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

219update_session(SessionID, LastUsed, Updated, Peer) :- 220 transaction(update_session_(SessionID, LastUsed, Updated, Peer)). 221 222update_session_(SessionID, LastUsed, Updated, Peer) :- 223 update_last_used(SessionID, Updated, LastUsed), 224 update_peer(SessionID, Peer). 225 226update_last_used(SessionID, Updated, LastUsed), nonvar(LastUsed) => 227 ( last_used(SessionID, LastUsed) 228 -> true 229 ; retractall(last_used(SessionID, _)), 230 asserta(last_used(SessionID, LastUsed)), 231 Updated = true 232 ). 233update_last_used(_, _, _) => 234 true. 235 236update_peer(SessionID, Peer), nonvar(Peer) => 237 ( peer(SessionID, Peer) 238 -> true 239 ; retractall(peer(SessionID, _)), 240 asserta(peer(SessionID, Peer)) 241 ). 242update_peer(_, _) => 243 true. 244 245 246 /******************************* 247 * SCHEDULE TIMEOUT * 248 *******************************/ 249 250expire(SessionID, Timeout) :- 251 get_time(Now), 252 Time is integer(Now+Timeout), 253 session_expire_db(rw, DB, Key), 254 redis(DB, zadd(Key, Time, SessionID)). 255 256gc_sessions :- 257 session_expire_db(ro, DB, Key), 258 get_time(Now), 259 End is integer(Now), 260 redis(DB, zrangebyscore(Key, "-inf", End), TimedOut as atom), 261 forall(member(SessionID, TimedOut), 262 gc_session(SessionID)). 263 264gc_session(_) :- 265 prolog_current_frame(Frame), 266 prolog_frame_attribute(Frame, parent, PFrame), 267 prolog_frame_attribute(PFrame, parent_goal, gc_session(_)), 268 !. 269gc_session(SessionID) :- 270 debug(http_session(gc), 'GC session ~p', [SessionID]), 271 session_db(ro, SessionID, DB, SessionKey), 272 session_expire_db(rw, DB, TMOKey), 273 redis(DB, zrem(TMOKey, SessionID)), 274 redis(DB, hget(SessionKey, peer), PeerS), 275 ip_name(Peer, PeerS), 276 broadcast(http_session(end(SessionID, Peer))), 277 session_db(rw, SessionID, DBw, SessionKey), 278 redis(DBw, del(SessionKey)), 279 session_data_db(rw, SessionID, DBw, DataKey), 280 redis(DBw, del(DataKey)), 281 retractall(peer(SessionID, _)), 282 retractall(last_used(SessionID, _)). 283 284 285 /******************************* 286 * UTIL * 287 *******************************/

291session_db(RW, SessionID, DB, Key) :- 292 nonvar(SessionID), 293 !, 294 redis_db(RW, DB), 295 key_prefix(Prefix), 296 atomics_to_string([Prefix,session,SessionID], :, Key). 297session_db(RW, SessionID, DB, Key) :- 298 session_expire_db(RW, DB, TMOKey), 299 redis_zscan(DB, TMOKey, Pairs, []), 300 member(SessionIDS-_Timeout, Pairs), 301 atom_string(SessionID, SessionIDS), 302 key_prefix(Prefix), 303 atomics_to_string([Prefix,session,SessionID], :, Key). 304 305session_expire_db(RW, DB, Key) :- 306 redis_db(RW, DB), 307 key_prefix(Prefix), 308 atomics_to_string([Prefix,expire], :, Key). 309 310session_data_db(RW, SessionID, DB, Key) :- 311 redis_db(RW, DB), 312 key_prefix(Prefix), 313 atomics_to_string([Prefix,data,SessionID], :, Key). 314 315key_prefix(Prefix) :- 316 http_session:session_setting(redis_prefix(Prefix)), 317 !. 318key_prefix('swipl:http:sessions'). 319 320redis_db(ro, DB) :- 321 http_session:session_setting(redis_ro(DB0)), 322 !, 323 DB = DB0. 324redis_db(_, DB) :- 325 http_session:session_setting(redis_db(DB))