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).

 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.

  238make_socket(Address, M:Options0, Options) :-
  239    tcp_address(Address),
  240    make_socket_hook(Address, M:Options0, Options),
  241    !.
  242make_socket(Address, _:Options0, Options) :-
  243    option(tcp_socket(_), Options0),
  244    !,
  245    make_addr_atom('httpd', Address, Queue),
  246    Options = [ queue(Queue)
  247              | Options0
  248              ].
  249make_socket(Address, _:Options0, Options) :-
  250    tcp_address(Address),
  251    !,
  252    tcp_socket(Socket),
  253    tcp_setopt(Socket, reuseaddr),
  254    tcp_bind(Socket, Address),
  255    tcp_listen(Socket, 64),
  256    make_addr_atom('httpd', Address, Queue),
  257    Options = [ queue(Queue),
  258                tcp_socket(Socket)
  259              | Options0
  260              ].
  261:- if(current_predicate(unix_domain_socket/1)).  262make_socket(Address, _:Options0, Options) :-
  263    Address = unix_socket(Path),
  264    !,
  265    unix_domain_socket(Socket),
  266    tcp_bind(Socket, Path),
  267    tcp_listen(Socket, 64),
  268    make_addr_atom('httpd', Address, Queue),
  269    Options = [ queue(Queue),
  270                tcp_socket(Socket)
  271              | Options0
  272              ].
  273:- endif.

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

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

  280make_addr_atom(Scheme, Address, Atom) :-
  281    phrase(address_parts(Address), Parts),
  282    atomic_list_concat([Scheme,@|Parts], Atom).
  283
  284address_parts(Var) -->
  285    { var(Var),
  286      !,
  287      instantiation_error(Var)
  288    }.
  289address_parts(Atomic) -->
  290    { atomic(Atomic) },
  291    !,
  292    [Atomic].
  293address_parts(Host:Port) -->
  294    !,
  295    address_parts(Host), [:], address_parts(Port).
  296address_parts(ip(A,B,C,D)) -->
  297    !,
  298    [ A, '.', B, '.', C, '.', D ].
  299address_parts(unix_socket(Path)) -->
  300    [Path].
  301address_parts(Address) -->
  302    { 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.

  310create_server(Goal, Address, Options) :-
  311    get_time(StartTime),
  312    memberchk(queue(Queue), Options),
  313    scheme(Scheme, Options),
  314    autoload_https(Scheme),
  315    address_port(Address, Port),
  316    make_addr_atom(Scheme, Port, Alias),
  317    thread_self(Initiator),
  318    thread_create(accept_server(Goal, Initiator, Options), _,
  319                  [ alias(Alias)
  320                  ]),
  321    thread_get_message(server_started),
  322    assert(current_server(Port, Goal, Alias, Queue, Scheme, StartTime)).
  323
  324scheme(Scheme, Options) :-
  325    option(scheme(Scheme), Options),
  326    !.
  327scheme(Scheme, Options) :-
  328    (   option(ssl(_), Options)
  329    ;   option(ssl_instance(_), Options)
  330    ),
  331    !,
  332    Scheme = https.
  333scheme(http, _).
  334
  335autoload_https(https) :-
  336    \+ clause(accept_hook(_Goal, _Options), _),
  337    exists_source(library(http/http_ssl_plugin)),
  338    !,
  339    use_module(library(http/http_ssl_plugin)).
  340autoload_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))

  348http_current_server(Goal, Port) :-
  349    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.

  365http_server_property(_:Port, Property) :-
  366    integer(Port),
  367    !,
  368    server_property(Property, Port).
  369http_server_property(Port, Property) :-
  370    server_property(Property, Port).
  371
  372server_property(goal(Goal), Port) :-
  373    current_server(Port, Goal, _, _, _, _).
  374server_property(scheme(Scheme), Port) :-
  375    current_server(Port, _, _, _, Scheme, _).
  376server_property(start_time(Time), Port) :-
  377    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.

  387http_workers(Port, Workers) :-
  388    must_be(ground, Port),
  389    current_server(Port, _, _, Queue, _, _),
  390    !,
  391    (   integer(Workers)
  392    ->  resize_pool(Queue, Workers)
  393    ;   findall(W, queue_worker(Queue, W), WorkerIDs),
  394        length(WorkerIDs, Workers)
  395    ).
  396http_workers(Port, _) :-
  397    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.

