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)  2002-2022, 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,
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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:- autoload(library(uri), [uri_resolve/3]).   61
   62:- predicate_options(http_server/2, 2,
   63                     [ port(any),
   64                       unix_socket(atom),
   65                       entry_page(atom),
   66                       tcp_socket(any),
   67                       workers(positive_integer),
   68                       timeout(number),
   69                       keep_alive_timeout(number),
   70                       silent(boolean),
   71                       ssl(list(any)),  % if http/http_ssl_plugin is loaded
   72                       pass_to(system:thread_create/3, 3)
   73                     ]).   74:- predicate_options(http_spawn/2, 2,
   75                     [ pool(atom),
   76                       pass_to(system:thread_create/3, 3),
   77                       pass_to(thread_pool:thread_create_in_pool/4, 4)
   78                     ]).   79:- predicate_options(http_add_worker/2, 2,
   80                     [ timeout(number),
   81                       keep_alive_timeout(number),
   82                       max_idle_time(number),
   83                       pass_to(system:thread_create/3, 3)
   84                     ]).

  112:- meta_predicate
  113    http_server(1, :),
  114    http_current_server(1, ?),
  115    http_spawn(0, +).  116
  117:- dynamic
  118    current_server/6,       % Port, Goal, Thread, Queue, Scheme, StartTime
  119    queue_worker/2,         % Queue, ThreadID
  120    queue_options/2.        % Queue, Options
  121
  122:- multifile
  123    make_socket_hook/3,
  124    accept_hook/2,
  125    close_hook/1,
  126    open_client_hook/6,
  127    discard_client_hook/1,
  128    http:create_pool/1,
  129    http:schedule_workers/1.  130
  131:- meta_predicate
  132    thread_repeat_wait(0).

 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.

unix_socket(+Path)

Instead of binding to a TCP port, bind to a Unix Domain Socket at Path.

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.

  197http_server(Goal, M:Options0) :-
  198    server_address(Address, Options0),
  199    !,
  200    make_socket(Address, M:Options0, Options),
  201    create_workers(Options),
  202    create_server(Goal, Address, Options),
  203    (   option(silent(true), Options0)
  204    ->  true
  205    ;   print_message(informational,
  206                      httpd_started_server(Address, Options0))
  207    ).
  208http_server(_Goal, _:Options0) :-
  209    existence_error(server_address, Options0).
  210
  211server_address(Address, Options) :-
  212    (   option(port(Port), Options)
  213    ->  Address = Port
  214    ;   option(unix_socket(Path), Options)
  215    ->  Address = unix_socket(Path)
  216    ).
  217
  218address_port(_IFace:Port, Port) :- !.
  219address_port(unix_socket(Path), Path) :- !.
  220address_port(Address, Address) :- !.
  221
  222tcp_address(Port) :-
  223    var(Port),
  224    !.
  225tcp_address(Port) :-
  226    integer(Port),
  227    !.
  228tcp_address(_Iface:_Port).
  229
  230address_domain(localhost:_Port, Domain) =>
  231    Domain = inet.
  232address_domain(Iface:_Port, Domain) =>
  233    (   catch(ip_name(IP, Iface), error(_,_), fail),
  234        functor(IP, ip, 8)
  235    ->  Domain = inet6
  236    ;   Domain = inet
  237    ).
  238address_domain(_, Domain) =>
  239    Domain = inet.

 make_socket(+Address, :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.

  250make_socket(Address, M:Options0, Options) :-
  251    tcp_address(Address),
  252    make_socket_hook(Address, M:Options0, Options),
  253    !.
  254make_socket(Address, _:Options0, Options) :-
  255    option(tcp_socket(_), Options0),
  256    !,
  257    make_addr_atom('httpd', Address, Queue),
  258    Options = [ queue(Queue)
  259              | Options0
  260              ].
  261make_socket(Address, _:Options0, Options) :-
  262    tcp_address(Address),
  263    !,
  264    address_domain(Address, Domain),
  265    socket_create(Socket, [domain(Domain)]),
  266    tcp_setopt(Socket, reuseaddr),
  267    tcp_bind(Socket, Address),
  268    tcp_listen(Socket, 64),
  269    make_addr_atom('httpd', Address, Queue),
  270    Options = [ queue(Queue),
  271                tcp_socket(Socket)
  272              | Options0
  273              ].
  274:- if(current_predicate(unix_domain_socket/1)).  275make_socket(Address, _:Options0, Options) :-
  276    Address = unix_socket(Path),
  277    !,
  278    unix_domain_socket(Socket),
  279    tcp_bind(Socket, Path),
  280    tcp_listen(Socket, 64),
  281    make_addr_atom('httpd', Address, Queue),
  282    Options = [ queue(Queue),
  283                tcp_socket(Socket)
  284              | Options0
  285              ].
  286:- endif.

