/* Part of SWI-Prolog Author: Jan Wielemaker E-mail: J.Wielemaker@vu.nl WWW: http://www.swi-prolog.org Copyright (c) 2000-2020, University of Amsterdam VU University Amsterdam CWI, Amsterdam All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ :- 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_getopt/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 ]). :- autoload(library(debug),[debug/3]). :- autoload(library(lists),[last/2]). /** 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(StreamPair), close(StreamPair)). handle_service(StreamPair) :- ... == ## Socket exceptions {#socket-exceptions} Errors that are trapped by the low-level library are mapped to an exception of the shape below. In this term, `Code` is a lower case atom that corresponds to the C macro name, e.g., `epipe` for a broken pipe. `Message` is the human readable string for the error code returned by the OS or the same as `Code` if the OS does not provide this functionality. Note that `Code` is derived from a static set of macros that may or may not be defines for the target OS. If the macro name is not known, `Code` is =|ERROR_nnn|=, where _nnn_ is an integer. error(socket_error(Code, Message), _) Note that on Windows `Code` is a ``wsa*`` code which makes it hard to write portable code that handles specific socket errors. Even on POSIX systems the exact set of errors produced by the network stack is not defined. ## 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. :- if(current_predicate(unix_domain_socket/1)). :- export(unix_domain_socket/1). % -Socket :- 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. 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_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. /******************************* * 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). % % @arg 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. % % @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):- make_socket(Address, Socket), catch(tcp_connect(Socket, Address, StreamPair), Error, ( tcp_close_socket(Socket), throw(Error) )). :- if(current_predicate(unix_domain_socket/1)). make_socket(Address, Socket) :- ( atom(Address) ; string(Address) ), !, unix_domain_socket(Socket). :- endif. make_socket(_Address, Socket) :- 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 tcp_select(ListOfStreams, ReadyList, TimeOut) :- wait_for_input(ListOfStreams, ReadyList, TimeOut). /******************************* * 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. % % - 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. tcp_fcntl(Socket, setfl, nonblock) :- !, 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. % % @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(Code, Message), _) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */ :- multifile prolog:error_message//1. prolog:error_message(socket_error(_Code, 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] ].