1/* Prolog Machine Query Interface 2 Author: Eric Zinda 3 E-mail: ericz@inductorsoftware.com 4 WWW: http://www.inductorsoftware.com 5 Copyright (c) 2021, Eric Zinda 6 All rights reserved. 7 8 Redistribution and use in source and binary forms, with or without 9 modification, are permitted provided that the following conditions 10 are met: 11 12 1. Redistributions of source code must retain the above copyright 13 notice, this list of conditions and the following disclaimer. 14 15 2. Redistributions in binary form must reproduce the above copyright 16 notice, this list of conditions and the following disclaimer in 17 the documentation and/or other materials provided with the 18 distribution. 19 20 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 21 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 22 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 23 FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 24 COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 25 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 26 BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 27 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 28 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 30 ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 31 POSSIBILITY OF SUCH DAMAGE. 32*/ 33 34:- module(mqi, 35 [ mqi_start/0, 36 mqi_start/1, % +Options 37 mqi_stop/1, % ?Thread 38 mqi_version/2 % ?Major_Version, ?Minor_Version 39 ]).
swiplserver Python library, but starting manually can be useful when debugging Prolog code in some scenarios. See the documentation on "Standalone Mode" for more information.
Once started, the MQI listens for TCP/IP or Unix Domain Socket connections and authenticates them using the password provided (or created depending on options) before processing any messages. The messages processed by the MQI are described below.
For debugging, the server outputs traces using the debug/3 predicate so that the server operation can be observed by using the debug/1 predicate. Run the following commands to see them:
debug(mqi(protocol)): Traces protocol messages to show the flow of commands and connections. It is designed to avoid filling the screen with large queries and results to make it easier to read.debug(mqi(query)): Traces messages that involve each query and its results. Therefore it can be quite verbose depending on the query.
__Options__
Options is a list containing any combination of the following options. When used in the Prolog top level (i.e. in Standalone Mode), these are specified as normal Prolog options like this:
mqi_start([unix_domain_socket(Socket), password('a password')])
When using "Embedded Mode" they are passed using the same name but as normal command line arguments like this:
swipl mqi --write_connection_values=true
--password="a password" --create_unix_domain_socket=true
Note the use of quotes around values that could confuse command line
processing like spaces (e.g. "a password") and that
unix_domain_socket(Variable) is written as
--create_unix_domain_socket=true on the command line. See below for
more information.
write_connection_values(true) is set, the selected port is output to STDOUT followed by \n on startup to allow the client language library to retrieve it in "Embedded Mode".
To have one generated instead (recommended), pass Unix_Domain_Socket_Path_And_File as a variable when calling from the Prolog top level and the variable will be unified with a created filename. If launching in "Embedded Mode", instead pass --create_unix_domain_socket=true since there isn't a way to specify variables from the command line. When generating the file, a temporary directory will be created using tmp_file/2 and a socket file will be created within that directory following the below requirements. If the directory and file are unable to be created for some reason, mqi_start/1 fails.
Regardless of whether the file is specified or generated, if the option write_connection_values(true) is set, the fully qualified path to the generated file is output to STDOUT followed by \n on startup to allow the client language library to retrieve it.
Specifying a file to use should follow the same guidelines as the generated file:
write_connection_values(true) is set, the password is output to STDOUT followed by \n on startup to allow the client language library to retrieve it. This is the recommended way to integrate the MQI with a language as it avoids including the password as source code. This option is only included so that a known password can be supplied for when the MQI is running in Standalone Mode.query_timeout(+Seconds)
Sets the default time in seconds that a query is allowed to run before it is cancelled. This can be overridden on a query by query basis. If not set, the default is no timeout (-1).pending_connections(+Count)
Sets the number of pending connections allowed for the MQI as in tcp_listen/2. If not provided, the default is 5.run_server_on_thread(+Run_Server_On_Thread)
Determines whether mqi_start/1 runs in the background on its own thread or blocks until the MQI shuts down. Must be missing or set to true when running in "Embedded Mode" so that the SWI Prolog process can exit properly. If not set, the default is true.run_server_on_thread(true). Passing in an atom for Server_Thread will only set the server thread name if run_server_on_thread(true). If Server_Thread is a variable, it is unified with a generated name.write_connection_values(+Write_Connection_Values)
Determines whether the server writes the port (or generated Unix Domain Socket) and password to STDOUT as it initializes. Used by language libraries to retrieve this information for connecting. If not set, the default is false.write_output_to_file(+File)
Redirects STDOUT and STDERR to the file path specified. Useful for debugging the MQI when it is being used in "Embedded Mode". If using multiple MQI instances in one SWI Prolog instance, only set this on the first one. Each time it is set the output will be redirected.
*/
110:- use_module(library(socket)). 111:- use_module(library(http/json)). 112:- use_module(library(http/json_convert)). 113:- use_module(library(http/http_stream)). 114:- use_module(library(option)). 115:- use_module(library(term_to_json)). 116:- use_module(library(debug)). 117:- use_module(library(filesex)). 118:- use_module(library(gensym)). 119:- use_module(library(lists)). 120:- use_module(library(main)). 121:- use_module(library(make)). 122:- use_module(library(prolog_source)). 123:- use_module(library(time)). 124:- use_module(library(uuid)). 125 126% One for every Machine Query Interface running 127:- dynamic(mqi_thread/3). 128 129% One for every active connection 130:- dynamic(mqi_worker_threads/3). 131:- dynamic(mqi_socket/5). 132 133% Indicates that a query is in progress on the goal thread or hasn't had its results drained 134% Deleted once the last result from the queue has been drained 135% Only deleted by the communication thread to avoid race conditions 136:- dynamic(query_in_progress/1). 137 138% Indicates to the communication thread that we are in a place 139% that can be cancelled 140:- dynamic(safe_to_cancel/1).