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

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

  293make_addr_atom(Scheme, Address, Atom) :-
  294    phrase(address_parts(Address), Parts),
  295    atomic_list_concat([Scheme,@|Parts], Atom).
  296
  297address_parts(Var) -->
  298    { var(Var),
  299      !,
  300      instantiation_error(Var)
  301    }.
  302address_parts(Atomic) -->
  303    { atomic(Atomic) },
  304    !,
  305    [Atomic].
  306address_parts(Host:Port) -->
  307    !,
  308    address_parts(Host), [:], address_parts(Port).
  309address_parts(ip(A,B,C,D)) -->
  310    !,
  311    [ A, '.', B, '.', C, '.', D ].
  312address_parts(unix_socket(Path)) -->
  313    [Path].
  314address_parts(Address) -->
  315    { domain_error(http_server_address, Address) }.

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

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

  323create_server(Goal, Address, Options) :-
  324    get_time(StartTime),
  325    memberchk(queue(Queue), Options),
  326    scheme(Scheme, Options),
  327    autoload_https(Scheme),
  328    address_port(Address, Port),
  329    make_addr_atom(Scheme, Port, Alias),
  330    thread_self(Initiator),
  331    thread_create(accept_server(Goal, Initiator, Options), _,
  332                  [ alias(Alias)
  333                  ]),
  334    thread_get_message(server_started),
  335    assert(current_server(Port, Goal, Alias, Queue, Scheme, StartTime)).
  336
  337scheme(Scheme, Options) :-
  338    option(scheme(Scheme), Options),
  339    !.
  340scheme(Scheme, Options) :-
  341    (   option(ssl(_), Options)
  342    ;   option(ssl_instance(_), Options)
  343    ),
  344    !,
  345    Scheme = https.
  346scheme(http, _).
  347
  348autoload_https(https) :-
  349    \+ clause(accept_hook(_Goal, _Options), _),
  350    exists_source(library(http/http_ssl_plugin)),
  351    !,
  352    use_module(library(http/http_ssl_plugin)).
  353autoload_https(_).

 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))

  361http_current_server(Goal, Port) :-
  362    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.

  378http_server_property(_:Port, Property) :-
  379    integer(Port),
  380    !,
  381    server_property(Property, Port).
  382http_server_property(Port, Property) :-
  383    server_property(Property, Port).
  384
  385server_property(goal(Goal), Port) :-
  386    current_server(Port, Goal, _, _, _, _).
  387server_property(scheme(Scheme), Port) :-
  388    current_server(Port, _, _, _, Scheme, _).
  389server_property(start_time(Time), Port) :-
  390    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.

  400http_workers(Port, Workers) :-
  401    must_be(ground, Port),
  402    current_server(Port, _, _, Queue, _, _),
  403    !,
  404    (   integer(Workers)
  405    ->  resize_pool(Queue, Workers)
  406    ;   findall(W, queue_worker(Queue, W), WorkerIDs),
  407        length(WorkerIDs, Workers)
  408    ).
  409http_workers(Port, _) :-
  410    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.

  423http_add_worker(Port, Options) :-
  424    must_be(ground, Port),
  425    current_server(Port, _, _, Queue, _, _),
  426    !,
  427    queue_options(Queue, QueueOptions),
  428    merge_options(Options, QueueOptions, WorkerOptions),
  429    atom_concat(Queue, '_', AliasBase),
  430    create_workers(1, 1, Queue, AliasBase, WorkerOptions).
  431http_add_worker(Port, _) :-
  432    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.

  442http_current_worker(Port, ThreadID) :-
  443    current_server(Port, _, _, Queue, _, _),
  444    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.

