)).   53:- use_module(library(error)).   54:- use_module(library(option)).   55:- use_module(library(socket)).   56:- use_module(library(thread_pool)).   57:- use_module(library(gensym)).   58:- use_module(http_wrapper).   59:- use_module(http_path).   60
   61:- autoload(library(uri), [uri_resolve/3]).   62:- autoload(library(aggregate), [aggregate_all/3]).   63
   64:- predicate_options(http_server/2, 2,
   65                     [ port(any),
   66                       unix_socket(atom),
   67                       entry_page(atom),
   68                       tcp_socket(any),
   69                       workers(positive_integer),
   70                       timeout(number),
   71                       keep_alive_timeout(number),
   72                       silent(boolean),
   73                       ssl(list(any)),  % if http/http_ssl_plugin is loaded
   74                       pass_to(system:thread_create/3, 3)
   75                     ]).   76:- predicate_options(http_spawn/2, 2,
   77                     [ pool(atom),
   78                       pass_to(system:thread_create/3, 3),
   79                       pass_to(thread_pool:thread_create_in_pool/4, 4)
   80                     ]).   81:- predicate_options(http_add_worker/2, 2,
   82                     [ timeout(number),
   83                       keep_alive_timeout(number),
   84                       max_idle_time(number),
   85                       pass_to(system:thread_create/3, 3)
   86                     ]).   87
   88/** <module> Threaded HTTP server
   89
   90Most   code   doesn't   need  to   use  this   directly;  instead   use
   91library(http/http_server),  which  combines   this  library  with   the
   92typical HTTP libraries that most servers need.
   93
   94This library defines the HTTP server  frontend of choice for SWI-Prolog.
   95It is based on the multi-threading   capabilities of SWI-Prolog and thus
   96exploits multiple cores  to  serve   requests  concurrently.  The server
   97scales well and can cooperate with   library(thread_pool) to control the
   98number of concurrent requests of a given   type.  For example, it can be
   99configured to handle 200 file download requests concurrently, 2 requests
  100that potentially uses a lot of memory and   8 requests that use a lot of
  101CPU resources.
  102
  103On   Unix   systems,    this    library     can    be    combined   with
  104library(http/http_unix_daemon) to realise a proper  Unix service process
  105that creates a web server at  port   80,  runs under a specific account,
  106optionally detaches from the controlling terminal, etc.
  107
  108Combined with library(http/http_ssl_plugin) from the   SSL package, this
  109library   can   be   used   to    create     an    HTTPS   server.   See
  110<plbase>/doc/packages/examples/ssl/https for an example   server using a
  111self-signed SSL certificate.
  112*/
  113
  114:- meta_predicate
  115    http_server(1, :),
  116    http_current_server(1, ?),
  117    http_spawn(0, +).  118
  119:- dynamic
  120    current_server/6,       % Port, Goal, Thread, Queue, Scheme, StartTime
  121    queue_worker/2,         % Queue, ThreadID
  122    queue_options/2.        % Queue, Options
  123
  124:- multifile
  125    make_socket_hook/3,
  126    accept_hook/2,
  127    close_hook/1,
  128    open_client_hook/6,
  129    discard_client_hook/1,
  130    http:create_pool/1,
  131    http:schedule_workers/1.  132
  133:- meta_predicate
  134    thread_repeat_wait(0).  135
  136%!  http_server(:Goal, :Options) is det.
  137%
  138%   Create a server at Port that calls Goal for each parsed request.
  139%   Options provide a list of options. Defined options are
  140%
  141%     * port(?Address)
  142%     Port to bind to.  Address is either a port or a term
  143%     Host:Port. The port may be a variable, causing the system
  144%     to select a free port.  See tcp_bind/2.
  145%
  146%     * unix_socket(+Path)
  147%     Instead of binding to a TCP port, bind to a _Unix Domain
  148%     Socket_ at Path.
  149%
  150%     * entry_page(+URI)
  151%     Affects the message printed while the server is started.
  152%     Interpreted as a URI relative to the server root.
  153%
  154%     * tcp_socket(+Socket)
  155%     If provided, use this socket instead of the creating one and
  156%     binding it to an address.  The socket must be bound to an
  157%     address.  Note that this also allows binding an HTTP server to
  158%     a Unix domain socket (``AF_UNIX``).  See socket_create/2.
  159%
  160%     * workers(+Count)
  161%     Determine the number of worker threads.  Default is 5.  This
  162%     is fine for small scale usage.  Public servers typically need
  163%     a higher number.
  164%
  165%     * timeout(+Seconds)
  166%     Maximum time of inactivity trying to read the request after a
  167%     connection has been opened.  Default is 60 seconds.  See
  168%     set_stream/1 using the _timeout_ option.
  169%
  170%     * keep_alive_timeout(+Seconds)
  171%     Time to keep `Keep alive' connections alive.  Default is
  172%     2 seconds.
  173%
  174%     * stack_limit(+Bytes)
  175%     Stack limit to use for the workers.  The default is inherited
  176%     from the `main` thread.
  177%     If you need to control resource usage you may consider the
  178%     `spawn` option of http_handler/3 and library(thread_pool).
  179%
  180%     * silent(Bool)
  181%     If `true` (default `false`), do not print an informational
  182%     message that the server was started.
  183%
  184%   A  typical  initialization  for  an    HTTP   server  that  uses
  185%   http_dispatch/1 to relay requests to predicates is:
  186%
  187%     ==
  188%     :- use_module(library(http/thread_httpd)).
