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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   37
   38:- module(thread_httpd,
   39          [ http_current_server/2,      % ?:Goal, ?Port
   40            http_server_property/2,     % ?Port, ?Property
   41            http_server/2,              % :Goal, +Options
   42            http_workers/2,             % +Port, ?WorkerCount
   43            http_add_worker/2,          % +Port, +Options
   44            http_current_worker/2,      % ?Port, ?ThreadID
   45            http_stop_server/2,         % +Port, +Options
   46            http_spawn/2,               % :Goal, +Options
   47
   48            http_requeue/1,             % +Request
   49            http_close_connection/1,    % +Request
   50            http_enough_workers/3       % +Queue, +Why, +Peer
   51          ]).   52:- use_module(library(debug)).   53:- use_module(library(error)).   54:- use_module(library(option)).   55:- use_module(library(socket)).   56:- use_module(library(thread_pool)).   57:- use_module(library(gensym)).   58:- use_module(http_wrapper).   59:- use_module(http_path).   60
   61:- autoload(library(uri), [uri_resolve/3]).   62:- autoload(library(aggregate), [aggregate_all/3]).   63
   64:- predicate_options(http_server/2, 2,
   65                     [ port(any),
   66                       unix_socket(atom),
   67                       entry_page(atom),
   68                       tcp_socket(any),
   69                       workers(positive_integer),
   70                       timeout(number),
   71                       keep_alive_timeout(number),
   72                       silent(boolean),
   73                       ssl(list(any)),  % if http/http_ssl_plugin is loaded
   74                       pass_to(system:thread_create/3, 3)
   75                     ]).   76:- predicate_options(http_spawn/2, 2,
   77                     [ pool(atom),
   78                       pass_to(system:thread_create/3, 3),
   79                       pass_to(thread_pool:thread_create_in_pool/4, 4)
   80                     ]).   81:- predicate_options(http_add_worker/2, 2,
   82                     [ timeout(number),
   83                       keep_alive_timeout(number),
   84                       max_idle_time(number),
   85                       pass_to(system:thread_create/3, 3)
   86                     ]).

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

 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.

  200http_server(Goal, M:Options0) :-
  201    server_address(Address, Options0),
  202    !,
  203    make_socket(Address, M:Options0, Options),
  204    create_workers(Options),
  205    create_server(Goal, Address, Options),
  206    (   option(silent(true), Options0)
  207    ->  true
  208    ;   print_message(informational,
  209                      httpd_started_server(Address, Options0))
  210    ).
  211http_server(_Goal, _:Options0) :-
  212    existence_error(server_address, Options0).
  213
  214server_address(Address, Options) :-
  215    (   option(port(Port), Options)
  216    ->  Address = Port
  217    ;   option(unix_socket(Path), Options)
  218    ->  Address = unix_socket(Path)
  219    ).
  220
  221address_port(_IFace:Port, Port) :- !.
  222address_port(unix_socket(Path), Path) :- !.
  223address_port(Address, Address) :- !.
  224
  225tcp_address(Port) :-
  226    var(Port),
  227    !.
  228tcp_address(Port) :-
  229    integer(Port),
  230    !.
  231tcp_address(_Iface:_Port).
  232
  233address_domain(localhost:_Port, Domain) =>
  234    Domain = inet.
  235address_domain(Iface:_Port, Domain) =>
  236    (   catch(ip_name(IP, Iface), error(_,_), fail),
  237        functor(IP, ip, 8)
  238    ->  Domain = inet6
  239    ;   Domain = inet
  240    ).
  241address_domain(_, Domain) =>
  242    Domain = inet.

 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.

