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22<h1>ADODB Session 2 Management Manual</h1>
23<p>
24v4.991 16 Oct 2008 (c) 2000-2008 John Lim (jlim#natsoft.com)
25</p>
26<p> <font size="1">This software is dual licensed using BSD-Style and
27LGPL. This means you can use it in compiled proprietary and commercial
28products. </font>
29<p>Useful ADOdb links: <a href="http://adodb.sourceforge.net/#download">Download</a>
30&nbsp; <a href="http://adodb.sourceforge.net/#docs">Other Docs</a>
31</p>
32<h2>Introduction</h2>
33<p> This document discusses the newer session handler adodb-session2.php. If
34  you have used the older adodb-session.php, then be forewarned that you will
35  need to alter your session table format. Otherwise everything is <a href="#compat">backward
36  compatible</a>.
37  Here are the <a href="docs-session.old.htm">older
38    docs</a> for
39  adodb-session.php.</p>
40<h2>Why Session Variables in a Database? </h2>
41<p>We store state information specific to a user or web
42    client in session variables. These session variables persist throughout a
43session, as the user moves from page to page. </p>
44<p>To use session variables, call session_start() at the beginning of
45your web page, before your HTTP headers are sent. Then for every
46variable you want to keep alive for the duration of the session, call
47session_register($variable_name). By default, the session handler will
48keep track of the session by using a cookie. You can save objects or
49arrays in session variables also.
50</p>
51<p>The default method of storing sessions is to store it in a file.
52However if you have special needs such as you:
53</p>
54<ul>
55  <li>Have multiple web servers that need to share session info</li>
56  <li>Need to do special processing of each session</li>
57  <li>Require notification when a session expires</li>
58</ul>
59<p>The ADOdb session handler provides you with the above
60additional capabilities by storing the session information as records
61in a database table that can be shared across multiple servers. </p>
62<p>These records will be garbage collected based on the php.ini [session] timeout settings.
63You can register a notification function to notify you when the record has expired and
64is about to be freed by the garbage collector.</p>
65<p>An alternative to using a database backed session handler is to use <a href="http://www.danga.com/memcached/">memcached</a>.
66  This is a distributed memory based caching system suitable for storing session
67  information.
68  </p>
69<h2> The Improved Session Handler</h2>
70<p>In ADOdb 4.91, we added a new session handler, in adodb-session2.php.
71It features the following improvements:
72<ul>
73<li>Fully supports server farms using a new database table format. The
74  previous version used the web server time for timestamps, which can cause problems
75  on a system with multiple web servers with possibly inconsistent
76  times. The new version uses the database server time instead for all timestamps.
77<li>The older database table format is obsolete. The database table must be modified
78  to support storage of the database server time mentioned above. Also the field
79  named DATA has been changed to SESSDATA. In some databases, DATA is a reserved
80  word.
81<li>The functions dataFieldName() and syncSeconds() is obsolete.
82</ul>
83
84<p>Usage is
85
86<pre>
87include_once("adodb/session/adodb-session2.php");
88ADOdb_Session::config($driver, $host, $user, $password, $database,$options=false);
89session_start();
90
91<font
92 color="#004040">#<br># Test session vars, the following should increment on refresh<br>#<br>$_SESSION['AVAR'] += 1;<br>print "&lt;p&gt;\$_SESSION['AVAR']={$_SESSION['AVAR']}&lt;/p&gt;";</font>
93</pre>
94
95<p>When the session is created in session_start( ), the global variable $<b>ADODB_SESS_CONN</b> holds
96the connection object.
