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)  2000-2022, 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;
   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(socket,
   39          [ tcp_socket/1,               % -Socket
   40            tcp_close_socket/1,         % +Socket
   41            tcp_open_socket/3,          % +Socket, -Read, -Write
   42            tcp_connect/2,              % +Socket, +Address
   43            tcp_connect/3,              % +Socket, +Address, -StreamPair
   44            tcp_connect/4,              % +Socket, +Address, -Read, -Write)
   45            tcp_bind/2,                 % +Socket, +Address
   46            tcp_accept/3,               % +Master, -Slave, -PeerName
   47            tcp_listen/2,               % +Socket, +BackLog
   48            tcp_fcntl/3,                % +Socket, +Command, ?Arg
   49            tcp_setopt/2,               % +Socket, +Option
   50            tcp_getopt/2,               % +Socket, ?Option
   51            tcp_host_to_address/2,      % ?HostName, ?Ip-nr
   52            tcp_select/3,               % +Inputs, -Ready, +Timeout
   53            gethostname/1,              % -HostName
   54
   55            tcp_open_socket/2,          % +Socket, -StreamPair
   56
   57            udp_socket/1,               % -Socket
   58            udp_receive/4,              % +Socket, -Data, -Sender, +Options
   59            udp_send/4,                 % +Socket, +Data, +Sender, +Options
   60
   61            negotiate_socks_connection/2% +DesiredEndpoint, +StreamPair
   62          ]).   63:- autoload(library(debug),[debug/3]).   64:- autoload(library(lists),[last/2]).

dump_swi_homepage :-
    setup_call_cleanup(
        tcp_connect(www.swi-prolog.org:http, Stream, []),
        ( format(Stream,
                 'GET / HTTP/1.1~n\c
                  Host: www.swi-prolog.org~n\c
                  Connection: close~n~n', []),
          flush_output(Stream),
          copy_stream_data(Stream, current_output)
        ),
        close(S)).

create_server(Port) :-
      tcp_socket(Socket),
      tcp_bind(Socket, Port),
      tcp_listen(Socket, 5),
      tcp_open_socket(Socket, AcceptFd, _),
      <dispatch>

dispatch(AcceptFd) :-
        tcp_accept(AcceptFd, Socket, Peer),
        thread_create(process_client(Socket, Peer), _,
                      [ detached(true)
                      ]),
        dispatch(AcceptFd).

process_client(Socket, Peer) :-
        setup_call_cleanup(
            tcp_open_socket(Socket, StreamPair),
            handle_service(StreamPair),
            close(StreamPair)).

handle_service(StreamPair) :-
        ...

error(socket_error(Code, Message), _)

  172:- multifile
  173    tcp_connect_hook/3,             % +Socket, +Addr, -In, -Out
  174    tcp_connect_hook/4,             % +Socket, +Addr, -Stream
  175    proxy_for_url/3,                % +URL, +Host, -ProxyList
  176    try_proxy/4.                    % +Proxy, +Addr, -Socket, -Stream
  177
  178:- predicate_options(tcp_connect/3, 3,
  179                     [ bypass_proxy(boolean),
  180                       nodelay(boolean)
  181                     ]).  182
  183:- use_foreign_library(foreign(socket)).  184:- public tcp_debug/1.                  % set debugging.
  185
  186:- if(current_predicate(unix_domain_socket/1)).  187:- export(unix_domain_socket/1).  % -Socket
  188:- endif.

 tcp_socket(-SocketId) is det

Creates an INET-domain stream-socket and unifies an identifier to it with SocketId. On MS-Windows, if the socket library is not yet initialised, this will also initialise the library.

 tcp_close_socket(+SocketId) is det

Closes the indicated socket, making SocketId invalid. Normally, sockets are closed by closing both stream handles returned by open_socket/3. There are two cases where tcp_close_socket/1 is used because there are no stream-handles:

• If, after tcp_accept/3, the server uses fork/1 to handle the client in a sub-process. In this case the accepted socket is not longer needed from the main server and must be discarded using tcp_close_socket/1.
• If, after discovering the connecting client with tcp_accept/3, the server does not want to accept the connection, it should discard the accepted socket immediately using tcp_close_socket/1.

 tcp_open_socket(+SocketId, -StreamPair) is det

Create streams to communicate to SocketId. If SocketId is a master socket (see tcp_bind/2), StreamPair should be used for tcp_accept/3. If SocketId is a connected (see tcp_connect/2) or accepted socket (see tcp_accept/3), StreamPair is unified to a stream pair (see stream_pair/3) that can be used for reading and writing. The stream or pair must be closed with close/1, which also closes SocketId.

  222tcp_open_socket(Socket, Stream) :-
  223    tcp_open_socket(Socket, In, Out),
  224    (   var(Out)
  225    ->  Stream = In
  226    ;   stream_pair(Stream, In, Out)
  227    ).

 tcp_open_socket(+SocketId, -InStream, -OutStream) is det

Similar to tcp_open_socket/2, but creates two separate sockets where tcp_open_socket/2 would have created a stream pair.

deprecated

- New code should use tcp_open_socket/2 because closing a stream pair is much easier to perform safely.

 tcp_bind(SocketId, ?Address) is det

Bind the socket to Address on the current machine. This operation, together with tcp_listen/2 and tcp_accept/3 implement the server-side of the socket interface. Address is either an plain Port or a term HostPort. The first form binds the socket to the given port on all interfaces, while the second only binds to the matching interface. A typical example is below, causing the socket to listen only on port 8080 on the local machine's network.

  tcp_bind(Socket, localhost:8080)

If Port is unbound, the system picks an arbitrary free port and unifies Port with the selected port number. Port is either an integer or the name of a registered service. See also tcp_connect/4.

 tcp_listen(+SocketId, +BackLog) is det

Tells, after tcp_bind/2, the socket to listen for incoming requests for connections. Backlog indicates how many pending connection requests are allowed. Pending requests are requests that are not yet acknowledged using tcp_accept/3. If the indicated number is exceeded, the requesting client will be signalled that the service is currently not available. A commonly used default value for Backlog is 5.

 tcp_accept(+Socket, -Slave, -Peer) is det

This predicate waits on a server socket for a connection request by a client. On success, it creates a new socket for the client and binds the identifier to Slave. Peer is bound to the IP-address of the client or the atom af_unix if Socket is an AF_UNIX socket (see unix_domain_socket/1).

 tcp_connect(+SocketId, +Address) is det

Connect SocketId. After successful completion, tcp_open_socket/3 can be used to create I/O-Streams to the remote socket. This predicate is part of the low level client API. A connection to a particular host and port is realised using these steps:

    tcp_socket(Socket),
    tcp_connect(Socket, Host:Port),
    tcp_open_socket(Socket, StreamPair)

Typical client applications should use the high level interface provided by tcp_connect/3 which avoids resource leaking if a step in the process fails, and can be hooked to support proxies. For example:

    setup_call_cleanup(
        tcp_connect(Host:Port, StreamPair, []),
        talk(StreamPair),
        close(StreamPair))

If SocketId is an AF_UNIX socket (see unix_domain_socket/1), Address is an atom or string denoting a file name.

  304                 /*******************************
  305                 *      HOOKABLE CONNECT        *
  306                 *******************************/

 tcp_connect(+Socket, +Address, -Read, -Write) is det

Connect a (client) socket to Address and return a bi-directional connection through the stream-handles Read and Write. This predicate may be hooked by defining tcp_connect_hook/4 with the same signature. Hooking can be used to deal with proxy connections. E.g.,

:- multifile socket:tcp_connect_hook/4.

socket:tcp_connect_hook(Socket, Address, Read, Write) :-
    proxy(ProxyAdress),
    tcp_connect(Socket, ProxyAdress),
    tcp_open_socket(Socket, Read, Write),
    proxy_connect(Address, Read, Write).

deprecated

- New code should use tcp_connect/3 called as tcp_connect(+Address, -StreamPair, +Options).