Note that the initial version of the MQI did not have a version predicate so The proper way for callers to check the version is:
use_module(library(mqi)),
( current_predicate(mqi_version/2)
-> mqi_version(Major_Version, Minor_Version)
; Major_Version = 0, Minor_Version = 0
)
Major versions are increased when there is a change to the protocol that will likely break clients written to the previous version. Minor versions are increased when there is new functionality that will not break clients written to the old version
This allows a client written to MQI version 'Client_Major_Version.Client_Minor_Version' to check for non-breaking compatibility like this:
Client_Major_Version = MQI_Major_Version and Client_Minor_Version <= MQI_Minor_Version
Breaking changes (i.e. Major version increments) should be very rare as the goal is to have the broadest adoption possible.
Protocol Version History:
175mqi_version(1, 0). 176 177 178% Password is carefully constructed to be a string (not an atom) so that it is not 179% globally visible 180% Add ".\n" to the password since it will be added by the message when received 181mqi_start(Options) :- 182 Encoding = utf8, 183 option(pending_connections(Connection_Count), Options, 5), 184 option(query_timeout(Query_Timeout), Options, -1), 185 option(port(Port), Options, _), 186 option(run_server_on_thread(Run_Server_On_Thread), Options, true), 187 option(exit_main_on_failure(Exit_Main_On_Failure), Options, false), 188 option(write_connection_values(Write_Connection_Values), Options, false), 189 option(unix_domain_socket(Unix_Domain_Socket_Path_And_File), Options, _), 190 ( ( memberchk(unix_domain_socket(_), Options), 191 var(Unix_Domain_Socket_Path_And_File) 192 ) 193 -> unix_domain_socket_path(Unix_Domain_Socket_Path, Unix_Domain_Socket_Path_And_File) 194 ; true 195 ), 196 option(server_thread(Server_Thread_ID), Options, _), 197 ( var(Server_Thread_ID) 198 -> gensym(mqi, Server_Thread_ID) 199 ; true 200 ), 201 option(password(Password), Options, _), 202 ( var(Password) 203 -> ( current_prolog_flag(bounded, false) 204 -> uuid(UUID, [format(integer)]) 205 ; UUID is random(1<<62) 206 ), 207 format(string(Password), '~d', [UUID]) 208 ; true 209 ), 210 string_concat(Password, '.\n', Final_Password), 211 bind_socket(Server_Thread_ID, Unix_Domain_Socket_Path_And_File, Port, Socket, Client_Address), 212 send_client_startup_data(Write_Connection_Values, user_output, Unix_Domain_Socket_Path_And_File, Client_Address, Password), 213 option(write_output_to_file(File), Options, _), 214 ( var(File) 215 -> true 216 ; write_output_to_file(File) 217 ), 218 Server_Goal = ( 219 catch(server_thread(Server_Thread_ID, Socket, Client_Address, Final_Password, Connection_Count, Encoding, Query_Timeout, Exit_Main_On_Failure), error(E1, E2), true), 220 debug(mqi(protocol), "Stopped MQI on thread: ~w due to exception: ~w", [Server_Thread_ID, error(E1, E2)]) 221 ), 222 start_server_thread(Run_Server_On_Thread, Server_Thread_ID, Server_Goal, Unix_Domain_Socket_Path, Unix_Domain_Socket_Path_And_File). 223 224opt_type(port, port, natural). 225opt_type(create_unix_domain_socket, create_unix_domain_socket, boolean). 226opt_type(unix_domain_socket, unix_domain_socket, file(write)). 227opt_type(password, password, string). 228opt_type(pending_connections, pending_connections, nonneg). 229opt_type(query_timeout, query_timeout, float). 230opt_type(run_server_on_thread, run_server_on_thread, boolean). 231opt_type(exit_main_on_failure, exit_main_on_failure, boolean). 232opt_type(write_connection_values, write_connection_values, boolean). 233opt_type(write_output_to_file, write_output_to_file, file(write)). 234 235opt_help(port, "TCP/IP port for clients to connect to"). 236opt_help(create_unix_domain_socket, "Create a Unix domain socket for clients to connect to"). 237opt_help(unix_domain_socket, "File path for the Unix domain socket"). 238opt_help(password, "Connection password"). 239opt_help(pending_connections, "Max number of queued connections (5)"). 240opt_help(query_timeout, "Max query runtime in seconds (default infinite)"). 241opt_help(run_server_on_thread, "Run server in a background thread (true)"). 242opt_help(exit_main_on_failure, "Exit the process on a failure"). 243opt_help(write_connection_values, "Print info for clients to connect"). 244opt_help(write_output_to_file, "Write stdout and stderr to file").
To launch embedded mode:
swipl mqi --write_connection_values=true
This will start SWI Prolog and invoke the mqi_start/0 predicate and
exit the process when that predicate stops. Any command line
arguments after the standalone -- will be passed as Options. These
are the same Options that mqi_start/1 accepts and are passed to it
directly. Some options are expressed differently due to command line
limitations, see mqi_start/1 Options for more information.
Any Option values that cause issues during command line parsing (such
as spaces) should be passed with "" like this:
swipl mqi --write_connection_values=true --password="HGJ SOWLWW"
For help on commandline options run
swipl mqi --help
283% Turn off int signal when running in embedded mode so the client language 284% debugger signal doesn't put Prolog into debug mode 285% run_server_on_thread must be missing or true (the default) so we can exit 286% properly 287% create_unix_domain_socket=true/false is only used as a command line argument 288% since it doesn't seem possible to pass create_unix_domain_socket=_ on the command line 289% and have it interpreted as a variable. 290mqi_start :- 291 current_prolog_flag(argv, Argv), 292 argv_options(Argv, _Args, Options), 293 merge_options(Options, [exit_main_on_failure(true)], Options1), 294 select_option(create_unix_domain_socket(Create_Unix_Domain_Socket), Options1, Options2, false), 295 ( Create_Unix_Domain_Socket == true 296 -> merge_options(Options2, [unix_domain_socket(_)], FinalOptions) 297 ; FinalOptions = Options2 298 ), 299 option(run_server_on_thread(Run_Server_On_Thread), FinalOptions, true), 300 ( Run_Server_On_Thread == true 301 -> true 302 ; throw(domain_error(cannot_be_set_in_embedded_mode, run_server_on_thread)) 303 ), 304 mqi_start(FinalOptions), 305 on_signal(int, _, quit), 306 thread_get_message(quit_mqi). 307 308 309quit(_) :- 310 thread_send_message(main, quit_mqi).