  410http_add_worker(Port, Options) :-
  411    must_be(ground, Port),
  412    current_server(Port, _, _, Queue, _, _),
  413    !,
  414    queue_options(Queue, QueueOptions),
  415    merge_options(Options, QueueOptions, WorkerOptions),
  416    atom_concat(Queue, '_', AliasBase),
  417    create_workers(1, 1, Queue, AliasBase, WorkerOptions).
  418http_add_worker(Port, _) :-
  419    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.

  429http_current_worker(Port, ThreadID) :-
  430    current_server(Port, _, _, Queue, _, _),
  431    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.

  439accept_server(Goal, Initiator, Options) :-
  440    catch(accept_server2(Goal, Initiator, Options), http_stop, true),
  441    thread_self(Thread),
  442    debug(http(stop), '[~p]: accept server received http_stop', [Thread]),
  443    retract(current_server(_Port, _, Thread, Queue, _Scheme, _StartTime)),
  444    close_pending_accepts(Queue),
  445    close_server_socket(Options).
  446
  447accept_server2(Goal, Initiator, Options) :-
  448    thread_send_message(Initiator, server_started),
  449    repeat,
  450      (   catch(accept_server3(Goal, Options), E, true)
  451      ->  (   var(E)
  452          ->  fail
  453          ;   accept_rethrow_error(E)
  454          ->  throw(E)
  455          ;   print_message(error, E),
  456              fail
  457          )
  458      ;   print_message(error,      % internal error
  459                        goal_failed(accept_server3(Goal, Options))),
  460          fail
  461      ).
  462
  463accept_server3(Goal, Options) :-
  464    accept_hook(Goal, Options),
  465    !.
  466accept_server3(Goal, Options) :-
  467    memberchk(tcp_socket(Socket), Options),
  468    memberchk(queue(Queue), Options),
  469    debug(http(connection), 'Waiting for connection', []),
  470    tcp_accept(Socket, Client, Peer),
  471    sig_atomic(send_to_worker(Queue, Client, Goal, Peer)),
  472    http_enough_workers(Queue, accept, Peer).
  473
  474send_to_worker(Queue, Client, Goal, Peer) :-
  475    debug(http(connection), 'New HTTP connection from ~p', [Peer]),
  476    thread_send_message(Queue, tcp_client(Client, Goal, Peer)).
  477
  478accept_rethrow_error(http_stop).
  479accept_rethrow_error('$aborted').

 close_server_socket(+Options)

Close the server socket.

  486close_server_socket(Options) :-
  487    close_hook(Options),
  488    !.
  489close_server_socket(Options) :-
  490    memberchk(tcp_socket(Socket), Options),
  491    !,
  492    tcp_close_socket(Socket).

 close_pending_accepts(+Queue)

  496close_pending_accepts(Queue) :-
  497    (   thread_get_message(Queue, Msg, [timeout(0)])
  498    ->  close_client(Msg),
  499        close_pending_accepts(Queue)
  500    ;   true
  501    ).
  502
  503close_client(tcp_client(Client, _Goal, _0Peer)) =>
  504    debug(http(stop), 'Closing connection from ~p during shut-down', [_0Peer]),
  505    tcp_close_socket(Client).
  506close_client(Msg) =>
  507    (   discard_client_hook(Msg)
  508    ->  true
  509    ;   print_message(warning, http_close_client(Msg))
  510    ).

 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

  520http_stop_server(Host:Port, Options) :-         % e.g., localhost:4000
  521    ground(Host),
  522    !,
  523    http_stop_server(Port, Options).
  524http_stop_server(Port, _Options) :-
  525    http_workers(Port, 0),                  % checks Port is ground
  526    current_server(Port, _, Thread, Queue, _Scheme, _Start),
  527    retractall(queue_options(Queue, _)),
  528    debug(http(stop), 'Signalling HTTP server thread ~p to stop', [Thread]),
  529    thread_signal(Thread, throw(http_stop)),
  530    catch(connect(localhost:Port), _, true),
  531    thread_join(Thread, _0Status),
  532    debug(http(stop), 'Joined HTTP server thread ~p (~p)', [Thread, _0Status]),
  533    message_queue_destroy(Queue).
  534
  535connect(Address) :-
  536    setup_call_cleanup(
  537        tcp_socket(Socket),
  538        tcp_connect(Socket, Address),
  539        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.

