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.
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   17       notice, this list of conditions and the following disclaimer.
   18
   19    2. Redistributions in binary form must reproduce the above copyright
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   22       distribution.
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   25    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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   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:- use_module(http_stream).   61
   62:- autoload(library(uri), [uri_resolve/3]).   63:- autoload(library(aggregate), [aggregate_all/3]).   64
   65:- predicate_options(http_server/2, 2,
   66                     [ port(any),
   67                       unix_socket(atom),
   68                       entry_page(atom),
   69                       tcp_socket(any),
   70                       workers(positive_integer),
   71                       timeout(number),
   72                       keep_alive_timeout(number),
   73                       silent(boolean),
   74                       ssl(list(any)),  % if http/http_ssl_plugin is loaded
   75                       pass_to(system:thread_create/3, 3)
   76                     ]).   77:- predicate_options(http_spawn/2, 2,
   78                     [ pool(atom),
   79                       pass_to(system:thread_create/3, 3),
   80                       pass_to(thread_pool:thread_create_in_pool/4, 4)
   81                     ]).   82:- predicate_options(http_add_worker/2, 2,
   83                     [ timeout(number),
   84                       keep_alive_timeout(number),
   85                       max_idle_time(number),
   86                       pass_to(system:thread_create/3, 3)
   87                     ]).

  115:- meta_predicate
  116    http_server(1, :),
  117    http_current_server(1, ?),
  118    http_spawn(0, +).  119
  120:- dynamic
  121    current_server/6,       % Port, Goal, Thread, Queue, Scheme, StartTime
  122    queue_worker/2,         % Queue, ThreadID
  123    queue_options/2.        % Queue, Options
  124
  125:- multifile
  126    make_socket_hook/3,
  127    accept_hook/2,
  128    close_hook/1,
  129    open_client_hook/6,
  130    discard_client_hook/1,
  131    http:create_pool/1,
  132    http:schedule_workers/1.  133
  134:- meta_predicate
  135    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. Note that this also allows binding an HTTP server to a Unix domain socket (AF_UNIX). See socket_create/2.

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.

  201http_server(Goal, M:Options0) :-
  202    server_address(Address, Options0),
  203    !,
  204    make_socket(Address, M:Options0, Options),
  205    create_workers(Options),
  206    create_server(Goal, Address, Options),
  207    (   option(silent(true), Options0)
  208    ->  true
  209    ;   print_message(informational,
  210                      httpd_started_server(Address, Options0))
  211    ).
  212http_server(_Goal, _:Options0) :-
  213    existence_error(server_address, Options0).
  214
  215server_address(Address, Options) :-
  216    (   option(port(Port), Options)
  217    ->  Address = Port
  218    ;   option(unix_socket(Path), Options)
  219    ->  Address = unix_socket(Path)
  220    ).
  221
  222address_port(_IFace:Port, Port) :- !.
  223address_port(unix_socket(Path), Path) :- !.
  224address_port(Address, Address) :- !.
  225
  226tcp_address(Port) :-
  227    var(Port),
  228    !.
  229tcp_address(Port) :-
  230    integer(Port),
  231    !.
  232tcp_address(_Iface:_Port).
  233
  234address_domain(localhost:_Port, Domain) =>
  235    Domain = inet.
  236address_domain(Iface:_Port, Domain) =>
  237    (   catch(ip_name(IP, Iface), error(_,_), fail),
  238        functor(IP, ip, 8)
  239    ->  Domain = inet6
  240    ;   Domain = inet
  241    ).
  242address_domain(_, Domain) =>
  243    Domain = inet.

 make_socket(+Address, :OptionsIn, -OptionsOut) is det

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

Arguments:

