/* Part of SWI-Prolog Author: Jeffrey Rosenwald and Jan Wielemaker E-mail: jeffrose@acm.org WWW: http://www.swi-prolog.org Copyright (c) 2012-2013, Jeffrey Rosenwald 2018-2020, 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(udp_broadcast, [ udp_broadcast_initialize/2, % +IPAddress, +Options udp_broadcast_close/1, % +Scope udp_peer_add/2, % +Scope, +IP udp_peer_del/2, % +Scope, ?IP udp_peer/2 % +Scope, -IP ]). :- autoload(library(apply),[maplist/2,maplist/3]). :- autoload(library(backcomp),[thread_at_exit/1]). :- autoload(library(broadcast), [broadcast_request/1,broadcast/1,listening/3,listen/3]). :- use_module(library(debug),[debug/3]). :- autoload(library(error), [must_be/2,syntax_error/1,domain_error/2,existence_error/2]). :- autoload(library(option),[option/3]). :- autoload(library(socket), [ tcp_close_socket/1, udp_socket/1, tcp_bind/2, tcp_getopt/2, tcp_setopt/2, udp_receive/4, udp_send/4 ]). % :- debug(udp(broadcast)). /** A UDP broadcast proxy SWI-Prolog's broadcast library provides a means that may be used to facilitate publish and subscribe communication regimes between anonymous members of a community of interest. The members of the community are however, necessarily limited to a single instance of Prolog. The UDP broadcast library removes that restriction. With this library loaded, any member on your local IP subnetwork that also has this library loaded may hear and respond to your broadcasts. This library support three styles of networking as described below. Each of these networks have their own advantages and disadvantages. Please study the literature to understand the consequences. $ broadcast : Broadcast messages are sent to the LAN subnet. The broadcast implementation uses two UDP ports: a public to address the whole group and a private one to address a specific node. Broadcasting is generally a good choice if the subnet is small and traffic is low. $ unicast : Unicast sends copies of packages to known peers. Unicast networks can easily be routed. The unicast version uses a single UDP port per node. Unicast is generally a good choice for a small party, in particular if the peers are in different networks. $ multicast : Multicast is like broadcast, but it can be configured to work accross networks and may work more efficiently on VLAN networks. Like the broadcast setup, two UDP ports are used. Multicasting can in general deliver the most efficient LAN and WAN networks, but requires properly configured routing between the peers. After initialization and, in the case of a _unicast_ network managing the set of peers, communication happens through broadcast/1, broadcast_request/1 and listen/1,2,3. A broadcast/1 or broadcast_request/1 of the shape udp(Scope, Term) or udp(Scope, Term, TimeOut) is forwarded over the UDP network to all peers that joined the same `Scope`. To prevent the potential for feedback loops, only the plain `Term` is broadcasted locally. The timeout is optional. It specifies the amount to time to wait for replies to arrive in response to a broadcast_request/1. The default period is 0.250 seconds. The timeout is ignored for broadcasts. An example of three separate processes cooperating in the same _scope_ called `peers`: == Process A: ?- listen(number(X), between(1, 5, X)). true. ?- Process B: ?- listen(number(X), between(7, 9, X)). true. ?- Process C: ?- findall(X, broadcast_request(udp(peers, number(X))), Xs). Xs = [1, 2, 3, 4, 5, 7, 8, 9]. ?