  452accept_server(Goal, Initiator, Options) :-
  453    Ex = http_stop(Stopper),
  454    catch(accept_server2(Goal, Initiator, Options), Ex, true),
  455    thread_self(Thread),
  456    debug(http(stop), '[~p]: accept server received ~p', [Thread, Ex]),
  457    retract(current_server(_Port, _, Thread, Queue, _Scheme, _StartTime)),
  458    close_pending_accepts(Queue),
  459    close_server_socket(Options),
  460    thread_send_message(Stopper, http_stopped).
  461
  462accept_server2(Goal, Initiator, Options) :-
  463    thread_send_message(Initiator, server_started),
  464    repeat,
  465      (   catch(accept_server3(Goal, Options), E, true)
  466      ->  (   var(E)
  467          ->  fail
  468          ;   accept_rethrow_error(E)
  469          ->  throw(E)
  470          ;   print_message(error, E),
  471              fail
  472          )
  473      ;   print_message(error,      % internal error
  474                        goal_failed(accept_server3(Goal, Options))),
  475          fail
  476      ).
  477
  478accept_server3(Goal, Options) :-
  479    accept_hook(Goal, Options),
  480    !.
  481accept_server3(Goal, Options) :-
  482    memberchk(tcp_socket(Socket), Options),
  483    memberchk(queue(Queue), Options),
  484    debug(http(connection), 'Waiting for connection', []),
  485    tcp_accept(Socket, Client, Peer),
  486    sig_atomic(send_to_worker(Queue, Client, Goal, Peer)),
  487    http_enough_workers(Queue, accept, Peer).
  488
  489send_to_worker(Queue, Client, Goal, Peer) :-
  490    debug(http(connection), 'New HTTP connection from ~p', [Peer]),
  491    thread_send_message(Queue, tcp_client(Client, Goal, Peer)).
  492
  493accept_rethrow_error(http_stop(_)).
  494accept_rethrow_error('$aborted').

 close_server_socket(+Options)

Close the server socket.

  501close_server_socket(Options) :-
  502    close_hook(Options),
  503    !.
  504close_server_socket(Options) :-
  505    memberchk(tcp_socket(Socket), Options),
  506    !,
  507    tcp_close_socket(Socket).

 close_pending_accepts(+Queue)

  511close_pending_accepts(Queue) :-
  512    (   thread_get_message(Queue, Msg, [timeout(0)])
  513    ->  close_client(Msg),
  514        close_pending_accepts(Queue)
  515    ;   true
  516    ).
  517
  518close_client(tcp_client(Client, _Goal, _0Peer)) =>
  519    debug(http(stop), 'Closing connection from ~p during shut-down', [_0Peer]),
  520    tcp_close_socket(Client).
  521close_client(Msg) =>
  522    (   discard_client_hook(Msg)
  523    ->  true
  524    ;   print_message(warning, http_close_client(Msg))
  525    ).

 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

  535http_stop_server(Host:Port, Options) :-         % e.g., localhost:4000
  536    ground(Host),
  537    !,
  538    http_stop_server(Port, Options).
  539http_stop_server(Port, _Options) :-
  540    http_workers(Port, 0),                  % checks Port is ground
  541    current_server(Port, _, Thread, Queue, _Scheme, _Start),
  542    retractall(queue_options(Queue, _)),
  543    debug(http(stop), 'Signalling HTTP server thread ~p to stop', [Thread]),
  544    thread_self(Stopper),
  545    thread_signal(Thread, throw(http_stop(Stopper))),
  546    (   thread_get_message(Stopper, http_stopped, [timeout(0.1)])
  547    ->  true
  548    ;   catch(connect(localhost:Port), _, true)
  549    ),
  550    thread_join(Thread, _0Status),
  551    debug(http(stop), 'Joined HTTP server thread ~p (~p)', [Thread, _0Status]),
  552    message_queue_destroy(Queue).
  553
  554connect(Address) :-
  555    setup_call_cleanup(
  556        tcp_socket(Socket),
  557        tcp_connect(Socket, Address),
  558        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.