  329tcp_connect(Socket, Address, Read, Write) :-
  330    tcp_connect_hook(Socket, Address, Read, Write),
  331    !.
  332tcp_connect(Socket, Address, Read, Write) :-
  333    tcp_connect(Socket, Address),
  334    tcp_open_socket(Socket, Read, Write).

 tcp_connect(+Address, -StreamPair, +Options) is det

tcp_connect(+Socket, +Address, -StreamPair) is det

Establish a TCP communication as a client. The +,-,+ mode is the preferred way for a client to establish a connection. This predicate can be hooked to support network proxies. To use a proxy, the hook proxy_for_url/3 must be defined. Permitted options are:

bypass_proxy(+Boolean)

Defaults to false. If true, do not attempt to use any proxies to obtain the connection

nodelay(+Boolean)

Defaults to false. If true, set nodelay on the resulting socket using tcp_setopt(Socket, nodelay)

The +,+,- mode is deprecated and does not support proxies. It behaves like tcp_connect/4, but creates a stream pair (see stream_pair/3).

Arguments:

Address

- is either a Host:Port term or a file name (atom or string). The latter connects to an AF_UNIX socket and requires unix_domain_socket/1.

Errors

- proxy_error(tried(ResultList)) is raised by mode (+,-,+) if proxies are defines by proxy_for_url/3 but no proxy can establsh the connection. ResultList contains one or more terms of the form false(Proxy) for a hook that simply failed or error(Proxy, ErrorTerm) for a hook that raised an exception.

See also

- library(http/http_proxy) defines a hook that allows to connect through HTTP proxies that support the CONNECT method.

  371% Main mode: +,-,+
  372tcp_connect(Address, StreamPair, Options) :-
  373    var(StreamPair),
  374    !,
  375    (   memberchk(bypass_proxy(true), Options)
  376    ->  tcp_connect_direct(Address, Socket, StreamPair)
  377    ;   findall(Result,
  378                try_a_proxy(Address, Result),
  379                ResultList),
  380        last(ResultList, Status)
  381    ->  (   Status = true(_Proxy, Socket, StreamPair)
  382        ->  true
  383        ;   throw(error(proxy_error(tried(ResultList)), _))
  384        )
  385    ;   tcp_connect_direct(Address, Socket, StreamPair)
  386    ),
  387    (   memberchk(nodelay(true), Options)
  388    ->  tcp_setopt(Socket, nodelay)
  389    ;   true
  390    ).
  391% backward compatibility mode +,+,-
  392tcp_connect(Socket, Address, StreamPair) :-
  393    tcp_connect_hook(Socket, Address, StreamPair0),
  394    !,
  395    StreamPair = StreamPair0.
  396tcp_connect(Socket, Address, StreamPair) :-
  397    tcp_connect(Socket, Address, Read, Write),
  398    stream_pair(StreamPair, Read, Write).
  399
  400
  401tcp_connect_direct(Address, Socket, StreamPair):-
  402    make_socket(Address, Socket),
  403    catch(tcp_connect(Socket, Address, StreamPair),
  404          Error,
  405          ( tcp_close_socket(Socket),
  406            throw(Error)
  407          )).
  408
  409:- if(current_predicate(unix_domain_socket/1)).  410make_socket(Address, Socket) :-
  411    (   atom(Address)
  412    ;   string(Address)
  413    ),
  414    !,
  415    unix_domain_socket(Socket).
  416:- endif.  417make_socket(_Address, Socket) :-
  418    tcp_socket(Socket).

 tcp_select(+ListOfStreams, -ReadyList, +TimeOut)