OptionsIn

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

  254make_socket(Address, M:Options0, Options) :-
  255    tcp_address(Address),
  256    make_socket_hook(Address, M:Options0, Options),
  257    !.
  258make_socket(Address, _:Options0, Options) :-
  259    option(tcp_socket(_), Options0),
  260    !,
  261    make_addr_atom('httpd', Address, Queue),
  262    Options = [ queue(Queue)
  263              | Options0
  264              ].
  265make_socket(Address, _:Options0, Options) :-
  266    tcp_address(Address),
  267    !,
  268    address_domain(Address, Domain),
  269    socket_create(Socket, [domain(Domain)]),
  270    tcp_setopt(Socket, reuseaddr),
  271    tcp_bind(Socket, Address),
  272    tcp_listen(Socket, 64),
  273    make_addr_atom('httpd', Address, Queue),
  274    Options = [ queue(Queue),
  275                tcp_socket(Socket)
  276              | Options0
  277              ].
  278:- if(current_predicate(unix_domain_socket/1)).  279make_socket(Address, _:Options0, Options) :-
  280    Address = unix_socket(Path),
  281    !,
  282    unix_domain_socket(Socket),
  283    tcp_bind(Socket, Path),
  284    tcp_listen(Socket, 64),
  285    make_addr_atom('httpd', Address, Queue),
  286    Options = [ queue(Queue),
  287                tcp_socket(Socket)
  288              | Options0
  289              ].
  290:- endif.

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

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

  297make_addr_atom(Scheme, Address, Atom) :-
  298    phrase(address_parts(Address), Parts),
  299    atomic_list_concat([Scheme,@|Parts], Atom).
  300
  301address_parts(Var) -->
  302    { var(Var),
  303      !,
  304      instantiation_error(Var)
  305    }.
  306address_parts(Atomic) -->
  307    { atomic(Atomic) },
  308    !,
  309    [Atomic].
  310address_parts(Host:Port) -->
  311    !,
  312    address_parts(Host), [:], address_parts(Port).
  313address_parts(ip(A,B,C,D)) -->
  314    !,
  315    [ A, '.', B, '.', C, '.', D ].
  316address_parts(unix_socket(Path)) -->
  317    [Path].
  318address_parts(Address) -->
  319    { 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.

  327create_server(Goal, Address, Options) :-
  328    get_time(StartTime),
  329    memberchk(queue(Queue), Options),
  330    scheme(Scheme, Options),
  331    autoload_https(Scheme),
  332    address_port(Address, Port),
  333    make_addr_atom(Scheme, Port, Alias),
  334    thread_self(Initiator),
  335    thread_create(accept_server(Goal, Initiator, Options), _,
  336                  [ alias(Alias)
  337                  ]),
  338    thread_get_message(server_started),
  339    assert(current_server(Port, Goal, Alias, Queue, Scheme, StartTime)).
  340
  341scheme(Scheme, Options) :-
  342    option(scheme(Scheme), Options),
  343    !.
  344scheme(Scheme, Options) :-
  345    (   option(ssl(_), Options)
  346    ;   option(ssl_instance(_), Options)
  347    ),
  348    !,
  349    Scheme = https.
  350scheme(http, _).
  351
  352autoload_https(https) :-
  353    \+ clause(accept_hook(_Goal, _Options), _),
  354    exists_source(library(http/http_ssl_plugin)),
  355    !,
  356    use_module(library(http/http_ssl_plugin)).
  357autoload_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))

  365http_current_server(Goal, Port) :-
  366    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.

  382http_server_property(_:Port, Property) :-
  383    integer(Port),
  384    !,
  385    server_property(Property, Port).
  386http_server_property(Port, Property) :-
  387    server_property(Property, Port).
  388
  389server_property(goal(Goal), Port) :-
  390    current_server(Port, Goal, _, _, _, _).
  391server_property(scheme(Scheme), Port) :-
  392    current_server(Port, _, _, _, Scheme, _).
  393server_property(start_time(Time), Port) :-
  394    current_server(Port, _, _, _, _, Time).

 http_workers(?Port, -Workers) is nondet

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.

See also

- library(http/http_dyn_workers) implements dynamic management of the worker pool depending on usage.