  253make_socket(Address, M:Options0, Options) :-
  254    tcp_address(Address),
  255    make_socket_hook(Address, M:Options0, Options),
  256    !.
  257make_socket(Address, _:Options0, Options) :-
  258    option(tcp_socket(_), Options0),
  259    !,
  260    make_addr_atom('httpd', Address, Queue),
  261    Options = [ queue(Queue)
  262              | Options0
  263              ].
  264make_socket(Address, _:Options0, Options) :-
  265    tcp_address(Address),
  266    !,
  267    address_domain(Address, Domain),
  268    socket_create(Socket, [domain(Domain)]),
  269    tcp_setopt(Socket, reuseaddr),
  270    tcp_bind(Socket, Address),
  271    tcp_listen(Socket, 64),
  272    make_addr_atom('httpd', Address, Queue),
  273    Options = [ queue(Queue),
  274                tcp_socket(Socket)
  275              | Options0
  276              ].
  277:- if(current_predicate(unix_domain_socket/1)).  278make_socket(Address, _:Options0, Options) :-
  279    Address = unix_socket(Path),
  280    !,
  281    unix_domain_socket(Socket),
  282    tcp_bind(Socket, Path),
  283    tcp_listen(Socket, 64),
  284    make_addr_atom('httpd', Address, Queue),
  285    Options = [ queue(Queue),
  286                tcp_socket(Socket)
  287              | Options0
  288              ].
  289:- endif.

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

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

  296make_addr_atom(Scheme, Address, Atom) :-
  297    phrase(address_parts(Address), Parts),
  298    atomic_list_concat([Scheme,@|Parts], Atom).
  299
  300address_parts(Var) -->
  301    { var(Var),
  302      !,
  303      instantiation_error(Var)
  304    }.
  305address_parts(Atomic) -->
  306    { atomic(Atomic) },
  307    !,
  308    [Atomic].
  309address_parts(Host:Port) -->
  310    !,
  311    address_parts(Host), [:], address_parts(Port).
  312address_parts(ip(A,B,C,D)) -->
  313    !,
  314    [ A, '.', B, '.', C, '.', D ].
  315address_parts(unix_socket(Path)) -->
  316    [Path].
  317address_parts(Address) -->
  318    { domain_error(http_server_address, Address) }.

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

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

  326create_server(Goal, Address, Options) :-
  327    get_time(StartTime),
  328    memberchk(queue(Queue), Options),
  329    scheme(Scheme, Options),
  330    autoload_https(Scheme),
  331    address_port(Address, Port),
  332    make_addr_atom(Scheme, Port, Alias),
  333    thread_self(Initiator),
  334    thread_create(accept_server(Goal, Initiator, Options), _,
  335                  [ alias(Alias)
  336                  ]),
  337    thread_get_message(server_started),
  338    assert(current_server(Port, Goal, Alias, Queue, Scheme, StartTime)).
  339
  340scheme(Scheme, Options) :-
  341    option(scheme(Scheme), Options),
  342    !.
  343scheme(Scheme, Options) :-
  344    (   option(ssl(_), Options)
  345    ;   option(ssl_instance(_), Options)
  346    ),
  347    !,
  348    Scheme = https.
  349scheme(http, _).
  350
  351autoload_https(https) :-
  352    \+ clause(accept_hook(_Goal, _Options), _),
  353    exists_source(library(http/http_ssl_plugin)),
  354    !,
  355    use_module(library(http/http_ssl_plugin)).
  356autoload_https(_).

 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))

  364http_current_server(Goal, Port) :-
  365    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.

  381http_server_property(_:Port, Property) :-
  382    integer(Port),
  383    !,
  384    server_property(Property, Port).
  385http_server_property(Port, Property) :-
  386    server_property(Property, Port).
  387
  388server_property(goal(Goal), Port) :-
  389    current_server(Port, Goal, _, _, _, _).
  390server_property(scheme(Scheme), Port) :-
  391    current_server(Port, _, _, _, Scheme, _).
  392server_property(start_time(Time), Port) :-
  393    current_server(Port, _, _, _, _, Time).

 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.

  406http_workers(Port, Workers) :-
  407    integer(Workers),
  408    !,
  409    must_be(ground, Port),
  410    (   current_server(Port, _, _, Queue, _, _)
  411    ->  resize_pool(Queue, Workers)
  412    ;   existence_error(http_server, Port)
  413    ).
  414http_workers(Port, Workers) :-
  415    current_server(Port, _, _, Queue, _, _),
  416    aggregate_all(count, queue_worker(Queue, _Worker), Workers).

 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.

