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 --quiet -g mqi_start -t halt -- --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: 0.0 -> First published version. Had a protocol bug that required messages sent to MQI to count Unicode code points instead of bytes for the message header. 1.0 -> Breaking change: Fixed protocol bug so that it properly accepted byte count instead of Unicode code point count in the message header for messages sent to MQI.
174mqi_version(1, 0). 175 176 177% Password is carefully constructed to be a string (not an atom) so that it is not 178% globally visible 179% Add ".\n" to the password since it will be added by the message when received 180mqi_start(Options) :- 181 Encoding = utf8, 182 option(pending_connections(Connection_Count), Options, 5), 183 option(query_timeout(Query_Timeout), Options, -1), 184 option(port(Port), Options, _), 185 option(run_server_on_thread(Run_Server_On_Thread), Options, true), 186 option(exit_main_on_failure(Exit_Main_On_Failure), Options, false), 187 option(write_connection_values(Write_Connection_Values), Options, false), 188 option(unix_domain_socket(Unix_Domain_Socket_Path_And_File), Options, _), 189 ( ( memberchk(unix_domain_socket(_), Options), 190 var(Unix_Domain_Socket_Path_And_File) 191 ) 192 -> unix_domain_socket_path(Unix_Domain_Socket_Path, Unix_Domain_Socket_Path_And_File) 193 ; true 194 ), 195 option(server_thread(Server_Thread_ID), Options, _), 196 ( var(Server_Thread_ID) 197 -> gensym(mqi, Server_Thread_ID) 198 ; true 199 ), 200 option(password(Password), Options, _), 201 ( var(Password) 202 -> ( current_prolog_flag(bounded, false) 203 -> uuid(UUID, [format(integer)]) 204 ; UUID is random(1<<62) 205 ), 206 format(string(Password), '~d', [UUID]) 207 ; true 208 ), 209 string_concat(Password, '.\n', Final_Password), 210 bind_socket(Server_Thread_ID, Unix_Domain_Socket_Path_And_File, Port, Socket, Client_Address), 211 send_client_startup_data(Write_Connection_Values, user_output, Unix_Domain_Socket_Path_And_File, Client_Address, Password), 212 option(write_output_to_file(File), Options, _), 213 ( var(File) 214 -> true 215 ; write_output_to_file(File) 216 ), 217 Server_Goal = ( 218 catch(server_thread(Server_Thread_ID, Socket, Client_Address, Final_Password, Connection_Count, Encoding, Query_Timeout, Exit_Main_On_Failure), error(E1, E2), true), 219 debug(mqi(protocol), "Stopped MQI on thread: ~w due to exception: ~w", [Server_Thread_ID, error(E1, E2)]) 220 ), 221 start_server_thread(Run_Server_On_Thread, Server_Thread_ID, Server_Goal, Unix_Domain_Socket_Path, Unix_Domain_Socket_Path_And_File). 222 223opt_type(port, port, natural). 224opt_type(create_unix_domain_socket, create_unix_domain_socket, boolean). 225opt_type(unix_domain_socket, unix_domain_socket, file(write)). 226opt_type(password, password, string). 227opt_type(pending_connections, pending_connections, nonneg). 228opt_type(query_timeout, query_timeout, float). 229opt_type(run_server_on_thread, run_server_on_thread, boolean). 230opt_type(exit_main_on_failure, exit_main_on_failure, boolean). 231opt_type(write_connection_values, write_connection_values, boolean). 232opt_type(write_output_to_file, write_output_to_file, file(write)). 233 234opt_help(port, "TCP/IP port for clients to connect to"). 235opt_help(create_unix_domain_socket, "Create a Unix domain socket for clients to connect to"). 236opt_help(unix_domain_socket, "File path for the Unix domain socket"). 237opt_help(password, "Connection password"). 238opt_help(pending_connections, "Max number of queued connections (5)"). 239opt_help(query_timeout, "Max query runtime in seconds (default infinite)"). 240opt_help(run_server_on_thread, "Run server in a background thread (true)"). 241opt_help(exit_main_on_failure, "Exit the process on a failure"). 242opt_help(write_connection_values, "Print info for clients to connect"). 243opt_help(write_output_to_file, "Write stdout and stderr to file").