  407http_workers(Port, Workers) :-
  408    integer(Workers),
  409    !,
  410    must_be(ground, Port),
  411    (   current_server(Port, _, _, Queue, _, _)
  412    ->  resize_pool(Queue, Workers)
  413    ;   existence_error(http_server, Port)
  414    ).
  415http_workers(Port, Workers) :-
  416    current_server(Port, _, _, Queue, _, _),
  417    aggregate_all(count, queue_worker(Queue, _Worker), Workers).

 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.

  430http_add_worker(Port, Options) :-
  431    must_be(ground, Port),
  432    current_server(Port, _, _, Queue, _, _),
  433    !,
  434    queue_options(Queue, QueueOptions),
  435    merge_options(Options, QueueOptions, WorkerOptions),
  436    atom_concat(Queue, '_', AliasBase),
  437    create_workers(1, 1, Queue, AliasBase, WorkerOptions).
  438http_add_worker(Port, _) :-
  439    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.

  449http_current_worker(Port, ThreadID) :-
  450    current_server(Port, _, _, Queue, _, _),
  451    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.

  459accept_server(Goal, Initiator, Options) :-
  460    Ex = http_stop(Stopper),
  461    catch(accept_server2(Goal, Initiator, Options), Ex, true),
  462    thread_self(Thread),
  463    debug(http(stop), '[~p]: accept server received ~p', [Thread, Ex]),
  464    retract(current_server(_Port, _, Thread, Queue, _Scheme, _StartTime)),
  465    close_pending_accepts(Queue),
  466    close_server_socket(Options),
  467    thread_send_message(Stopper, http_stopped).
  468
  469accept_server2(Goal, Initiator, Options) :-
  470    thread_send_message(Initiator, server_started),
  471    repeat,
  472      (   catch(accept_server3(Goal, Options), E, true)
  473      ->  (   var(E)
  474          ->  fail
  475          ;   accept_rethrow_error(E)
  476          ->  throw(E)
  477          ;   print_message(error, E),
  478              fail
  479          )
  480      ;   print_message(error,      % internal error
  481                        goal_failed(accept_server3(Goal, Options))),
  482          fail
  483      ).
  484
  485accept_server3(Goal, Options) :-
  486    accept_hook(Goal, Options),
  487    !.
  488accept_server3(Goal, Options) :-
  489    memberchk(tcp_socket(Socket), Options),
  490    memberchk(queue(Queue), Options),
  491    debug(http(connection), 'Waiting for connection', []),
  492    tcp_accept(Socket, Client, Peer),
  493    sig_atomic(send_to_worker(Queue, Client, Goal, Peer)),
  494    http_enough_workers(Queue, accept, Peer).
  495
  496send_to_worker(Queue, Client, Goal, Peer) :-
  497    debug(http(connection), 'New HTTP connection from ~p', [Peer]),
  498    thread_send_message(Queue, tcp_client(Client, Goal, Peer)).
  499
  500accept_rethrow_error(http_stop(_)).

 close_server_socket(+Options)

Close the server socket.

  506close_server_socket(Options) :-
  507    close_hook(Options),
  508    !.
  509close_server_socket(Options) :-
  510    memberchk(tcp_socket(Socket), Options),
  511    !,
  512    tcp_close_socket(Socket).

 close_pending_accepts(+Queue)

  516close_pending_accepts(Queue) :-
  517    (   thread_get_message(Queue, Msg, [timeout(0)])
  518    ->  close_client(Msg),
  519        close_pending_accepts(Queue)
  520    ;   true
  521    ).
  522
  523close_client(tcp_client(Client, _Goal, _0Peer)) =>
  524    debug(http(stop), 'Closing connection from ~p during shut-down', [_0Peer]),
  525    tcp_close_socket(Client).
  526close_client(Msg) =>
  527    (   discard_client_hook(Msg)
  528    ->  true
  529    ;   print_message(warning, http_close_client(Msg))
  530    ).