  566http_enough_workers(Queue, _Why, _Peer) :-
  567    message_queue_property(Queue, waiting(_0)),
  568    !,
  569    debug(http(scheduler), '~D waiting for work; ok', [_0]).
  570http_enough_workers(Queue, Why, Peer) :-
  571    message_queue_property(Queue, size(Size)),
  572    (   enough(Size, Why)
  573    ->  debug(http(scheduler), '~D in queue; ok', [Size])
  574    ;   current_server(Port, _, _, Queue, _, _),
  575        Data = _{ port:Port,
  576                  reason:Why,
  577                  peer:Peer,
  578                  waiting:Size,
  579                  queue:Queue
  580                },
  581        debug(http(scheduler), 'Asking to reschedule: ~p', [Data]),
  582        catch(http:schedule_workers(Data),
  583              Error,
  584              print_message(error, Error))
  585    ->  true
  586    ;   true
  587    ).
  588
  589enough(0, _).
  590enough(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.

  620                 /*******************************
  621                 *    WORKER QUEUE OPERATIONS   *
  622                 *******************************/

 create_workers(+Options)

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

  629create_workers(Options) :-
  630    option(workers(N), Options, 5),
  631    option(queue(Queue), Options),
  632    catch(message_queue_create(Queue), _, true),
  633    atom_concat(Queue, '_', AliasBase),
  634    create_workers(1, N, Queue, AliasBase, Options),
  635    assert(queue_options(Queue, Options)).
  636
  637create_workers(I, N, _, _, _) :-
  638    I > N,
  639    !.
  640create_workers(I, N, Queue, AliasBase, Options) :-
  641    gensym(AliasBase, Alias),
  642    thread_create(http_worker(Options), Id,
  643                  [ alias(Alias)
  644                  | Options
  645                  ]),
  646    assertz(queue_worker(Queue, Id)),
  647    I2 is I + 1,
  648    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.

  656resize_pool(Queue, Size) :-
  657    findall(W, queue_worker(Queue, W), Workers),
  658    length(Workers, Now),
  659    (   Now < Size
  660    ->  queue_options(Queue, Options),
  661        atom_concat(Queue, '_', AliasBase),
  662        I0 is Now+1,
  663        create_workers(I0, Size, Queue, AliasBase, Options)
  664    ;   Now == Size
  665    ->  true
  666    ;   Now > Size
  667    ->  Excess is Now - Size,
  668        thread_self(Me),
  669        forall(between(1, Excess, _), thread_send_message(Queue, quit(Me))),
  670        forall(between(1, Excess, _), thread_get_message(quitted(_)))
  671    ).

 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.

  682http_worker(Options) :-
  683    debug(http(scheduler), 'New worker', []),
  684    prolog_listen(this_thread_exit, done_worker),
  685    option(queue(Queue), Options),
  686    option(max_idle_time(MaxIdle), Options, infinite),
  687    thread_repeat_wait(get_work(Queue, Message, MaxIdle)),
  688      debug(http(worker), 'Waiting for a job ...', []),
  689      debug(http(worker), 'Got job ~p', [Message]),
  690      (   Message = quit(Sender)
  691      ->  !,
  692          thread_self(Self),
  693          thread_detach(Self),
  694          (   Sender == idle
  695          ->  true
  696          ;   retract(queue_worker(Queue, Self)),
  697              thread_send_message(Sender, quitted(Self))
  698          )
  699      ;   open_client(Message, Queue, Goal, In, Out,
  700                      Options, ClientOptions),
  701          (   catch(http_process(Goal, In, Out, ClientOptions),
  702                    Error, true)
  703          ->  true
  704          ;   Error = goal_failed(http_process/4)
  705          ),
  706          (   var(Error)
  707          ->  fail
  708          ;   current_message_level(Error, Level),
  709              print_message(Level, Error),
  710              memberchk(peer(Peer), ClientOptions),
  711              close_connection(Peer, In, Out),
  712              fail
  713          )
  714      ).
  715
  716get_work(Queue, Message, infinite) :-
  717    !,
  718    thread_get_message(Queue, Message).
  719get_work(Queue, Message, MaxIdle) :-
  720    (   thread_get_message(Queue, Message, [timeout(MaxIdle)])
  721    ->  true
  722    ;   Message = quit(idle)
  723    ).

 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.