To launch embedded mode:
swipl --quiet -g mqi_start -t halt -- --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 --quiet -g mqi_start -t halt -- --write_connection_values=true \
--password="HGJ SOWLWW WNDSJD"
For help on commandline options run
swipl -g mqi_start -- --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 = ( @(user:Goal, user), 457 Answers = [Binding_List], 458 send_next_result(Respond_To_Thread_ID, Answers, _, Find_All) 459 ) 460 ), 461 All_Answers_Goal = run_cancellable_goal(Self_ID, findall(Answers, One_Answer_Goal, [Find_All_Answers | _])), 462 ( Query_Timeout == -1 463 -> catch(All_Answers_Goal, Top_Exception, true) 464 ; catch(call_with_time_limit(Query_Timeout, All_Answers_Goal), Top_Exception, true) 465 ), 466 ( var(Top_Exception) 467 -> ( 468 -> send_next_result(Respond_To_Thread_ID, Find_All_Answers, _, Find_All) 469 ; send_next_result(Respond_To_Thread_ID, [], no_more_results, Find_All) 470 ) 471 ; send_next_result(Respond_To_Thread_ID, [], Top_Exception, true) 472 ), 473 goal_thread(Respond_To_Thread_ID). 474 475 476% Used only for testing unhandled exceptions outside of the "safe zone" 477throw_if_testing(Self_ID) :- 478 ( thread_peek_message(Self_ID, testThrow(Test_Exception)) 479 -> ( debug(mqi(query), "TESTING: Throwing test exception: ~w", [Test_Exception]), 480 throw(Test_Exception) 481 ) 482 ; true 483 ). 484 485 486% run_cancellable_goal handles the communication 487% to ensure the cancel exception from the communication thread 488% is injected at a place we are prepared to handle in the goal_thread 489% Before the goal is run, sets a fact to indicate we are in the "safe to cancel" 490% zone for the communication thread. 491% Then it doesn't exit this "safe to cancel" zone if the 492% communication thread is about to cancel 493run_cancellable_goal(Mutex_ID, Goal) :- 494 thread_self(Self_ID), 495 setup_call_cleanup( 496 assert(safe_to_cancel(Self_ID), Assertion), 497 Goal, 498 with_mutex(Mutex_ID, erase(Assertion)) 499 ). 500 501 502% Worker predicate for the communication thread. 503% Processes messages and sends goals to the goal thread. 504% Continues processing messages until communication_thread_listen() throws or ends with true/false 505% 506% Catches all exceptions from communication_thread_listen so that it can do an orderly shutdown of the goal 507% thread if there is a communication failure. 508% 509% True means user explicitly called close or there was an exception 510% only exit the main thread if there was an exception and we are supposed to Exit_Main_On_Failure 511% otherwise just exit the session 512communication_thread(Password, Socket, Encoding, Server_Thread_ID, Goal_Thread_ID, Query_Timeout, Exit_Main_On_Failure) :- 513 thread_self(Self_ID), 514 ( ( 515 catch(communication_thread_listen(Password, Socket, Encoding, Server_Thread_ID, Goal_Thread_ID, Query_Timeout), error(Serve_Exception1, Serve_Exception2), true), 516 debug(mqi(protocol), "Session finished. Communication thread exception: ~w", [error(Serve_Exception1, Serve_Exception2)]), 517 abortSilentExit(Goal_Thread_ID, _), 518 retractall(mqi_worker_threads(Server_Thread_ID, Self_ID, Goal_Thread_ID)) 519 ) 520 -> Halt = (nonvar(Serve_Exception1), Exit_Main_On_Failure) 521 ; Halt = true 522 ), 523 ( 524 -> ( debug(mqi(protocol), "Ending session and halting Prolog server due to thread ~w: exception(~w)", [Self_ID, error(Serve_Exception1, Serve_Exception2)]), 525 quit(_) 526 ) 527 ; ( debug(mqi(protocol), "Ending session ~w", [Self_ID]), 528 catch(tcp_close_socket(Socket), error(_, _), true) 529 ) 530 ). 