  429http_add_worker(Port, Options) :-
  430    must_be(ground, Port),
  431    current_server(Port, _, _, Queue, _, _),
  432    !,
  433    queue_options(Queue, QueueOptions),
  434    merge_options(Options, QueueOptions, WorkerOptions),
  435    atom_concat(Queue, '_', AliasBase),
  436    create_workers(1, 1, Queue, AliasBase, WorkerOptions).
  437http_add_worker(Port, _) :-
  438    existence_error(http_server, Port).

 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.

  448http_current_worker(Port, ThreadID) :-
  449    current_server(Port, _, _, Queue, _, _),
  450    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.

  458accept_server(Goal, Initiator, Options) :-
  459    Ex = http_stop(Stopper),
  460    catch(accept_server2(Goal, Initiator, Options), Ex, true),
  461    thread_self(Thread),
  462    debug(http(stop), '[~p]: accept server received ~p', [Thread, Ex]),
  463    retract(current_server(_Port, _, Thread, Queue, _Scheme, _StartTime)),
  464    close_pending_accepts(Queue),
  465    close_server_socket(Options),
  466    thread_send_message(Stopper, http_stopped).
  467
  468accept_server2(Goal, Initiator, Options) :-
  469    thread_send_message(Initiator, server_started),
  470    repeat,
  471      (   catch(accept_server3(Goal, Options), E, true)
  472      ->  (   var(E)
  473          ->  fail
  474          ;   accept_rethrow_error(E)
  475          ->  throw(E)
  476          ;   print_message(error, E),
  477              fail
  478          )
  479      ;   print_message(error,      % internal error
  480                        goal_failed(accept_server3(Goal, Options))),
  481          fail
  482      ).
  483
  484accept_server3(Goal, Options) :-
  485    accept_hook(Goal, Options),
  486    !.
  487accept_server3(Goal, Options) :-
  488    memberchk(tcp_socket(Socket), Options),
  489    memberchk(queue(Queue), Options),
  490    debug(http(connection), 'Waiting for connection', []),
  491    tcp_accept(Socket, Client, Peer),
  492    sig_atomic(send_to_worker(Queue, Client, Goal, Peer)),
  493    http_enough_workers(Queue, accept, Peer).
  494
  495send_to_worker(Queue, Client, Goal, Peer) :-
  496    debug(http(connection), 'New HTTP connection from ~p', [Peer]),
  497    thread_send_message(Queue, tcp_client(Client, Goal, Peer)).
  498
  499accept_rethrow_error(http_stop(_)).

 close_server_socket(+Options)

Close the server socket.

  505close_server_socket(Options) :-
  506    close_hook(Options),
  507    !.
  508close_server_socket(Options) :-
  509    memberchk(tcp_socket(Socket), Options),
  510    !,
  511    tcp_close_socket(Socket).

 close_pending_accepts(+Queue)

  515close_pending_accepts(Queue) :-
  516    (   thread_get_message(Queue, Msg, [timeout(0)])
  517    ->  close_client(Msg),
  518        close_pending_accepts(Queue)
  519    ;   true
  520    ).
  521
  522close_client(tcp_client(Client, _Goal, _0Peer)) =>
  523    debug(http(stop), 'Closing connection from ~p during shut-down', [_0Peer]),
  524    tcp_close_socket(Client).
  525close_client(Msg) =>
  526    (   discard_client_hook(Msg)
  527    ->  true
  528    ;   print_message(warning, http_close_client(Msg))
  529    ).

 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

  539http_stop_server(Host:Port, Options) :-         % e.g., localhost:4000
  540    ground(Host),
  541    !,
  542    http_stop_server(Port, Options).
  543http_stop_server(Port, _Options) :-
  544    http_workers(Port, 0),                  % checks Port is ground
  545    current_server(Port, _, Thread, Queue, _Scheme, _Start),
  546    retractall(queue_options(Queue, _)),
  547    debug(http(stop), 'Signalling HTTP server thread ~p to stop', [Thread]),
  548    thread_self(Stopper),
  549    thread_signal(Thread, throw(http_stop(Stopper))),
  550    (   thread_get_message(Stopper, http_stopped, [timeout(0.1)])
  551    ->  true
  552    ;   catch(connect(localhost:Port), _, true)
  553    ),
  554    thread_join(Thread, _0Status),
  555    debug(http(stop), 'Joined HTTP server thread ~p (~p)', [Thread, _0Status]),
  556    message_queue_destroy(Queue).
  557
  558connect(Address) :-
  559    setup_call_cleanup(
  560        tcp_socket(Socket),
  561        tcp_connect(Socket, Address),
  562        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.