- == It is also possible to carry on a private dialog with a single responder. To do this, you supply a compound of the form, Term:PortId, to a UDP scoped broadcast/1 or broadcast_request/1, where PortId is the ip-address and port-id of the intended listener. If you supply an unbound variable, PortId, to broadcast_request, it will be unified with the address of the listener that responds to Term. You may send a directed broadcast to a specific member by simply providing this address in a similarly structured compound to a UDP scoped broadcast/1. The message is sent via unicast to that member only by way of the member's broadcast listener. It is received by the listener just as any other broadcast would be. The listener does not know the difference. For example, in order to discover who responded with a particular value: == Host B Process 1: ?- listen(number(X), between(1, 5, X)). true. ?- Host A Process 1: ?- listen(number(X), between(7, 9, X)). true. ?- Host A Process 2: ?- listen(number(X), between(1, 5, X)). true. ?- bagof(X, broadcast_request(udp(peers,number(X):From,1)), Xs). From = ip(192, 168, 1, 103):34855, Xs = [7, 8, 9] ; From = ip(192, 168, 1, 103):56331, Xs = [1, 2, 3, 4, 5] ; From = ip(192, 168, 1, 104):3217, Xs = [1, 2, 3, 4, 5]. == All incomming trafic is handled by a single thread with the alias `udp_inbound_proxy`. This thread also performs the internal dispatching using broadcast/1 and broadcast_request/1. Future versions may provide for handling these requests in separate threads. ## Caveats {#udp-broadcase-caveats} While the implementation is mostly transparent, there are some important and subtle differences that must be taken into consideration: * UDP broadcast requires an initialization step in order to launch the broadcast listener proxy. See udp_broadcast_initialize/2. * Prolog's broadcast_request/1 is nondet. It sends the request, then evaluates the replies synchronously, backtracking as needed until a satisfactory reply is received. The remaining potential replies are not evaluated. With UDP, all peers will send all answers to the query. The receiver may however stop listening. * A UDP broadcast/1 is completely asynchronous. * A UDP broadcast_request/1 is partially synchronous. A broadcast_request/1 is sent, then the sender balks for a period of time (default: 250 ms) while the replies are collected. Any reply that is received after this period is silently discarded. A optional second argument is provided so that a sender may specify more (or less) time for replies. * Replies are presented to the user as a choice point on arrival, until the broadcast request timer finally expires. This allows traffic to propagate through the system faster and provides the requestor with the opportunity to terminate a broadcast request early if desired, by simply cutting choice points. * Please beware that broadcast request transactions remain active and resources consumed until broadcast_request finally fails on backtracking, an uncaught exception occurs, or until choice points are cut. Failure to properly manage this will likely result in chronic exhaustion of UDP sockets. * If a listener is connected to a generator that always succeeds (e.g. a random number generator), then the broadcast request will never terminate and trouble is bound to ensue. * broadcast_request/1 with =|udp_subnet|= scope is _not_ reentrant. If a listener performs a broadcast_request/1 with UDP scope recursively, then disaster looms certain. This caveat does not apply to a UDP scoped broadcast/1, which can safely be performed from a listener context. * UDP broadcast's capacity is not infinite. While it can tolerate substantial bursts of activity, it is designed for short bursts of small messages. Unlike TIPC, UDP is unreliable and has no QOS protections. Congestion is likely to cause trouble in the form of non-Byzantine failure. That is, late, lost (e.g. infinitely late), or duplicate datagrams. Caveat emptor. * A UDP broadcast_request/1 term that is grounded