  547http_enough_workers(Queue, _Why, _Peer) :-
  548    message_queue_property(Queue, waiting(_0)),
  549    !,
  550    debug(http(scheduler), '~D waiting for work; ok', [_0]).
  551http_enough_workers(Queue, Why, Peer) :-
  552    message_queue_property(Queue, size(Size)),
  553    (   enough(Size, Why)
  554    ->  debug(http(scheduler), '~D in queue; ok', [Size])
  555    ;   current_server(Port, _, _, Queue, _, _),
  556        Data = _{ port:Port,
  557                  reason:Why,
  558                  peer:Peer,
  559                  waiting:Size,
  560                  queue:Queue
  561                },
  562        debug(http(scheduler), 'Asking to reschedule: ~p', [Data]),
  563        catch(http:schedule_workers(Data),
  564              Error,
  565              print_message(error, Error))
  566    ->  true
  567    ;   true
  568    ).
  569
  570enough(0, _).
  571enough(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.

  601                 /*******************************
  602                 *    WORKER QUEUE OPERATIONS   *
  603                 *******************************/

 create_workers(+Options)

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

  610create_workers(Options) :-
  611    option(workers(N), Options, 5),
  612    option(queue(Queue), Options),
  613    catch(message_queue_create(Queue), _, true),
  614    atom_concat(Queue, '_', AliasBase),
  615    create_workers(1, N, Queue, AliasBase, Options),
  616    assert(queue_options(Queue, Options)).
  617
  618create_workers(I, N, _, _, _) :-
  619    I > N,
  620    !.
  621create_workers(I, N, Queue, AliasBase, Options) :-
  622    gensym(AliasBase, Alias),
  623    thread_create(http_worker(Options), Id,
  624                  [ alias(Alias)
  625                  | Options
  626                  ]),
  627    assertz(queue_worker(Queue, Id)),
  628    I2 is I + 1,
  629    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.

  637resize_pool(Queue, Size) :-
  638    findall(W, queue_worker(Queue, W), Workers),
  639    length(Workers, Now),
  640    (   Now < Size
  641    ->  queue_options(Queue, Options),
  642        atom_concat(Queue, '_', AliasBase),
  643        I0 is Now+1,
  644        create_workers(I0, Size, Queue, AliasBase, Options)
  645    ;   Now == Size
  646    ->  true
  647    ;   Now > Size
  648    ->  Excess is Now - Size,
  649        thread_self(Me),
  650        forall(between(1, Excess, _), thread_send_message(Queue, quit(Me))),
  651        forall(between(1, Excess, _), thread_get_message(quitted(_)))
  652    ).

 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.

  663http_worker(Options) :-
  664    debug(http(scheduler), 'New worker', []),
  665    prolog_listen(this_thread_exit, done_worker),
  666    option(queue(Queue), Options),
  667    option(max_idle_time(MaxIdle), Options, infinite),
  668    thread_repeat_wait(get_work(Queue, Message, MaxIdle)),
  669      debug(http(worker), 'Waiting for a job ...', []),
  670      debug(http(worker), 'Got job ~p', [Message]),
  671      (   Message = quit(Sender)
  672      ->  !,
  673          thread_self(Self),
  674          thread_detach(Self),
  675          (   Sender == idle
  676          ->  true
  677          ;   retract(queue_worker(Queue, Self)),
  678              thread_send_message(Sender, quitted(Self))
  679          )
  680      ;   open_client(Message, Queue, Goal, In, Out,
  681                      Options, ClientOptions),
  682          (   catch(http_process(Goal, In, Out, ClientOptions),
  683                    Error, true)
  684          ->  true
  685          ;   Error = goal_failed(http_process/4)
  686          ),
  687          (   var(Error)
  688          ->  fail
  689          ;   current_message_level(Error, Level),
  690              print_message(Level, Error),
  691              memberchk(peer(Peer), ClientOptions),
  692              close_connection(Peer, In, Out),
  693              fail
  694          )
  695      ).
  696
  697get_work(Queue, Message, infinite) :-
  698    !,
  699    thread_get_message(Queue, Message).
  700get_work(Queue, Message, MaxIdle) :-
  701    (   thread_get_message(Queue, Message, [timeout(MaxIdle)])
  702    ->  true
  703    ;   Message = quit(idle)
  704    ).