  189%     :- use_module(library(http/http_dispatch)).
  190%
  191%     start_server(Port) :-
  192%         http_server(http_dispatch, [port(Port)]).
  193%     ==
  194%
  195%   Note that multiple servers  can  coexist   in  the  same  Prolog
  196%   process. A notable application of this is   to have both an HTTP
  197%   and HTTPS server, where the HTTP   server redirects to the HTTPS
  198%   server for handling sensitive requests.
  199
  200http_server(Goal, M:Options0) :-
  201    server_address(Address, Options0),
  202    !,
  203    make_socket(Address, M:Options0, Options),
  204    create_workers(Options),
  205    create_server(Goal, Address, Options),
  206    (   option(silent(true), Options0)
  207    ->  true
  208    ;   print_message(informational,
  209                      httpd_started_server(Address, Options0))
  210    ).
  211http_server(_Goal, _:Options0) :-
  212    existence_error(server_address, Options0).
  213
  214server_address(Address, Options) :-
  215    (   option(port(Port), Options)
  216    ->  Address = Port
  217    ;   option(unix_socket(Path), Options)
  218    ->  Address = unix_socket(Path)
  219    ).
  220
  221address_port(_IFace:Port, Port) :- !.
  222address_port(unix_socket(Path), Path) :- !.
  223address_port(Address, Address) :- !.
  224
  225tcp_address(Port) :-
  226    var(Port),
  227    !.
  228tcp_address(Port) :-
  229    integer(Port),
  230    !.
  231tcp_address(_Iface:_Port).
  232
  233address_domain(localhost:_Port, Domain) =>
  234    Domain = inet.
  235address_domain(Iface:_Port, Domain) =>
  236    (   catch(ip_name(IP, Iface), error(_,_), fail),
  237        functor(IP, ip, 8)
  238    ->  Domain = inet6
  239    ;   Domain = inet
  240    ).
  241address_domain(_, Domain) =>
  242    Domain = inet.
  243
  244
  245%!  make_socket(+Address, :OptionsIn, -OptionsOut) is det.
  246%
  247%   Create the HTTP server socket and  worker pool queue. OptionsOut
  248%   is quaranteed to hold the option queue(QueueId).
  249%
  250%   @arg   OptionsIn   is   qualified   to     allow   passing   the
  251%   module-sensitive ssl option argument.
  252
  253make_socket(Address, M:Options0, Options) :-
  254    tcp_address(Address),
  255    make_socket_hook(Address, M:Options0, Options),
  256    !.
  257make_socket(Address, _:Options0, Options) :-
  258    option(tcp_socket(_), Options0),
  259    !,
  260    make_addr_atom('httpd', Address, Queue),
  261    Options = [ queue(Queue)
  262              | Options0
  263              ].
  264make_socket(Address, _:Options0, Options) :-
  265    tcp_address(Address),
  266    !,
  267    address_domain(Address, Domain),
  268    socket_create(Socket, [domain(Domain)]),
  269    tcp_setopt(Socket, reuseaddr),
  270    tcp_bind(Socket, Address),
  271    tcp_listen(Socket, 64),
  272    make_addr_atom('httpd', Address, Queue),
  273    Options = [ queue(Queue),
  274                tcp_socket(Socket)
  275              | Options0
  276              ].
  277:- if(current_predicate(unix_domain_socket/1)).  278make_socket(Address, _:Options0, Options) :-
  279    Address = unix_socket(Path),
  280    !,
  281    unix_domain_socket(Socket),
  282    tcp_bind(Socket, Path),
  283    tcp_listen(Socket, 64),
  284    make_addr_atom('httpd', Address, Queue),
  285    Options = [ queue(Queue),
  286                tcp_socket(Socket)
  287              | Options0
  288              ].
  289:- endif.  290
  291%!  make_addr_atom(+Scheme, +Address, -Atom) is det.
  292%
  293%   Create an atom that identifies  the   server's  queue and thread
  294%   resources.
  295
  296make_addr_atom(Scheme, Address, Atom) :-
  297    phrase(address_parts(Address), Parts),
  298    atomic_list_concat([Scheme,@|Parts], Atom).
  299
  300address_parts(Var) -->
  301    { var(Var),
  302      !,
  303      instantiation_error(Var)
  304    }.
  305address_parts(Atomic) -->
  306    { atomic(Atomic) },
  307    !,
  308    [Atomic].
  309address_parts(Host:Port) -->
  310    !,
  311    address_parts(Host), [:], address_parts(Port).
  312address_parts(ip(A,B,C,D)) -->
  313    !,
  314    [ A, '.', B, '.', C, '.', D ].
  315address_parts(unix_socket(Path)) -->
  316    [Path].
  317address_parts(Address) -->
  318    { domain_error(http_server_address, Address) }.
  319
  320
  321%!  create_server(:Goal, +Address, +Options) is det.
  322%
  323%   Create the main server thread that runs accept_server/2 to
  324%   listen to new requests.
  325
  326create_server(Goal, Address, Options) :-
  327    get_time(StartTime),
  328    memberchk(queue(Queue), Options),
  329    scheme(Scheme, Options),
  330    autoload_https(Scheme),
  331    address_port(Address, Port),
  332    make_addr_atom(Scheme, Port, Alias),
  333    thread_self(Initiator),
  334    thread_create(accept_server(Goal, Initiator, Options), _,
  335                  [ alias(Alias)
  336                  ]),
  337    thread_get_message(server_started),
  338    assert(current_server(Port, Goal, Alias, Queue, Scheme, StartTime)).