Always succeeds.
319% tcp_close_socket(Socket) will shut down the server thread cleanly so the socket is released and can be used again in the same session 320% Closes down any pending connections using abort even if there were no matching server threads since the server thread could have died. 321% At this point only threads associated with live connections (or potentially a goal thread that hasn't detected its missing communication thread) 322% should be left so seeing abort warning messages in the console seems OK 323mqi_stop(Server_Thread_ID) :- 324 % First shut down any matching servers to stop new connections 325 forall(retract(mqi_thread(Server_Thread_ID, _, Socket)), 326 ( 327 debug(mqi(protocol), "Found server: ~w", [Server_Thread_ID]), 328 catch(tcp_close_socket(Socket), Socket_Exception, true), 329 abortSilentExit(Server_Thread_ID, Server_Thread_Exception), 330 debug(mqi(protocol), "Stopped server thread: ~w, socket_close_exception(~w), stop_thread_exception(~w)", [Server_Thread_ID, Socket_Exception, Server_Thread_Exception]) 331 )), 332 forall(retract(mqi_worker_threads(Server_Thread_ID, Communication_Thread_ID, Goal_Thread_ID)), 333 ( 334 abortSilentExit(Communication_Thread_ID, CommunicationException), 335 debug(mqi(protocol), "Stopped server: ~w communication thread: ~w, exception(~w)", [Server_Thread_ID, Communication_Thread_ID, CommunicationException]), 336 abortSilentExit(Goal_Thread_ID, Goal_Exception), 337 debug(mqi(protocol), "Stopped server: ~w goal thread: ~w, exception(~w)", [Server_Thread_ID, Goal_Thread_ID, Goal_Exception]) 338 )). 339 340 341start_server_thread(Run_Server_On_Thread, Server_Thread_ID, Server_Goal, Unix_Domain_Socket_Path, Unix_Domain_Socket_Path_And_File) :- 342 ( 343 -> ( thread_create(Server_Goal, _, [ alias(Server_Thread_ID), 344 at_exit((delete_unix_domain_socket_file(Unix_Domain_Socket_Path, Unix_Domain_Socket_Path_And_File), 345 detach_if_expected(Server_Thread_ID) 346 )) 347 ]), 348 debug(mqi(protocol), "Started server on thread: ~w", [Server_Thread_ID]) 349 ) 350 ; ( , 351 delete_unix_domain_socket_file(Unix_Domain_Socket_Path, Unix_Domain_Socket_Path_And_File), 352 debug(mqi(protocol), "Halting.", []) 353 ) 354 ). 355 356 357% Unix domain sockets create a file that needs to be cleaned up 358% If mqi generated it, there is also a directory that needs to be cleaned up 359% that will only contain that file 360delete_unix_domain_socket_file(Unix_Domain_Socket_Path, Unix_Domain_Socket_Path_And_File) :- 361 ( nonvar(Unix_Domain_Socket_Path) 362 -> catch(delete_directory_and_contents(Unix_Domain_Socket_Path), error(_, _), true) 363 ; ( nonvar(Unix_Domain_Socket_Path_And_File) 364 -> catch(delete_file(Unix_Domain_Socket_Path_And_File), error(_, _), true) 365 ; true 366 ) 367 ). 368 369:- if(current_predicate(unix_domain_socket/1)). 370 optional_unix_domain_socket(Socket) :- 371 unix_domain_socket(Socket). 372:- else. 373 optional_unix_domain_socket(_). 374:- endif. 375 376% Always bind only to localhost for security reasons 377% Delete the socket file in case it is already around so that the same name can be reused 378bind_socket(Server_Thread_ID, Unix_Domain_Socket_Path_And_File, Port, Socket, Client_Address) :- 379 ( nonvar(Unix_Domain_Socket_Path_And_File) 380 -> debug(mqi(protocol), "Using Unix domain socket name: ~w", [Unix_Domain_Socket_Path_And_File]), 381 optional_unix_domain_socket(Socket), 382 catch(delete_file(Unix_Domain_Socket_Path_And_File), error(_, _), true), 383 tcp_bind(Socket, Unix_Domain_Socket_Path_And_File), 384 Client_Address = Unix_Domain_Socket_Path_And_File 385 ; ( tcp_socket(Socket), 386 tcp_setopt(Socket, reuseaddr), 387 tcp_bind(Socket, '127.0.0.1':Port), 388 debug(mqi(protocol), "Using TCP/IP port: ~w", ['127.0.0.1':Port]), 389 Client_Address = Port 390 ) 391 ), 392 assert(mqi_thread(Server_Thread_ID, Unix_Domain_Socket_Path_And_File, Socket)). 393 394% Communicates the used port and password to the client via STDOUT so the client 395% language library can use them to connect 396send_client_startup_data(Write_Connection_Values, Stream, Unix_Domain_Socket_Path_And_File, Port, Password) :- 397 ( 398 -> ( ( var(Unix_Domain_Socket_Path_And_File) 399 -> format(Stream, "~d\n", [Port]) 400 ; format(Stream, "~w\n", [Unix_Domain_Socket_Path_And_File]) 401 ), 402 format(Stream, "~w\n", [Password]), 403 flush_output(Stream) 404 ) 405 ; true 406 ). 407 408 409% Server thread worker predicate 410% Listen for connections and create a connection for each in its own communication thread 411% Uses tail recursion to ensure the stack doesn't grow 412server_thread(Server_Thread_ID, Socket, Address, Password, Connection_Count, Encoding, Query_Timeout, Exit_Main_On_Failure) :- 413 debug(mqi(protocol), "Listening on address: ~w", [Address]), 414 tcp_listen(Socket, Connection_Count), 415 tcp_open_socket(Socket, AcceptFd, _), 416 create_connection(Server_Thread_ID, AcceptFd, Password, Encoding, Query_Timeout, Exit_Main_On_Failure), 417 server_thread(Server_Thread_ID, Socket, Address, Password, Connection_Count, Encoding, Query_Timeout, Exit_Main_On_Failure). 