97<p>The default name of the table is sessions2. If you want to override it:
98 
99<pre>
100include_once("adodb/session/adodb-session2.php");
101$options['table'] = 'mytablename';
102ADOdb_Session::config($driver, $host, $user, $password, $database,$options);
103session_start();
104</pre>
105
106
107<h3>ADOdb Session Handler Features</h3>
108<ul>
109  <li>Ability to define a notification function that is called when a
110session expires. Typically
111used to detect session logout and release global resources. </li>
112  <li>Optimization of database writes. We crc32 the session data and
113only perform an update
114to the session data if there is a data change. </li>
115  <li>Support for large amounts of session data with CLOBs (see
116adodb-session-clob2.php). Useful
117for Oracle. </li>
118  <li>Support for encrypted session data, see
119adodb-cryptsession2.php. Enabling encryption is simply a matter of
120including adodb-cryptsession2.php instead of adodb-session2.php. </li>
121</ul>
122<h3>Session Handler Files </h3>
123<p>There are 3 session management files that you can use:
124</p>
125<pre>adodb-session2.php        : The default<br>adodb-cryptsession2.php   : Use this if you want to store encrypted session data in the database<br>adodb-session-clob2.php   : Use this if you are storing DATA in clobs and you are NOT using oci8 driver</pre>
126<h2><strong>Usage Examples</strong></h2>
127<p>To force non-persistent connections, call <font color="#004040"><b>Persist</b></font>() first before session_start():
128
129 
130<pre>
131 <font color="#004040">
132include_once("adodb/session/adodb-session2.php");
133$driver = 'mysql'; $host = 'localhost'; $user = 'auser'; $pwd = 'secret'; $database = 'sessiondb';
134ADOdb_Session::config($driver, $host, $user, $password, $database,$options=false);<b><br>ADOdb_session::Persist($connectMode=false);</b>
135session_start();<br> </font>
136</pre>
137<p> The parameter to the Persist( ) method sets the connection mode. You can
138  pass the following:</p>
139<table width="50%" border="1">
140  <tr>
141    <td><b>$connectMode</b></td>
142    <td><b>Connection Method</b></td>
143  </tr>
144  <tr>
145    <td>true</td>
146    <td><p>PConnect( )</p></td>
147  </tr>
148  <tr>
149    <td>false</td>
150    <td>Connect( )</td>
151  </tr>
152  <tr>
153    <td>'N'</td>
154    <td>NConnect( )</td>
155  </tr>
156  <tr>
157    <td>'P'</td>
158    <td>PConnect( )</td>
159  </tr>
160  <tr>
161    <td>'C'</td>
162    <td>Connect( )</td>
163  </tr>
164</table>
165<p>To use a encrypted sessions, simply replace the file adodb-session2.php:</p>
166 <pre> <font
167 color="#004040"><b><br>include('adodb/session/adodb-cryptsession2.php');</b><br>$driver = 'mysql'; $host = 'localhost'; $user = 'auser'; $pwd = 'secret'; $database = 'sessiondb';
168ADOdb_Session::config($driver, $host, $user, $password, $database,$options=false);<b><br>adodb_sess_open(false,false,$connectMode=false);</b>
169session_start();<br></font></pre>
170 <p>And the same technique for adodb-session-clob2.php:</p>
171 <pre>  <font
172 color="#004040"><br><b>include('adodb/session/adodb-session2-clob2.php');</b><br>$driver = 'oci8'; $host = 'localhost'; $user = 'auser'; $pwd = 'secret'; $database = 'sessiondb';
173ADOdb_Session::config($driver, $host, $user, $password, $database,$options=false);<b><br>adodb_sess_open(false,false,$connectMode=false);</b>
174session_start();</font></pre>
175 <h2>Installation</h2>
176<p>1. Create this table in your database. Here is the MySQL version:
177<pre> <a
178 name="sessiontab"></a> <font color="#004040">
179CREATE TABLE sessions2(
180      sesskey VARCHAR( 64 ) NOT NULL DEFAULT '',
181      expiry DATETIME NOT NULL ,
182      expireref VARCHAR( 250 ) DEFAULT '',
183      created DATETIME NOT NULL ,
184      modified DATETIME NOT NULL ,
185      sessdata LONGTEXT DEFAULT '',
186      PRIMARY KEY ( sesskey ) ,
187      INDEX sess2_expiry( expiry ),
188      INDEX sess2_expireref( expireref )
189)</font></pre>
190
191 <p> For PostgreSQL, use:
192 <pre>CREATE TABLE sessions2(
193 sesskey VARCHAR( 64 ) NOT NULL DEFAULT '',
194 expiry TIMESTAMP NOT NULL ,
195 expireref VARCHAR( 250 ) DEFAULT '',
196 created TIMESTAMP NOT NULL ,
197 modified TIMESTAMP NOT NULL ,
198 sessdata TEXT DEFAULT '',
199 PRIMARY KEY ( sesskey )
200 );
201</pre>
202 <pre>create INDEX sess2_expiry on sessions2( expiry );
203create INDEX sess2_expireref on sessions2 ( expireref );</pre>
204 <p>Here is the Oracle definition, which uses a CLOB for the SESSDATA field:
205 <pre>
206  <font
207 color="#004040">CREATE TABLE SESSIONS2<br>(<br>   SESSKEY    VARCHAR2(48 BYTE)                  NOT NULL,<br>   EXPIRY     DATE                               NOT NULL,<br>   EXPIREREF  VARCHAR2(200 BYTE),<br>   CREATED    DATE                               NOT NULL,<br>   MODIFIED   DATE                               NOT NULL,<br>   SESSDATA   CLOB,<br>  PRIMARY KEY(SESSKEY)<br>);
208<br>CREATE INDEX SESS2_EXPIRY ON SESSIONS2(EXPIRY);
209CREATE INDEX SESS2_EXPIREREF ON SESSIONS2(EXPIREREF);</font></pre>
210<p> We need to use a CLOB here because for text greater than 4000 bytes long,
211  Oracle requires you to use the CLOB data type. If you are using the oci8 driver,
212  ADOdb will automatically enable CLOB handling. So you can use either adodb-session2.php
213  or adodb-session-clob2.php - in this case it doesn't matter. <br>   
214<h2>Notifications</h2>
215<p>You can receive notification when your session is cleaned up by the session garbage collector or
216when you call session_destroy().
