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 112http_session:hook(assert_session(SessionID, Peer)) :- 113 session_db(SessionID, DB, Key), 114 http_session:session_setting(timeout(Timeout)), 115 peer_string(Peer, PeerS), 116 get_time(Now), 117 redis(DB, hset(Key, 118 peer, PeerS, 119 last_used, Now)), 120 expire(SessionID, Timeout). 121http_session:hook(set_session_option(SessionID, Setting)) :- 122 session_db(SessionID, DB, Key), 123 Setting =.. [Name,Value], 124 redis(DB, hset(Key, Name, Value as prolog)), 125 ( Setting = timeout(Timeout) 126 -> expire(SessionID, Timeout) 127 ; true 128 ). 129http_session:hook(get_session_option(SessionID, Setting)) :- 130 session_db(SessionID, DB, Key), 131 Setting =.. [Name,Value], 132 redis(DB, hget(Key, Name), Value). 133http_session:hook(active_session(SessionID, Peer, LastUsed)) :- 134 session_db(SessionID, DB, Key), 135 redis(DB, hget(Key, peer), PeerS), 136 peer_string(Peer, PeerS), 137 redis(DB, hget(Key, last_used), LastUsed as number). 138http_session:hook(set_last_used(SessionID, Now, Timeout)) :- 139 session_db(SessionID, DB, Key), 140 redis(DB, hset(Key, 141 last_used, Now)), 142 Expire is Now+Timeout, 143 expire(SessionID, Expire). 144http_session:hook(asserta(session_data(SessionID, Data))) :- 145 must_be(ground, Data), 146 session_data_db(SessionID, DB, Key), 147 redis(DB, lpush(Key, Data as prolog)). 148http_session:hook(assertz(session_data(SessionID, Data))) :- 149 must_be(ground, Data), 150 session_data_db(SessionID, DB, Key), 151 redis(DB, rpush(Key, Data as prolog)). 152http_session:hook(retract(session_data(SessionID, Data))) :- 153 session_data_db(SessionID, DB, Key), 154 redis_get_list(DB, Key, 10, List), 155 member(Data, List), 156 redis(DB, lrem(Key, 1, Data as prolog)). 157http_session:hook(retractall(session_data(SessionID, Data))) :- 158 forall(http_session:hook(retract(session_data(SessionID, Data))), 159 true). 160http_session:hook(session_data(SessionID, Data)) :- 161 session_data_db(SessionID, DB, Key), 162 redis_get_list(DB, Key, 10, List), 163 member(Data, List). 164http_session:hook(current_session(SessionID, Data)) :- 165 session_db(SessionID, DB, Key), 166 redis(DB, hget(Key, last_used), Time as number), 167 get_time(Now), 168 Idle is Now - Time, 169 ( http_session:session_setting(SessionID, timeout(TMO)), 170 TMO > 0 171 -> Idle =< TMO 172 ; true 173 ), 174 ( Data = peer(Peer), 175 redis(DB, hget(Key, peer), PeerS), 176 peer_string(Peer, PeerS) 177 ; Data = idle(Idle) 178 ; non_reserved_property(Data), 179 http_session:hook(session_data(SessionID, Data)) 180 ). 181http_session:hook(close_session(SessionID)) :- 182 gc_session(SessionID). 183http_session:hook(gc_sessions) :- 184 gc_sessions. 185 186non_reserved_property(P) :- 187 var(P), 188 !. 189non_reserved_property(peer(_)) :- !, fail. 190non_reserved_property(idle(_)) :- !, fail. 191non_reserved_property(_). 192 193 194 /******************************* 195 * SCHEDULE TIMEOUT * 196 *******************************/ 197 198expire(SessionID, Timeout) :- 199 get_time(Now), 200 Time is Now+Timeout, 201 session_expire_db(DB, Key), 202 redis(DB, zadd(Key, Time, SessionID)). 203 204gc_sessions :- 205 session_expire_db(DB, Key), 206 get_time(Now), 207 redis(DB, zrangebyscore(Key, "-inf", Now), TimedOut as atom), 208 forall(member(SessionID, TimedOut), 209 gc_session(SessionID)). 210 211gc_session(SessionID) :- 212 debug(http_session(gc), 'GC session ~p', [SessionID]), 213 session_db(SessionID, DB, SessionKey), 214 session_expire_db(DB, TMOKey), 215 redis(DB, zrem(TMOKey, SessionID)), 216 redis(DB, hget(SessionKey, peer), PeerS), 217 peer_string(Peer, PeerS), 218 broadcast(http_session(end(SessionID, Peer))), 219 redis(DB, del(SessionKey)), 220 session_data_db(SessionID, DB, DataKey), 221 redis(DB, del(DataKey)). 222 223 224 /******************************* 225 * 226 * UTIL * 227 *******************************/ 228 229peer_string(ip(A,B,C,D), String) :- 230 nonvar(String), 231 !, 232 split_string(String, ".", "", List), 233 maplist(number_string, [A,B,C,D], List). 234peer_string(ip(A,B,C,D), String) :- 235 atomics_to_string([A,B,C,D], ".", String). 236 237session_db(SessionID, DB, Key) :- 238 nonvar(SessionID), 239 !, 240 http_session:session_setting(redis_db(DB)), 241 key_prefix(Prefix), 242 atomics_to_string([Prefix,session,SessionID], :, Key). 243session_db(SessionID, DB, Key) :- 244 session_expire_db(DB, TMOKey), 245 redis_zscan(DB, TMOKey, Pairs, []), 246 member(SessionIDS-_Timeout, Pairs), 247 atom_string(SessionID, SessionIDS), 248 key_prefix(Prefix), 249 atomics_to_string([Prefix,session,SessionID], :, Key). 250 251session_expire_db(DB, Key) :- 252 http_session:session_setting(redis_db(DB)), 253 key_prefix(Prefix), 254 atomics_to_string([Prefix,expire], :, Key). 255 256session_data_db(SessionID, DB, Key) :- 257 http_session:session_setting(redis_db(DB)), 258 key_prefix(Prefix), 259 atomics_to_string([Prefix,data,SessionID], :, Key). 260 261key_prefix(Prefix) :- 262 http_session:session_setting(redis_prefix(Prefix)), 263 !. 264key_prefix('swipl:http:sessions')