  732open_client(requeue(In, Out, Goal, ClOpts),
  733            _, Goal, In, Out, Opts, ClOpts) :-
  734    !,
  735    memberchk(peer(Peer), ClOpts),
  736    option(keep_alive_timeout(KeepAliveTMO), Opts, 2),
  737    check_keep_alive_connection(In, KeepAliveTMO, Peer, In, Out).
  738open_client(Message, Queue, Goal, In, Out, Opts,
  739            [ pool(client(Queue, Goal, In, Out)),
  740              timeout(Timeout)
  741            | Options
  742            ]) :-
  743    catch(open_client(Message, Goal, In, Out, Options, Opts),
  744          E, report_error(E)),
  745    option(timeout(Timeout), Opts, 60),
  746    (   debugging(http(connection))
  747    ->  memberchk(peer(Peer), Options),
  748        debug(http(connection), 'Opened connection from ~p', [Peer])
  749    ;   true
  750    ).

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

  756open_client(Message, Goal, In, Out, ClientOptions, Options) :-
  757    open_client_hook(Message, Goal, In, Out, ClientOptions, Options),
  758    !.
  759open_client(tcp_client(Socket, Goal, Peer), Goal, In, Out,
  760            [ peer(Peer),
  761              protocol(http)
  762            ], _) :-
  763    tcp_open_socket(Socket, In, Out).
  764
  765report_error(E) :-
  766    print_message(error, E),
  767    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.

  776check_keep_alive_connection(In, TMO, Peer, In, Out) :-
  777    stream_property(In, timeout(Old)),
  778    set_stream(In, timeout(TMO)),
  779    debug(http(keep_alive), 'Waiting for keep-alive ...', []),
  780    catch(peek_code(In, Code), E, true),
  781    (   var(E),                     % no exception
  782        Code \== -1                 % no end-of-file
  783    ->  set_stream(In, timeout(Old)),
  784        debug(http(keep_alive), '\tre-using keep-alive connection', [])
  785    ;   (   Code == -1
  786        ->  debug(http(keep_alive), '\tRemote closed keep-alive connection', [])
  787        ;   debug(http(keep_alive), '\tTimeout on keep-alive connection', [])
  788        ),
  789        close_connection(Peer, In, Out),
  790        fail
  791    ).

 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.

  800done_worker :-
  801    thread_self(Self),
  802    thread_detach(Self),
  803    retract(queue_worker(Queue, Self)),
  804    thread_property(Self, status(Status)),
  805    !,
  806    (   catch(recreate_worker(Status, Queue), _, fail)
  807    ->  print_message(informational,
  808                      httpd_restarted_worker(Self))
  809    ;   done_status_message_level(Status, Level),
  810        print_message(Level,
  811                      httpd_stopped_worker(Self, Status))
  812    ).
  813done_worker :-                                  % received quit(Sender)
  814    thread_self(Self),
  815    thread_property(Self, status(Status)),
  816    done_status_message_level(Status, Level),
  817    print_message(Level,
  818                  httpd_stopped_worker(Self, Status)).
  819
  820done_status_message_level(true, silent) :- !.
  821done_status_message_level(exception('$aborted'), silent) :- !.
  822done_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?

  837recreate_worker(exception(error(io_error(write,user_error),_)), _Queue) :-
  838    halt(2).
  839recreate_worker(exception(Error), Queue) :-
  840    recreate_on_error(Error),
  841    queue_options(Queue, Options),
  842    atom_concat(Queue, '_', AliasBase),
  843    create_workers(1, 1, Queue, AliasBase, Options).
  844
  845recreate_on_error('$aborted').
  846recreate_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.

  855:- multifile
  856    message_level/2.  857
  858message_level(error(io_error(read, _), _),               silent).
  859message_level(error(socket_error(epipe,_), _),           silent).
  860message_level(error(http_write_short(_Obj,_Written), _), silent).
  861message_level(error(timeout_error(read, _), _),          informational).
  862message_level(keep_alive_timeout,                        silent).
  863
  864current_message_level(Term, Level) :-
  865    (   message_level(Term, Level)
  866    ->  true
  867    ;   Level = error
  868    ).

 http_requeue(+Header)

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

  876http_requeue(Header) :-
  877    requeue_header(Header, ClientOptions),
  878    memberchk(pool(client(Queue, Goal, In, Out)), ClientOptions),
  879    memberchk(peer(Peer), ClientOptions),
  880    http_enough_workers(Queue, keep_alive, Peer),
  881    thread_send_message(Queue, requeue(In, Out, Goal, ClientOptions)),
  882    !.
  883http_requeue(Header) :-
  884    debug(http(error), 'Re-queue failed: ~p', [Header]),
  885    fail.
  886
  887requeue_header([], []).
  888requeue_header([H|T0], [H|T]) :-
  889    requeue_keep(H),
  890    !,
  891    requeue_header(T0, T).
  892requeue_header([_|T0], T) :-
  893    requeue_header(T0, T).
  894
  895requeue_keep(pool(_)).
  896requeue_keep(peer(_)).
  897requeue_keep(protocol(_)).

 http_process(Message, Queue, +Options)

Handle a single client message on the given stream.

