1/* Part of SWI-Prolog 2 3 Author: Jan Wielemaker 4 E-mail: jan@swi-prolog.org 5 WWW: http://www.swi-prolog.org 6 Copyright (c) 2020-2024, SWI-Prolog Solutions b.v. 7 All rights reserved. 8 9 Redistribution and use in source and binary forms, with or without 10 modification, are permitted provided that the following conditions 11 are met: 12 13 1. Redistributions of source code must retain the above copyright 14 notice, this list of conditions and the following disclaimer. 15 16 2. Redistributions in binary form must reproduce the above copyright 17 notice, this list of conditions and the following disclaimer in 18 the documentation and/or other materials provided with the 19 distribution. 20 21 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 22 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 23 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 24 FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 25 COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 26 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 27 BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 28 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 29 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 31 ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 32 POSSIBILITY OF SUCH DAMAGE. 33*/ 34 35:- module(http_redis_plugin, []). 36:- use_module(library(http/http_session)). 37:- autoload(library(error), [must_be/2]). 38:- autoload(library(lists), [member/2]). 39:- autoload(library(redis), [redis/3, redis/2, redis_get_list/4, redis_zscan/4]). 40:- autoload(library(broadcast), [broadcast/1]). 41:- use_module(library(debug), [debug/3]). 42:- autoload(library(socket), [ip_name/2]).

Hook session management to use Redis

This module acts as a plugin for library(http/http_session), storing session information on a Redis server. This has several consequences:

The Prolog server may be restarted without loosing session data. This is notably useful when long session timeouts are used.
Multiple Prolog servers can act as a cluster while session management is used.
Associating Prolog data with sessions is relatively slow. The assert/retract is replaced by managing a Redis list. Data in this list is matched sequentially, where each term needs to be parsed before it can be matched.
Associated data is currently limited to ground terms.

The library is activated by loading it in addition to library(http/http_session) and using http_set_session_options/1 to configure the Redis database as below. The redis_server/2 predicate from library(redis) can be used to specify the parameters for the redis server such as host, port or authentication.

:- http_set_session_options(
       [ redis_db(default),
         redis_prefix('swipl:http:session')
       ]).

Redis key usage

All Redis keys reside under a prefix specified by the option redis_prefix(Prefix), which defaults to 'swipl:http:session'. Here we find:

An ordered set at <prefix>:expire that contains the session ids, ordered by the time the session expires. Session enumeration and garbage collection is based on this set.
A hash at <prefix>:session:<id> which contains the peer address, the last used time and optionally session specific settings.
If there is session data, a list at <prefix>:data:<id> of Prolog terms, represented as strings that contain the session data. */