217<p>PHP's session extension will automatically run a special garbage collection function based on
218your php.ini session.cookie_lifetime and session.gc_probability settings. This will in turn call
219adodb's garbage collection function, which can be setup to do notification.
220<p>
221<pre>
222    PHP Session --> ADOdb Session  --> Find all recs  --> Send          --> Delete queued
223    GC Function     GC Function        to be deleted      notification      records
224    executed at     called by                             for all recs
225    random time     Session Extension                     queued for deletion
226</pre>
227<p>When a session is created, we need to store a value in the session record (in the EXPIREREF field), typically
228the userid of the session. Later when the session has expired,  just before the record is deleted,
229we reload the EXPIREREF field and call the notification function with the value of EXPIREREF, which
230is the userid of the person being logged off.
231<p>ADOdb uses a global variable $ADODB_SESSION_EXPIRE_NOTIFY that you must predefine before session
232start to store the notification configuration.
233$ADODB_SESSION_EXPIRE_NOTIFY is an array with 2 elements, the
234first being the name of the session variable you would like to store in
235the EXPIREREF field, and the 2nd is the notification function's name. </p>
236<p>For example, suppose we want to be notified when a user's session has expired,
237based on the userid. When the user logs in, we store the id in the global session variable
238$USERID. The function name is 'NotifyFn'.
239<p>
240So we define (before session_start() is called): </p>
241<pre> <font color="#004040">
242    $ADODB_SESSION_EXPIRE_NOTIFY = array('USERID','NotifyFn');
243</font></pre>
244And when the NotifyFn is called (when the session expires), the
245$USERID is passed in as the first parameter, eg. NotifyFn($userid, $sesskey). The
246session key (which is the primary key of the record in the sessions
247table) is the 2nd parameter.
248<p> Here is an example of a Notification function that deletes some
249records in the database and temporary files: </p>
250<pre><font color="#004040">
251    function NotifyFn($expireref, $sesskey)
252    {
253        global $ADODB_SESS_CONN; # the session connection object
254        $user = $ADODB_SESS_CONN-&gt;qstr($expireref);
255       
256        $ADODB_SESS_CONN-&gt;Execute("delete from shopping_cart where user=$user");         
257        system("rm /work/tmpfiles/$expireref/*");
258    }</font> 
259              </pre>
260<p> NOTE 1: If you have register_globals disabled in php.ini, then you
261will have to manually set the EXPIREREF. E.g. </p>
262<pre> <font color="#004040">
263$GLOBALS['USERID'] = GetUserID();
264$ADODB_SESSION_EXPIRE_NOTIFY = array('USERID','NotifyFn');</font>
265</pre>
266<p> NOTE 2: If you want to change the EXPIREREF after the session
267record has been created, you will need to modify any session variable
268to force a database record update.
269</p>
270<h3>Synchronizing Page Frames</h3>
271<p>Sometimes you need to load multiple pages in a frameset and make sure that the session variables are synchronized.
272For example we have a page frame.php with an iframe child1.php:
273<pre>
274   frame.php
275       child1.php
276</pre>
277<p>Assume frame.php receives some $_GET variables and it updates the $_SESSION variables in memory. However the $_SESSION variables are only
278updated in the database when the page ends. So is possible that child1.php
279will still have the old $_SESSION variables.