  904http_process(Goal, In, Out, Options) :-
  905    debug(http(server), 'Running server goal ~p on ~p -> ~p',
  906          [Goal, In, Out]),
  907    option(timeout(TMO), Options, 60),
  908    set_stream(In, timeout(TMO)),
  909    set_stream(Out, timeout(TMO)),
  910    http_wrapper(Goal, In, Out, Connection,
  911                 [ request(Request)
  912                 | Options
  913                 ]),
  914    next(Connection, Request).
  915
  916next(Connection, Request) :-
  917    next_(Connection, Request), !.
  918next(Connection, Request) :-
  919    print_message(warning, goal_failed(next(Connection,Request))).
  920
  921next_(switch_protocol(SwitchGoal, _SwitchOptions), Request) :-
  922    !,
  923    memberchk(pool(client(_Queue, _Goal, In, Out)), Request),
  924    (   catch(call(SwitchGoal, In, Out), E,
  925              (   print_message(error, E),
  926                  fail))
  927    ->  true
  928    ;   http_close_connection(Request)
  929    ).
  930next_(spawned(ThreadId), _) :-
  931    !,
  932    debug(http(spawn), 'Handler spawned to thread ~w', [ThreadId]).
  933next_(Connection, Request) :-
  934    downcase_atom(Connection, 'keep-alive'),
  935    http_requeue(Request),
  936    !.
  937next_(_, Request) :-
  938    http_close_connection(Request).

 http_close_connection(+Request)

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

  945http_close_connection(Request) :-
  946    memberchk(pool(client(_Queue, _Goal, In, Out)), Request),
  947    memberchk(peer(Peer), Request),
  948    close_connection(Peer, In, Out).

 close_connection(+Peer, +In, +Out)

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

  955close_connection(Peer, In, Out) :-
  956    debug(http(connection), 'Closing connection from ~p', [Peer]),
  957    catch(close(In, [force(true)]), _, true),
  958    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.

  976http_spawn(Goal, Options) :-
  977    select_option(pool(Pool), Options, ThreadOptions),
  978    !,
  979    current_output(CGI),
  980    catch(thread_create_in_pool(Pool,
  981                                wrap_spawned(CGI, Goal), Id,
  982                                [ detached(true)
  983                                | ThreadOptions
  984                                ]),
  985          Error,
  986          true),
  987    (   var(Error)
  988    ->  http_spawned(Id)
  989    ;   Error = error(resource_error(threads_in_pool(_)), _)
  990    ->  throw(http_reply(busy))
  991    ;   Error = error(existence_error(thread_pool, Pool), _),
  992        create_pool(Pool)
  993    ->  http_spawn(Goal, Options)
  994    ;   throw(Error)
  995    ).
  996http_spawn(Goal, Options) :-
  997    current_output(CGI),
  998    thread_create(wrap_spawned(CGI, Goal), Id,
  999                  [ detached(true)
 1000                  | Options
 1001                  ]),
 1002    http_spawned(Id).
 1003
 1004wrap_spawned(CGI, Goal) :-
 1005    set_output(CGI),
 1006    http_wrap_spawned(Goal, Request, Connection),
 1007    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.

 1017create_pool(Pool) :-
 1018    E = error(permission_error(create, thread_pool, Pool), _),
 1019    catch(http:create_pool(Pool), E, true).
 1020create_pool(Pool) :-
 1021    print_message(informational, httpd(created_pool(Pool))),
 1022    thread_pool_create(Pool, 10, []).
 1023
 1024
 1025		 /*******************************
 1026		 *         WAIT POLICIES	*
 1027		 *******************************/
 1028
 1029:- meta_predicate
 1030    thread_repeat_wait(0).

 thread_repeat_wait(:Goal) is multi

Acts as repeat, thread_idle(Goal), choosing whether to use a long or short idle time based on the average firing rate.