418 419 420% Wait for the next connection and create communication and goal threads to support it 421% Create known IDs for the threads so we can pass them along before the threads are created 422% First create the goal thread to avoid a race condition where the communication 423% thread tries to queue a goal before it is created 424create_connection(Server_Thread_ID, AcceptFd, Password, Encoding, Query_Timeout, Exit_Main_On_Failure) :- 425 debug(mqi(protocol), "Waiting for client connection...", []), 426 tcp_accept(AcceptFd, Socket, _Peer), 427 debug(mqi(protocol), "Client connected", []), 428 gensym('conn', Connection_Base), 429 atomic_list_concat([Server_Thread_ID, "_", Connection_Base, '_comm'], Thread_Alias), 430 atomic_list_concat([Server_Thread_ID, "_", Connection_Base, '_goal'], Goal_Alias), 431 mutex_create(Goal_Alias, [alias(Goal_Alias)]), 432 assert(mqi_worker_threads(Server_Thread_ID, Thread_Alias, Goal_Alias)), 433 thread_create(goal_thread(Thread_Alias), 434 _, 435 [alias(Goal_Alias), at_exit(detach_if_expected(Goal_Alias))]), 436 thread_create(communication_thread(Password, Socket, Encoding, Server_Thread_ID, Goal_Alias, Query_Timeout, Exit_Main_On_Failure), 437 _, 438 [alias(Thread_Alias), at_exit(detach_if_expected(Thread_Alias))]). 439 440 441% The worker predicate for the Goal thread. 442% Looks for a message from the connection thread, processes it, then recurses. 443% 444% Goals always run in the same thread in case the user is setting thread local information. 445% For each answer to the user's query (including an exception), the goal thread will queue a message 446% to the communication thread of the form result(Answer, Find_All), where Find_All == true if the user wants all answers at once 447% Tail recurse to avoid growing the stack 448goal_thread(Respond_To_Thread_ID) :- 449 thread_self(Self_ID), 450 throw_if_testing(Self_ID), 451 thread_get_message(Self_ID, goal(Unexpanded_Goal, Binding_List, Query_Timeout, Find_All)), 452 expand_goal(Unexpanded_Goal, Goal), 453 debug(mqi(query), "Received Findall = ~w, Query_Timeout = ~w, binding list: ~w, unexpanded: ~w, goal: ~w", [Find_All, Query_Timeout, Binding_List, Unexpanded_Goal, Goal]), 454 ( 455 -> One_Answer_Goal = findall(Binding_List, @(user:Goal, user), Answers) 456 ; One_Answer_Goal = ( findall( One_Answer, 457 ( @(user:Goal, user), 458 One_Answer = [Binding_List], 459 send_next_result(Respond_To_Thread_ID, One_Answer, _, Find_All) 460 ), 461 Answers 462 ), 463 ( Answers == [] 464 -> send_next_result(Respond_To_Thread_ID, [], _, Find_All) 465 ; true 466 ) 467 ) 468 ), 469 Cancellable_Goal = run_cancellable_goal(Self_ID, One_Answer_Goal), 470 ( Query_Timeout == -1 471 -> catch(Cancellable_Goal, Top_Exception, true) 472 ; catch(call_with_time_limit(Query_Timeout, Cancellable_Goal), Top_Exception, true) 473 ), 474 ( var(Top_Exception) 475 -> ( 476 -> send_next_result(Respond_To_Thread_ID, Answers, _, Find_All) 477 ; send_next_result(Respond_To_Thread_ID, [], no_more_results, Find_All) 478 ) 479 ; send_next_result(Respond_To_Thread_ID, [], Top_Exception, true) 480 ), 481 goal_thread(Respond_To_Thread_ID). 482 483 484% Used only for testing unhandled exceptions outside of the "safe zone" 485throw_if_testing(Self_ID) :- 486 ( thread_peek_message(Self_ID, testThrow(Test_Exception)) 487 -> ( debug(mqi(query), "TESTING: Throwing test exception: ~w", [Test_Exception]), 488 throw(Test_Exception) 489 ) 490 ; true 491 ). 492 493 494% run_cancellable_goal handles the communication 495% to ensure the cancel exception from the communication thread 496% is injected at a place we are prepared to handle in the goal_thread 497% Before the goal is run, sets a fact to indicate we are in the "safe to cancel" 498% zone for the communication thread. 499% Then it doesn't exit this "safe to cancel" zone if the 500% communication thread is about to cancel 501run_cancellable_goal(Mutex_ID, Goal) :- 502 thread_self(Self_ID), 503 setup_call_cleanup( 504 assert(safe_to_cancel(Self_ID), Assertion), 505 Goal, 506 with_mutex(Mutex_ID, erase(Assertion)) 507 ). 508 509 510% Worker predicate for the communication thread. 511% Processes messages and sends goals to the goal thread. 512% Continues processing messages until communication_thread_listen() throws or ends with true/false 513% 514% Catches all exceptions from communication_thread_listen so that it can do an orderly shutdown of the goal 515% thread if there is a communication failure. 516% 517% True means user explicitly called close or there was an exception 518% only exit the main thread if there was an exception and we are supposed to Exit_Main_On_Failure 519% otherwise just exit the session 520communication_thread(Password, Socket, Encoding, Server_Thread_ID, Goal_Thread_ID, Query_Timeout, Exit_Main_On_Failure) :- 521 thread_self(Self_ID), 522 ( ( 523 catch(communication_thread_listen(Password, Socket, Encoding, Server_Thread_ID, Goal_Thread_ID, Query_Timeout), error(Serve_Exception1, Serve_Exception2), true), 524 debug(mqi(protocol), "Session finished. Communication thread exception: ~w", [error(Serve_Exception1, Serve_Exception2)]), 525 abortSilentExit(Goal_Thread_ID, _), 526 retractall(mqi_worker_threads(Server_Thread_ID, Self_ID, Goal_Thread_ID)) 527 ) 528 -> Halt = (nonvar(Serve_Exception1), Exit_Main_On_Failure) 529 ; Halt = true 530 ), 531 ( 532 -> ( debug(mqi(protocol), "Ending session and halting Prolog server due to thread ~w: exception(~w)", [Self_ID, error(Serve_Exception1, Serve_Exception2)]), 533 quit(_) 534 ) 535 ; ( debug(mqi(protocol), "Ending session ~w", [Self_ID]), 536 catch(tcp_close_socket(Socket), error(_, _), true) 537 ) 538 ). 