87:- multifile 88 http_session:hooked/0, 89 http_session:hook/1, 90 http_session:session_setting/1, 91 http_session:session_option/2. 92 93http_session:session_option(redis_db, atom). 94http_session:session_option(redis_ro, atom). 95http_session:session_option(redis_prefix, atom). 96 97http_session:hooked :- 98 http_session:session_setting(redis_db(_)). 99 100%http_session:hook(assert_session(SessionID, Peer)). 101%http_session:hook(set_session_option(SessionId, Setting)). 102%http_session:hook(get_session_option(SessionId, Setting)). 103%http_session:hook(active_session(SessionID, Peer, LastUsed)). 104%http_session:hook(set_last_used(SessionID, Now, TimeOut)). 105%http_session:hook(asserta(session_data(SessionId, Data))). 106%http_session:hook(assertz(session_data(SessionId, Data))). 107%http_session:hook(retract(session_data(SessionId, Data))). 108%http_session:hook(retractall(session_data(SessionId, Data))). 109%http_session:hook(session_data(SessionId, Data)). 110%http_session:hook(current_session(SessionID, Data)). 111%http_session:hook(close_session(?SessionID)). 112%http_session:hook(gc_sessions). 113 114:- dynamic 115 peer/2, % SessionID, Peer 116 last_used/2. % SessionID, Time 117 118 119http_session:hook(assert_session(SessionID, Peer)) :- 120 session_db(rw, SessionID, DB, Key), 121 http_session:session_setting(timeout(Timeout)), 122 asserta(peer(SessionID, Peer)), 123 ip_name(Peer, PeerS), 124 get_time(Now), 125 redis(DB, hset(Key, 126 peer, PeerS, 127 last_used, Now)), 128 expire(SessionID, Timeout). 129http_session:hook(set_session_option(SessionID, Setting)) :- 130 session_db(rw, SessionID, DB, Key), 131 Setting =.. [Name,Value], 132 redis(DB, hset(Key, Name, Value as prolog)), 133 ( Setting = timeout(Timeout) 134 -> expire(SessionID, Timeout) 135 ; true 136 ). 137http_session:hook(get_session_option(SessionID, Setting)) :- 138 session_db(ro, SessionID, DB, Key), 139 Setting =.. [Name,Value], 140 redis(DB, hget(Key, Name), Value). 141http_session:hook(active_session(SessionID, Peer, LastUsed)) :- 142 ( last_used(SessionID, LastUsed0), 143 peer(SessionID, Peer0) 144 -> LastUsed = LastUsed0, 145 Peer = Peer0 146 ; session_db(ro, SessionID, DB, Key), 147 redis(DB, hget(Key, peer), PeerS), 148 ip_name(Peer, PeerS), 149 redis(DB, hget(Key, last_used), LastUsed as number), 150 update_session(SessionID, LastUsed, _, Peer) 151 ). 152http_session:hook(set_last_used(SessionID, Now, Timeout)) :- 153 http_session:session_setting(granularity(TimeGranularity)), 154 LastUsed is floor(Now/TimeGranularity)*TimeGranularity, 155 update_session(SessionID, LastUsed, Updated, _Peer), 156 ( Updated == true 157 -> session_db(rw, SessionID, DB, Key), 158 redis(DB, hset(Key, last_used, Now)), 159 expire(SessionID, Timeout) 160 ; true 161 ). 162http_session:hook(asserta(session_data(SessionID, Data))) :- 163 must_be(ground, Data), 164 session_data_db(rw, SessionID, DB, Key), 165 redis(DB, lpush(Key, Data as prolog)). 166http_session:hook(assertz(session_data(SessionID, Data))) :- 167 must_be(ground, Data), 168 session_data_db(rw, SessionID, DB, Key), 169 redis(DB, rpush(Key, Data as prolog)). 170http_session:hook(retract(session_data(SessionID, Data))) :- 171 session_data_db(rw, SessionID, DB, Key), 172 redis_get_list(DB, Key, 10, List), 173 member(Data, List), 174 redis(DB, lrem(Key, 1, Data as prolog)). 175http_session:hook(retractall(session_data(SessionID, Data))) :- 176 forall(http_session:hook(retract(session_data(SessionID, Data))), 177 true). 178http_session:hook(session_data(SessionID, Data)) :- 179 session_data_db(rw, SessionID, DB, Key), 180 redis_get_list(DB, Key, 10, List), 181 member(Data, List). 182http_session:hook(current_session(SessionID, Data)) :- 183 session_db(ro, SessionID, DB, Key), 184 redis(DB, hget(Key, last_used), Time as number), 185 number(Time), 186 get_time(Now), 187 Idle is Now - Time, 188 ( nonvar(Data) 189 -> ( Data = peer(Peer) 190 -> redis(DB, hget(Key, peer), PeerS), 191 ip_name(Peer, PeerS) 192 ; Data = idle(Idle0) 193 -> Idle0 = Idle 194 ; http_session:hook(session_data(SessionID, Data)) 195 ) 196 ; ( Data = peer(Peer), 197 redis(DB, hget(Key, peer), PeerS), 198 ip_name(Peer, PeerS) 199 ; Data = idle(Idle) 200 ; non_reserved_property(Data), 201 http_session:hook(session_data(SessionID, Data)) 202 ) 203 ). 204http_session:hook(close_session(SessionID)) :- 205 gc_session(SessionID). 206http_session:hook(gc_sessions) :- 207 gc_sessions. 208 209non_reserved_property(P) :- 210 var(P), 211 !. 212non_reserved_property(peer(_)) :- !, fail. 213non_reserved_property(idle(_)) :- !, fail. 214non_reserved_property(_).