is considered to be a broadcast only. No replies are collected unless the there is at least one unbound variable to unify. * A UDP broadcast/1 always succeeds, even if there are no listeners. * A UDP broadcast_request/1 that receives no replies will fail. * Replies may be coming from many different places in the network (or none at all). No ordering of replies is implied. * Prolog terms are sent to others after first converting them to atoms using term_string/3. Serialization does not deal with cycles, attributes or sharing. The hook udp_term_string_hook/3 may be defined to change the message serialization and support different message formats and/or encryption. * The broadcast model is based on anonymity and a presumption of trust--a perfect recipe for compromise. UDP is an Internet protocol. A UDP broadcast listener exposes a public port, which is static and shared by all listeners, and a private port, which is semi-static and unique to the listener instance. Both can be seen from off-cluster nodes and networks. Usage of this module exposes the node and consequently, the cluster to significant security risks. So have a care when designing your application. You must talk only to those who share and contribute to your concerns using a carefully prescribed protocol. * UDP broadcast categorically and silently ignores all message traffic originating from or terminating on nodes that are not members of the local subnet. This security measure only keeps honest people honest! @author Jeffrey Rosenwald (JeffRose@acm.org), Jan Wielemaker @license BSD-2 @see tipc.pl */ :- multifile udp_term_string_hook/3, % +Scope, ?Term, ?String udp_unicast_join_hook/3, % +Scope, +From, +Data black_list/1. % +Term :- meta_predicate safely(0), safely_det(0). safely(Predicate) :- Err = error(_,_), catch(Predicate, Err, print_message_fail(Err)). safely_det(Predicate) :- Err = error(_,_), catch(Predicate, Err, print_message_fail(Err)), !. safely_det(_). print_message_fail(Term) :- print_message(error, Term), fail. udp_broadcast_address(IPAddress, Subnet, BroadcastAddress) :- IPAddress = ip(A1, A2, A3, A4), Subnet = ip(S1, S2, S3, S4), BroadcastAddress = ip(B1, B2, B3, B4), B1 is A1 \/ (S1 xor 255), B2 is A2 \/ (S2 xor 255), B3 is A3 \/ (S3 xor 255), B4 is A4 \/ (S4 xor 255). %! udp_broadcast_service(?Scope, ?Address) is nondet. % % provides the UDP broadcast address for a given Scope. At present, % only one scope is supported, =|udp_subnet|=. %! udp_scope(?ScopeName, ?ScopeDef) :- dynamic udp_scope/2, udp_scope_peer/2. :- volatile udp_scope/2, udp_scope_peer/2. % % Here's a UDP proxy to Prolog's broadcast library % % A sender may extend a broadcast to a subnet of a UDP network by % specifying a =|udp_subnet|= scoping qualifier in his/her broadcast. % The qualifier has the effect of selecting the appropriate multi-cast % address for the transmission. Thus, the sender of the message has % control over the scope of his/her traffic on a per-message basis. % % All in-scope listeners receive the broadcast and simply rebroadcast % the message locally. All broadcast replies, if any, are sent directly % to the sender via the port-id that was received with the broadcast. % % Each listener exposes two UDP ports, a shared public port that is % bound to a well-known port number and a private port that uniquely % indentifies the listener. Broadcasts are received on the public port % and replies are sent on the private port. Directed broadcasts % (unicasts) are received on the private port and replies are sent on % the private port. % Thread 1 listens for directed traffic on the private port. % :- dynamic udp_private_socket/3, % Port, Socket, FileNo udp_public_socket/4, % Scope, Port, Socket, FileNo