  339
  340scheme(Scheme, Options) :-
  341    option(scheme(Scheme), Options),
  342    !.
  343scheme(Scheme, Options) :-
  344    (   option(ssl(_), Options)
  345    ;   option(ssl_instance(_), Options)
  346    ),
  347    !,
  348    Scheme = https.
  349scheme(http, _).
  350
  351autoload_https(https) :-
  352    \+ clause(accept_hook(_Goal, _Options), _),
  353    exists_source(library(http/http_ssl_plugin)),
  354    !,
  355    use_module(library(http/http_ssl_plugin)).
  356autoload_https(_).
  357
  358%!  http_current_server(:Goal, ?Port) is nondet.
  359%
  360%   True if Goal is the goal of a server at Port.
  361%
  362%   @deprecated Use http_server_property(Port, goal(Goal))
  363
  364http_current_server(Goal, Port) :-
  365    current_server(Port, Goal, _, _, _, _).
  366
  367
  368%!  http_server_property(?Port, ?Property) is nondet.
  369%
  370%   True if Property is a property of the HTTP server running at
  371%   Port.  Defined properties are:
  372%
  373%       * goal(:Goal)
  374%       Goal used to start the server. This is often
  375%       http_dispatch/1.
  376%       * scheme(-Scheme)
  377%       Scheme is one of `http` or `https`.
  378%       * start_time(?Time)
  379%       Time-stamp when the server was created.
  380
  381http_server_property(_:Port, Property) :-
  382    integer(Port),
  383    !,
  384    server_property(Property, Port).
  385http_server_property(Port, Property) :-
  386    server_property(Property, Port).
  387
  388server_property(goal(Goal), Port) :-
  389    current_server(Port, Goal, _, _, _, _).
  390server_property(scheme(Scheme), Port) :-
  391    current_server(Port, _, _, _, Scheme, _).
  392server_property(start_time(Time), Port) :-
  393    current_server(Port, _, _, _, _, Time).
  394
  395
  396%!  http_workers(?Port, -Workers) is nondet.
  397%!  http_workers(+Port, +Workers:int) is det.
  398%
  399%   Query or set the number of workers for  the server at this port. The
  400%   number of workers is dynamically modified. Setting it to 1 (one) can
  401%   be used to profile the worker using tprofile/1.
  402%
  403%   @see library(http/http_dyn_workers) implements dynamic management of
  404%   the worker pool depending on usage.
  405
  406http_workers(Port, Workers) :-
  407    integer(Workers),
  408    !,
  409    must_be(ground, Port),
  410    (   current_server(Port, _, _, Queue, _, _)
  411    ->  resize_pool(Queue, Workers)
  412    ;   existence_error(http_server, Port)
  413    ).
  414http_workers(Port, Workers) :-
  415    current_server(Port, _, _, Queue, _, _),
  416    aggregate_all(count, queue_worker(Queue, _Worker), Workers).
  417
  418
  419%!  http_add_worker(+Port, +Options) is det.
  420%
  421%   Add a new worker to  the  HTTP   server  for  port Port. Options
  422%   overrule the default queue  options.   The  following additional
  423%   options are processed:
  424%
  425%     - max_idle_time(+Seconds)
  426%     The created worker will automatically terminate if there is
  427%     no new work within Seconds.
  428
  429http_add_worker(Port, Options) :-
  430    must_be(ground, Port),
  431    current_server(Port, _, _, Queue, _, _),
  432    !,
  433    queue_options(Queue, QueueOptions),
  434    merge_options(Options, QueueOptions, WorkerOptions),
  435    atom_concat(Queue, '_', AliasBase),
  436    create_workers(1, 1, Queue, AliasBase, WorkerOptions).
  437http_add_worker(Port, _) :-
  438    existence_error(http_server, Port).
  439
  440
  441%!  http_current_worker(?Port, ?ThreadID) is nondet.
  442%
  443%   True if ThreadID is the identifier   of  a Prolog thread serving
  444%   Port. This predicate is  motivated  to   allow  for  the  use of
  445%   arbitrary interaction with the worker thread for development and
  446%   statistics.
  447
  448http_current_worker(Port, ThreadID) :-
  449    current_server(Port, _, _, Queue, _, _),
  450    queue_worker(Queue, ThreadID).
  451
  452
  453%!  accept_server(:Goal, +Initiator, +Options)
  454%
  455%   The goal of a small server-thread accepting new requests and
  456%   posting them to the queue of workers.
  457
  458accept_server(Goal, Initiator, Options) :-
  459    Ex = http_stop(Stopper),
  460    catch(accept_server2(Goal, Initiator, Options), Ex, true),
  461    thread_self(Thread),
  462    debug(http(stop), '[~p]: accept server received ~p', [Thread, Ex]),
  463    retract(current_server(_Port, _, Thread, Queue, _Scheme, _StartTime)),
  464    close_pending_accepts(Queue),
  465    close_server_socket(Options),
  466    thread_send_message(Stopper, http_stopped).
