/* Part of SWI-Prolog Author: Jan Wielemaker E-mail: J.Wielemaker@vu.nl WWW: http://www.swi-prolog.org Copyright (C): 1985-2015, University of Amsterdam VU University Amsterdam This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA As a special exception, if you link this library with other files, compiled with a Free Software compiler, to produce an executable, this library does not by itself cause the resulting executable to be covered by the GNU General Public License. This exception does not however invalidate any other reasons why the executable file might be covered by the GNU General Public License. */ :- module(socket, [ tcp_socket/1, % -Socket tcp_close_socket/1, % +Socket tcp_open_socket/3, % +Socket, -Read, -Write tcp_connect/2, % +Socket, +Address tcp_connect/3, % +Socket, +Address, -StreamPair tcp_connect/4, % +Socket, +Address, -Read, -Write) tcp_bind/2, % +Socket, +Address tcp_accept/3, % +Master, -Slave, -PeerName tcp_listen/2, % +Socket, +BackLog tcp_fcntl/3, % +Socket, +Command, ?Arg tcp_setopt/2, % +Socket, +Option tcp_host_to_address/2, % ?HostName, ?Ip-nr tcp_select/3, % +Inputs, -Ready, +Timeout gethostname/1, % -HostName tcp_open_socket/2, % +Socket, -StreamPair udp_socket/1, % -Socket udp_receive/4, % +Socket, -Data, -Sender, +Options udp_send/4, % +Socket, +Data, +Sender, +Options negotiate_socks_connection/2% +DesiredEndpoint, +StreamPair ]). :- use_module(library(shlib)). :- use_module(library(debug)). :- use_module(library(lists)). /** Network socket (TCP and UDP) library The library(socket) provides TCP and UDP inet-domain sockets from SWI-Prolog, both client and server-side communication. The interface of this library is very close to the Unix socket interface, also supported by the MS-Windows _winsock_ API. SWI-Prolog applications that wish to communicate with multiple sources have three options: - Use I/O multiplexing based on wait_for_input/3. On Windows systems this can only be used for sockets, not for general (device-) file handles. - Use multiple threads, handling either a single blocking socket or a pool using I/O multiplexing as above. - Using XPCE's class `socket` which synchronises socket events in the GUI event-loop. ## Client applications {#socket-server} Using this library to establish a TCP connection to a server is as simple as opening a file. See also http_open/3. == 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)). == To deal with timeouts and multiple connections, threads, wait_for_input/3 and/or non-blocking streams (see tcp_fcntl/3) can be used. ## Server applications {#socket-client} The typical sequence for generating a server application is given below. To close the server, use close/1 on `AcceptFd`. == create_server(Port) :- tcp_socket(Socket), tcp_bind(Socket, Port), tcp_listen(Socket, 5), tcp_open_socket(Socket, AcceptFd, _), == There are various options for . The most commonly used option is to start a Prolog thread to handle the connection. Alternatively, input from multiple clients can be handled in a single thread by listening to these clients using wait_for_input/3. Finally, on Unix systems, we can use fork/1 to handle the connection in a new process. Note that fork/1 and threads do not cooperate well. Combinations can be realised but require good understanding of POSIX thread and fork-semantics. Below is the typical example using a thread. Note the use of setup_call_cleanup/3 to guarantee that all resources are reclaimed, also in case of failure or exceptions. == 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(In, StreamPair), close(StreamPair)). handle_service(StreamPair) :- ... == ## TCP socket predicates {#socket-predicates} */ :- multifile tcp_connect_hook/3, % +Socket, +Addr, -In, -Out tcp_connect_hook/4, % +Socket, +Addr, -Stream proxy_for_url/3, % +URL, +Host, -ProxyList try_proxy/4. % +Proxy, +Addr, -Socket, -Stream :- predicate_options(tcp_connect/3, 3, [ bypass_proxy(boolean), nodelay(boolean) ]). :- use_foreign_library(foreign(socket), install_socket). :- public tcp_debug/1. % set debugging. %% 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. tcp_open_socket(Socket, Stream) :- tcp_open_socket(Socket, In, Out), ( var(Out) -> Stream = In ; stream_pair(Stream, In, Out) ). %% 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_connect(+SocketId, +HostAndPort) 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_cal_cleanup( % tcp_connect(Host:Port, StreamPair, []), % talk(StreamPair), % close(StreamPair)) % == /******************************* * HOOKABLE CONNECT * *******************************/ %% 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 socket: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). tcp_connect(Socket, Address, Read, Write) :- tcp_connect_hook(Socket, Address, Read, Write), !. tcp_connect(Socket, Address, Read, Write) :- tcp_connect(Socket, Address), 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). % % @error 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 library(http/http_proxy) defines a hook that allows to % connect through HTTP proxies that support the =CONNECT= method. % Main mode: +,-,+ tcp_connect(Address, StreamPair, Options) :- var(StreamPair), !, ( memberchk(bypass_proxy(true), Options) -> tcp_connect_direct(Address, Socket, StreamPair) ; findall(Result, try_a_proxy(Address, Result), ResultList), last(ResultList, Status) -> ( Status = true(_Proxy, Socket, StreamPair) -> true ; throw(error(proxy_error(tried(ResultList)), _)) ) ; tcp_connect_direct(Address, Socket, StreamPair) ), ( memberchk(nodelay(true), Options) -> tcp_setopt(Socket, nodelay) ; true ). % backward compatibility mode +,+,- tcp_connect(Socket, Address, StreamPair) :- tcp_connect_hook(Socket, Address, StreamPair0), !, StreamPair = StreamPair0. tcp_connect(Socket, Address, StreamPair) :- tcp_connect(Socket, Address, Read, Write), stream_pair(StreamPair, Read, Write). tcp_connect_direct(Address, Socket, StreamPair):- tcp_socket(Socket), catch(tcp_connect(Socket, Address, StreamPair), Error, ( tcp_close_socket(Socket), throw(Error) )). /******************************* * PROXY SUPPORT * *******************************/ try_a_proxy(Address, Result) :- format(atom(URL), 'socket://~w', [Address]), ( Address = Host:_ -> true ; Host = Address ), proxy_for_url(URL, Host, Proxy), debug(socket(proxy), 'Socket connecting via ~w~n', [Proxy]), ( catch(try_proxy(Proxy, Address, Socket, Stream), E, true) -> ( var(E) -> !, Result = true(Proxy, Socket, Stream) ; Result = error(Proxy, E) ) ; Result = false(Proxy) ), 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 :- multifile try_proxy/4. try_proxy(direct, Address, Socket, StreamPair) :- !, tcp_connect_direct(Address, Socket, StreamPair). try_proxy(socks(Host, Port), Address, Socket, StreamPair) :- !, tcp_connect_direct(Host:Port, Socket, StreamPair), catch(negotiate_socks_connection(Address, StreamPair), Error, ( close(StreamPair, [force(true)]), throw(Error) )). %% 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](http://en.wikipedia.org/wiki/Proxy_auto-config). % Additional methods can be returned if suitable clauses for % http:http_connection_over_proxy/6 or try_proxy/4 are defined. :- multifile proxy_for_url/3. /******************************* * OPTIONS * *******************************/ %% 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](http://en.wikipedia.org/wiki/Nagle's_algorithm) % 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. % % - 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=. %% 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. tcp_fcntl(Socket, setfl, nonblock) :- !, tcp_setopt(Socket, nonblock). %% 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. % % @tbd 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(). /******************************* * SOCKS * *******************************/ %% 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 % % @error socks_error(Details) if the SOCKS negotiation failed. negotiate_socks_connection(Host:Port, StreamPair):- format(StreamPair, '~s', [[0x5, % Version 5 0x1, % 1 auth method supported 0x0]]), % which is 'no auth' flush_output(StreamPair), get_byte(StreamPair, ServerVersion), get_byte(StreamPair, AuthenticationMethod), ( ServerVersion =\= 0x05 -> throw(error(socks_error(invalid_version(5, ServerVersion)), _)) ; AuthenticationMethod =:= 0xff -> throw(error(socks_error(invalid_authentication_method( 0xff, AuthenticationMethod)), _)) ; true ), ( Host = ip(A,B,C,D) -> AddressType = 0x1, % IPv4 Address format(atom(Address), '~s', [[A, B, C, D]]) ; AddressType = 0x3, % Domain atom_length(Host, Length), format(atom(Address), '~s~w', [[Length], Host]) ), P1 is Port /\ 0xff, P2 is Port >> 8, format(StreamPair, '~s~w~s', [[0x5, % Version 5 0x1, % Please establish a connection 0x0, % reserved AddressType], Address, [P2, P1]]), flush_output(StreamPair), get_byte(StreamPair, _EchoedServerVersion), get_byte(StreamPair, Status), ( Status =:= 0 % Established! -> get_byte(StreamPair, _Reserved), get_byte(StreamPair, EchoedAddressType), ( EchoedAddressType =:= 0x1 -> get_byte(StreamPair, _), % read IP4 get_byte(StreamPair, _), get_byte(StreamPair, _), get_byte(StreamPair, _) ; get_byte(StreamPair, Length), % read host name forall(between(1, Length, _), get_byte(StreamPair, _)) ), get_byte(StreamPair, _), % read port get_byte(StreamPair, _) ; throw(error(socks_error(negotiation_rejected(Status)), _)) ). /******************************* * MESSAGES * *******************************/ /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - The C-layer generates exceptions of the following format, where Message is extracted from the operating system. error(socket_error(Message), _) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */ :- multifile prolog:error_message//1. prolog:error_message(socket_error(Message)) --> [ 'Socket error: ~w'-[Message] ]. prolog:error_message(socks_error(Error)) --> socks_error(Error). prolog:error_message(proxy_error(tried(Tried))) --> [ 'Failed to connect using a proxy. Tried:'-[], nl], proxy_tried(Tried). socks_error(invalid_version(Supported, Got)) --> [ 'SOCKS: unsupported version: ~p (supported: ~p)'- [ Got, Supported ] ]. socks_error(invalid_authentication_method(Supported, Got)) --> [ 'SOCKS: unsupported authentication method: ~p (supported: ~p)'- [ Got, Supported ] ]. socks_error(negotiation_rejected(Status)) --> [ 'SOCKS: connection failed: ~p'-[Status] ]. proxy_tried([]) --> []. proxy_tried([H|T]) --> proxy_tried(H), proxy_tried(T). proxy_tried(error(Proxy, Error)) --> [ '~w: '-[Proxy] ], '$messages':translate_message(Error). proxy_tried(false(Proxy)) --> [ '~w: failed with unspecified error'-[Proxy] ].