udp_closed/1. % Scope udp_inbound_proxy(Master) :- thread_at_exit(inbound_proxy_died), make_private_socket, thread_send_message(Master, udp_inbound_ready), udp_inbound_proxy_loop. udp_inbound_proxy_loop :- forall(udp_scope(Scope, ScopeData), make_public_socket(ScopeData, Scope)), retractall(udp_closed(_)), findall(FileNo, udp_socket_file_no(FileNo), FileNos), catch(dispatch_inbound(FileNos), E, dispatch_exception(E)), udp_inbound_proxy_loop. dispatch_exception(E) :- E = error(_,_), !, print_message(warning, E). dispatch_exception(_). %! make_private_socket is det. % % Create our private socket. This socket is used for messages that are % directed to me. Note that we only need this for broadcast networks. % If we use a unicast network we use our public port to contact this % specific server. make_private_socket :- udp_private_socket(_Port, S, _F), !, ( ( udp_scope(Scope, broadcast(_,_,_)) ; udp_scope(Scope, multicast(_,_)) ), \+ udp_closed(Scope) -> true ; tcp_close_socket(S), retractall(udp_private_socket(_,_,_)) ). make_private_socket :- udp_scope(_, broadcast(_,_,_)), !, udp_socket(S), tcp_bind(S, Port), tcp_getopt(S, file_no(F)), tcp_setopt(S, broadcast), assertz(udp_private_socket(Port, S, F)). make_private_socket :- udp_scope(_, multicast(_,_)), !, udp_socket(S), tcp_bind(S, Port), tcp_getopt(S, file_no(F)), assertz(udp_private_socket(Port, S, F)). make_private_socket. %! make_public_socket(+ScopeData, +Scope) % % Create the public port Scope. make_public_socket(_, Scope) :- udp_public_socket(Scope, _Port, S, _), !, ( udp_closed(Scope) -> tcp_close_socket(S), retractall(udp_public_socket(Scope, _, _, _)) ; true ). make_public_socket(broadcast(_SubNet, _Broadcast, Port), Scope) :- udp_socket(S), tcp_setopt(S, reuseaddr), tcp_bind(S, Port), tcp_getopt(S, file_no(F)), assertz(udp_public_socket(Scope, Port, S, F)). make_public_socket(multicast(Group, Port), Scope) :- udp_socket(S), tcp_setopt(S, reuseaddr), tcp_bind(S, Port), tcp_setopt(S, ip_add_membership(Group)), tcp_getopt(S, file_no(F)), assertz(udp_public_socket(Scope, Port, S, F)). make_public_socket(unicast(Port), Scope) :- udp_socket(S), tcp_bind(S, Port), tcp_getopt(S, file_no(F)), assertz(udp_public_socket(Scope, Port, S, F)). udp_socket_file_no(FileNo) :- udp_private_socket(_,_,FileNo). udp_socket_file_no(FileNo) :- udp_public_socket(_,_,_,FileNo). %! dispatch_inbound(+FileNos) % % Dispatch inbound traffic. This loop uses wait_for_input/3 to wait % for one or more UDP sockets and dispatches the requests using the % internal broadcast service. For an incomming broadcast _request_ we % send the reply only to the requester and therefore we must use a % socket that is not in broadcast mode. dispatch_inbound(FileNos) :- debug(udp(broadcast), 'Waiting for ~p', [FileNos]), wait_for_input(FileNos, Ready, infinite), debug(udp(broadcast), 'Ready: ~p', [Ready]), maplist(dispatch_ready, Ready), dispatch_inbound(FileNos). dispatch_ready(FileNo) :- udp_private_socket(_Port, Private, FileNo), !, udp_receive(Private, Data, From, [max_message_size(65535)]), debug(udp(broadcast), 'Inbound on private port', []), ( in_scope(Scope, From), udp_term_string(Scope, Term, Data) % only accept valid data -> ld_dispatch(Private, Term, From, Scope) ; true ). dispatch_ready(FileNo) :- udp_public_socket(Scope, _PublicPort, Public, FileNo), !, udp_receive(Public, Data, From, [max_message_size(65535)]), debug(udp(broadcast), 'Inbound on public port from ~p for scope ~p', [From, Scope]), ( in_scope(Scope, From), udp_term_string(Scope, Term, Data) % only accept valid data -> ( udp_scope(Scope, unicast(_)) -> ld_dispatch(Public, Term, From, Scope) ; udp_private_socket(_PrivatePort, Private, _FileNo), ld_dispatch(Private, Term, From, Scope) ) ; udp_scope(Scope, unicast(_)), udp_term_string(Scope, Term, Data), unicast_out_of_scope_request(Scope, From, Term) -> true ; true ). in_scope(Scope, Address) :- udp_scope(Scope, ScopeData), in_scope(ScopeData, Scope, Address), !. in_scope(Scope, From) :- debug(udp(broadcast), 'Out-of-scope ~p datagram from ~p', [Scope, From]), fail. in_scope(broadcast(Subnet, Broadcast, _PublicPort), _Scope, IP:_FromPort) :- udp_broadcast_address(IP, Subnet, Broadcast). in_scope(multicast(_Group, _Port), _Scope, _From). in_scope(unicast(_PublicPort), Scope, IP:_) :- udp_peer(Scope, IP:_). %! ld_dispatch(+PrivateSocket, +Term, +From, +Scope) % % Locally dispatch Term received from From. If it concerns a broadcast % request, send the replies to PrivateSocket to From. The multifile % hook black_list/1 can be used to ignore certain messages. ld_dispatch(_S, Term, From, _Scope) :- debug(udp(broadcast), 'ld_dispatch(~p) from ~p', [Term, From]), fail. ld_dispatch(_S, Term, _From, _Scope) :- blacklisted(Term), !. ld_dispatch(S, request(Key, Term), From, Scope) :- !, forall(safely(broadcast_request(Term)), safely((udp_term_string(Scope, reply(Key,Term), Message), udp_send(S, Message, From, [])))). ld_dispatch(_S, send(Term), _From, _Scope) :- !, safely_det(broadcast(Term)). ld_dispatch(_S, reply(Key, Term), From, _Scope) :- ( reply_queue(Key, Queue) -> safely(thread_send_message(Queue, Term:From)) ; true ). blacklisted(send(Term)) :- black_list(Term). blacklisted(request(_,Term)) :- black_list(Term). blacklisted(reply(_,Term)) :- black_list(Term). %! reload_udp_proxy % % Update the UDP relaying proxy service. The proxy consists of three % forwarding mechanisms: % % - Listen on our _scope_. If any messages are received, hand them % to udp_broadcast/3 to be broadcasted to _scope_ or sent to a % specific recipient. % - Listen on the _scope_ public port. Incomming messages are % relayed to the internal broadcast mechanism and replies are sent % to from our private socket. % - Listen on our private port and reply using the same port. reload_udp_proxy :- reload_outbound_proxy, reload_inbound_proxy. reload_outbound_proxy :- listening(udp_broadcast, udp(_,_), _), !. reload_outbound_proxy :- listen(udp_broadcast, udp(Scope,Message), udp_broadcast(Message, Scope, 0.25)), listen(udp_broadcast, udp(Scope,Message,Timeout), udp_broadcast(Message, Scope, Timeout)), listen(udp_broadcast, udp_subnet(Message), % backward compatibility udp_broadcast(Message, subnet, 0.25)), listen(udp_broadcast, udp_subnet(Message,Timeout), udp_broadcast(Message, subnet, Timeout)). reload_inbound_proxy :- catch(thread_signal(udp_inbound_proxy, throw(udp_reload)), error(existence_error(thread, _),_), fail), !. reload_inbound_proxy :- thread_self(Me), thread_create(udp_inbound_proxy(Me), _, [ alias(udp_inbound_proxy), detached(true) ]), thread_get_message(Me, udp_inbound_ready, [timeout(10)]). inbound_proxy_died :- thread_self(Self), thread_property(Self, status(Status)), ( catch(recreate_proxy(Status), _, fail) -> print_message(informational, httpd_restarted_worker(Self)) ; done_status_message_level(Status, Level), print_message(Level, httpd_stopped_worker(Self, Status)) ). recreate_proxy(exception(Error)) :- recreate_on_error(Error), reload_inbound_proxy. recreate_on_error('$aborted'). % old recreate_on_error(unwind(abort)). recreate_on_error(time_limit_exceeded). done_status_message_level(true, silent) :- !. done_status_message_level(exception('$aborted'), silent) :- !. done_status_message_level(exception(unwind(abort)), silent) :- !. done_status_message_level(_, informational). %! udp_broadcast_close(+Scope) % % Close a UDP broadcast