  467
  468accept_server2(Goal, Initiator, Options) :-
  469    thread_send_message(Initiator, server_started),
  470    repeat,
  471      (   catch(accept_server3(Goal, Options), E, true)
  472      ->  (   var(E)
  473          ->  fail
  474          ;   accept_rethrow_error(E)
  475          ->  throw(E)
  476          ;   print_message(error, E),
  477              fail
  478          )
  479      ;   print_message(error,      % internal error
  480                        goal_failed(accept_server3(Goal, Options))),
  481          fail
  482      ).
  483
  484accept_server3(Goal, Options) :-
  485    accept_hook(Goal, Options),
  486    !.
  487accept_server3(Goal, Options) :-
  488    memberchk(tcp_socket(Socket), Options),
  489    memberchk(queue(Queue), Options),
  490    debug(http(connection), 'Waiting for connection', []),
  491    tcp_accept(Socket, Client, Peer),
  492    sig_atomic(send_to_worker(Queue, Client, Goal, Peer)),
  493    http_enough_workers(Queue, accept, Peer).
  494
  495send_to_worker(Queue, Client, Goal, Peer) :-
  496    debug(http(connection), 'New HTTP connection from ~p', [Peer]),
  497    thread_send_message(Queue, tcp_client(Client, Goal, Peer)).
  498
  499accept_rethrow_error(http_stop(_)).
  500accept_rethrow_error('$aborted').
  501
  502
  503%!  close_server_socket(+Options)
  504%
  505%   Close the server socket.
  506
  507close_server_socket(Options) :-
  508    close_hook(Options),
  509    !.
  510close_server_socket(Options) :-
  511    memberchk(tcp_socket(Socket), Options),
  512    !,
  513    tcp_close_socket(Socket).
  514
  515%!  close_pending_accepts(+Queue)
  516
  517close_pending_accepts(Queue) :-
  518    (   thread_get_message(Queue, Msg, [timeout(0)])
  519    ->  close_client(Msg),
  520        close_pending_accepts(Queue)
  521    ;   true
  522    ).
  523
  524close_client(tcp_client(Client, _Goal, _0Peer)) =>
  525    debug(http(stop), 'Closing connection from ~p during shut-down', [_0Peer]),
  526    tcp_close_socket(Client).
  527close_client(Msg) =>
  528    (   discard_client_hook(Msg)
  529    ->  true
  530    ;   print_message(warning, http_close_client(Msg))
  531    ).
  532
  533
  534%!  http_stop_server(+Port, +Options)
  535%
  536%   Stop the indicated  HTTP  server   gracefully.  First  stops all
  537%   workers, then stops the server.
  538%
  539%   @tbd    Realise non-graceful stop
  540
  541http_stop_server(Host:Port, Options) :-         % e.g., localhost:4000
  542    ground(Host),
  543    !,
  544    http_stop_server(Port, Options).
  545http_stop_server(Port, _Options) :-
  546    http_workers(Port, 0),                  % checks Port is ground
  547    current_server(Port, _, Thread, Queue, _Scheme, _Start),
  548    retractall(queue_options(Queue, _)),
  549    debug(http(stop), 'Signalling HTTP server thread ~p to stop', [Thread]),
  550    thread_self(Stopper),
  551    thread_signal(Thread, throw(http_stop(Stopper))),
  552    (   thread_get_message(Stopper, http_stopped, [timeout(0.1)])
  553    ->  true
  554    ;   catch(connect(localhost:Port), _, true)
  555    ),
  556    thread_join(Thread, _0Status),
  557    debug(http(stop), 'Joined HTTP server thread ~p (~p)', [Thread, _0Status]),
  558    message_queue_destroy(Queue).
  559
  560connect(Address) :-
  561    setup_call_cleanup(
  562        tcp_socket(Socket),
  563        tcp_connect(Socket, Address),
  564        tcp_close_socket(Socket)).
  565
  566%!  http_enough_workers(+Queue, +Why, +Peer) is det.
  567%
  568%   Check that we have enough workers in our queue. If not, call the
  569%   hook http:schedule_workers/1 to extend  the   worker  pool. This
  570%   predicate can be used by accept_hook/2.
  571
  572http_enough_workers(Queue, _Why, _Peer) :-
  573    message_queue_property(Queue, waiting(_0)),
  574    !,
  575    debug(http(scheduler), '~D waiting for work; ok', [_0]).
  576http_enough_workers(Queue, Why, Peer) :-
  577    message_queue_property(Queue, size(Size)),
  578    (   enough(Size, Why)
  579    ->  debug(http(scheduler), '~D in queue; ok', [Size])
  580    ;   current_server(Port, _, _, Queue, _, _),
  581        Data = _{ port:Port,
  582                  reason:Why,
  583                  peer:Peer,
  584                  waiting:Size,
  585                  queue:Queue
  586                },
  587        debug(http(scheduler), 'Asking to reschedule: ~p', [Data]),
  588        catch(http:schedule_workers(Data),
  589              Error,
  590              print_message(error, Error))
  591    ->  true
  592    ;   true
  593    ).
  594
  595enough(0, _).
  596enough(1, keep_alive).                  % I will be ready myself
  597
  598
  599%!  http:schedule_workers(+Data:dict) is semidet.
  600%
  601%   Hook called if a  new  connection   or  a  keep-alive connection
  602%   cannot be scheduled _immediately_ to a worker. Dict contains the
  603%   following keys:
  604%
  605%     - port:Port
  606%     Port number that identifies the server.
  607%     - reason:Reason
  608%     One of =accept= for a new connection or =keep_alive= if a
  609%     worker tries to reschedule itself.
