Initial Import
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+<td><h1>Code Igniter User Guide Version 1.4.0</h1></td>
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+Session Class
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+
+<h1>Session Class</h1>
+
+<p>The Session class permits you maintain a user's "state" and track their activity while they browse your site.
+The Session class stores session information for each user as serialized (and optionally encrypted) data in a cookie.
+It can also store the session data in a database table for added security, as this permits the session ID in the
+user's cookie to be matched against the stored session ID. By default only the cookie is saved. If you choose to
+use the database option you'll need to create the session table as indicated below.
+</p>
+
+<p class="important"><strong>Note:</strong> The Session class does <strong>not</strong> utilize native PHP sessions. It
+generates its own session data, offering more flexibility for developers.</p>
+
+<h2>Initializing a Session</h2>
+
+<p>Sessions will typically run globally with each page load, so the session class must either be
+<a href="../general/libraries.html">initialized</a> in your
+<a href="../general/controllers.html">controller</a> constructors, or it can be
+<a href="../general/autoloader.html">auto-loaded</a> by the system.
+For the most part the session class will run unattended in the background, so simply initializing the class
+will cause it to read, create, and update sessions.</p>
+
+
+<p>To initialize the Session class manually in your controller constructor, use the <dfn>$this->load->library</dfn> function:</p>
+
+<code>$this->load->library('session');</code>
+<p>Once loaded, the Sessions library object will be available using: <dfn>$this->session</dfn></p>
+
+
+<h2>How do Sessions work?</h2>
+
+<p>When a page is loaded, the session class will check to see if valid session data exists in the user's session cookie.
+If sessions data does <strong>not</strong> exist (or if it has expired) a new session will be created and saved in the cookie.
+If a session does exist, its information will be updated and the cookie will be updated.</p>
+
+<p>It's important for you to understand that once initialized, the Session class runs automatically. There is nothing
+you need to do to cause the above behavior to happen. You can, as you'll see below, work with session data or
+even add your own data to a user's session, but the process of reading, writing, and updating a session is automatic.</p>
+
+
+<h2>What is Session Data?</h2>
+
+<p>A <em>session</em>, as far as Code Igniter is concerned, is simply an array containing the following information:</p>
+
+<ul>
+<li>The user's unique Session ID (this is a statistically random string with very strong entropy, hashed with MD5 for portability)</li>
+<li>The user's IP Address</li>
+<li>The user's User Agent data (the first 50 characters of the browser data string)</li>
+<li>The "last activity" and "last visit" time stamps.</li>
+</ul>
+
+<p>The above data is stored in a cookie as a serialized array with this prototype:</p>
+
+<code>[array]<br />
+(<br />
+ 'session_id' => random hash,<br />
+ 'ip_address' => 'string - user IP address',<br />
+ 'user_agent' => 'string - user agent data',<br />
+ 'last_activity' => timestamp,<br />
+ 'last_visit' => timestamp<br />
+)</code>
+
+<p>If you have the encryption option enabled, the serialized array will be encrypted before being stored in the cookie,
+making the data highly secure and impervious to being read or altered by someone. More info regarding encryption
+can be <a href="encryption.html">found here</a>, although the Session class will take care of initializing
+and encrypting the data automatically.</p>
+
+<p>Note: Session cookies are only updated every five minutes to reduce processor load. If you repeatedly reload a page
+you'll notice that the "last activity" time only updates if five minutes or more has passed since the last time
+the cookie was written.</p>
+
+<h2>Retrieving Session Data</h2>
+
+<p>Any piece of information from the session array is available using the following function:</p>
+
+<code>$this->session->userdata('<samp>item</samp>');</code>
+
+<p>Where <samp>item</samp> is the array index corresponding to the item you wish to fetch. For example, to fetch the session ID you
+will do this:</p>
+
+<code>$session_id = $this->session->userdata('<samp>session_id</samp>');</code>
+
+<p><strong>Note:</strong> The function returns FALSE (boolean) if the item you are trying to access does not exist.</p>
+
+
+<h2>Adding Custom Session Data</h2>
+
+<p>A useful aspect of the session array is that you can add your own data to it and it will be stored in the user's cookie.