221update_session(SessionID, LastUsed, Updated, Peer) :- 222 transaction(update_session_(SessionID, LastUsed, Updated, Peer)). 223 224update_session_(SessionID, LastUsed, Updated, Peer) :- 225 update_last_used(SessionID, Updated, LastUsed), 226 update_peer(SessionID, Peer). 227 228update_last_used(SessionID, Updated, LastUsed), nonvar(LastUsed) => 229 ( last_used(SessionID, LastUsed) 230 -> true 231 ; retractall(last_used(SessionID, _)), 232 asserta(last_used(SessionID, LastUsed)), 233 Updated = true 234 ). 235update_last_used(_, _, _) => 236 true. 237 238update_peer(SessionID, Peer), nonvar(Peer) => 239 ( peer(SessionID, Peer) 240 -> true 241 ; retractall(peer(SessionID, _)), 242 asserta(peer(SessionID, Peer)) 243 ). 244update_peer(_, _) => 245 true. 246 247 248 /******************************* 249 * SCHEDULE TIMEOUT * 250 *******************************/ 251 252expire(SessionID, Timeout) :- 253 get_time(Now), 254 Time is integer(Now+Timeout), 255 session_expire_db(rw, DB, Key), 256 redis(DB, zadd(Key, Time, SessionID)). 257 258gc_sessions :- 259 session_expire_db(ro, DB, Key), 260 session_expire_db(rw, DB, TMOKey), 261 get_time(Now), 262 End is integer(Now), 263 redis(DB, zrangebyscore(Key, "-inf", End), TimedOut as atom), 264 ( member(SessionID, TimedOut), 265 redis(DB, zrem(TMOKey, SessionID), 1), % 0 if someone else deleted this 266 gc_session(SessionID), 267 fail 268 ; true 269 ).

273gc_session(_) :- 274 prolog_current_frame(Frame), 275 prolog_frame_attribute(Frame, parent, PFrame), 276 prolog_frame_attribute(PFrame, parent_goal, gc_session(_)), 277 !. 278gc_session(SessionID) :- 279 debug(http_session(gc), 'GC session ~p', [SessionID]), 280 session_db(ro, SessionID, DB, SessionKey), 281 redis(DB, hget(SessionKey, peer), PeerS), 282 ip_name(Peer, PeerS), 283 broadcast(http_session(end(SessionID, Peer))), 284 session_db(rw, SessionID, DBw, SessionKey), 285 redis(DBw, del(SessionKey)), 286 session_data_db(rw, SessionID, DBw, DataKey), 287 redis(DBw, del(DataKey)), 288 retractall(peer(SessionID, _)), 289 retractall(last_used(SessionID, _)). 290 291 292 /******************************* 293 * UTIL * 294 *******************************/

298session_db(RW, SessionID, DB, Key) :- 299 nonvar(SessionID), 300 !, 301 redis_db(RW, DB), 302 key_prefix(Prefix), 303 atomics_to_string([Prefix,session,SessionID], :, Key). 304session_db(RW, SessionID, DB, Key) :- 305 session_expire_db(RW, DB, TMOKey), 306 redis_zscan(DB, TMOKey, Pairs, []), 307 member(SessionIDS-_Timeout, Pairs), 308 atom_string(SessionID, SessionIDS), 309 key_prefix(Prefix), 310 atomics_to_string([Prefix,session,SessionID], :, Key). 311 312session_expire_db(RW, DB, Key) :- 313 redis_db(RW, DB), 314 key_prefix(Prefix), 315 atomics_to_string([Prefix,expire], :, Key). 316 317session_data_db(RW, SessionID, DB, Key) :- 318 redis_db(RW, DB), 319 key_prefix(Prefix), 320 atomics_to_string([Prefix,data,SessionID], :, Key). 321 322key_prefix(Prefix) :- 323 http_session:session_setting(redis_prefix(Prefix)), 324 !. 325key_prefix('swipl:http:sessions'). 326 327redis_db(ro, DB) :- 328 http_session:session_setting(redis_ro(DB0)), 329 !, 330 DB = DB0. 331redis_db(_, DB) :- 332 http_session:session_setting(redis_db(DB))