280<ul>
281<li>   $_GET variables are posted to frame.php
282<li>   frame.php updates $_SESSION variables, but not the database
283<li>   child1.php is sent to browser, using old $_SESSION variables it loads from database
284<li>    frame.php completes it's processing and saves new $_SESSION variables into database -- too late!
285</ul>
286   <p>We can fix this by using the php function <a href=http://php.net/session_commit>session_commit</a>:
287<pre>
288&lt;?php
289session_start();
290.
291# do any required processing...
292
293session_commit();
294
295# now session variables have been saved to the database, and child1.php will get the latest $_SESSION variables.
296?>
297&lt;html>
298    &lt;body>
299    &lt;iframe src=child1.php>
300    &lt;/iframe>
301    &lt;/body>
302&lt;/html>
303</pre>
304<h3>Neat Notification Tricks</h3>
305<p><i>ExpireRef</i> normally holds the user id of the current session.
306</p>
307<p>1. You can then write a session monitor, scanning expireref to see
308who is currently logged on.
309</p>
310<p>2. If you delete the sessions record for a specific user, eg.
311</p>
312<pre>delete from sessions where expireref = '$USER'<br></pre>
313then the user is logged out. Useful for ejecting someone from a
314site.
315<p>3. You can scan the sessions table to ensure no user
316can be logged in twice. Useful for security reasons.
317</p>
318<h2>Compression/Encryption Schemes</h2>
319Since ADOdb 4.05, thanks to Ross Smith, multiple encryption and
320compression schemes are supported. Currently, supported are:
321<p>
322<pre>  MD5Crypt (crypt.inc.php)<br>  MCrypt<br>  Secure (Horde's emulation of MCrypt, if MCrypt module is not available.)<br>  GZip<br>  BZip2<br></pre>
323<p>These are stackable. E.g.
324<pre>ADODB_Session::filter(new ADODB_Compress_Bzip2());<br>ADODB_Session::filter(new ADODB_Encrypt_MD5());<br></pre>
325will compress and then encrypt the record in the database.
326<h2>Session Cookie Regeneration: adodb_session_regenerate_id()</h2>
327<p>Dynamically change the current session id with a newly generated one and update
328  database. Currently only works with cookies. Useful to improve security by
329  reducing the risk of session-hijacking. See this article on <a href=http://shiflett.org/articles/security-corner-feb2004>Session
330  Fixation</a> for more info
331on the theory behind this feature. Usage:<pre>
332    include('path/to/adodb/session/adodb-session2.php');
333   
334    session_start();
335    # Approximately every 10 page loads, reset cookie for safety.
336    # This is extremely simplistic example, better
337    # to regenerate only when the user logs in or changes
338    # user privilege levels.
339    if ((rand()%10) == 0) adodb_session_regenerate_id();
340</pre>
341<p>This function calls session_regenerate_id() internally or simulates it if the function does not exist.
342<h2>Vacuum/Optimize Database</h2>
343<p>During session garbage collection, if postgresql is detected,
344  ADOdb can be set to run VACUUM. If mysql is detected, then optimize database
345  could be called.You can turn this on or off using:</p>
346<pre>$turnOn = true; # or false
347ADODB_Session::optimize($turnOn);
348</pre>
349<p>The default  is optimization is disabled.</p>
350<h2><a name=compat></a>Backwards Compatability </h2>
351<p>The older method of connecting to ADOdb using global variables is still supported:</p>
352<pre> $ADODB_SESSION_DRIVER='mysql';
353 $ADODB_SESSION_CONNECT='localhost';
354 $ADODB_SESSION_USER ='root';
355 $ADODB_SESSION_PWD ='abc';
356 $ADODB_SESSION_DB ='phplens';
357 
358 include('path/to/adodb/session/adodb-<strong>session2</strong>.php'); </pre>
359<p>In the above example, the only things you need to change in your code to upgrade
360  is </p>
361<ul>
362  <li>your session table format to the new one.</li>
363  <li>the include file from adodb-session.php to adodb-session2.php. </li>
364</ul>
365<h2>More Info</h2>
366<p>Also see the <a href="docs-adodb.htm">core ADOdb documentation</a>. And if
367  you are interested in the obsolete adodb-session.php, see <a href="docs-session.old.htm">old
368    session documentation</a>. </p>
369</body>
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