  570http_enough_workers(Queue, _Why, _Peer) :-
  571    message_queue_property(Queue, waiting(_0)),
  572    !,
  573    debug(http(scheduler), '~D waiting for work; ok', [_0]).
  574http_enough_workers(Queue, Why, Peer) :-
  575    message_queue_property(Queue, size(Size)),
  576    (   enough(Size, Why)
  577    ->  debug(http(scheduler), '~D in queue; ok', [Size])
  578    ;   current_server(Port, _, _, Queue, _, _),
  579        Data = _{ port:Port,
  580                  reason:Why,
  581                  peer:Peer,
  582                  waiting:Size,
  583                  queue:Queue
  584                },
  585        debug(http(scheduler), 'Asking to reschedule: ~p', [Data]),
  586        catch(http:schedule_workers(Data),
  587              Error,
  588              print_message(error, Error))
  589    ->  true
  590    ;   true
  591    ).
  592
  593enough(0, _).
  594enough(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.

  624                 /*******************************
  625                 *    WORKER QUEUE OPERATIONS   *
  626                 *******************************/

 create_workers(+Options)

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

  633create_workers(Options) :-
  634    option(workers(N), Options, 5),
  635    option(queue(Queue), Options),
  636    catch(message_queue_create(Queue), _, true),
  637    atom_concat(Queue, '_', AliasBase),
  638    create_workers(1, N, Queue, AliasBase, Options),
  639    assert(queue_options(Queue, Options)).
  640
  641create_workers(I, N, _, _, _) :-
  642    I > N,
  643    !.
  644create_workers(I, N, Queue, AliasBase, Options) :-
  645    gensym(AliasBase, Alias),
  646    thread_create(http_worker(Options), Id,
  647                  [ alias(Alias)
  648                  | Options
  649                  ]),
  650    assertz(queue_worker(Queue, Id)),
  651    I2 is I + 1,
  652    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.

  660resize_pool(Queue, Size) :-
  661    findall(W, queue_worker(Queue, W), Workers),
  662    length(Workers, Now),
  663    (   Now < Size
  664    ->  queue_options(Queue, Options),
  665        atom_concat(Queue, '_', AliasBase),
  666        I0 is Now+1,
  667        create_workers(I0, Size, Queue, AliasBase, Options)
  668    ;   Now == Size
  669    ->  true
  670    ;   Now > Size
  671    ->  Excess is Now - Size,
  672        thread_self(Me),
  673        forall(between(1, Excess, _), thread_send_message(Queue, quit(Me))),
  674        forall(between(1, Excess, _), thread_get_message(quitted(_)))
  675    ).

 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.

  686http_worker(Options) :-
  687    debug(http(scheduler), 'New worker', []),
  688    prolog_listen(this_thread_exit, done_worker),
  689    option(queue(Queue), Options),
  690    option(max_idle_time(MaxIdle), Options, infinite),
  691    thread_repeat_wait(get_work(Queue, Message, MaxIdle)),
  692      debug(http(worker), 'Waiting for a job ...', []),
  693      debug(http(worker), 'Got job ~p', [Message]),
  694      (   Message = quit(Sender)
  695      ->  !,
  696          thread_self(Self),
  697          thread_detach(Self),
  698          (   Sender == idle
  699          ->  true
  700          ;   retract(queue_worker(Queue, Self)),
  701              thread_send_message(Sender, quitted(Self))
  702          )
  703      ;   open_client(Message, Queue, Goal, In, Out,
  704                      Options, ClientOptions),
  705          (   catch(http_process(Goal, In, Out, ClientOptions),
  706                    Error, true)
  707          ->  true
  708          ;   Error = goal_failed(http_process/4)
  709          ),
  710          (   var(Error)
  711          ->  fail
  712          ;   current_message_level(Error, Level),
  713              print_message(Level, Error),
  714              memberchk(peer(Peer), ClientOptions),
  715              close_connection(Peer, In, Out),
  716              fail
  717          )
  718      ).
  719
  720get_work(Queue, Message, infinite) :-
  721    !,
  722    thread_get_message(Queue, Message).
  723get_work(Queue, Message, MaxIdle) :-
  724    (   thread_get_message(Queue, Message, [timeout(MaxIdle)])
  725    ->  true
  726    ;   Message = quit(idle)
  727    ).