+Why would you want to do this? Here's one example:</p>
+
+<p>Let's say a particular user logs into your site. Once authenticated,
+you could add their username and email address to the session cookie, making that data globally available to you without
+having to run a database query when you need it.</p>
+
+<p>To add your data to the session array involves passing an array containing your new data to this function:</p>
+
+<code>$this->session->set_userdata(<samp>$array</samp>);</code>
+
+<p>Where <samp>$array</samp> is an associative array containing your new data. Here's an example:</p>
+
+
+<code>$newdata = array(<br />
+ 'username' => 'johndoe',<br />
+ 'email' => 'johndoe@some-site.com',<br />
+ 'logged_in' => TRUE<br />
+ );<br />
+<br />
+$this->session->set_userdata(<samp>$newdata</samp>);</code>
+
+<p class="important"><strong>Note:</strong> Cookies can only hold 4KB of data, so be careful not to exceed the capacity. The
+encryption process in particular produces a longer data string than the original so keep careful track of how much data you are storing.</p>
+
+<h2>Saving Session Data to a Database</h2>
+
+<p>While the session data array stored in the user's cookie contains a Session ID,
+unless you store session data in a database there is no way to validate it. For some applications that require little or no
+security, session ID validation may not be needed, but if your application requires security, validation is mandatory.</p>
+
+<p>When session data is available in a database, every time a valid session is found in the user's cookie, a database
+query is performed to match it. If the session ID does not match, the session is destroyed. Session IDs can never
+be updated, they can only be generated when a new session is created.</p>
+
+<p>In order to store sessions, you must first create a database table for this purpose. Here is the basic
+prototype required by the session class:</p>
+
+<textarea class="textarea" style="width:100%" cols="50" rows="8">
+CREATE TABLE IF NOT EXISTS `ci_sessions` (
+session_id varchar(40) DEFAULT '0' NOT NULL,
+ip_address varchar(16) DEFAULT '0' NOT NULL,
+user_agent varchar(50) NOT NULL,
+last_activity int(10) unsigned DEFAULT 0 NOT NULL,
+PRIMARY KEY (session_id)
+);</textarea>
+
+<p><strong>Note:</strong> By default the table is called <dfn>ci_sessions</dfn>, but you can name it anything you want
+as long as you update the <kbd>application/config/config.php</kbd> file so that it contains the name you have chosen.
+Once you have created your database table you can enable the database option in your config.php file as follows:</p>
+
+<code>$config['sess_use_database'] = TRUE;</code>
+
+<p>Once enabled, the Session class will store session data in the DB.</p>
+
+<h2>Session Preferences</h2>
+
+<p>You'll find the following Session related preferences in your <kbd>application/config/config.php</kbd> file:</p>
+
+
+<table cellpadding="0" cellspacing="1" border="0" style="width:100%" class="tableborder">
+<tr>
+<th>Preference</th>
+<th>Default</th>
+<th>Options</th>
+<th>Description</th>
+
+</tr><tr>
+<td class="td"><strong>sess_cookie_name</strong></td>
+<td class="td">ci_session</td
+><td class="td">None</td>
+<td class="td">The name you world the session cookie saved as.</td>
+
+</tr><tr>
+<td class="td"><strong>sess_expiration</strong></td>
+<td class="td">7200</td>
+<td class="td">None</td>
+<td class="td">The number of seconds you would like the session to last. The default value is 2 hours (7200 seconds).
+If you would like a non-expiring session set the value to zero: 0</td>
+
+
+</tr><tr>
+<td class="td"><strong>sess_encrypt_cookie</strong></td>
+<td class="td">TRUE</td>
+<td class="td">TRUE/FALSE (boolean)</td>
+<td class="td">Whether to encrypt the session data.</td>
+
+</tr><tr>
+<td class="td"><strong>sess_use_database</strong></td>
+<td class="td">FALSE</td>
+<td class="td">TRUE/FALSE (boolean)</td>
+<td class="td">Whether to save the session data to a database. You must create the table before enabling this option.</td>
+
+</tr><tr>
+<td class="td"><strong>sess_table_name</strong></td>
+<td class="td">ci_sessions</td
+><td class="td">Any valid SQL table name</td>
+<td class="td">The name of the session database table.</td>
+
+</tr><tr>
+<td class="td"><strong>sess_match_ip</strong></td>
+<td class="td">FALSE</td>
+<td class="td">TRUE/FALSE (boolean)</td>
+<td class="td">Whether to match the user's IP address when reading the session data. Note that some ISPs dynamically
+changes the IP, so if you want a non-expiring session you will likely set this to FALSE.</td>
+
+</tr><tr>
+<td class="td"><strong>sess_match_useragent</strong></td>
+<td class="td">TRUE</td>
+<td class="td">TRUE/FALSE (boolean)</td>
+<td class="td">Whether to match the User Agent when reading the session data.</td>
+
+
+</tr>
+</table>
+
+
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