Same as the built-in wait_for_input/3. Used to allow for interrupts and timeouts on Windows. A redesign of the Windows socket interface makes it impossible to do better than Windows select() call underlying wait_for_input/3. As input multiplexing typically happens in a background thread anyway we accept the loss of timeouts and interrupts.

deprecated

- Use wait_for_input/3

  432tcp_select(ListOfStreams, ReadyList, TimeOut) :-
  433    wait_for_input(ListOfStreams, ReadyList, TimeOut).
  434
  435
  436                 /*******************************
  437                 *        PROXY SUPPORT         *
  438                 *******************************/
  439
  440try_a_proxy(Address, Result) :-
  441    format(atom(URL), 'socket://~w', [Address]),
  442    (   Address = Host:_
  443    ->  true
  444    ;   Host = Address
  445    ),
  446    proxy_for_url(URL, Host, Proxy),
  447    debug(socket(proxy), 'Socket connecting via ~w~n', [Proxy]),
  448    (   catch(try_proxy(Proxy, Address, Socket, Stream), E, true)
  449    ->  (   var(E)
  450        ->  !, Result = true(Proxy, Socket, Stream)
  451        ;   Result = error(Proxy, E)
  452        )
  453    ;   Result = false(Proxy)
  454    ),
  455    debug(socket(proxy), 'Socket: ~w: ~p', [Proxy, Result]).

 try_proxy(+Proxy, +TargetAddress, -Socket, -StreamPair) is semidet

Attempt a socket-level connection via the given proxy to TargetAddress. The Proxy argument must match the output argument of proxy_for_url/3. The predicate tcp_connect/3 (and http_open/3 from the library(http/http_open)) collect the results of failed proxies and raise an exception no proxy is capable of realizing the connection.

The default implementation recognises the values for Proxy described below. The library(http/http_proxy) adds proxy(Host,Port) which allows for HTTP proxies using the CONNECT method.

direct

Do not use any proxy

socks(Host, Port)

Use a SOCKS5 proxy

  476:- multifile
  477    try_proxy/4.  478
  479try_proxy(direct, Address, Socket, StreamPair) :-
  480    !,
  481    tcp_connect_direct(Address, Socket, StreamPair).
  482try_proxy(socks(Host, Port), Address, Socket, StreamPair) :-
  483    !,
  484    tcp_connect_direct(Host:Port, Socket, StreamPair),
  485    catch(negotiate_socks_connection(Address, StreamPair),
  486          Error,
  487          ( close(StreamPair, [force(true)]),
  488            throw(Error)
  489          )).

 proxy_for_url(+URL, +Hostname, -Proxy) is nondet

This hook can be implemented to return a proxy to try when connecting to URL. Returned proxies are tried in the order in which they are returned by the multifile hook try_proxy/4. Pre-defined proxy methods are:

direct

connect directly to the resource

proxy(Host, Port)

Connect to the resource using an HTTP proxy. If the resource is not an HTTP URL, then try to connect using the CONNECT verb, otherwise, use the GET verb.

socks(Host, Port)

Connect to the resource via a SOCKS5 proxy

These correspond to the proxy methods defined by PAC Proxy auto-config. Additional methods can be returned if suitable clauses for http:http_connection_over_proxy/6 or try_proxy/4 are defined.

  512:- multifile
  513    proxy_for_url/3.  514
  515
  516                 /*******************************
  517                 *            OPTIONS           *
  518                 *******************************/

 tcp_setopt(+SocketId, +Option) is det

Set options on the socket. Defined options are:

reuseaddr

Allow servers to reuse a port without the system being completely sure the port is no longer in use.

bindtodevice(+Device)

Bind the socket to Device (an atom). For example, the code below binds the socket to the loopback device that is typically used to realise the localhost. See the manual pages for setsockopt() and the socket interface (e.g., socket(7) on Linux) for details.