 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.

  713open_client(requeue(In, Out, Goal, ClOpts),
  714            _, Goal, In, Out, Opts, ClOpts) :-
  715    !,
  716    memberchk(peer(Peer), ClOpts),
  717    option(keep_alive_timeout(KeepAliveTMO), Opts, 2),
  718    check_keep_alive_connection(In, KeepAliveTMO, Peer, In, Out).
  719open_client(Message, Queue, Goal, In, Out, Opts,
  720            [ pool(client(Queue, Goal, In, Out)),
  721              timeout(Timeout)
  722            | Options
  723            ]) :-
  724    catch(open_client(Message, Goal, In, Out, Options, Opts),
  725          E, report_error(E)),
  726    option(timeout(Timeout), Opts, 60),
  727    (   debugging(http(connection))
  728    ->  memberchk(peer(Peer), Options),
  729        debug(http(connection), 'Opened connection from ~p', [Peer])
  730    ;   true
  731    ).

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

  737open_client(Message, Goal, In, Out, ClientOptions, Options) :-
  738    open_client_hook(Message, Goal, In, Out, ClientOptions, Options),
  739    !.
  740open_client(tcp_client(Socket, Goal, Peer), Goal, In, Out,
  741            [ peer(Peer),
  742              protocol(http)
  743            ], _) :-
  744    tcp_open_socket(Socket, In, Out).
  745
  746report_error(E) :-
  747    print_message(error, E),
  748    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.

  757check_keep_alive_connection(In, TMO, Peer, In, Out) :-
  758    stream_property(In, timeout(Old)),
  759    set_stream(In, timeout(TMO)),
  760    debug(http(keep_alive), 'Waiting for keep-alive ...', []),
  761    catch(peek_code(In, Code), E, true),
  762    (   var(E),                     % no exception
  763        Code \== -1                 % no end-of-file
  764    ->  set_stream(In, timeout(Old)),
  765        debug(http(keep_alive), '\tre-using keep-alive connection', [])
  766    ;   (   Code == -1
  767        ->  debug(http(keep_alive), '\tRemote closed keep-alive connection', [])
  768        ;   debug(http(keep_alive), '\tTimeout on keep-alive connection', [])
  769        ),
  770        close_connection(Peer, In, Out),
  771        fail
  772    ).

 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.

  781done_worker :-
  782    thread_self(Self),
  783    thread_detach(Self),
  784    retract(queue_worker(Queue, Self)),
  785    thread_property(Self, status(Status)),
  786    !,
  787    (   catch(recreate_worker(Status, Queue), _, fail)
  788    ->  print_message(informational,
  789                      httpd_restarted_worker(Self))
  790    ;   done_status_message_level(Status, Level),
  791        print_message(Level,
  792                      httpd_stopped_worker(Self, Status))
  793    ).
  794done_worker :-                                  % received quit(Sender)
  795    thread_self(Self),
  796    thread_property(Self, status(Status)),
  797    done_status_message_level(Status, Level),
  798    print_message(Level,
  799                  httpd_stopped_worker(Self, Status)).
  800
  801done_status_message_level(true, silent) :- !.
  802done_status_message_level(exception('$aborted'), silent) :- !.
  803done_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?

  818recreate_worker(exception(error(io_error(write,user_error),_)), _Queue) :-
  819    halt(2).
  820recreate_worker(exception(Error), Queue) :-
  821    recreate_on_error(Error),
  822    queue_options(Queue, Options),
  823    atom_concat(Queue, '_', AliasBase),
  824    create_workers(1, 1, Queue, AliasBase, Options).
  825
  826recreate_on_error('$aborted').
  827recreate_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.