 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.

  736open_client(requeue(In, Out, Goal, ClOpts),
  737            _, Goal, In, Out, Opts, ClOpts) :-
  738    !,
  739    memberchk(peer(Peer), ClOpts),
  740    option(keep_alive_timeout(KeepAliveTMO), Opts, 2),
  741    check_keep_alive_connection(In, KeepAliveTMO, Peer, In, Out).
  742open_client(Message, Queue, Goal, In, Out, Opts,
  743            [ pool(client(Queue, Goal, In, Out)),
  744              timeout(Timeout)
  745            | Options
  746            ]) :-
  747    catch(open_client(Message, Goal, In, Out, Options, Opts),
  748          E, report_error(E)),
  749    option(timeout(Timeout), Opts, 60),
  750    (   debugging(http(connection))
  751    ->  memberchk(peer(Peer), Options),
  752        debug(http(connection), 'Opened connection from ~p', [Peer])
  753    ;   true
  754    ).

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

  760open_client(Message, Goal, In, Out, ClientOptions, Options) :-
  761    open_client_hook(Message, Goal, In, Out, ClientOptions, Options),
  762    !.
  763open_client(tcp_client(Socket, Goal, Peer), Goal, In, Out,
  764            [ peer(Peer),
  765              protocol(http)
  766            ], _) :-
  767    tcp_open_socket(Socket, In, Out).
  768
  769report_error(E) :-
  770    print_message(error, E),
  771    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.

  780check_keep_alive_connection(In, TMO, Peer, In, Out) :-
  781    stream_property(In, timeout(Old)),
  782    set_stream(In, timeout(TMO)),
  783    debug(http(keep_alive), 'Waiting for keep-alive ...', []),
  784    catch(peek_code(In, Code), E, true),
  785    (   var(E),                     % no exception
  786        Code \== -1                 % no end-of-file
  787    ->  set_stream(In, timeout(Old)),
  788        debug(http(keep_alive), '\tre-using keep-alive connection', [])
  789    ;   (   Code == -1
  790        ->  debug(http(keep_alive), '\tRemote closed keep-alive connection', [])
  791        ;   debug(http(keep_alive), '\tTimeout on keep-alive connection', [])
  792        ),
  793        close_connection(Peer, In, Out),
  794        fail
  795    ).

 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.

  804done_worker :-
  805    thread_self(Self),
  806    thread_detach(Self),
  807    retract(queue_worker(Queue, Self)),
  808    thread_property(Self, status(Status)),
  809    !,
  810    (   catch(recreate_worker(Status, Queue), _, fail)
  811    ->  print_message(informational,
  812                      httpd_restarted_worker(Self))
  813    ;   done_status_message_level(Status, Level),
  814        print_message(Level,
  815                      httpd_stopped_worker(Self, Status))
  816    ).
  817done_worker :-                                  % received quit(Sender)
  818    thread_self(Self),
  819    thread_property(Self, status(Status)),
  820    done_status_message_level(Status, Level),
  821    print_message(Level,
  822                  httpd_stopped_worker(Self, Status)).
  823
  824done_status_message_level(true, silent) :- !.
  825done_status_message_level(exception('$aborted'), silent) :- !.
  826done_status_message_level(exception(unwind(abort)), silent) :- !.
  827done_status_message_level(exception(unwind(halt(_))), silent) :- !.
  828done_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?

  843recreate_worker(exception(error(io_error(write,user_error),_)), _Queue) :-
  844    halt(2).
  845recreate_worker(exception(Error), Queue) :-
  846    recreate_on_error(Error),
  847    queue_options(Queue, Options),
  848    atom_concat(Queue, '_', AliasBase),
  849    create_workers(1, 1, Queue, AliasBase, Options).
  850
  851recreate_on_error('$aborted').
  852recreate_on_error(unwind(abort)).
  853recreate_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.