 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

  540http_stop_server(Host:Port, Options) :-         % e.g., localhost:4000
  541    ground(Host),
  542    !,
  543    http_stop_server(Port, Options).
  544http_stop_server(Port, _Options) :-
  545    http_workers(Port, 0),                  % checks Port is ground
  546    current_server(Port, _, Thread, Queue, _Scheme, _Start),
  547    retractall(queue_options(Queue, _)),
  548    debug(http(stop), 'Signalling HTTP server thread ~p to stop', [Thread]),
  549    thread_self(Stopper),
  550    thread_signal(Thread, throw(http_stop(Stopper))),
  551    (   thread_get_message(Stopper, http_stopped, [timeout(0.1)])
  552    ->  true
  553    ;   catch(connect(localhost:Port), _, true)
  554    ),
  555    thread_join(Thread, _0Status),
  556    debug(http(stop), 'Joined HTTP server thread ~p (~p)', [Thread, _0Status]),
  557    message_queue_destroy(Queue).
  558
  559connect(Address) :-
  560    setup_call_cleanup(
  561        tcp_socket(Socket),
  562        tcp_connect(Socket, Address),
  563        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.

  571http_enough_workers(Queue, _Why, _Peer) :-
  572    message_queue_property(Queue, waiting(_0)),
  573    !,
  574    debug(http(scheduler), '~D waiting for work; ok', [_0]).
  575http_enough_workers(Queue, Why, Peer) :-
  576    message_queue_property(Queue, size(Size)),
  577    (   enough(Size, Why)
  578    ->  debug(http(scheduler), '~D in queue; ok', [Size])
  579    ;   current_server(Port, _, _, Queue, _, _),
  580        Data = _{ port:Port,
  581                  reason:Why,
  582                  peer:Peer,
  583                  waiting:Size,
  584                  queue:Queue
  585                },
  586        debug(http(scheduler), 'Asking to reschedule: ~p', [Data]),
  587        catch(http:schedule_workers(Data),
  588              Error,
  589              print_message(error, Error))
  590    ->  true
  591    ;   true
  592    ).
  593
  594enough(0, _).
  595enough(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.

  625                 /*******************************
  626                 *    WORKER QUEUE OPERATIONS   *
  627                 *******************************/

 create_workers(+Options)

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

  634create_workers(Options) :-
  635    option(workers(N), Options, 5),
  636    option(queue(Queue), Options),
  637    catch(message_queue_create(Queue), _, true),
  638    atom_concat(Queue, '_', AliasBase),
  639    create_workers(1, N, Queue, AliasBase, Options),
  640    assert(queue_options(Queue, Options)).
  641
  642create_workers(I, N, _, _, _) :-
  643    I > N,
  644    !.
  645create_workers(I, N, Queue, AliasBase, Options) :-
  646    gensym(AliasBase, Alias),
  647    thread_create(http_worker(Options), Id,
  648                  [ alias(Alias)
  649                  | Options
  650                  ]),
  651    assertz(queue_worker(Queue, Id)),
  652    I2 is I + 1,
  653    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.

  661resize_pool(Queue, Size) :-
  662    findall(W, queue_worker(Queue, W), Workers),
  663    length(Workers, Now),
  664    (   Now < Size
  665    ->  queue_options(Queue, Options),
  666        atom_concat(Queue, '_', AliasBase),
  667        I0 is Now+1,
  668        create_workers(I0, Size, Queue, AliasBase, Options)
  669    ;   Now == Size
  670    ->  true
  671    ;   Now > Size
  672    ->  Excess is Now - Size,
  673        thread_self(Me),
  674        forall(between(1, Excess, _), thread_send_message(Queue, quit(Me))),
  675        forall(between(1, Excess, _), thread_get_message(quitted(_)))
  676    ).

 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.