tcp_socket(Socket),
tcp_setopt(Socket, bindtodevice(lo))

nodelay

nodelay(true)

If true, disable the Nagle optimization on this socket, which is enabled by default on almost all modern TCP/IP stacks. The Nagle optimization joins small packages, which is generally desirable, but sometimes not. Please note that the underlying TCP_NODELAY setting to setsockopt() is not available on all platforms and systems may require additional privileges to change this option. If the option is not supported, tcp_setopt/2 raises a domain_error exception. See Wikipedia for details.

broadcast

UDP sockets only: broadcast the package to all addresses matching the address. The address is normally the address of the local subnet (i.e. 192.168.1.255). See udp_send/4.

ip_add_membership(+MultiCastGroup)

ip_add_membership(+MultiCastGroup, +LocalInterface)

ip_add_membership(+MultiCastGroup, +LocalInterface, +InterfaceIndex)

ip_drop_membership(+MultiCastGroup)

ip_drop_membership(+MultiCastGroup, +LocalInterface)

ip_drop_membership(+MultiCastGroup, +LocalInterface, +InterfaceIndex)

Join/leave a multicast group. Calls setsockopt() with the corresponding arguments.

dispatch(+Boolean)

In GUI environments (using XPCE or the Windows swipl-win.exe executable) this flags defines whether or not any events are dispatched on behalf of the user interface. Default is true. Only very specific situations require setting this to false.

sndbuf(+Integer)

Sets the send buffer size to Integer (bytes). On Windows this defaults (now) to 64kb. Higher latency links may benefit from increasing this further since the maximum theoretical throughput on a link is given by buffer-size / latency. See https://support.microsoft.com/en-gb/help/823764/slow-performance-occurs-when-you-copy-data-to-a-tcp-server-by-using-a for Microsoft's discussion

 tcp_fcntl(+Stream, +Action, ?Argument) is det

Interface to the fcntl() call. Currently only suitable to deal switch stream to non-blocking mode using:

  tcp_fcntl(Stream, setfl, nonblock),

An attempt to read from a non-blocking stream while there is no data available returns -1 (or end_of_file for read/1), but at_end_of_stream/1 fails. On actual end-of-input, at_end_of_stream/1 succeeds.

  596tcp_fcntl(Socket, setfl, nonblock) :-
  597    !,
  598    tcp_setopt(Socket, nonblock).

 tcp_getopt(+Socket, ?Option) is semidet

Get information about Socket. Defined properties are below. Requesting an unknown option results in a domain_error exception.

file_no(-File)

Get the OS file handle as an integer. This may be used for debugging and integration.

 tcp_host_to_address(?HostName, ?Address) is det

Translate between a machines host-name and it's (IP-)address. If HostName is an atom, it is resolved using getaddrinfo() and the IP-number is unified to Address using a term of the format ip(Byte1,Byte2,Byte3,Byte4). Otherwise, if Address is bound to an ip(Byte1,Byte2,Byte3,Byte4) term, it is resolved by gethostbyaddr() and the canonical hostname is unified with HostName.

To be done

- This function should support more functionality provided by gethostbyaddr, probably by adding an option-list.

 gethostname(-Hostname) is det

Return the canonical fully qualified name of this host. This is achieved by calling gethostname() and return the canonical name returned by getaddrinfo().

  629                 /*******************************
  630                 *            SOCKS             *
  631                 *******************************/

 negotiate_socks_connection(+DesiredEndpoint, +StreamPair) is det

Negotiate a connection to DesiredEndpoint over StreamPair. DesiredEndpoint should be in the form of either:

• hostname : port
• ip(A,B,C,D) : port

Errors

- socks_error(Details) if the SOCKS negotiation failed.

