1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker & Steve Prior
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2004-2023, University of Amsterdam
    7                              VU University Amsterdam
    8                              CWI, Amsterdam
    9                              SWI-Prolog Solutions b.v.
   10    All rights reserved.
   11
   12    Redistribution and use in source and binary forms, with or without
   13    modification, are permitted provided that the following conditions
   14    are met:
   15
   16    1. Redistributions of source code must retain the above copyright
   17       notice, this list of conditions and the following disclaimer.
   18
   19    2. Redistributions in binary form must reproduce the above copyright
   20       notice, this list of conditions and the following disclaimer in
   21       the documentation and/or other materials provided with the
   22       distribution.
   23
   24    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   25    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   26    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   27    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   28    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   29    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   30    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   31    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   32    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   33    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   34    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   35    POSSIBILITY OF SUCH DAMAGE.
   36*/
   37
   38:- module(prolog_server,
   39          [ prolog_server/2             % +Port, +Options
   40          ]).   41
   42:- autoload(library(lists), [member/2]).   43:- autoload(library(socket),
   44            [ tcp_socket/1,
   45              tcp_setopt/2,
   46              tcp_bind/2,
   47              tcp_listen/2,
   48              tcp_accept/3,
   49              tcp_open_socket/3,
   50              tcp_host_to_address/2,
   51              ip_name/2
   52            ]).

 prolog_server(?Port, +Options)

Create a TCP/IP based server on the given Port, so you can telnet into Prolog and run an interactive session. This library is intended to provide access for debugging and management of embedded servers.

Currently defined options are:

allow(IP)

Allow access from IP, a term of the format ip(A,B,C,D). Multiple of such terms can exist and access is granted if the peer IP address unifies to one of them. If no allow option is provided access is only granted from ip(127,0,0,1) (localhost).

For example:

?- prolog_server(4000, []).

% netcat -N localhost 4000
Welcome to the SWI-Prolog server on thread 3

1 ?-

See also

- The add-on libssh provides an embedded SSH server. This provides encryption as well as a pseudo terminal for a better user experience.

bug

- As the connection does not involve a terminal, command history and completion are not provided. Neither are interrupts (Control-C). The Prolog shell can be terminated if netcat shuts down the socket on ^D (using the -N option). Otherwise one must enter the command "end_of_file."

   91prolog_server(Port, Options) :-
   92    tcp_socket(ServerSocket),
   93    tcp_setopt(ServerSocket, reuseaddr),
   94    tcp_bind(ServerSocket, Port),
   95    tcp_listen(ServerSocket, 5),
   96    thread_create(server_loop(ServerSocket, Options), _,
   97                  [ alias(prolog_server)
   98                  ]).
   99
  100server_loop(ServerSocket, Options) :-
  101    tcp_accept(ServerSocket, Slave, Peer),
  102    tcp_open_socket(Slave, InStream, OutStream),
  103    set_stream(InStream, close_on_abort(false)),
  104    set_stream(OutStream, close_on_abort(false)),
  105    catch(tcp_host_to_address(Host, Peer),
  106          error(socket_error(_,_),_),
  107          ip_name(Peer, Host)),
  108    (   Postfix = []
  109    ;   between(2, 1000, Num),
  110        Postfix = [-, Num]
  111    ),
  112    atomic_list_concat(['client@', Host | Postfix], Alias),
  113    catch(thread_create(
  114              service_client(InStream, OutStream, Peer, Options),
  115              _,
  116              [ alias(Alias),
  117                detached(true)
  118              ]),
  119          error(permission_error(create, thread, Alias), _),
  120          fail),
  121    !,
  122    server_loop(ServerSocket, Options).
  123
  124service_client(InStream, OutStream, Peer, Options) :-
  125    allow(Peer, Options),
  126    !,
  127    thread_self(Id),
  128    set_prolog_IO(InStream, OutStream, OutStream),
  129    set_stream(InStream, tty(true)),
  130    set_prolog_flag(tty_control, false),
  131    current_prolog_flag(encoding, Enc),
  132    set_stream(user_input, encoding(Enc)),
  133    set_stream(user_output, encoding(Enc)),
  134    set_stream(user_error, encoding(Enc)),
  135    set_stream(user_input, newline(detect)),
  136    set_stream(user_output, newline(dos)),
  137    set_stream(user_error, newline(dos)),
  138    format(user_error,
  139           'Welcome to the SWI-Prolog server on thread ~w~n~n',
  140           [Id]),
  141    call_cleanup(prolog,
  142                 ( close(InStream, [force(true)]),
  143                   close(OutStream, [force(true)]))).
  144service_client(InStream, OutStream, _, _):-
  145    thread_self(Id),
  146    format(OutStream, 'Go away!!~n', []),
  147    close(InStream),
  148    close(OutStream),
  149    thread_detach(Id).
  150
  151
  152allow(Peer, Options) :-
  153    (   member(allow(Allow), Options)
  154    *-> Peer = Allow,
  155        !
  156    ;   Peer = ip(127,0,0,1)
  157    )