  610%     - peer:Peer
  611%     Identify the other end of the connection
  612%     - waiting:Size
  613%     Number of messages waiting in the queue.
  614%     - queue:Queue
  615%     Message queue used to dispatch accepted messages.
  616%
  617%   Note that, when called with `reason:accept`,   we  are called in
  618%   the time critical main accept loop.   An  implementation of this
  619%   hook shall typically send  the  event   to  thread  dedicated to
  620%   dynamic worker-pool management.
  621%
  622%   @see    http_add_worker/2 may be used to create (temporary) extra
  623%           workers.
  624
  625
  626                 /*******************************
  627                 *    WORKER QUEUE OPERATIONS   *
  628                 *******************************/
  629
  630%!  create_workers(+Options)
  631%
  632%   Create the pool of HTTP worker-threads. Each worker has the
  633%   alias http_worker_N.
  634
  635create_workers(Options) :-
  636    option(workers(N), Options, 5),
  637    option(queue(Queue), Options),
  638    catch(message_queue_create(Queue), _, true),
  639    atom_concat(Queue, '_', AliasBase),
  640    create_workers(1, N, Queue, AliasBase, Options),
  641    assert(queue_options(Queue, Options)).
  642
  643create_workers(I, N, _, _, _) :-
  644    I > N,
  645    !.
  646create_workers(I, N, Queue, AliasBase, Options) :-
  647    gensym(AliasBase, Alias),
  648    thread_create(http_worker(Options), Id,
  649                  [ alias(Alias)
  650                  | Options
  651                  ]),
  652    assertz(queue_worker(Queue, Id)),
  653    I2 is I + 1,
  654    create_workers(I2, N, Queue, AliasBase, Options).
  655
  656
  657%!  resize_pool(+Queue, +Workers) is det.
  658%
  659%   Create or destroy workers. If workers   are  destroyed, the call
  660%   waits until the desired number of waiters is reached.
  661
  662resize_pool(Queue, Size) :-
  663    findall(W, queue_worker(Queue, W), Workers),
  664    length(Workers, Now),
  665    (   Now < Size
  666    ->  queue_options(Queue, Options),
  667        atom_concat(Queue, '_', AliasBase),
  668        I0 is Now+1,
  669        create_workers(I0, Size, Queue, AliasBase, Options)
  670    ;   Now == Size
  671    ->  true
  672    ;   Now > Size
  673    ->  Excess is Now - Size,
  674        thread_self(Me),
  675        forall(between(1, Excess, _), thread_send_message(Queue, quit(Me))),
  676        forall(between(1, Excess, _), thread_get_message(quitted(_)))
  677    ).
  678
  679
  680%!  http_worker(+Options)
  681%
  682%   Run HTTP worker main loop. Workers   simply  wait until they are
  683%   passed an accepted socket to process  a client.
  684%
  685%   If the message quit(Sender) is read   from the queue, the worker
  686%   stops.
  687
  688http_worker(Options) :-
  689    debug(http(scheduler), 'New worker', []),
  690    prolog_listen(this_thread_exit, done_worker),
  691    option(queue(Queue), Options),
  692    option(max_idle_time(MaxIdle), Options, infinite),
  693    thread_repeat_wait(get_work(Queue, Message, MaxIdle)),
  694      debug(http(worker), 'Waiting for a job ...', []),
  695      debug(http(worker), 'Got job ~p', [Message]),
  696      (   Message = quit(Sender)
  697      ->  !,
  698          thread_self(Self),
  699          thread_detach(Self),
  700          (   Sender == idle
  701          ->  true
  702          ;   retract(queue_worker(Queue, Self)),
  703              thread_send_message(Sender, quitted(Self))
  704          )
  705      ;   open_client(Message, Queue, Goal, In, Out,
  706                      Options, ClientOptions),
  707          (   catch(http_process(Goal, In, Out, ClientOptions),
  708                    Error, true)
  709          ->  true
  710          ;   Error = goal_failed(http_process/4)
  711          ),
  712          (   var(Error)
  713          ->  fail
  714          ;   current_message_level(Error, Level),
  715              print_message(Level, Error),
  716              memberchk(peer(Peer), ClientOptions),
  717              close_connection(Peer, In, Out),
  718              fail
  719          )
  720      ).
  721
  722get_work(Queue, Message, infinite) :-
  723    !,
  724    thread_get_message(Queue, Message).
  725get_work(Queue, Message, MaxIdle) :-
  726    (   thread_get_message(Queue, Message, [timeout(MaxIdle)])
  727    ->  true
  728    ;   Message = quit(idle)
  729    ).
  730
  731
  732%!  open_client(+Message, +Queue, -Goal, -In, -Out,
  733%!              +Options, -ClientOptions) is semidet.
  734%
  735%   Opens the connection to the client in a worker from the message
  736%   sent to the queue by accept_server/2.
  737
  738open_client(requeue(In, Out, Goal, ClOpts),
  739            _, Goal, In, Out, Opts, ClOpts) :-
  740    !,
  741    memberchk(peer(Peer), ClOpts),
  742    option(keep_alive_timeout(KeepAliveTMO), Opts, 2),
  743    check_keep_alive_connection(In, KeepAliveTMO, Peer, In, Out).