539 540 541% Open socket and begin processing the streams for a connection using the Encoding if the password matches 542% true: session ended 543% exception: communication failure or an internal failure (like a thread threw or shutdown unexpectedly) 544% false: halt 545communication_thread_listen(Password, Socket, Encoding, Server_Thread_ID, Goal_Thread_ID, Query_Timeout) :- 546 tcp_open_socket(Socket, Read_Stream, Write_Stream), 547 thread_self(Communication_Thread_ID), 548 assert(mqi_socket(Server_Thread_ID, Communication_Thread_ID, Socket, Read_Stream, Write_Stream)), 549 set_stream(Read_Stream, encoding(Encoding)), 550 set_stream(Write_Stream, encoding(Encoding)), 551 read_message(Read_Stream, Sent_Password), 552 ( Password == Sent_Password 553 -> ( debug(mqi(protocol), "Password matched.", []), 554 thread_self(Self_ID), 555 mqi_version(Major, Minor), 556 reply(Write_Stream, true([[threads(Self_ID, Goal_Thread_ID), version(Major, Minor)]])) 557 ) 558 ; ( debug(mqi(protocol), "Password mismatch, failing. ~w", [Sent_Password]), 559 reply_error(Write_Stream, password_mismatch), 560 throw(password_mismatch) 561 ) 562 ), 563 process_mqi_messages(Read_Stream, Write_Stream, Goal_Thread_ID, Query_Timeout), 564 debug(mqi(protocol), "Session finished.", []). 565 566 567% process_mqi_messages implements the main interface to the Machine Query Interface. 568% Continuously reads a Machine Query Interface message from Read_Stream and writes a response to Write_Stream, 569% until the connection fails or a `quit` or `close` message is sent. 570% 571% Read_Stream and Write_Stream can be any valid stream using any encoding. 572% 573% Goal_Thread_ID must be the threadID of a thread started on the goal_thread predicate 574% 575% uses tail recursion to ensure the stack doesn't grow 576% 577% true: indicates we should terminate the session (clean termination) 578% false: indicates we should exit the process if running in embedded mode 579% exception: indicates we should terminate the session (communication failure termination) or 580% thread was asked to halt 581process_mqi_messages(Read_Stream, Write_Stream, Goal_Thread_ID, Query_Timeout) :- 582 process_mqi_message(Read_Stream, Write_Stream, Goal_Thread_ID, Query_Timeout, Command), 583 ( Command == close 584 -> ( debug(mqi(protocol), "Command: close. Client closed the connection cleanly.", []), 585 true 586 ) 587 ; ( Command == quit 588 -> ( debug(mqi(protocol), "Command: quit.", []), 589 false 590 ) 591 ; 592 process_mqi_messages(Read_Stream, Write_Stream, Goal_Thread_ID, Query_Timeout) 593 ) 594 ). 595 596% process_mqi_message manages the protocol for the connection: receive message, parse it, process it. 597% - Reads a single message from Read_Stream. 598% - Processes it and issues a response on Write_Stream. 599% - The message will be unified with Command to allow the caller to handle it. 600% 601% Read_Stream and Write_Stream can be any valid stream using any encoding. 602% 603% True if the message understood. A response will always be sent. 604% False if the message was malformed. 605% Exceptions will be thrown by the underlying stream if there are communication failures writing to Write_Stream or the thread was asked to exit. 606% 607% state_* predicates manage the state transitions of the protocol 608% They only bubble up exceptions if there is a communication failure 609% 610% state_process_command will never return false 611% since errors should be sent to the client 612% It can throw if there are communication failures, though. 613process_mqi_message(Read_Stream, Write_Stream, Goal_Thread_ID, Query_Timeout, Command) :- 614 debug(mqi(protocol), "Waiting for next message ...", []), 615 ( state_receive_raw_message(Read_Stream, Message_String) 616 -> ( state_parse_command(Write_Stream, Message_String, Command, Binding_List) 617 -> state_process_command(Write_Stream, Goal_Thread_ID, Query_Timeout, Command, Binding_List) 618 ; true 619 ) 620 ; false 621 ). 622 623 624% state_receive_raw_message: receive a raw message, which is simply a string 625% true: valid message received 626% false: invalid message format 627% exception: communication failure OR thread asked to exit 628state_receive_raw_message(Read, Command_String) :- 629 read_message(Read, Command_String), 630 debug(mqi(protocol), "Valid message: ~w", [Command_String]). 631 632 633% state_parse_command: attempt to parse the message string into a valid command 634% 635% Use read_term_from_atom instead of read_term(stream) so that we don't hang 636% indefinitely if the caller didn't properly finish the term 637% parse in the context of module 'user' to properly bind operators, do term expansion, etc 638% 639% true: command could be parsed 640% false: command cannot be parsed. An error is sent to the client in this case 641% exception: communication failure on sending a reply 642state_parse_command(Write_Stream, Command_String, Parsed_Command, Binding_List) :- 643 ( catch(read_term_from_atom(Command_String, Parsed_Command, [variable_names(Binding_List), module(user)]), Parse_Exception, true) 644 -> ( var(Parse_Exception) 645 -> debug(mqi(protocol), "Parse Success: ~w", [Parsed_Command]) 646 ; ( reply_error(Write_Stream, Parse_Exception), 647 fail 648 ) 649 ) 650 ; ( reply_error(Write_Stream, error(couldNotParseCommand, _)), 651 fail 652 ) 653 ). 654 655 656% state_process_command(): execute the requested Command 657% 658% First wait until we have removed all results from any previous query. 659% If query_in_progress(Goal_Thread_ID) exists then there is at least one 660% more result to drain, by definition. Because the predicate is 661% deleted by get_next_result in the communication thread when the last result is drained 662% 663% true: if the command itself succeeded, failed or threw an exception. 