531 532 533% Open socket and begin processing the streams for a connection using the Encoding if the password matches 534% true: session ended 535% exception: communication failure or an internal failure (like a thread threw or shutdown unexpectedly) 536% false: halt 537communication_thread_listen(Password, Socket, Encoding, Server_Thread_ID, Goal_Thread_ID, Query_Timeout) :- 538 tcp_open_socket(Socket, Read_Stream, Write_Stream), 539 thread_self(Communication_Thread_ID), 540 assert(mqi_socket(Server_Thread_ID, Communication_Thread_ID, Socket, Read_Stream, Write_Stream)), 541 set_stream(Read_Stream, encoding(Encoding)), 542 set_stream(Write_Stream, encoding(Encoding)), 543 read_message(Read_Stream, Sent_Password), 544 ( Password == Sent_Password 545 -> ( debug(mqi(protocol), "Password matched.", []), 546 thread_self(Self_ID), 547 mqi_version(Major, Minor), 548 reply(Write_Stream, true([[threads(Self_ID, Goal_Thread_ID), version(Major, Minor)]])) 549 ) 550 ; ( debug(mqi(protocol), "Password mismatch, failing. ~w", [Sent_Password]), 551 reply_error(Write_Stream, password_mismatch), 552 throw(password_mismatch) 553 ) 554 ), 555 process_mqi_messages(Read_Stream, Write_Stream, Goal_Thread_ID, Query_Timeout), 556 debug(mqi(protocol), "Session finished.", []). 557 558 559% process_mqi_messages implements the main interface to the Machine Query Interface. 560% Continuously reads a Machine Query Interface message from Read_Stream and writes a response to Write_Stream, 561% until the connection fails or a `quit` or `close` message is sent. 562% 563% Read_Stream and Write_Stream can be any valid stream using any encoding. 564% 565% Goal_Thread_ID must be the threadID of a thread started on the goal_thread predicate 566% 567% uses tail recursion to ensure the stack doesn't grow 568% 569% true: indicates we should terminate the session (clean termination) 570% false: indicates we should exit the process if running in embedded mode 571% exception: indicates we should terminate the session (communication failure termination) or 572% thread was asked to halt 573process_mqi_messages(Read_Stream, Write_Stream, Goal_Thread_ID, Query_Timeout) :- 574 process_mqi_message(Read_Stream, Write_Stream, Goal_Thread_ID, Query_Timeout, Command), 575 ( Command == close 576 -> ( debug(mqi(protocol), "Command: close. Client closed the connection cleanly.", []), 577 true 578 ) 579 ; ( Command == quit 580 -> ( debug(mqi(protocol), "Command: quit.", []), 581 false 582 ) 583 ; 584 process_mqi_messages(Read_Stream, Write_Stream, Goal_Thread_ID, Query_Timeout) 585 ) 586 ). 587 588% process_mqi_message manages the protocol for the connection: receive message, parse it, process it. 589% - Reads a single message from Read_Stream. 590% - Processes it and issues a response on Write_Stream. 591% - The message will be unified with Command to allow the caller to handle it. 592% 593% Read_Stream and Write_Stream can be any valid stream using any encoding. 594% 595% True if the message understood. A response will always be sent. 596% False if the message was malformed. 597% Exceptions will be thrown by the underlying stream if there are communication failures writing to Write_Stream or the thread was asked to exit. 598% 599% state_* predicates manage the state transitions of the protocol 600% They only bubble up exceptions if there is a communication failure 601% 602% state_process_command will never return false 603% since errors should be sent to the client 604% It can throw if there are communication failures, though. 