  744open_client(Message, Queue, Goal, In, Out, Opts,
  745            [ pool(client(Queue, Goal, In, Out)),
  746              timeout(Timeout)
  747            | Options
  748            ]) :-
  749    catch(open_client(Message, Goal, In, Out, Options, Opts),
  750          E, report_error(E)),
  751    option(timeout(Timeout), Opts, 60),
  752    (   debugging(http(connection))
  753    ->  memberchk(peer(Peer), Options),
  754        debug(http(connection), 'Opened connection from ~p', [Peer])
  755    ;   true
  756    ).
  757
  758
  759%!  open_client(+Message, +Goal, -In, -Out,
  760%!              -ClientOptions, +Options) is det.
  761
  762open_client(Message, Goal, In, Out, ClientOptions, Options) :-
  763    open_client_hook(Message, Goal, In, Out, ClientOptions, Options),
  764    !.
  765open_client(tcp_client(Socket, Goal, Peer), Goal, In, Out,
  766            [ peer(Peer),
  767              protocol(http)
  768            ], _) :-
  769    tcp_open_socket(Socket, In, Out).
  770
  771report_error(E) :-
  772    print_message(error, E),
  773    fail.
  774
  775
  776%!  check_keep_alive_connection(+In, +TimeOut, +Peer, +In, +Out) is semidet.
  777%
  778%   Wait for the client for at most  TimeOut seconds. Succeed if the
  779%   client starts a new request within   this  time. Otherwise close
  780%   the connection and fail.
  781
  782check_keep_alive_connection(In, TMO, Peer, In, Out) :-
  783    stream_property(In, timeout(Old)),
  784    set_stream(In, timeout(TMO)),
  785    debug(http(keep_alive), 'Waiting for keep-alive ...', []),
  786    catch(peek_code(In, Code), E, true),
  787    (   var(E),                     % no exception
  788        Code \== -1                 % no end-of-file
  789    ->  set_stream(In, timeout(Old)),
  790        debug(http(keep_alive), '\tre-using keep-alive connection', [])
  791    ;   (   Code == -1
  792        ->  debug(http(keep_alive), '\tRemote closed keep-alive connection', [])
  793        ;   debug(http(keep_alive), '\tTimeout on keep-alive connection', [])
  794        ),
  795        close_connection(Peer, In, Out),
  796        fail
  797    ).
  798
  799
  800%!  done_worker
  801%
  802%   Called when worker is terminated  due   to  http_workers/2  or a
  803%   (debugging) exception. In  the   latter  case, recreate_worker/2
  804%   creates a new worker.
  805
  806done_worker :-
  807    thread_self(Self),
  808    thread_detach(Self),
  809    retract(queue_worker(Queue, Self)),
  810    thread_property(Self, status(Status)),
  811    !,
  812    (   catch(recreate_worker(Status, Queue), _, fail)
  813    ->  print_message(informational,
  814                      httpd_restarted_worker(Self))
  815    ;   done_status_message_level(Status, Level),
  816        print_message(Level,
  817                      httpd_stopped_worker(Self, Status))
  818    ).
  819done_worker :-                                  % received quit(Sender)
  820    thread_self(Self),
  821    thread_property(Self, status(Status)),
  822    done_status_message_level(Status, Level),
  823    print_message(Level,
  824                  httpd_stopped_worker(Self, Status)).
  825
  826done_status_message_level(true, silent) :- !.
  827done_status_message_level(exception('$aborted'), silent) :- !.
  828done_status_message_level(_, informational).
  829
  830
  831%!  recreate_worker(+Status, +Queue) is semidet.
  832%
  833%   Deal with the possibility  that   threads  are,  during development,
  834%   killed with abort/0. We recreate the worker to avoid that eventually
  835%   we run out of workers. If  we  are   aborted  due  to a halt/0 call,
  836%   thread_create/3 will raise a permission error.
  837%
  838%   The first clause deals with the possibility  that we cannot write to
  839%   `user_error`. This is possible when Prolog   is started as a service
  840%   using some service managers. Would be  nice   if  we  could write an
  841%   error, but where?
  842
  843recreate_worker(exception(error(io_error(write,user_error),_)), _Queue) :-
  844    halt(2).
  845recreate_worker(exception(Error), Queue) :-
  846    recreate_on_error(Error),
  847    queue_options(Queue, Options),
  848    atom_concat(Queue, '_', AliasBase),
  849    create_workers(1, 1, Queue, AliasBase, Options).
  850
  851recreate_on_error('$aborted').
  852recreate_on_error(time_limit_exceeded).
  853
  854%!  thread_httpd:message_level(+Exception, -Level)
  855%
  856%   Determine the message stream used  for   exceptions  that  may occur
  857%   during server_loop/5. Being multifile, clauses can   be added by the
  858%   application to refine error handling.   See  also message_hook/3 for
  859%   further programming error handling.
  860
  861:- multifile
  862    message_level/2.  863
  864message_level(error(io_error(read, _), _),               silent).
  865message_level(error(socket_error(epipe,_), _),           silent).
  866message_level(error(http_write_short(_Obj,_Written), _), silent).
  867message_level(error(timeout_error(read, _), _),          informational).
  868message_level(keep_alive_timeout,                        silent).
  869
  870current_message_level(Term, Level) :-
  871    (   message_level(Term, Level)
  872    ->  true
  873    ;   Level = error
  874    ).
  875
  876
  877%!  http_requeue(+Header)
  878%
  879%   Re-queue a connection to  the  worker   pool.  This  deals  with
  880%   processing additional requests on keep-alive connections.