664% In that case, the outcome is sent to the client 665% exception: only communication or thread failures are allowed to bubble up 666% See mqi(Options) documentation 667state_process_command(Stream, Goal_Thread_ID, Query_Timeout, run(Goal, Timeout), Binding_List) :- 668 !, 669 debug(mqi(protocol), "Command: run/1. Timeout: ~w", [Timeout]), 670 repeat_until_false(( 671 query_in_progress(Goal_Thread_ID), 672 debug(mqi(protocol), "Draining unretrieved result for ~w", [Goal_Thread_ID]), 673 heartbeat_until_result(Goal_Thread_ID, Stream, Unused_Answer), 674 debug(mqi(protocol), "Drained result for ~w", [Goal_Thread_ID]), 675 debug(mqi(query), " Discarded answer: ~w", [Unused_Answer]) 676 )), 677 debug(mqi(protocol), "All previous results drained", []), 678 send_goal_to_thread(Stream, Goal_Thread_ID, Query_Timeout, Timeout, Goal, Binding_List, true), 679 heartbeat_until_result(Goal_Thread_ID, Stream, Answers), 680 reply_with_result(Goal_Thread_ID, Stream, Answers). 681 682 683% See mqi(Options) documentation for documentation 684% See notes in run(Goal, Timeout) re: draining previous query 685state_process_command(Stream, Goal_Thread_ID, Query_Timeout, run_async(Goal, Timeout, Find_All), Binding_List) :- 686 !, 687 debug(mqi(protocol), "Command: run_async/1.", []), 688 debug(mqi(query), " Goal: ~w", [Goal]), 689 repeat_until_false(( 690 query_in_progress(Goal_Thread_ID), 691 debug(mqi(protocol), "Draining unretrieved result for ~w", [Goal_Thread_ID]), 692 heartbeat_until_result(Goal_Thread_ID, Stream, Unused_Answer), 693 debug(mqi(protocol), "Drained result for ~w", [Goal_Thread_ID]), 694 debug(mqi(query), " Discarded answer: ~w", [Unused_Answer]) 695 )), 696 debug(mqi(protocol), "All previous results drained", []), 697 send_goal_to_thread(Stream, Goal_Thread_ID, Query_Timeout, Timeout, Goal, Binding_List, Find_All), 698 reply(Stream, true([[]])). 699 700 701% See mqi(Options) documentation for documentation 702state_process_command(Stream, Goal_Thread_ID, _, async_result(Timeout), _) :- 703 !, 704 debug(mqi(protocol), "Command: async_result, timeout: ~w.", [Timeout]), 705 ( once((var(Timeout) ; Timeout == -1)) 706 -> Options = [] 707 ; Options = [timeout(Timeout)] 708 ), 709 ( query_in_progress(Goal_Thread_ID) 710 -> ( ( debug(mqi(protocol), "Pending query results exist for ~w", [Goal_Thread_ID]), 711 get_next_result(Goal_Thread_ID, Stream, Options, Result) 712 ) 713 -> reply_with_result(Goal_Thread_ID, Stream, Result) 714 ; reply_error(Stream, result_not_available) 715 ) 716 ; ( debug(mqi(protocol), "No pending query results for ~w", [Goal_Thread_ID]), 717 reply_error(Stream, no_query) 718 ) 719 ). 720 721 722% See mqi(Options) documentation for documentation 723% To ensure the goal thread is in a place it is safe to cancel, 724% we lock a mutex first that the goal thread checks before exiting 725% the "safe to cancel" zone. 726% It is not in the safe zone: it either finished 727% or was never running. 728state_process_command(Stream, Goal_Thread_ID, _, cancel_async, _) :- 729 !, 730 debug(mqi(protocol), "Command: cancel_async/0.", []), 731 with_mutex(Goal_Thread_ID, ( 732 ( safe_to_cancel(Goal_Thread_ID) 733 -> ( thread_signal(Goal_Thread_ID, throw(cancel_goal)), 734 reply(Stream, true([[]])) 735 ) 736 ; ( query_in_progress(Goal_Thread_ID) 737 -> ( debug(mqi(protocol), "Pending query results exist for ~w", [Goal_Thread_ID]), 738 reply(Stream, true([[]])) 739 ) 740 ; ( debug(mqi(protocol), "No pending query results for ~w", [Goal_Thread_ID]), 741 reply_error(Stream, no_query) 742 ) 743 ) 744 ) 745 )). 746 747 748% Used for testing how the system behaves when the goal thread is killed unexpectedly 749% Needs to run a bogus command `run(true, -1)` to 750% get the goal thread to process the exception 751state_process_command(Stream, Goal_Thread_ID, Query_Timeout, testThrowGoalThread(Test_Exception), Binding_List) :- 752 !, 753 debug(mqi(protocol), "TESTING: requested goal thread unhandled exception", []), 754 thread_send_message(Goal_Thread_ID, testThrow(Test_Exception)), 755 state_process_command(Stream, Goal_Thread_ID, Query_Timeout, run(true, -1), Binding_List). 756 757 758state_process_command(Stream, _, _, close, _) :- 759 !, 760 reply(Stream, true([[]])). 761 762 763state_process_command(Stream, _, _, quit, _) :- 764 !, 765 reply(Stream, true([[]])). 766 767 768% Send an exception if the command is not known 769state_process_command(Stream, _, _, Command, _) :- 770 debug(mqi(protocol), "Unknown command ~w", [Command]), 771 reply_error(Stream, unknownCommand). 772 773 774% Wait for a result (and put in Answers) from the goal thread, but send a heartbeat message 775% every so often until it arrives to detect if the socket is broken. 776% Throws if If the heartbeat failed which will 777% and then shutdown the communication thread 778% Tail recurse to not grow the stack 779heartbeat_until_result(Goal_Thread_ID, Stream, Answers) :- 780 ( get_next_result(Goal_Thread_ID, Stream, [timeout(2)], Answers) 781 -> debug(mqi(query), "Received answer from goal thread: ~w", [Answers]) 782 ; ( debug(mqi(protocol), "heartbeat...", []), 783 write_heartbeat(Stream), 784 heartbeat_until_result(Goal_Thread_ID, Stream, Answers) 785 ) 786 ). 787 788 789% True if write succeeded, otherwise throws as that 790% indicates that heartbeat failed because the other 791% end of the pipe terminated 792write_heartbeat(Stream) :- 793 put_char(Stream, '.'), 794 flush_output(Stream). 