  687http_worker(Options) :-
  688    debug(http(scheduler), 'New worker', []),
  689    prolog_listen(this_thread_exit, done_worker),
  690    option(queue(Queue), Options),
  691    option(max_idle_time(MaxIdle), Options, infinite),
  692    thread_repeat_wait(get_work(Queue, Message, MaxIdle)),
  693      debug(http(worker), 'Waiting for a job ...', []),
  694      debug(http(worker), 'Got job ~p', [Message]),
  695      (   Message = quit(Sender)
  696      ->  !,
  697          thread_self(Self),
  698          thread_detach(Self),
  699          (   Sender == idle
  700          ->  true
  701          ;   retract(queue_worker(Queue, Self)),
  702              thread_send_message(Sender, quitted(Self))
  703          )
  704      ;   open_client(Message, Queue, Goal, In, Out,
  705                      Options, ClientOptions),
  706          (   catch(http_process(Goal, In, Out, ClientOptions),
  707                    Error, true)
  708          ->  true
  709          ;   Error = goal_failed(http_process/4)
  710          ),
  711          (   var(Error)
  712          ->  fail
  713          ;   current_message_level(Error, Level),
  714              print_message(Level, Error),
  715              memberchk(peer(Peer), ClientOptions),
  716              close_connection(Peer, In, Out),
  717              fail
  718          )
  719      ).
  720
  721get_work(Queue, Message, infinite) :-
  722    !,
  723    thread_get_message(Queue, Message).
  724get_work(Queue, Message, MaxIdle) :-
  725    (   thread_get_message(Queue, Message, [timeout(MaxIdle)])
  726    ->  true
  727    ;   Message = quit(idle)
  728    ).

 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.

  737open_client(requeue(In, Out, Goal, ClOpts),
  738            _, Goal, In, Out, Opts, ClOpts) :-
  739    !,
  740    memberchk(peer(Peer), ClOpts),
  741    option(keep_alive_timeout(KeepAliveTMO), Opts, 2),
  742    check_keep_alive_connection(In, KeepAliveTMO, Peer, In, Out).
  743open_client(Message, Queue, Goal, In, Out, Opts,
  744            [ pool(client(Queue, Goal, In, Out)),
  745              timeout(Timeout)
  746            | Options
  747            ]) :-
  748    catch(open_client(Message, Goal, In, Out, Options, Opts),
  749          E, report_error(E)),
  750    option(timeout(Timeout), Opts, 60),
  751    (   debugging(http(connection))
  752    ->  memberchk(peer(Peer), Options),
  753        debug(http(connection), 'Opened connection from ~p', [Peer])
  754    ;   true
  755    ).

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

  761open_client(Message, Goal, In, Out, ClientOptions, Options) :-
  762    open_client_hook(Message, Goal, In, Out, ClientOptions, Options),
  763    !.
  764open_client(tcp_client(Socket, Goal, Peer), Goal, In, Out,
  765            [ peer(Peer),
  766              protocol(http)
  767            ], _) :-
  768    tcp_open_socket(Socket, In, Out).
  769
  770report_error(E) :-
  771    print_message(error, E),
  772    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.

  781check_keep_alive_connection(In, TMO, Peer, In, Out) :-
  782    stream_property(In, timeout(Old)),
  783    set_stream(In, timeout(TMO)),
  784    debug(http(keep_alive), 'Waiting for keep-alive ...', []),
  785    catch(peek_code(In, Code), E, true),
  786    (   var(E),                     % no exception
  787        Code \== -1                 % no end-of-file
  788    ->  set_stream(In, timeout(Old)),
  789        debug(http(keep_alive), '\tre-using keep-alive connection', [])
  790    ;   (   Code == -1
  791        ->  debug(http(keep_alive), '\tRemote closed keep-alive connection', [])
  792        ;   debug(http(keep_alive), '\tTimeout on keep-alive connection', [])
  793        ),
  794        close_connection(Peer, In, Out),
  795        fail
  796    ).

 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.