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

 http_requeue(+Header)

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

  883http_requeue(Header) :-
  884    requeue_header(Header, ClientOptions),
  885    memberchk(pool(client(Queue, Goal, In, Out)), ClientOptions),
  886    memberchk(peer(Peer), ClientOptions),
  887    http_enough_workers(Queue, keep_alive, Peer),
  888    thread_send_message(Queue, requeue(In, Out, Goal, ClientOptions)),
  889    !.
  890http_requeue(Header) :-
  891    debug(http(error), 'Re-queue failed: ~p', [Header]),
  892    fail.
  893
  894requeue_header([], []).
  895requeue_header([H|T0], [H|T]) :-
  896    requeue_keep(H),
  897    !,
  898    requeue_header(T0, T).
  899requeue_header([_|T0], T) :-
  900    requeue_header(T0, T).
  901
  902requeue_keep(pool(_)).
  903requeue_keep(peer(_)).
  904requeue_keep(protocol(_)).

 http_process(Message, Queue, +Options)

Handle a single client message on the given stream.

  911http_process(Goal, In, Out, Options) :-
  912    debug(http(server), 'Running server goal ~p on ~p -> ~p',
  913          [Goal, In, Out]),
  914    option(timeout(TMO), Options, 60),
  915    set_stream(In, timeout(TMO)),
  916    set_stream(Out, timeout(TMO)),
  917    http_wrapper(Goal, In, Out, Connection,
  918                 [ request(Request)
  919                 | Options
  920                 ]),
  921    next(Connection, Request).
  922
  923next(Connection, Request) :-
  924    next_(Connection, Request), !.
  925next(Connection, Request) :-
  926    print_message(warning, goal_failed(next(Connection,Request))).
  927
  928next_(switch_protocol(SwitchGoal, _SwitchOptions), Request) :-
  929    !,
  930    memberchk(pool(client(_Queue, _Goal, In, Out)), Request),
  931    (   catch(call(SwitchGoal, In, Out), E,
  932              (   print_message(error, E),
  933                  fail))
  934    ->  true
  935    ;   http_close_connection(Request)
  936    ).
  937next_(spawned(ThreadId), _) :-
  938    !,
  939    debug(http(spawn), 'Handler spawned to thread ~w', [ThreadId]).
  940next_(Connection, Request) :-
  941    downcase_atom(Connection, 'keep-alive'),
  942    http_requeue(Request),
  943    !.
  944next_(_, Request) :-
  945    http_close_connection(Request).

 http_close_connection(+Request)

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

  952http_close_connection(Request) :-
  953    memberchk(pool(client(_Queue, _Goal, In, Out)), Request),
  954    memberchk(peer(Peer), Request),
  955    close_connection(Peer, In, Out).

 close_connection(+Peer, +In, +Out)

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

  962close_connection(Peer, In, Out) :-
  963    debug(http(connection), 'Closing connection from ~p', [Peer]),
  964    catch(close(In, [force(true)]), _, true),
  965    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.

  983http_spawn(Goal, Options) :-
  984    select_option(pool(Pool), Options, ThreadOptions),
  985    !,
  986    current_output(CGI),
  987    catch(thread_create_in_pool(Pool,
  988                                wrap_spawned(CGI, Goal), Id,
  989                                [ detached(true)
  990                                | ThreadOptions
  991                                ]),
  992          Error,
  993          true),
  994    (   var(Error)
  995    ->  http_spawned(Id)
  996    ;   Error = error(resource_error(threads_in_pool(_)), _)
  997    ->  throw(http_reply(busy))
  998    ;   Error = error(existence_error(thread_pool, Pool), _),
  999        create_pool(Pool)
 1000    ->  http_spawn(Goal, Options)
 1001    ;   throw(Error)
 1002    ).
 1003http_spawn(Goal, Options) :-
 1004    current_output(CGI),
 1005    thread_create(wrap_spawned(CGI, Goal), Id,
 1006                  [ detached(true)
 1007                  | Options
 1008                  ]),
 1009    http_spawned(Id).
 1010
 1011wrap_spawned(CGI, Goal) :-
 1012    set_output(CGI),
 1013    http_wrap_spawned(Goal, Request, Connection),
 1014    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.