scope. udp_broadcast_close(Scope) :- udp_scope(Scope, _ScopeData), !, assert(udp_closed(Scope)), reload_udp_proxy. udp_broadcast_close(_). %! udp_broadcast(+What, +Scope, +TimeOut) % % Send a broadcast request to my UDP peers in Scope. What is either of % the shape `Term:Address` to send Term to a specific address or query % the address from which term is answered or it is a plain `Term`. % % If `Term` is nonground, it is considered is a _request_ (see % broadcast_request/1) and the predicate succeeds for each answer % received within TimeOut seconds. If Term is ground it is considered % an asynchronous broadcast and udp_broadcast/3 is deterministic. udp_broadcast(Term:To, Scope, _Timeout) :- ground(Term), ground(To), % broadcast to single listener !, udp_basic_broadcast(send(Term), Scope, single(To)). udp_broadcast(Term, Scope, _Timeout) :- ground(Term), % broadcast to all listeners !, udp_basic_broadcast(send(Term), Scope, broadcast). udp_broadcast(Term:To, Scope, Timeout) :- ground(To), % request to single listener !, setup_call_cleanup( request_queue(Id, Queue), ( udp_basic_broadcast(request(Id, Term), Scope, single(To)), udp_br_collect_replies(Queue, Timeout, Term:To) ), destroy_request_queue(Queue)). udp_broadcast(Term:From, Scope, Timeout) :- !, % request to all listeners, collect sender setup_call_cleanup( request_queue(Id, Queue), ( udp_basic_broadcast(request(Id, Term), Scope, broadcast), udp_br_collect_replies(Queue, Timeout, Term:From) ), destroy_request_queue(Queue)). udp_broadcast(Term, Scope, Timeout) :- % request to all listeners udp_broadcast(Term:_, Scope, Timeout). :- dynamic reply_queue/2. request_queue(Id, Queue) :- Id is random(1<<63), message_queue_create(Queue), asserta(reply_queue(Id, Queue)). destroy_request_queue(Queue) :- % leave queue to GC retractall(reply_queue(_, Queue)). %! udp_basic_broadcast(+Term, +Dest) is multi. % % Create a UDP private socket and use it to send Term to Address. If % Address is our broadcast address, set the socket in broadcast mode. % % This predicate succeeds with a choice point. Committing the choice % point closes S. % % @arg Dest is one of single(Target) or `broadcast`. udp_basic_broadcast(Term, Scope, Dest) :- debug(udp(broadcast), 'UDP proxy outbound ~p to ~p', [Term, Dest]), udp_term_string(Scope, Term, String), udp_send_message(Dest, String, Scope). udp_send_message(single(Address), String, Scope) :- ( udp_scope(Scope, unicast(_)) -> udp_public_socket(Scope, _Port, S, _) ; udp_private_socket(_Port, S, _F) ), safely(udp_send(S, String, Address, [])). udp_send_message(broadcast, String, Scope) :- ( udp_scope(Scope, unicast(_)) -> udp_public_socket(Scope, _Port, S, _), forall(udp_peer(Scope, Address), ( debug(udp(broadcast), 'Unicast to ~p', [Address]), safely(udp_send(S, String, Address, [])))) ; udp_scope(Scope, broadcast(_SubNet, Broadcast, Port)) -> udp_private_socket(_PrivatePort, S, _F), udp_send(S, String, Broadcast:Port, []) ; udp_scope(Scope, multicast(Group, Port)) -> udp_private_socket(_PrivatePort, S, _F), udp_send(S, String, Group:Port, []) ). % ! udp_br_collect_replies(+Queue, +TimeOut, -TermAndFrom) is nondet. % % Collect replies on Socket for TimeOut seconds. Succeed for each % received message. udp_br_collect_replies(Queue, Timeout, Reply) :- get_time(Start), Deadline is Start+Timeout, repeat, ( thread_get_message(Queue, Reply, [ deadline(Deadline) ]) -> true ; !, fail ). %! udp_broadcast_initialize(+IPAddress, +Options) is semidet. % % Initialized UDP broadcast bridge. IPAddress is the IP address on the % network we want to broadcast on. IP addresses are terms ip(A,B,C,D) % or an atom or string of the format =|A.B.C.D|=. Options processed: % % - scope(+ScopeName) % Name of the scope. Default is `subnet`. % - subnet_mask(+SubNet) % Subnet to broadcast on. This uses the