605process_mqi_message(Read_Stream, Write_Stream, Goal_Thread_ID, Query_Timeout, Command) :- 606 debug(mqi(protocol), "Waiting for next message ...", []), 607 ( state_receive_raw_message(Read_Stream, Message_String) 608 -> ( state_parse_command(Write_Stream, Message_String, Command, Binding_List) 609 -> state_process_command(Write_Stream, Goal_Thread_ID, Query_Timeout, Command, Binding_List) 610 ; true 611 ) 612 ; false 613 ). 614 615 616% state_receive_raw_message: receive a raw message, which is simply a string 617% true: valid message received 618% false: invalid message format 619% exception: communication failure OR thread asked to exit 620state_receive_raw_message(Read, Command_String) :- 621 read_message(Read, Command_String), 622 debug(mqi(protocol), "Valid message: ~w", [Command_String]). 623 624 625% state_parse_command: attempt to parse the message string into a valid command 626% 627% Use read_term_from_atom instead of read_term(stream) so that we don't hang 628% indefinitely if the caller didn't properly finish the term 629% parse in the context of module 'user' to properly bind operators, do term expansion, etc 630% 631% true: command could be parsed 632% false: command cannot be parsed. An error is sent to the client in this case 633% exception: communication failure on sending a reply 634state_parse_command(Write_Stream, Command_String, Parsed_Command, Binding_List) :- 635 ( catch(read_term_from_atom(Command_String, Parsed_Command, [variable_names(Binding_List), module(user)]), Parse_Exception, true) 636 -> ( var(Parse_Exception) 637 -> debug(mqi(protocol), "Parse Success: ~w", [Parsed_Command]) 638 ; ( reply_error(Write_Stream, Parse_Exception), 639 fail 640 ) 641 ) 642 ; ( reply_error(Write_Stream, error(couldNotParseCommand, _)), 643 fail 644 ) 645 ). 646 647 648% state_process_command(): execute the requested Command 649% 650% First wait until we have removed all results from any previous query. 651% If query_in_progress(Goal_Thread_ID) exists then there is at least one 652% more result to drain, by definition. Because the predicate is 653% deleted by get_next_result in the communication thread when the last result is drained 654% 655% true: if the command itself succeeded, failed or threw an exception. 656% In that case, the outcome is sent to the client 657% exception: only communication or thread failures are allowed to bubble up 658% See mqi(Options) documentation 659state_process_command(Stream, Goal_Thread_ID, Query_Timeout, run(Goal, Timeout), Binding_List) :- 660 !, 661 debug(mqi(protocol), "Command: run/1. Timeout: ~w", [Timeout]), 662 repeat_until_false(( 663 query_in_progress(Goal_Thread_ID), 664 debug(mqi(protocol), "Draining unretrieved result for ~w", [Goal_Thread_ID]), 665 heartbeat_until_result(Goal_Thread_ID, Stream, Unused_Answer), 666 debug(mqi(protocol), "Drained result for ~w", [Goal_Thread_ID]), 667 debug(mqi(query), " Discarded answer: ~w", [Unused_Answer]) 668 )), 669 debug(mqi(protocol), "All previous results drained", []), 670 send_goal_to_thread(Stream, Goal_Thread_ID, Query_Timeout, Timeout, Goal, Binding_List, true), 671 heartbeat_until_result(Goal_Thread_ID, Stream, Answers), 672 reply_with_result(Goal_Thread_ID, Stream, Answers). 673 674 675% See mqi(Options) documentation for documentation 676% See notes in run(Goal, Timeout) re: draining previous query 677state_process_command(Stream, Goal_Thread_ID, Query_Timeout, run_async(Goal, Timeout, Find_All), Binding_List) :- 678 !, 679 debug(mqi(protocol), "Command: run_async/1.", []), 680 debug(mqi(query), " Goal: ~w", [Goal]), 681 repeat_until_false(( 682 query_in_progress(Goal_Thread_ID), 683 debug(mqi(protocol), "Draining unretrieved result for ~w", [Goal_Thread_ID]), 684 heartbeat_until_result(Goal_Thread_ID, Stream, Unused_Answer), 685 debug(mqi(protocol), "Drained result for ~w", [Goal_Thread_ID]), 686 debug(mqi(query), " Discarded answer: ~w", [Unused_Answer]) 687 )), 688 debug(mqi(protocol), "All previous results drained", []), 689 send_goal_to_thread(Stream, Goal_Thread_ID, Query_Timeout, Timeout, Goal, Binding_List, Find_All), 690 reply(Stream, true([[]])). 