795 796 797% Send a goal to the goal thread in its queue 798% 799% Remember that we are now running a query using assert. 800% This will be retracted once all the answers have been drained. 801% 802% If Goal_Thread_ID died, thread_send_message throws and, if we don't respond, 803% the client could hang so catch and give them a good message before propagating 804% the exception 805send_goal_to_thread(Stream, Goal_Thread_ID, Default_Timeout, Timeout, Goal, Binding_List, Find_All) :- 806 ( var(Timeout) 807 -> Timeout = Default_Timeout 808 ; true 809 ), 810 ( var(Binding_List) 811 -> Binding_List = [] 812 ; true 813 ), 814 debug(mqi(query), "Sending to goal thread with timeout = ~w: ~w", [Timeout, Goal]), 815 assert(query_in_progress(Goal_Thread_ID)), 816 catch(thread_send_message(Goal_Thread_ID, goal(Goal, Binding_List, Timeout, Find_All)), Send_Message_Exception, true), 817 ( var(Send_Message_Exception) 818 -> true 819 ; ( reply_error(Stream, connection_failed), 820 throw(Send_Message_Exception) 821 ) 822 ). 823 824 825% Send a result from the goal thread to the communication thread in its queue 826send_next_result(Respond_To_Thread_ID, Answer, Exception_In_Goal, Find_All) :- 827 ( var(Exception_In_Goal) 828 -> ( ( debug(mqi(query), "Sending result of goal to communication thread, Result: ~w", [Answer]), 829 Answer == [] 830 ) 831 -> thread_send_message(Respond_To_Thread_ID, result(false, Find_All)) 832 ; handle_constraints(Answer, Final_Answer), 833 thread_send_message(Respond_To_Thread_ID, result(true(Final_Answer), Find_All)) 834 ) 835 ; ( debug(mqi(query), "Sending result of goal to communication thread, Exception: ~w", [Exception_In_Goal]), 836 thread_send_message(Respond_To_Thread_ID, result(error(Exception_In_Goal), Find_All)) 837 ) 838 ). 839 840 841handle_constraints(Answer, Final_Answer) :- 842 ( term_attvars(Answer, []) 843 -> Final_Answer = Answer 844 ; findall( Single_Answer_With_Attributes, 845 ( member(Single_Answer, Answer), 846 copy_term(Single_Answer, Single_Answer_Copy, Attributes), 847 append(['$residuals' = Attributes], Single_Answer_Copy, Single_Answer_With_Attributes) 848 ), 849 Final_Answer 850 ), 851 debug(mqi(query), "Constraints detected, converted: ~w to ~w", [Answer, Final_Answer]) 852 ). 853 854 855% Gets the next result from the goal thread in the communication thread queue, 856% and retracts query_in_progress/1 when the last result has been sent. 857% Find_All == true only returns one message, so delete query_in_progress 858% no matter what it is 859% \+ Find_All: There may be more than one result. The first one we hit with any exception 860% (note that no_more_results is also returned as an exception) means we are done 861get_next_result(Goal_Thread_ID, Stream, Options, Answers) :- 862 ( thread_property(Goal_Thread_ID, status(running)) 863 -> true 864 ; ( reply_error(Stream, connection_failed), 865 throw(connection_failed) 866 ) 867 ), 868 thread_self(Self_ID), 869 thread_get_message(Self_ID, result(Answers, Find_All), Options), 870 ( 871 -> ( debug(mqi(protocol), "Query completed and answers drained for findall ~w", [Goal_Thread_ID]), 872 retractall(query_in_progress(Goal_Thread_ID)) 873 ) 874 ; ( Answers = error(_) 875 -> ( debug(mqi(protocol), "Query completed and answers drained for non-findall ~w", [Goal_Thread_ID]), 876 retractall(query_in_progress(Goal_Thread_ID)) 877 ) 878 ; true 879 ) 880 ). 881 882 883% reply_with_result predicates are used to consistently return 884% answers for a query from either run() or run_async() 885reply_with_result(_, Stream, error(Error)) :- 886 !, 887 reply_error(Stream, Error). 888 889% Gracefully handle exceptions that can occur during conversion to JSON 890reply_with_result(_, Stream, Result) :- 891 !, 892 catch(reply(Stream, Result), error(Exception, _), reply_with_result(_, Stream, error(Exception))). 893 894 895% Reply with a normal term 896% Convert term to an actual JSON string 897reply(Stream, Term) :- 898 debug(mqi(query), "Responding with Term: ~w", [Term]), 899 term_to_json_string(Term, Json_String), 900 write_message(Stream, Json_String). 901 902 903% Special handling for exceptions since they can have parts that are not 904% "serializable". Ensures they they are always returned in an exception/1 term 905reply_error(Stream, Error_Term) :- 906 debug(mqi(query), "Responding with exception: ~w", [Error_Term]), 907 ( error(Error_Value, _) = Error_Term 908 -> Response = exception(Error_Value) 909 ; ( atom(Error_Term) 910 -> 911 Response = exception(Error_Term) 912 ; ( compound_name_arity(Error_Term, Name, _), 913 Response = exception(Name) 914 ) 915 ) 916 ), 917 reply(Stream, Response). 918 919 920% Send and receive messages are simply strings preceded by their length + ".\n" 921% i.e. "<stringlength>.\n<string>" 922% The desired encoding must be set on the Stream before calling this predicate 923 924 925% Writes the next message. 926% Throws if there is an unexpected exception 927write_message(Stream, String) :- 928 write_string_length(Stream, String), 929 write(Stream, String), 930 flush_output(Stream). 931 932 933% Reads the next message. 934% Throws if there is an unexpected exception or thread has been requested to quit 935% the length passed must match the actual number of bytes in the stream 936% in whatever encoding is being used 937read_message(Stream, String) :- 938 read_string_length(Stream, Length), 939 stream_property(Stream, encoding(Encoding)), 940 setup_call_cleanup( 941 stream_range_open(Stream, Tmp, [size(Length)]), 942 ( set_stream(Tmp, encoding(Encoding)), 943 read_string(Tmp, _, String) 944 ), 945 close(Tmp)). 