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, 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(apply), [maplist/3]). 38:- autoload(library(error), [must_be/2]). 39:- autoload(library(lists), [member/2]). 40:- autoload(library(redis), [redis/3]). 41:- autoload(library(broadcast), [broadcast/1]). 42:- use_module(library(debug), [debug/3]).

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

209update_session(SessionID, LastUsed, Updated, Peer) :- 210 transaction(update_session_(SessionID, LastUsed, Updated, Peer)). 211 212update_session_(SessionID, LastUsed, Updated, Peer) :- 213 update_last_used(SessionID, Updated, LastUsed), 214 update_peer(SessionID, Peer). 215 216update_last_used(SessionID, Updated, LastUsed), nonvar(LastUsed) => 217 ( last_used(SessionID, LastUsed) 218 -> true 219 ; retractall(last_used(SessionID, _)), 220 asserta(last_used(SessionID, LastUsed)), 221 Updated = true 222 ). 223update_last_used(_, _, _) => 224 true. 225 226update_peer(SessionID, Peer), nonvar(Peer) => 227 ( peer(SessionID, Peer) 228 -> true 229 ; retractall(peer(SessionID, _)), 230 asserta(peer(SessionID, Peer)) 231 ). 232update_peer(_, _) => 233 true. 234 235 236 /******************************* 237 * SCHEDULE TIMEOUT * 238 *******************************/ 239 240expire(SessionID, Timeout) :- 241 get_time(Now), 242 Time is Now+Timeout, 243 session_expire_db(DB, Key), 244 redis(DB, zadd(Key, Time, SessionID)). 245 246gc_sessions :- 247 session_expire_db(DB, Key), 248 get_time(Now), 249 redis(DB, zrangebyscore(Key, "-inf", Now), TimedOut as atom), 250 forall(member(SessionID, TimedOut), 251 gc_session(SessionID)). 252 253gc_session(_) :- 254 prolog_current_frame(Frame), 255 prolog_frame_attribute(Frame, parent, PFrame), 256 prolog_frame_attribute(PFrame, parent_goal, gc_session(_)), 257 !. 258gc_session(SessionID) :- 259 debug(http_session(gc), 'GC session ~p', [SessionID]), 260 session_db(SessionID, DB, SessionKey), 261 session_expire_db(DB, TMOKey), 262 redis(DB, zrem(TMOKey, SessionID)), 263 redis(DB, hget(SessionKey, peer), PeerS), 264 peer_string(Peer, PeerS), 265 broadcast(http_session(end(SessionID, Peer))), 266 redis(DB, del(SessionKey)), 267 session_data_db(SessionID, DB, DataKey), 268 redis(DB, del(DataKey)), 269 retractall(peer(SessionID, _)), 270 retractall(last_used(SessionID, _)). 271 272 273 /******************************* 274 * UTIL * 275 *******************************/ 276 277peer_string(ip(A,B,C,D), String) :- 278 nonvar(String), 279 !, 280 split_string(String, ".", "", List), 281 maplist(number_string, [A,B,C,D], List). 282peer_string(ip(A,B,C,D), String) :- 283 atomics_to_string([A,B,C,D], ".", String). 284 285session_db(SessionID, DB, Key) :- 286 nonvar(SessionID), 287 !, 288 http_session:session_setting(redis_db(DB)), 289 key_prefix(Prefix), 290 atomics_to_string([Prefix,session,SessionID], :, Key). 291session_db(SessionID, DB, Key) :- 292 session_expire_db(DB, TMOKey), 293 redis_zscan(DB, TMOKey, Pairs, []), 294 member(SessionIDS-_Timeout, Pairs), 295 atom_string(SessionID, SessionIDS), 296 key_prefix(Prefix), 297 atomics_to_string([Prefix,session,SessionID], :, Key). 298 299session_expire_db(DB, Key) :- 300 http_session:session_setting(redis_db(DB)), 301 key_prefix(Prefix), 302 atomics_to_string([Prefix,expire], :, Key). 303 304session_data_db(SessionID, DB, Key) :- 305 http_session:session_setting(redis_db(DB)), 306 key_prefix(Prefix), 307 atomics_to_string([Prefix,data,SessionID], :, Key). 308 309key_prefix(Prefix) :- 310 http_session:session_setting(redis_prefix(Prefix)), 311 !. 312key_prefix('swipl:http:sessions')