691 692 693% See mqi(Options) documentation for documentation 694state_process_command(Stream, Goal_Thread_ID, _, async_result(Timeout), _) :- 695 !, 696 debug(mqi(protocol), "Command: async_result, timeout: ~w.", [Timeout]), 697 ( once((var(Timeout) ; Timeout == -1)) 698 -> Options = [] 699 ; Options = [timeout(Timeout)] 700 ), 701 ( query_in_progress(Goal_Thread_ID) 702 -> ( ( debug(mqi(protocol), "Pending query results exist for ~w", [Goal_Thread_ID]), 703 get_next_result(Goal_Thread_ID, Stream, Options, Result) 704 ) 705 -> reply_with_result(Goal_Thread_ID, Stream, Result) 706 ; reply_error(Stream, result_not_available) 707 ) 708 ; ( debug(mqi(protocol), "No pending query results for ~w", [Goal_Thread_ID]), 709 reply_error(Stream, no_query) 710 ) 711 ). 712 713 714% See mqi(Options) documentation for documentation 715% To ensure the goal thread is in a place it is safe to cancel, 716% we lock a mutex first that the goal thread checks before exiting 717% the "safe to cancel" zone. 718% It is not in the safe zone: it either finished 719% or was never running. 720state_process_command(Stream, Goal_Thread_ID, _, cancel_async, _) :- 721 !, 722 debug(mqi(protocol), "Command: cancel_async/0.", []), 723 with_mutex(Goal_Thread_ID, ( 724 ( safe_to_cancel(Goal_Thread_ID) 725 -> ( thread_signal(Goal_Thread_ID, throw(cancel_goal)), 726 reply(Stream, true([[]])) 727 ) 728 ; ( query_in_progress(Goal_Thread_ID) 729 -> ( debug(mqi(protocol), "Pending query results exist for ~w", [Goal_Thread_ID]), 730 reply(Stream, true([[]])) 731 ) 732 ; ( debug(mqi(protocol), "No pending query results for ~w", [Goal_Thread_ID]), 733 reply_error(Stream, no_query) 734 ) 735 ) 736 ) 737 )). 738 739 740% Used for testing how the system behaves when the goal thread is killed unexpectedly 741% Needs to run a bogus command `run(true, -1)` to 742% get the goal thread to process the exception 743state_process_command(Stream, Goal_Thread_ID, Query_Timeout, testThrowGoalThread(Test_Exception), Binding_List) :- 744 !, 745 debug(mqi(protocol), "TESTING: requested goal thread unhandled exception", []), 746 thread_send_message(Goal_Thread_ID, testThrow(Test_Exception)), 747 state_process_command(Stream, Goal_Thread_ID, Query_Timeout, run(true, -1), Binding_List). 748 749 750state_process_command(Stream, _, _, close, _) :- 751 !, 752 reply(Stream, true([[]])). 753 754 755state_process_command(Stream, _, _, quit, _) :- 756 !, 757 reply(Stream, true([[]])). 758 759 760% Send an exception if the command is not known 761state_process_command(Stream, _, _, Command, _) :- 762 debug(mqi(protocol), "Unknown command ~w", [Command]), 763 reply_error(Stream, unknownCommand). 764 765 766% Wait for a result (and put in Answers) from the goal thread, but send a heartbeat message 767% every so often until it arrives to detect if the socket is broken. 768% Throws if If the heartbeat failed which will 769% and then shutdown the communication thread 770% Tail recurse to not grow the stack 771heartbeat_until_result(Goal_Thread_ID, Stream, Answers) :- 772 ( get_next_result(Goal_Thread_ID, Stream, [timeout(2)], Answers) 773 -> debug(mqi(query), "Received answer from goal thread: ~w", [Answers]) 774 ; ( debug(mqi(protocol), "heartbeat...", []), 775 write_heartbeat(Stream), 776 heartbeat_until_result(Goal_Thread_ID, Stream, Answers) 777 ) 778 ). 