  836:- multifile
  837    message_level/2.  838
  839message_level(error(io_error(read, _), _),               silent).
  840message_level(error(socket_error(epipe,_), _),           silent).
  841message_level(error(http_write_short(_Obj,_Written), _), silent).
  842message_level(error(timeout_error(read, _), _),          informational).
  843message_level(keep_alive_timeout,                        silent).
  844
  845current_message_level(Term, Level) :-
  846    (   message_level(Term, Level)
  847    ->  true
  848    ;   Level = error
  849    ).

 http_requeue(+Header)

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

  857http_requeue(Header) :-
  858    requeue_header(Header, ClientOptions),
  859    memberchk(pool(client(Queue, Goal, In, Out)), ClientOptions),
  860    memberchk(peer(Peer), ClientOptions),
  861    http_enough_workers(Queue, keep_alive, Peer),
  862    thread_send_message(Queue, requeue(In, Out, Goal, ClientOptions)),
  863    !.
  864http_requeue(Header) :-
  865    debug(http(error), 'Re-queue failed: ~p', [Header]),
  866    fail.
  867
  868requeue_header([], []).
  869requeue_header([H|T0], [H|T]) :-
  870    requeue_keep(H),
  871    !,
  872    requeue_header(T0, T).
  873requeue_header([_|T0], T) :-
  874    requeue_header(T0, T).
  875
  876requeue_keep(pool(_)).
  877requeue_keep(peer(_)).
  878requeue_keep(protocol(_)).

 http_process(Message, Queue, +Options)

Handle a single client message on the given stream.

  885http_process(Goal, In, Out, Options) :-
  886    debug(http(server), 'Running server goal ~p on ~p -> ~p',
  887          [Goal, In, Out]),
  888    option(timeout(TMO), Options, 60),
  889    set_stream(In, timeout(TMO)),
  890    set_stream(Out, timeout(TMO)),
  891    http_wrapper(Goal, In, Out, Connection,
  892                 [ request(Request)
  893                 | Options
  894                 ]),
  895    next(Connection, Request).
  896
  897next(Connection, Request) :-
  898    next_(Connection, Request), !.
  899next(Connection, Request) :-
  900    print_message(warning, goal_failed(next(Connection,Request))).
  901
  902next_(switch_protocol(SwitchGoal, _SwitchOptions), Request) :-
  903    !,
  904    memberchk(pool(client(_Queue, _Goal, In, Out)), Request),
  905    (   catch(call(SwitchGoal, In, Out), E,
  906              (   print_message(error, E),
  907                  fail))
  908    ->  true
  909    ;   http_close_connection(Request)
  910    ).
  911next_(spawned(ThreadId), _) :-
  912    !,
  913    debug(http(spawn), 'Handler spawned to thread ~w', [ThreadId]).
  914next_(Connection, Request) :-
  915    downcase_atom(Connection, 'keep-alive'),
  916    http_requeue(Request),
  917    !.
  918next_(_, Request) :-
  919    http_close_connection(Request).

 http_close_connection(+Request)

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

  926http_close_connection(Request) :-
  927    memberchk(pool(client(_Queue, _Goal, In, Out)), Request),
  928    memberchk(peer(Peer), Request),
  929    close_connection(Peer, In, Out).

 close_connection(+Peer, +In, +Out)

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

  936close_connection(Peer, In, Out) :-
  937    debug(http(connection), 'Closing connection from ~p', [Peer]),
  938    catch(close(In, [force(true)]), _, true),
  939    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.

  957http_spawn(Goal, Options) :-
  958    select_option(pool(Pool), Options, ThreadOptions),
  959    !,
  960    current_output(CGI),
  961    catch(thread_create_in_pool(Pool,
  962                                wrap_spawned(CGI, Goal), Id,
  963                                [ detached(true)
  964                                | ThreadOptions
  965                                ]),
  966          Error,
  967          true),
  968    (   var(Error)
  969    ->  http_spawned(Id)
  970    ;   Error = error(resource_error(threads_in_pool(_)), _)
  971    ->  throw(http_reply(busy))
  972    ;   Error = error(existence_error(thread_pool, Pool), _),
  973        create_pool(Pool)
  974    ->  http_spawn(Goal, Options)
  975    ;   throw(Error)
  976    ).
  977http_spawn(Goal, Options) :-
  978    current_output(CGI),
  979    thread_create(wrap_spawned(CGI, Goal), Id,
  980                  [ detached(true)
  981                  | Options
  982                  ]),
  983    http_spawned(Id).
  984
  985wrap_spawned(CGI, Goal) :-
  986    set_output(CGI),
  987    http_wrap_spawned(Goal, Request, Connection),
  988    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.