  805done_worker :-
  806    thread_self(Self),
  807    thread_detach(Self),
  808    retract(queue_worker(Queue, Self)),
  809    thread_property(Self, status(Status)),
  810    !,
  811    (   catch(recreate_worker(Status, Queue), _, fail)
  812    ->  print_message(informational,
  813                      httpd_restarted_worker(Self))
  814    ;   done_status_message_level(Status, Level),
  815        print_message(Level,
  816                      httpd_stopped_worker(Self, Status))
  817    ).
  818done_worker :-                                  % received quit(Sender)
  819    thread_self(Self),
  820    thread_property(Self, status(Status)),
  821    done_status_message_level(Status, Level),
  822    print_message(Level,
  823                  httpd_stopped_worker(Self, Status)).
  824
  825done_status_message_level(true, silent) :- !.
  826done_status_message_level(exception('$aborted'), silent) :- !.
  827done_status_message_level(exception(unwind(abort)), silent) :- !.
  828done_status_message_level(exception(unwind(halt(_))), silent) :- !.
  829done_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?

  844recreate_worker(exception(error(io_error(write,user_error),_)), _Queue) :-
  845    halt(2).
  846recreate_worker(exception(Error), Queue) :-
  847    recreate_on_error(Error),
  848    queue_options(Queue, Options),
  849    atom_concat(Queue, '_', AliasBase),
  850    create_workers(1, 1, Queue, AliasBase, Options).
  851
  852recreate_on_error('$aborted').
  853recreate_on_error(unwind(abort)).
  854recreate_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.

  863:- multifile
  864    message_level/2.  865
  866message_level(error(io_error(read, _), _),               silent).
  867message_level(error(socket_error(epipe,_), _),           silent).
  868message_level(error(http_write_short(_Obj,_Written), _), silent).
  869message_level(error(timeout_error(read, _), _),          informational).
  870message_level(keep_alive_timeout,                        silent).
  871
  872current_message_level(Term, Level) :-
  873    (   message_level(Term, Level)
  874    ->  true
  875    ;   Level = error
  876    ).

 read_remaining_request(+StartBody, +Request) is semidet

If our handler did not read the complete request we must read the remainder if we are dealing with a Keep-alive connection.

  883read_remaining_request(StartBody, Request) :-
  884    memberchk(content_length(Len), Request),
  885    !,
  886    memberchk(pool(client(_Queue, _Goal, In, _Out)), Request),
  887    byte_count(In, Here),
  888    Left is StartBody+Len-Here,
  889    read_incomplete(In, Left).
  890read_remaining_request(_, _Request).
  891
  892read_incomplete(_, 0) :-
  893    !.
  894read_incomplete(In, Left) :-
  895    % Left < 1 000 000,			% Optionally close anyway.
  896    catch(setup_call_cleanup(
  897              open_null_stream(Null),
  898              copy_stream_data(In, Null, Left),
  899              close(Null)),
  900          error(_,_),
  901          fail).

 http_requeue(+Header)

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

  908http_requeue(Header) :-
  909    requeue_header(Header, ClientOptions),
  910    memberchk(pool(client(Queue, Goal, In, Out)), ClientOptions),
  911    memberchk(peer(Peer), ClientOptions),
  912    http_enough_workers(Queue, keep_alive, Peer),
  913    thread_send_message(Queue, requeue(In, Out, Goal, ClientOptions)),
  914    !.
  915http_requeue(Header) :-
  916    debug(http(error), 'Re-queue failed: ~p', [Header]),
  917    fail.
  918
  919requeue_header([], []).
  920requeue_header([H|T0], [H|T]) :-
  921    requeue_keep(H),
  922    !,
  923    requeue_header(T0, T).
  924requeue_header([_|T0], T) :-
  925    requeue_header(T0, T).
  926
  927requeue_keep(pool(_)).
  928requeue_keep(peer(_)).
  929requeue_keep(protocol(_)).

 http_process(Message, Queue, +Options)

Handle a single client message on the given stream.