 1024create_pool(Pool) :-
 1025    E = error(permission_error(create, thread_pool, Pool), _),
 1026    catch(http:create_pool(Pool), E, true).
 1027create_pool(Pool) :-
 1028    print_message(informational, httpd(created_pool(Pool))),
 1029    thread_pool_create(Pool, 10, []).
 1030
 1031
 1032		 /*******************************
 1033		 *         WAIT POLICIES	*
 1034		 *******************************/
 1035
 1036:- meta_predicate
 1037    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.

 1044thread_repeat_wait(Goal) :-
 1045    new_rate_mma(5, 1000, State),
 1046    repeat,
 1047      update_rate_mma(State, MMA),
 1048      long(MMA, IsLong),
 1049      (   IsLong == brief
 1050      ->  call(Goal)
 1051      ;   thread_idle(Goal, IsLong)
 1052      ).
 1053
 1054long(MMA, brief) :-
 1055    MMA < 0.05,
 1056    !.
 1057long(MMA, short) :-
 1058    MMA < 1,
 1059    !.
 1060long(_, 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

 1074new_rate_mma(N, Resolution, rstate(Base, 0, MaxI, Resolution, N, 0)) :-
 1075    current_prolog_flag(max_tagged_integer, MaxI),
 1076    get_time(Base).
 1077
 1078update_rate_mma(State, MMAr) :-
 1079    State = rstate(Base, Last, MaxI, Resolution, N, MMA0),
 1080    get_time(Now),
 1081    Stamp is round((Now-Base)*Resolution),
 1082    (   Stamp > MaxI
 1083    ->  nb_setarg(1, State, Now),
 1084        nb_setarg(2, State, 0)
 1085    ;   true
 1086    ),
 1087    Diff is Stamp-Last,
 1088    nb_setarg(2, State, Stamp),
 1089    MMA is round(((N-1)*MMA0+Diff)/N),
 1090    nb_setarg(6, State, MMA),
 1091    MMAr is MMA/float(Resolution).
 1092
 1093
 1094                 /*******************************
 1095                 *            MESSAGES          *
 1096                 *******************************/
 1097
 1098:- multifile
 1099    prolog:message/3. 1100
 1101prolog:message(httpd_started_server(Port, Options)) -->
 1102    [ 'Started server at '-[] ],
 1103    http_root(Port, Options).
 1104prolog:message(httpd_stopped_worker(Self, Status)) -->
 1105    [ 'Stopped worker ~p: ~p'-[Self, Status] ].
 1106prolog:message(httpd_restarted_worker(Self)) -->
 1107    [ 'Replaced aborted worker ~p'-[Self] ].
 1108prolog:message(httpd(created_pool(Pool))) -->
 1109    [ 'Created thread-pool ~p of size 10'-[Pool], nl,
 1110      'Create this pool at startup-time or define the hook ', nl,
 1111      'http:create_pool/1 to avoid this message and create a ', nl,
 1112      'pool that fits the usage-profile.'
 1113    ].
 1114
 1115http_root(Address, Options) -->
 1116    { landing_page(Address, URI, Options) },
 1117    [ '~w'-[URI] ].
 1118
 1119landing_page(Host:Port, URI, Options) :-
 1120    !,
 1121    must_be(atom, Host),
 1122    must_be(integer, Port),
 1123    http_server_property(Port, scheme(Scheme)),
 1124    (   default_port(Scheme, Port)
 1125    ->  format(atom(Base), '~w://~w', [Scheme, Host])
 1126    ;   format(atom(Base), '~w://~w:~w', [Scheme, Host, Port])
 1127    ),
 1128    entry_page(Base, URI, Options).
 1129landing_page(unix_socket(Path), URI, _Options) :-
 1130    !,
 1131    format(string(URI), 'Unix domain socket "~w"', [Path]).
 1132landing_page(Port, URI, Options) :-
 1133    landing_page(localhost:Port, URI, Options).
 1134
 1135default_port(http, 80).
 1136default_port(https, 443).
 1137
 1138entry_page(Base, URI, Options) :-
 1139    option(entry_page(Entry), Options),
 1140    !,
 1141    uri_resolve(Entry, Base, URI).
 1142entry_page(Base, URI, _) :-
 1143    http_absolute_location(root(.), Entry, []),
 1144    uri_resolve(Entry, Base, URI)