  643negotiate_socks_connection(Host:Port, StreamPair):-
  644    format(StreamPair, '~s', [[0x5,    % Version 5
  645                               0x1,    % 1 auth method supported
  646                               0x0]]), % which is 'no auth'
  647    flush_output(StreamPair),
  648    get_byte(StreamPair, ServerVersion),
  649    get_byte(StreamPair, AuthenticationMethod),
  650    (   ServerVersion =\= 0x05
  651    ->  throw(error(socks_error(invalid_version(5, ServerVersion)), _))
  652    ;   AuthenticationMethod =:= 0xff
  653    ->  throw(error(socks_error(invalid_authentication_method(
  654                                    0xff,
  655                                    AuthenticationMethod)), _))
  656    ;   true
  657    ),
  658    (   Host = ip(A,B,C,D)
  659    ->  AddressType = 0x1,                  % IPv4 Address
  660        format(atom(Address), '~s', [[A, B, C, D]])
  661    ;   AddressType = 0x3,                  % Domain
  662        atom_length(Host, Length),
  663        format(atom(Address), '~s~w', [[Length], Host])
  664    ),
  665    P1 is Port /\ 0xff,
  666    P2 is Port >> 8,
  667    format(StreamPair, '~s~w~s', [[0x5,   % Version 5
  668                                   0x1,   % Please establish a connection
  669                                   0x0,   % reserved
  670                                   AddressType],
  671                                  Address,
  672                                  [P2, P1]]),
  673    flush_output(StreamPair),
  674    get_byte(StreamPair, _EchoedServerVersion),
  675    get_byte(StreamPair, Status),
  676    (   Status =:= 0                        % Established!
  677    ->  get_byte(StreamPair, _Reserved),
  678        get_byte(StreamPair, EchoedAddressType),
  679        (   EchoedAddressType =:= 0x1
  680        ->  get_byte(StreamPair, _),        % read IP4
  681            get_byte(StreamPair, _),
  682            get_byte(StreamPair, _),
  683            get_byte(StreamPair, _)
  684        ;   get_byte(StreamPair, Length),   % read host name
  685            forall(between(1, Length, _),
  686                   get_byte(StreamPair, _))
  687        ),
  688        get_byte(StreamPair, _),            % read port
  689        get_byte(StreamPair, _)
  690    ;   throw(error(socks_error(negotiation_rejected(Status)), _))
  691    ).
  692
  693
  694                 /*******************************
  695                 *             MESSAGES         *
  696                 *******************************/
  697
  698/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  699The C-layer generates exceptions of the  following format, where Message
  700is extracted from the operating system.
  701
  702        error(socket_error(Code, Message), _)
  703- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  704
  705:- multifile
  706    prolog:error_message//1.  707
  708prolog:error_message(socket_error(_Code, Message)) -->
  709    [ 'Socket error: ~w'-[Message] ].
  710prolog:error_message(socks_error(Error)) -->
  711    socks_error(Error).
  712prolog:error_message(proxy_error(tried(Tried))) -->
  713    [ 'Failed to connect using a proxy.  Tried:'-[], nl],
  714    proxy_tried(Tried).
  715
  716socks_error(invalid_version(Supported, Got)) -->
  717    [ 'SOCKS: unsupported version: ~p (supported: ~p)'-
  718      [ Got, Supported ] ].
  719socks_error(invalid_authentication_method(Supported, Got)) -->
  720    [ 'SOCKS: unsupported authentication method: ~p (supported: ~p)'-
  721      [ Got, Supported ] ].
  722socks_error(negotiation_rejected(Status)) -->
  723    [ 'SOCKS: connection failed: ~p'-[Status] ].
  724
  725proxy_tried([]) --> [].
  726proxy_tried([H|T]) -->
  727    proxy_tried(H),
  728    proxy_tried(T).
  729proxy_tried(error(Proxy, Error)) -->
  730    [ '~w: '-[Proxy] ],
  731    '$messages':translate_message(Error).
  732proxy_tried(false(Proxy)) -->
  733    [ '~w: failed with unspecified error'-[Proxy] ]