 1037thread_repeat_wait(Goal) :-
 1038    new_rate_mma(5, 1000, State),
 1039    repeat,
 1040      update_rate_mma(State, MMA),
 1041      long(MMA, IsLong),
 1042      (   IsLong == brief
 1043      ->  call(Goal)
 1044      ;   thread_idle(Goal, IsLong)
 1045      ).
 1046
 1047long(MMA, brief) :-
 1048    MMA < 0.05,
 1049    !.
 1050long(MMA, short) :-
 1051    MMA < 1,
 1052    !.
 1053long(_, long).

 new_rate_mma(+N, +Resolution, -State) is det

 update_rate_mma(!State, -MMA) is det

Implement Modified Moving Average computing the average time between requests as an exponential moving averate with alpha=1/N.

Arguments:

Resolution

- is the time resolution in 1/Resolution seconds. All storage is done in integers to avoid the need for stack freezing in nb_setarg/3.

See also

- https://en.wikipedia.org/wiki/Moving_average

 1067new_rate_mma(N, Resolution, rstate(Base, 0, MaxI, Resolution, N, 0)) :-
 1068    current_prolog_flag(max_tagged_integer, MaxI),
 1069    get_time(Base).
 1070
 1071update_rate_mma(State, MMAr) :-
 1072    State = rstate(Base, Last, MaxI, Resolution, N, MMA0),
 1073    get_time(Now),
 1074    Stamp is round((Now-Base)*Resolution),
 1075    (   Stamp > MaxI
 1076    ->  nb_setarg(1, State, Now),
 1077        nb_setarg(2, State, 0)
 1078    ;   true
 1079    ),
 1080    Diff is Stamp-Last,
 1081    nb_setarg(2, State, Stamp),
 1082    MMA is round(((N-1)*MMA0+Diff)/N),
 1083    nb_setarg(6, State, MMA),
 1084    MMAr is MMA/float(Resolution).
 1085
 1086
 1087                 /*******************************
 1088                 *            MESSAGES          *
 1089                 *******************************/
 1090
 1091:- multifile
 1092    prolog:message/3. 1093
 1094prolog:message(httpd_started_server(Port, Options)) -->
 1095    [ 'Started server at '-[] ],
 1096    http_root(Port, Options).
 1097prolog:message(httpd_stopped_worker(Self, Status)) -->
 1098    [ 'Stopped worker ~p: ~p'-[Self, Status] ].
 1099prolog:message(httpd_restarted_worker(Self)) -->
 1100    [ 'Replaced aborted worker ~p'-[Self] ].
 1101prolog:message(httpd(created_pool(Pool))) -->
 1102    [ 'Created thread-pool ~p of size 10'-[Pool], nl,
 1103      'Create this pool at startup-time or define the hook ', nl,
 1104      'http:create_pool/1 to avoid this message and create a ', nl,
 1105      'pool that fits the usage-profile.'
 1106    ].
 1107
 1108http_root(Address, Options) -->
 1109    { landing_page(Address, URI, Options) },
 1110    [ '~w'-[URI] ].
 1111
 1112landing_page(Host:Port, URI, Options) :-
 1113    !,
 1114    must_be(atom, Host),
 1115    must_be(integer, Port),
 1116    http_server_property(Port, scheme(Scheme)),
 1117    (   default_port(Scheme, Port)
 1118    ->  format(atom(Base), '~w://~w', [Scheme, Host])
 1119    ;   format(atom(Base), '~w://~w:~w', [Scheme, Host, Port])
 1120    ),
 1121    entry_page(Base, URI, Options).
 1122landing_page(unix_socket(Path), URI, _Options) :-
 1123    !,
 1124    format(string(URI), 'Unix domain socket "~w"', [Path]).
 1125landing_page(Port, URI, Options) :-
 1126    landing_page(localhost:Port, URI, Options).
 1127
 1128default_port(http, 80).
 1129default_port(https, 443).
 1130
 1131entry_page(Base, URI, Options) :-
 1132    option(entry_page(Entry), Options),
 1133    !,
 1134    uri_resolve(Entry, Base, URI).
 1135entry_page(Base, URI, _) :-
 1136    http_absolute_location(root(.), Entry, []),
 1137    uri_resolve(Entry, Base, URI)