  936http_process(Goal, In, Out, Options) :-
  937    debug(http(server), 'Running server goal ~p on ~p -> ~p',
  938          [Goal, In, Out]),
  939    option(timeout(TMO), Options, 60),
  940    set_stream(In, timeout(TMO)),
  941    set_stream(Out, timeout(TMO)),
  942    http_wrapper(Goal, In, Out, Connection,
  943                 [ request(Request),
  944                   byte_count(StartBody)
  945                 | Options
  946                 ]),
  947    next(Connection, StartBody, Request).
  948
  949next(Connection, StartBody, Request) :-
  950    next_(Connection, StartBody, Request), !.
  951next(Connection, StartBody, Request) :-
  952    print_message(warning, goal_failed(next(Connection,StartBody,Request))).
  953
  954next_(switch_protocol(SwitchGoal, _SwitchOptions), _, Request) :-
  955    !,
  956    memberchk(pool(client(_Queue, _Goal, In, Out)), Request),
  957    (   catch(call(SwitchGoal, In, Out), E,
  958              (   print_message(error, E),
  959                  fail))
  960    ->  true
  961    ;   http_close_connection(Request)
  962    ).
  963next_(spawned(ThreadId), _, _) :-
  964    !,
  965    debug(http(spawn), 'Handler spawned to thread ~w', [ThreadId]).
  966next_(Connection, StartBody, Request) :-
  967    downcase_atom(Connection, 'keep-alive'),
  968    read_remaining_request(StartBody, Request),
  969    http_requeue(Request),
  970    !.
  971next_(_, _, Request) :-
  972    http_close_connection(Request).

 http_close_connection(+Request)

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

  979http_close_connection(Request) :-
  980    memberchk(pool(client(_Queue, _Goal, In, Out)), Request),
  981    memberchk(peer(Peer), Request),
  982    close_connection(Peer, In, Out).

 close_connection(+Peer, +In, +Out)

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

  989close_connection(Peer, In, Out) :-
  990    debug(http(connection), 'Closing connection from ~p', [Peer]),
  991    catch(close(In, [force(true)]), _, true),
  992    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.

 1010http_spawn(Goal, Options) :-
 1011    select_option(pool(Pool), Options, ThreadOptions),
 1012    !,
 1013    current_output(CGI),
 1014    Error = error(Formal, _),
 1015    catch(thread_create_in_pool(Pool,
 1016                                wrap_spawned(CGI, Goal), Id,
 1017                                [ detached(true)
 1018                                | ThreadOptions
 1019                                ]),
 1020          Error,
 1021          true),
 1022    (   var(Formal)
 1023    ->  http_spawned(Id)
 1024    ;   Formal = resource_error(threads_in_pool(_))
 1025    ->  throw(http_reply(busy))
 1026    ;   Formal = existence_error(thread_pool, Pool),
 1027        create_pool(Pool)
 1028    ->  http_spawn(Goal, Options)
 1029    ;   throw(Error)
 1030    ).
 1031http_spawn(Goal, Options) :-
 1032    current_output(CGI),
 1033    thread_create(wrap_spawned(CGI, Goal), Id,
 1034                  [ detached(true)
 1035                  | Options
 1036                  ]),
 1037    http_spawned(Id).
 1038
 1039wrap_spawned(CGI, Goal) :-
 1040    set_output(CGI),
 1041    cgi_property(CGI, request(Request)),
 1042    memberchk(input(Input), Request),
 1043    byte_count(Input, StartBody),
 1044    http_wrap_spawned(Goal, Request, Connection),
 1045    next(Connection, StartBody, 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.

 1055create_pool(Pool) :-
 1056    E = error(permission_error(create, thread_pool, Pool), _),
 1057    catch(http:create_pool(Pool), E, true).
 1058create_pool(Pool) :-
 1059    print_message(informational, httpd(created_pool(Pool))),
 1060    thread_pool_create(Pool, 10, []).
 1061
 1062
 1063		 /*******************************
 1064		 *         WAIT POLICIES	*
 1065		 *******************************/
 1066
 1067:- meta_predicate
 1068    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.

