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)  2004-2022, 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;
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   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	    ]).

 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."

   90prolog_server(Port, Options) :-
   91    tcp_socket(ServerSocket),
   92    tcp_setopt(ServerSocket, reuseaddr),
   93    tcp_bind(ServerSocket, Port),
   94    tcp_listen(ServerSocket, 5),
   95    thread_create(server_loop(ServerSocket, Options), _,
   96                  [ alias(prolog_server)
   97                  ]).
   98
   99server_loop(ServerSocket, Options) :-
  100    tcp_accept(ServerSocket, Slave, Peer),
  101    tcp_open_socket(Slave, InStream, OutStream),
  102    set_stream(InStream, close_on_abort(false)),
  103    set_stream(OutStream, close_on_abort(false)),
  104    tcp_host_to_address(Host, Peer),
  105    (   Postfix = []
  106    ;   between(2, 1000, Num),
  107        Postfix = [-, Num]
  108    ),
  109    atomic_list_concat(['client@', Host | Postfix], Alias),
  110    catch(thread_create(
  111              service_client(InStream, OutStream, Peer, Options),
  112              _,
  113              [ alias(Alias),
  114                detached(true)
  115              ]),
  116          error(permission_error(create, thread, Alias), _),
  117          fail),
  118    !,
  119    server_loop(ServerSocket, Options).
  120
  121service_client(InStream, OutStream, Peer, Options) :-
  122    allow(Peer, Options),
  123    !,
  124    thread_self(Id),
  125    set_prolog_IO(InStream, OutStream, OutStream),
  126    set_stream(InStream, tty(true)),
  127    set_prolog_flag(tty_control, false),
  128    current_prolog_flag(encoding, Enc),
  129    set_stream(user_input, encoding(Enc)),
  130    set_stream(user_output, encoding(Enc)),
  131    set_stream(user_error, encoding(Enc)),
  132    set_stream(user_input, newline(detect)),
  133    set_stream(user_output, newline(dos)),
  134    set_stream(user_error, newline(dos)),
  135    format(user_error,
  136           'Welcome to the SWI-Prolog server on thread ~w~n~n',
  137           [Id]),
  138    call_cleanup(prolog,
  139                 ( close(InStream, [force(true)]),
  140                   close(OutStream, [force(true)]))).
  141service_client(InStream, OutStream, _, _):-
  142    thread_self(Id),
  143    format(OutStream, 'Go away!!~n', []),
  144    close(InStream),
  145    close(OutStream),
  146    thread_detach(Id).
  147
  148
  149allow(Peer, Options) :-
  150    (   member(allow(Allow), Options)
  151    *-> Peer = Allow,
  152        !
  153    ;   Peer = ip(127,0,0,1)
  154    )