same syntax as IPAddress. % Default classifies the network as class A, B or C depending on % the the first octet and applies the default mask. % - port(+Port) % Public port to use. Default is 20005. % - method(+Method) % Method to send a message to multiple peers. One of % - broadcast % Use UDP broadcast messages to the LAN. This is the % default % - multicast % Use UDP multicast messages. This can be used on WAN networks, % provided the intermediate routers understand multicast. % - unicast % Send the messages individually to all registered peers. % % For compatibility reasons Options may be the subnet mask. udp_broadcast_initialize(IP, Options) :- with_mutex(udp_broadcast, udp_broadcast_initialize_sync(IP, Options)). udp_broadcast_initialize_sync(IP, Options) :- nonvar(Options), Options = ip(_,_,_,_), !, udp_broadcast_initialize(IP, [subnet_mask(Options)]). udp_broadcast_initialize_sync(IP, Options) :- to_ip4(IP, IPAddress), option(method(Method), Options, broadcast), must_be(oneof([broadcast, multicast, unicast]), Method), udp_broadcast_initialize_sync(Method, IPAddress, Options), reload_udp_proxy. udp_broadcast_initialize_sync(broadcast, IPAddress, Options) :- option(subnet_mask(Subnet), Options, _), mk_subnet(Subnet, IPAddress, Subnet4), option(port(Port), Options, 20005), option(scope(Scope), Options, subnet), udp_broadcast_address(IPAddress, Subnet4, Broadcast), udp_broadcast_close(Scope), assertz(udp_scope(Scope, broadcast(Subnet4, Broadcast, Port))). udp_broadcast_initialize_sync(unicast, _IPAddress, Options) :- option(port(Port), Options, 20005), option(scope(Scope), Options, subnet), udp_broadcast_close(Scope), assertz(udp_scope(Scope, unicast(Port))). udp_broadcast_initialize_sync(multicast, IPAddress, Options) :- option(port(Port), Options, 20005), option(scope(Scope), Options, subnet), udp_broadcast_close(Scope), multicast_address(IPAddress), assertz(udp_scope(Scope, multicast(IPAddress, Port))). to_ip4(Atomic, ip(A,B,C,D)) :- atomic(Atomic), !, ( split_string(Atomic, ".", "", Strings), maplist(number_string, [A,B,C,D], Strings) -> true ; syntax_error(illegal_ip_address) ). to_ip4(IP, IP). mk_subnet(Var, IP, Subnet) :- var(Var), !, ( default_subnet(IP, Subnet) -> true ; domain_error(ip_with_subnet, IP) ). mk_subnet(Subnet, _, Subnet4) :- to_ip4(Subnet, Subnet4). %! default_subnet(+IP, -NetWork) % % Determine the default network address from an IP address. This % classifies the network as class A, B or C. % % @see https://docs.oracle.com/cd/E19504-01/802-5753/planning3-78185/index.html default_subnet(ip(A,_,_,_), ip(A,0,0,0)) :- between(0,127, A), !. default_subnet(ip(A,B,_,_), ip(A,B,0,0)) :- between(128,191, A), !. default_subnet(ip(A,B,C,_), ip(A,B,C,0)) :- between(192,223, A), !. multicast_address(ip(A,_,_,_)) :- between(224, 239, A), !. multicast_address(IP) :- domain_error(multicast_network, IP). /******************************* * UNICAST PEERS * *******************************/ %! udp_peer_add(+Scope, +Address) is det. %! udp_peer_del(+Scope, ?Address) is det. %! udp_peer(?Scope, ?Address) is nondet. % % Manage and query the set of known peers for a unicast network. % Address is either a term IP:Port or a plain IP address. In the % latter case the default port registered with the scope is used. % % @arg Address has canonical form ip(A,B,C,D):Port. udp_peer_add(Scope, Address) :- must_be(ground, Address), peer_address(Address, Scope, Canonical), ( udp_scope_peer(Scope, Canonical) -> true ; assertz(udp_scope_peer(Scope, Canonical)) ). udp_peer_del(Scope, Address) :- peer_address(Address, Scope, Canonical), retractall(udp_scope_peer(Scope, Canonical)). udp_peer(Scope, IPAddress) :- udp_scope_peer(Scope, IPAddress). peer_address(IP:Port, _Scope, IPAddress:Port) :- !, to_ip4(IP, IPAddress). peer_address(IP, Scope, IPAddress:Port) :- ( udp_scope(Scope, unicast(Port)) -> true ; existence_error(udp_scope, Scope) ), to_ip4(IP, IPAddress). /******************************* * HOOKS * *******************************/ %! udp_term_string_hook(+Scope, +Term, -String) is det. %! udp_term_string_hook(+Scope, -Term, +String) is semidet. % % Hook for serializing the message Term. The default writes % =|%prolog\n|=, followed by the Prolog term in quoted notation while % ignoring operators. This hook may use alternative serialization such % as fast_term_serialized/2, use library(ssl) to realise encrypted % messages, etc. % % @arg Scope is the scope for which the message is broadcasted. This % can be used to use different serialization for different scopes. % @arg Term encapsulates the term broadcasted by the application as % follows: % % - send(ApplTerm) % Is sent by broadcast(udp(Scope, ApplTerm)) % - request(Id,ApplTerm) % Is sent by broadcast_request/1, where Id is a unique large % (64 bit) integer. % - reply(Id,ApplTerm) % Is sent to reply on a broadcast_request/1 request that has % been received. Arguments are the same as above. % % @throws The hook may throw udp(invalid_message) to stop processing % the message. %! udp_term_string(+Scope, +Term, -String) is det. %! udp_term_string(+Scope, -Term, +String) is semidet. % % Serialize an arbitrary Prolog term as a string. The string is % prefixed by a magic key to ensure we only accept messages that are % meant for us. % % In mode (+,-), Term is written with the options ignore_ops(true) and % quoted(true). % % This predicate first calls udp_term_string_hook/3. udp_term_string(Scope, Term, String) :- catch(udp_term_string_hook(Scope, Term, String), udp(Error), true), !, ( var(Error) -> true ; Error == invalid_message -> fail ; throw(udp(Error)) ). udp_term_string(_Scope, Term, String) :- ( var(String) -> format(string(String), '%-prolog-\n~W', [ Term, [ ignore_ops(true), quoted(true) ] ]) ; sub_string(String, 0, _, _, '%-prolog-\n'), term_string(Term, String, [ syntax_errors(quiet) ]) ). %! unicast_out_of_scope_request(+Scope, +From, +Data) is semidet. %! udp_unicast_join_hook(+Scope, +From, +Data) is semidet. % % This multifile hook is called if an UDP package is received on the % port of the unicast network identified by Scope. From is the origin % IP and port and Data is the message data that is deserialized as % defined for the scope (see udp_term_string/3). % % This hook is intended to initiate a new node joining the network of % peers. We could in theory also omit the in-scope test and use a % normal broadcast to join. Using a different channal however provides % a basic level of security. A possibe implementation is below. The % first fragment is a hook added to the server, the second is a % predicate added to a client and the last initiates the request in % the client. The excanged term (join(X)) can be used to exchange a % welcome handshake. % % % ``` % :- multifile udp_broadcast:udp_unicast_join_hook/3. % udp_broadcast:udp_unicast_join_hook(Scope, From, join(welcome)) :- % udp_peer_add(Scope, From), % ``` % % ``` % join_request(Scope, Address, Reply) :- % udp_peer_add(Scope, Address), % broadcast_request(udp(Scope, join(X))). % ``` % % ``` % ?- join_request(myscope, "1.2.3.4":10001, Reply). % Reply = welcome. % ``` unicast_out_of_scope_request(Scope, From, send(Term)) :- udp_unicast_join_hook(Scope, From, Term). unicast_out_of_scope_request(Scope, From, request(Key, Term)) :- udp_unicast_join_hook(Scope, From, Term), udp_public_socket(Scope, _Port, Socket, _FileNo), safely((udp_term_string(Scope, reply(Key,Term), Message), udp_send(Socket, Message, From, []))).