 1075thread_repeat_wait(Goal) :-
 1076    new_rate_mma(5, 1000, State),
 1077    repeat,
 1078      notrace,
 1079      update_rate_mma(State, MMA),
 1080      long(MMA, IsLong),
 1081      (   IsLong == brief
 1082      ->  call(Goal)
 1083      ;   thread_idle(Goal, IsLong)
 1084      ).
 1085
 1086long(MMA, brief) :-
 1087    MMA < 0.05,
 1088    !.
 1089long(MMA, short) :-
 1090    MMA < 1,
 1091    !.
 1092long(_, 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 average 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

 1106new_rate_mma(N, Resolution, rstate(Base, 0, MaxI, Resolution, N, 0)) :-
 1107    current_prolog_flag(max_tagged_integer, MaxI),
 1108    get_time(Base).
 1109
 1110update_rate_mma(State, MMAr) :-
 1111    State = rstate(Base, Last, MaxI, Resolution, N, MMA0),
 1112    get_time(Now),
 1113    Stamp is round((Now-Base)*Resolution),
 1114    (   Stamp > MaxI
 1115    ->  nb_setarg(1, State, Now),
 1116        nb_setarg(2, State, 0)
 1117    ;   true
 1118    ),
 1119    Diff is Stamp-Last,
 1120    nb_setarg(2, State, Stamp),
 1121    MMA is round(((N-1)*MMA0+Diff)/N),
 1122    nb_setarg(6, State, MMA),
 1123    MMAr is MMA/float(Resolution).
 1124
 1125
 1126                 /*******************************
 1127                 *            MESSAGES          *
 1128                 *******************************/
 1129
 1130:- multifile
 1131    prolog:message/3. 1132
 1133prolog:message(httpd_started_server(Port, Options)) -->
 1134    [ 'Started server at '-[] ],
 1135    http_root(Port, Options).
 1136prolog:message(httpd_stopped_worker(Self, Status)) -->
 1137    [ 'Stopped worker ~p: ~p'-[Self, Status] ].
 1138prolog:message(httpd_restarted_worker(Self)) -->
 1139    [ 'Replaced aborted worker ~p'-[Self] ].
 1140prolog:message(httpd(created_pool(Pool))) -->
 1141    [ 'Created thread-pool ~p of size 10'-[Pool], nl,
 1142      'Create this pool at startup-time or define the hook ', nl,
 1143      'http:create_pool/1 to avoid this message and create a ', nl,
 1144      'pool that fits the usage-profile.'
 1145    ].
 1146
 1147http_root(Address, Options) -->
 1148    { landing_page(Address, URI, Options) },
 1149    [ url(URI) ].
 1150
 1151landing_page(Host:Port, URI, Options) :-
 1152    !,
 1153    must_be(atom, Host),
 1154    must_be(integer, Port),
 1155    http_server_property(Port, scheme(Scheme)),
 1156    (   default_port(Scheme, Port)
 1157    ->  format(atom(Base), '~w://~w', [Scheme, Host])
 1158    ;   format(atom(Base), '~w://~w:~w', [Scheme, Host, Port])
 1159    ),
 1160    entry_page(Base, URI, Options).
 1161landing_page(unix_socket(Path), URI, _Options) :-
 1162    !,
 1163    format(string(URI), 'Unix domain socket "~w"', [Path]).
 1164landing_page(Port, URI, Options) :-
 1165    landing_page(localhost:Port, URI, Options).
 1166
 1167default_port(http, 80).
 1168default_port(https, 443).
 1169
 1170entry_page(Base, URI, Options) :-
 1171    option(entry_page(Entry), Options),
 1172    !,
 1173    uri_resolve(Entry, Base, URI).
 1174entry_page(Base, URI, _) :-
 1175    http_absolute_location(root(.), Entry, []),
 1176    uri_resolve(Entry, Base, URI)