  881
  882http_requeue(Header) :-
  883    requeue_header(Header, ClientOptions),
  884    memberchk(pool(client(Queue, Goal, In, Out)), ClientOptions),
  885    memberchk(peer(Peer), ClientOptions),
  886    http_enough_workers(Queue, keep_alive, Peer),
  887    thread_send_message(Queue, requeue(In, Out, Goal, ClientOptions)),
  888    !.
  889http_requeue(Header) :-
  890    debug(http(error), 'Re-queue failed: ~p', [Header]),
  891    fail.
  892
  893requeue_header([], []).
  894requeue_header([H|T0], [H|T]) :-
  895    requeue_keep(H),
  896    !,
  897    requeue_header(T0, T).
  898requeue_header([_|T0], T) :-
  899    requeue_header(T0, T).
  900
  901requeue_keep(pool(_)).
  902requeue_keep(peer(_)).
  903requeue_keep(protocol(_)).
  904
  905
  906%!  http_process(Message, Queue, +Options)
  907%
  908%   Handle a single client message on the given stream.
  909
  910http_process(Goal, In, Out, Options) :-
  911    debug(http(server), 'Running server goal ~p on ~p -> ~p',
  912          [Goal, In, Out]),
  913    option(timeout(TMO), Options, 60),
  914    set_stream(In, timeout(TMO)),
  915    set_stream(Out, timeout(TMO)),
  916    http_wrapper(Goal, In, Out, Connection,
  917                 [ request(Request)
  918                 | Options
  919                 ]),
  920    next(Connection, Request).
  921
  922next(Connection, Request) :-
  923    next_(Connection, Request), !.
  924next(Connection, Request) :-
  925    print_message(warning, goal_failed(next(Connection,Request))).
  926
  927next_(switch_protocol(SwitchGoal, _SwitchOptions), Request) :-
  928    !,
  929    memberchk(pool(client(_Queue, _Goal, In, Out)), Request),
  930    (   catch(call(SwitchGoal, In, Out), E,
  931              (   print_message(error, E),
  932                  fail))
  933    ->  true
  934    ;   http_close_connection(Request)
  935    ).
  936next_(spawned(ThreadId), _) :-
  937    !,
  938    debug(http(spawn), 'Handler spawned to thread ~w', [ThreadId]).
  939next_(Connection, Request) :-
  940    downcase_atom(Connection, 'keep-alive'),
  941    http_requeue(Request),
  942    !.
  943next_(_, Request) :-
  944    http_close_connection(Request).
  945
  946
  947%!  http_close_connection(+Request)
  948%
  949%   Close connection associated to Request.  See also http_requeue/1.
  950
  951http_close_connection(Request) :-
  952    memberchk(pool(client(_Queue, _Goal, In, Out)), Request),
  953    memberchk(peer(Peer), Request),
  954    close_connection(Peer, In, Out).
  955
  956%!  close_connection(+Peer, +In, +Out)
  957%
  958%   Closes the connection from the server to the client.  Errors are
  959%   currently silently ignored.
  960
  961close_connection(Peer, In, Out) :-
  962    debug(http(connection), 'Closing connection from ~p', [Peer]),
  963    catch(close(In, [force(true)]), _, true),
  964    catch(close(Out, [force(true)]), _, true).
  965
  966%!  http_spawn(:Goal, +Options) is det.
  967%
  968%   Continue this connection on a  new   thread.  A handler may call
  969%   http_spawn/2 to start a new thread that continues processing the
  970%   current request using Goal. The original   thread returns to the
  971%   worker pool for processing new requests.   Options are passed to
  972%   thread_create/3, except for:
  973%
  974%       * pool(+Pool)
  975%       Interfaces to library(thread_pool), starting the thread
  976%       on the given pool.
  977%
  978%   If a pool does not exist, this predicate calls the multifile
  979%   hook http:create_pool/1 to create it. If this predicate succeeds
  980%   the operation is retried.
  981
  982http_spawn(Goal, Options) :-
  983    select_option(pool(Pool), Options, ThreadOptions),
  984    !,
  985    current_output(CGI),
  986    catch(thread_create_in_pool(Pool,
  987                                wrap_spawned(CGI, Goal), Id,
  988                                [ detached(true)
  989                                | ThreadOptions
  990                                ]),
  991          Error,
  992          true),
  993    (   var(Error)
  994    ->  http_spawned(Id)
  995    ;   Error = error(resource_error(threads_in_pool(_)), _)
  996    ->  throw(http_reply(busy))
  997    ;   Error = error(existence_error(thread_pool, Pool), _),
  998        create_pool(Pool)
  999    ->  http_spawn(Goal, Options)
 1000    ;   throw(Error)
 1001    ).
 1002http_spawn(Goal, Options) :-
 1003    current_output(CGI),
 1004    thread_create(wrap_spawned(CGI, Goal), Id,
 1005                  [ detached(true)
 1006                  | Options
 1007                  ]),
 1008    http_spawned(Id).
 1009
 1010wrap_spawned(CGI, Goal) :-
 1011    set_output(CGI),
 1012    http_wrap_spawned(Goal, Request, Connection),
 1013    next(Connection, Request).
 1014
 1015%!  create_pool(+Pool)
 1016%
 1017%   Lazy  creation  of  worker-pools  for   the  HTTP  server.  This
 1018%   predicate calls the hook http:create_pool/1.   If the hook fails
 1019%   it creates a default pool of size   10. This should suffice most
 1020%   typical usecases. Note that we  get   a  permission error if the
 1021%   pool is already created.  We can ignore this.