779 780 781% True if write succeeded, otherwise throws as that 782% indicates that heartbeat failed because the other 783% end of the pipe terminated 784write_heartbeat(Stream) :- 785 put_char(Stream, '.'), 786 flush_output(Stream). 787 788 789% Send a goal to the goal thread in its queue 790% 791% Remember that we are now running a query using assert. 792% This will be retracted once all the answers have been drained. 793% 794% If Goal_Thread_ID died, thread_send_message throws and, if we don't respond, 795% the client could hang so catch and give them a good message before propagating 796% the exception 797send_goal_to_thread(Stream, Goal_Thread_ID, Default_Timeout, Timeout, Goal, Binding_List, Find_All) :- 798 ( var(Timeout) 799 -> Timeout = Default_Timeout 800 ; true 801 ), 802 ( var(Binding_List) 803 -> Binding_List = [] 804 ; true 805 ), 806 debug(mqi(query), "Sending to goal thread with timeout = ~w: ~w", [Timeout, Goal]), 807 assert(query_in_progress(Goal_Thread_ID)), 808 catch(thread_send_message(Goal_Thread_ID, goal(Goal, Binding_List, Timeout, Find_All)), Send_Message_Exception, true), 809 ( var(Send_Message_Exception) 810 -> true 811 ; ( reply_error(Stream, connection_failed), 812 throw(Send_Message_Exception) 813 ) 814 ). 815 816 817% Send a result from the goal thread to the communication thread in its queue 818send_next_result(Respond_To_Thread_ID, Answer, Exception_In_Goal, Find_All) :- 819 ( var(Exception_In_Goal) 820 -> ( ( debug(mqi(query), "Sending result of goal to communication thread, Result: ~w", [Answer]), 821 Answer == [] 822 ) 823 -> thread_send_message(Respond_To_Thread_ID, result(false, Find_All)) 824 ; thread_send_message(Respond_To_Thread_ID, result(true(Answer), Find_All)) 825 ) 826 ; ( debug(mqi(query), "Sending result of goal to communication thread, Exception: ~w", [Exception_In_Goal]), 827 thread_send_message(Respond_To_Thread_ID, result(error(Exception_In_Goal), Find_All)) 828 ) 829 ). 830 831 832% Gets the next result from the goal thread in the communication thread queue, 833% and retracts query_in_progress/1 when the last result has been sent. 834% Find_All == true only returns one message, so delete query_in_progress 835% No matter what it is 836% \+ Find_All: There may be more than one result. The first one we hit with any exception 837% (note that no_more_results is also returned as an exception) means we are done 838get_next_result(Goal_Thread_ID, Stream, Options, Answers) :- 839 ( thread_property(Goal_Thread_ID, status(running)) 840 -> true 841 ; ( reply_error(Stream, connection_failed), 842 throw(connection_failed) 843 ) 844 ), 845 thread_self(Self_ID), 846 thread_get_message(Self_ID, result(Answers, Find_All), Options), 847 ( 848 -> ( debug(mqi(protocol), "Query completed and answers drained for findall ~w", [Goal_Thread_ID]), 849 retractall(query_in_progress(Goal_Thread_ID)) 850 ) 851 ; ( Answers = error(_) 852 -> ( debug(mqi(protocol), "Query completed and answers drained for non-findall ~w", [Goal_Thread_ID]), 853 retractall(query_in_progress(Goal_Thread_ID)) 854 ) 855 ; true 856 ) 857 ). 858 859 860% reply_with_result predicates are used to consistently return 861% answers for a query from either run() or run_async() 862reply_with_result(_, Stream, error(Error)) :- 863 !, 864 reply_error(Stream, Error). 865reply_with_result(_, Stream, Result) :- 866 !, 867 reply(Stream, Result). 868 869 870% Reply with a normal term 871% Convert term to an actual JSON string 872reply(Stream, Term) :- 873 debug(mqi(query), "Responding with Term: ~w", [Term]), 874 term_to_json_string(Term, Json_String), 875 write_message(Stream, Json_String). 