946 947 948% Terminate with '.\n' so we know that's the end of the count 949write_string_length(Stream, String) :- 950 stream_property(Stream, encoding(Encoding)), 951 string_encoding_length(String, Encoding, Length), 952 format(Stream, "~d.\n", [Length]). 953 954 955% Note: read_term requires ".\n" after the length 956% ... but does not consume the "\n" 957read_string_length(Stream, Length) :- 958 read_term(Stream, Length, []), 959 get_char(Stream, _). 960 961 962% converts a string to Codes using Encoding 963string_encoding_length(String, Encoding, Length) :- 964 setup_call_cleanup( 965 open_null_stream(Out), 966 ( set_stream(Out, encoding(Encoding)), 967 write(Out, String), 968 byte_count(Out, Length) 969 ), 970 close(Out)). 971 972 973% Convert Prolog Term to a Prolog JSON term 974% Add a final \n so that using netcat to debug works well 975term_to_json_string(Term, Json_String) :- 976 term_to_json(Term, Json), 977 with_output_to(string(Json_String), 978 ( current_output(Stream), 979 json_write(Stream, Json), 980 put(Stream, '\n') 981 )). 982 983 984% Execute the goal as once() without binding any variables 985% and keep executing it until it returns false (or throws) 986repeat_until_false(Goal) :- 987 (\+ (\+ )), !, repeat_until_false(Goal). 988repeat_until_false(_). 989 990 991% Used to kill a thread in an "expected" way so it doesn't leave around traces in thread_property/2 afterwards 992% 993% If the thread is alive OR it was already aborted (expected cases) then attempt to join 994% the thread so that no warnings are sent to the console. Other cases leave the thread for debugging. 995% There are some fringe cases (like calling external code) 996% where the call might not return for a long time. Do a timeout for those cases. 997abortSilentExit(Thread_ID, Exception) :- 998 catch(thread_signal(Thread_ID, abort), error(Exception, _), true), 999 debug(mqi(protocol), "Attempting to abort thread: ~w. thread_signal_exception: ~w", [Thread_ID, Exception]). 1000% Workaround SWI Prolog bug: https://github.com/SWI-Prolog/swipl-devel/issues/852 by not joining 1001% The workaround just stops joining the aborted thread, so an inert record will be left if thread_property/2 is called. 1002% , 1003% ( once((var(Exception) ; catch(thread_property(Thread_ID, status(exception('$aborted'))), error(_, _), true))) 1004% -> ( catch(call_with_time_limit(4, thread_join(Thread_ID)), error(JoinException1, JoinException2), true), 1005% debug(mqi(protocol), "thread_join attempted because thread: ~w exit was expected, exception: ~w", [Thread_ID, error(JoinException1, JoinException2)]) 1006% ) 1007% ; true 1008% ). 1009 1010 1011% Detach a thread that exits with true or false so that it doesn't leave around a record in thread_property/2 afterwards 1012% Don't detach a thread if it exits because of an exception so we can debug using thread_property/2 afterwards 1013% 1014% However, `abort` is an expected exception but detaching a thread that aborts will leave an unwanted 1015% thread_property/2 record *and* print a message to the console. To work around this, 1016% the goal thread is always aborted by the communication thread using abortSilentExit. 1017detach_if_expected(Thread_ID) :- 1018 thread_property(Thread_ID, status(Status)), 1019 debug(mqi(protocol), "Thread ~w exited with status ~w", [Thread_ID, Status]), 1020 ( once((Status = true ; Status = false)) 1021 -> ( debug(mqi(protocol), "Expected thread status, detaching thread ~w", [Thread_ID]), 1022 thread_detach(Thread_ID) 1023 ) 1024 ; true 1025 ). 1026 1027 1028write_output_to_file(File) :- 1029 debug(mqi(protocol), "Writing all STDOUT and STDERR to file:~w", [File]), 1030 open(File, write, Stream, [buffer(false)]), 1031 set_prolog_IO(user_input, Stream, Stream). 1032 1033 1034% Creates a Unix Domain Socket file in a secured directory. 1035% Throws if the directory or file cannot be created in /tmp for any reason 1036% Requirements for this file are: 1037% - The Prolog process will attempt to create and, if Prolog exits cleanly, 1038% delete this file when the server closes. This means the directory 1039% must have the appropriate permissions to allow the Prolog process 1040% to do so. 1041% - For security reasons, the filename should not be predictable and the 1042% directory it is contained in should have permissions set so that files 1043% created are only accessible to the current user. 1044% - The path must be below 92 *bytes* long (including null terminator) to 1045% be portable according to the Linux documentation 1046% 1047% tmp_file finds the right /tmp directory, even on Mac OS, so the path is small 1048% Set 700 (rwx------) permission so it is only accessible by current user 1049% Create a secure tmp file in the new directory 1050% {set,current}_prolog_flag is copied to a thread, so no need to use a mutex. 1051% Close the stream so sockets can use it 1052unix_domain_socket_path(Created_Directory, File_Path) :- 1053 tmp_file(udsock, Created_Directory), 1054 make_directory(Created_Directory), 1055 catch( chmod(Created_Directory, urwx), 1056 Exception, 1057 ( catch(delete_directory(Created_Directory), error(_, _), true), 1058 throw(Exception) 1059 ) 1060 ), 1061 setup_call_cleanup( ( current_prolog_flag(tmp_dir, Save_Tmp_Dir), 1062 set_prolog_flag(tmp_dir, Created_Directory) 1063 ), 1064 tmp_file_stream(File_Path, Stream, []), 1065 set_prolog_flag(tmp_dir, Save_Tmp_Dir) 1066 ), 1067 close(Stream)