  998create_pool(Pool) :-
  999    E = error(permission_error(create, thread_pool, Pool), _),
 1000    catch(http:create_pool(Pool), E, true).
 1001create_pool(Pool) :-
 1002    print_message(informational, httpd(created_pool(Pool))),
 1003    thread_pool_create(Pool, 10, []).
 1004
 1005
 1006		 /*******************************
 1007		 *         WAIT POLICIES	*
 1008		 *******************************/
 1009
 1010:- meta_predicate
 1011    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.

 1018thread_repeat_wait(Goal) :-
 1019    new_rate_mma(5, 1000, State),
 1020    repeat,
 1021      update_rate_mma(State, MMA),
 1022      long(MMA, IsLong),
 1023      (   IsLong == brief
 1024      ->  call(Goal)
 1025      ;   thread_idle(Goal, IsLong)
 1026      ).
 1027
 1028long(MMA, brief) :-
 1029    MMA < 0.05,
 1030    !.
 1031long(MMA, short) :-
 1032    MMA < 1,
 1033    !.
 1034long(_, 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

 1048new_rate_mma(N, Resolution, rstate(Base, 0, MaxI, Resolution, N, 0)) :-
 1049    current_prolog_flag(max_tagged_integer, MaxI),
 1050    get_time(Base).
 1051
 1052update_rate_mma(State, MMAr) :-
 1053    State = rstate(Base, Last, MaxI, Resolution, N, MMA0),
 1054    get_time(Now),
 1055    Stamp is round((Now-Base)*Resolution),
 1056    (   Stamp > MaxI
 1057    ->  nb_setarg(1, State, Now),
 1058        nb_setarg(2, State, 0)
 1059    ;   true
 1060    ),
 1061    Diff is Stamp-Last,
 1062    nb_setarg(2, State, Stamp),
 1063    MMA is round(((N-1)*MMA0+Diff)/N),
 1064    nb_setarg(6, State, MMA),
 1065    MMAr is MMA/float(Resolution).
 1066
 1067
 1068                 /*******************************
 1069                 *            MESSAGES          *
 1070                 *******************************/
 1071
 1072:- multifile
 1073    prolog:message/3. 1074
 1075prolog:message(httpd_started_server(Port, Options)) -->
 1076    [ 'Started server at '-[] ],
 1077    http_root(Port, Options).
 1078prolog:message(httpd_stopped_worker(Self, Status)) -->
 1079    [ 'Stopped worker ~p: ~p'-[Self, Status] ].
 1080prolog:message(httpd_restarted_worker(Self)) -->
 1081    [ 'Replaced aborted worker ~p'-[Self] ].
 1082prolog:message(httpd(created_pool(Pool))) -->
 1083    [ 'Created thread-pool ~p of size 10'-[Pool], nl,
 1084      'Create this pool at startup-time or define the hook ', nl,
 1085      'http:create_pool/1 to avoid this message and create a ', nl,
 1086      'pool that fits the usage-profile.'
 1087    ].
 1088
 1089http_root(Address, Options) -->
 1090    { landing_page(Address, URI, Options) },
 1091    [ '~w'-[URI] ].
 1092
 1093landing_page(Host:Port, URI, Options) :-
 1094    !,
 1095    must_be(atom, Host),
 1096    must_be(integer, Port),
 1097    http_server_property(Port, scheme(Scheme)),
 1098    (   default_port(Scheme, Port)
 1099    ->  format(atom(Base), '~w://~w', [Scheme, Host])
 1100    ;   format(atom(Base), '~w://~w:~w', [Scheme, Host, Port])
 1101    ),
 1102    entry_page(Base, URI, Options).
 1103landing_page(unix_socket(Path), URI, _Options) :-
 1104    !,
 1105    format(string(URI), 'Unix domain socket "~w"', [Path]).
 1106landing_page(Port, URI, Options) :-
 1107    landing_page(localhost:Port, URI, Options).
 1108
 1109default_port(http, 80).
 1110default_port(https, 443).
 1111
 1112entry_page(Base, URI, Options) :-
 1113    option(entry_page(Entry), Options),
 1114    !,
 1115    uri_resolve(Entry, Base, URI).
 1116entry_page(Base, URI, _) :-
 1117    http_absolute_location(root(.), Entry, []),
 1118    uri_resolve(Entry, Base, URI)