876 877 878% Special handling for exceptions since they can have parts that are not 879% "serializable". Ensures they they are always returned in an exception/1 term 880reply_error(Stream, Error_Term) :- 881 debug(mqi(query), "Responding with exception: ~w", [Error_Term]), 882 ( error(Error_Value, _) = Error_Term 883 -> Response = exception(Error_Value) 884 ; ( atom(Error_Term) 885 -> 886 Response = exception(Error_Term) 887 ; ( compound_name_arity(Error_Term, Name, _), 888 Response = exception(Name) 889 ) 890 ) 891 ), 892 reply(Stream, Response). 893 894 895% Send and receive messages are simply strings preceded by their length + ".\n" 896% i.e. "<stringlength>.\n<string>" 897% The desired encoding must be set on the Stream before calling this predicate 898 899 900% Writes the next message. 901% Throws if there is an unexpected exception 902write_message(Stream, String) :- 903 write_string_length(Stream, String), 904 write(Stream, String), 905 flush_output(Stream). 906 907 908% Reads the next message. 909% Throws if there is an unexpected exception or thread has been requested to quit 910% the length passed must match the actual number of bytes in the stream 911% in whatever encoding is being used 912read_message(Stream, String) :- 913 read_string_length(Stream, Length), 914 stream_property(Stream, encoding(Encoding)), 915 setup_call_cleanup( 916 stream_range_open(Stream, Tmp, [size(Length)]), 917 ( set_stream(Tmp, encoding(Encoding)), 918 read_string(Tmp, _, String) 919 ), 920 close(Tmp)). 921 922 923% Terminate with '.\n' so we know that's the end of the count 924write_string_length(Stream, String) :- 925 stream_property(Stream, encoding(Encoding)), 926 string_encoding_length(String, Encoding, Length), 927 format(Stream, "~d.\n", [Length]). 928 929 930% Note: read_term requires ".\n" after the length 931% ... but does not consume the "\n" 932read_string_length(Stream, Length) :- 933 read_term(Stream, Length, []), 934 get_char(Stream, _). 935 936 937% converts a string to Codes using Encoding 938string_encoding_length(String, Encoding, Length) :- 939 setup_call_cleanup( 940 open_null_stream(Out), 941 ( set_stream(Out, encoding(Encoding)), 942 write(Out, String), 943 byte_count(Out, Length) 944 ), 945 close(Out)). 946 947 948% Convert Prolog Term to a Prolog JSON term 949% Add a final \n so that using netcat to debug works well 950term_to_json_string(Term, Json_String) :- 951 term_to_json(Term, Json), 952 with_output_to(string(Json_String), 953 ( current_output(Stream), 954 json_write(Stream, Json), 955 put(Stream, '\n') 956 )). 957 958 959% Execute the goal as once() without binding any variables 960% and keep executing it until it returns false (or throws) 961repeat_until_false(Goal) :- 962 (\+ (\+ )), !, repeat_until_false(Goal). 963repeat_until_false(_). 964 965 966% Used to kill a thread in an "expected" way so it doesn't leave around traces in thread_property/2 afterwards 967% 968% If the thread is alive OR it was already aborted (expected cases) then attempt to join 969% the thread so that no warnings are sent to the console. Other cases leave the thread for debugging. 970% There are some fringe cases (like calling external code) 971% where the call might not return for a long time. Do a timeout for those cases. 972abortSilentExit(Thread_ID, Exception) :- 973 catch(thread_signal(Thread_ID, abort), error(Exception, _), true), 974 debug(mqi(protocol), "Attempting to abort thread: ~w. thread_signal_exception: ~w", [Thread_ID, Exception]). 975% Workaround SWI Prolog bug: https://github.com/SWI-Prolog/swipl-devel/issues/852 by not joining 976% The workaround just stops joining the aborted thread, so an inert record will be left if thread_property/2 is called. 