 1022
 1023create_pool(Pool) :-
 1024    E = error(permission_error(create, thread_pool, Pool), _),
 1025    catch(http:create_pool(Pool), E, true).
 1026create_pool(Pool) :-
 1027    print_message(informational, httpd(created_pool(Pool))),
 1028    thread_pool_create(Pool, 10, []).
 1029
 1030
 1031		 /*******************************
 1032		 *         WAIT POLICIES	*
 1033		 *******************************/
 1034
 1035:- meta_predicate
 1036    thread_repeat_wait(0). 1037
 1038%!  thread_repeat_wait(:Goal) is multi.
 1039%
 1040%   Acts as `repeat,  thread_idle(Goal)`,  choosing   whether  to  use a
 1041%   `long` or `short` idle time based on the average firing rate.
 1042
 1043thread_repeat_wait(Goal) :-
 1044    new_rate_mma(5, 1000, State),
 1045    repeat,
 1046      update_rate_mma(State, MMA),
 1047      long(MMA, IsLong),
 1048      (   IsLong == brief
 1049      ->  call(Goal)
 1050      ;   thread_idle(Goal, IsLong)
 1051      ).
 1052
 1053long(MMA, brief) :-
 1054    MMA < 0.05,
 1055    !.
 1056long(MMA, short) :-
 1057    MMA < 1,
 1058    !.
 1059long(_, long).
 1060
 1061%!  new_rate_mma(+N, +Resolution, -State) is det.
 1062%!  update_rate_mma(!State, -MMA) is det.
 1063%
 1064%   Implement _Modified Moving  Average_  computing   the  average  time
 1065%   between requests as an exponential moving averate with alpha=1/N.
 1066%
 1067%   @arg Resolution is the time resolution  in 1/Resolution seconds. All
 1068%   storage is done in integers to avoid  the need for stack freezing in
 1069%   nb_setarg/3.
 1070%
 1071%   @see https://en.wikipedia.org/wiki/Moving_average
 1072
 1073new_rate_mma(N, Resolution, rstate(Base, 0, MaxI, Resolution, N, 0)) :-
 1074    current_prolog_flag(max_tagged_integer, MaxI),
 1075    get_time(Base).
 1076
 1077update_rate_mma(State, MMAr) :-
 1078    State = rstate(Base, Last, MaxI, Resolution, N, MMA0),
 1079    get_time(Now),
 1080    Stamp is round((Now-Base)*Resolution),
 1081    (   Stamp > MaxI
 1082    ->  nb_setarg(1, State, Now),
 1083        nb_setarg(2, State, 0)
 1084    ;   true
 1085    ),
 1086    Diff is Stamp-Last,
 1087    nb_setarg(2, State, Stamp),
 1088    MMA is round(((N-1)*MMA0+Diff)/N),
 1089    nb_setarg(6, State, MMA),
 1090    MMAr is MMA/float(Resolution).
 1091
 1092
 1093                 /*******************************
 1094                 *            MESSAGES          *
 1095                 *******************************/
 1096
 1097:- multifile
 1098    prolog:message/3. 1099
 1100prolog:message(httpd_started_server(Port, Options)) -->
 1101    [ 'Started server at '-[] ],
 1102    http_root(Port, Options).
 1103prolog:message(httpd_stopped_worker(Self, Status)) -->
 1104    [ 'Stopped worker ~p: ~p'-[Self, Status] ].
 1105prolog:message(httpd_restarted_worker(Self)) -->
 1106    [ 'Replaced aborted worker ~p'-[Self] ].
 1107prolog:message(httpd(created_pool(Pool))) -->
 1108    [ 'Created thread-pool ~p of size 10'-[Pool], nl,
 1109      'Create this pool at startup-time or define the hook ', nl,
 1110      'http:create_pool/1 to avoid this message and create a ', nl,
 1111      'pool that fits the usage-profile.'
 1112    ].
 1113
 1114http_root(Address, Options) -->
 1115    { landing_page(Address, URI, Options) },
 1116    [ '~w'-[URI] ].
 1117
 1118landing_page(Host:Port, URI, Options) :-
 1119    !,
 1120    must_be(atom, Host),
 1121    must_be(integer, Port),
 1122    http_server_property(Port, scheme(Scheme)),
 1123    (   default_port(Scheme, Port)
 1124    ->  format(atom(Base), '~w://~w', [Scheme, Host])
 1125    ;   format(atom(Base), '~w://~w:~w', [Scheme, Host, Port])
 1126    ),
 1127    entry_page(Base, URI, Options).
 1128landing_page(unix_socket(Path), URI, _Options) :-
 1129    !,
 1130    format(string(URI), 'Unix domain socket "~w"', [Path]).
 1131landing_page(Port, URI, Options) :-
 1132    landing_page(localhost:Port, URI, Options).
 1133
 1134default_port(http, 80).
 1135default_port(https, 443).
 1136
 1137entry_page(Base, URI, Options) :-
 1138    option(entry_page(Entry), Options),
 1139    !,
 1140    uri_resolve(Entry, Base, URI).
 1141entry_page(Base, URI, _) :-
 1142    http_absolute_location(root(.), Entry, []),
 1143    uri_resolve(Entry, Base, URI)