977% , 978% ( once((var(Exception) ; catch(thread_property(Thread_ID, status(exception('$aborted'))), error(_, _), true))) 979% -> ( catch(call_with_time_limit(4, thread_join(Thread_ID)), error(JoinException1, JoinException2), true), 980% debug(mqi(protocol), "thread_join attempted because thread: ~w exit was expected, exception: ~w", [Thread_ID, error(JoinException1, JoinException2)]) 981% ) 982% ; true 983% ). 984 985 986% Detach a thread that exits with true or false so that it doesn't leave around a record in thread_property/2 afterwards 987% Don't detach a thread if it exits because of an exception so we can debug using thread_property/2 afterwards 988% 989% However, `abort` is an expected exception but detaching a thread that aborts will leave an unwanted 990% thread_property/2 record *and* print a message to the console. To work around this, 991% the goal thread is always aborted by the communication thread using abortSilentExit. 992detach_if_expected(Thread_ID) :- 993 thread_property(Thread_ID, status(Status)), 994 debug(mqi(protocol), "Thread ~w exited with status ~w", [Thread_ID, Status]), 995 ( once((Status = true ; Status = false)) 996 -> ( debug(mqi(protocol), "Expected thread status, detaching thread ~w", [Thread_ID]), 997 thread_detach(Thread_ID) 998 ) 999 ; true 1000 ). 1001 1002 1003write_output_to_file(File) :- 1004 debug(mqi(protocol), "Writing all STDOUT and STDERR to file:~w", [File]), 1005 open(File, write, Stream, [buffer(false)]), 1006 set_prolog_IO(user_input, Stream, Stream). 1007 1008 1009% Creates a Unix Domain Socket file in a secured directory. 1010% Throws if the directory or file cannot be created in /tmp for any reason 1011% Requirements for this file are: 1012% - The Prolog process will attempt to create and, if Prolog exits cleanly, 1013% delete this file when the server closes. This means the directory 1014% must have the appropriate permissions to allow the Prolog process 1015% to do so. 1016% - For security reasons, the filename should not be predictable and the 1017% directory it is contained in should have permissions set so that files 1018% created are only accessible to the current user. 1019% - The path must be below 92 *bytes* long (including null terminator) to 1020% be portable according to the Linux documentation 1021% 1022% tmp_file finds the right /tmp directory, even on Mac OS, so the path is small 1023% Set 700 (rwx------) permission so it is only accessible by current user 1024% Create a secure tmp file in the new directory 1025% {set,current}_prolog_flag is copied to a thread, so no need to use a mutex. 1026% Close the stream so sockets can use it 1027unix_domain_socket_path(Created_Directory, File_Path) :- 1028 tmp_file(udsock, Created_Directory), 1029 make_directory(Created_Directory), 1030 catch( chmod(Created_Directory, urwx), 1031 Exception, 1032 ( catch(delete_directory(Created_Directory), error(_, _), true), 1033 throw(Exception) 1034 ) 1035 ), 1036 setup_call_cleanup( ( current_prolog_flag(tmp_dir, Save_Tmp_Dir), 1037 set_prolog_flag(tmp_dir, Created_Directory) 1038 ), 1039 tmp_file_stream(File_Path, Stream, []), 1040 set_prolog_flag(tmp_dir, Save_Tmp_Dir) 1041 ), 1042 close(Stream). 1043 1044 1045% Helper for installing the mqi.pl file to the right 1046% library directory. 1047% Call using swipl -s mqi.pl -g "mqi:install_to_library('mqi.pl')" -t halt 1048install_to_library(File) :- 1049 once(find_library(Path)), 1050 copy_file(File, Path), 1051 make. 1052 1053 1054% Find the base library path, i.e. the one that ends in 1055% "library/" 1056find_library(Path) :- 1057 file_alias_path(library, Path), 1058 atomic_list_concat(Parts, '/', Path), 1059 reverse(Parts, Parts_Reverse), 1060 nth0(0, Parts_Reverse, ''), 1061 nth0(1, Parts_Reverse, Library), 1062 string_lower(Library, 'library')