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[zend.git] / documentation / manual / en / module_specs / Zend_Session-AdvancedUsage.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- Reviewed: no -->
<sect1 id="zend.session.advanced_usage">
    <title>Advanced Usage</title>

    <para>
        While the basic usage examples are a perfectly acceptable way to utilize Zend Framework
        sessions, there are some best practices to consider. This section discusses the finer
        details of session handling and illustrates more advanced usage of the
        <classname>Zend_Session</classname> component.
    </para>

    <sect2 id="zend.session.advanced_usage.starting_a_session">
        <title>Starting a Session</title>

        <para>
            If you want all requests to have a session facilitated by
            <classname>Zend_Session</classname>, then start the session in the bootstrap file:
        </para>

        <example id="zend.session.advanced_usage.starting_a_session.example">
            <title>Starting the Global Session</title>

            <programlisting language="php"><![CDATA[
Zend_Session::start();
]]></programlisting>
        </example>

        <para>
            By starting the session in the bootstrap file, you avoid the possibility that your
            session might be started after headers have been sent to the browser, which results in
            an exception, and possibly a broken page for website viewers. Various advanced features
            require <methodname>Zend_Session::start()</methodname> first. (More on advanced features
            later.)
        </para>

        <para>
            There are four ways to start a session, when using <classname>Zend_Session</classname>.
            Two are wrong.
        </para>

        <orderedlist>
            <listitem>
                <para>
                    Wrong: Do not enable <acronym>PHP</acronym>'s <ulink
                        url="http://www.php.net/manual/en/ref.session.php#ini.session.auto-start">
                        <code>session.auto_start</code> setting</ulink>. If you do not have the
                    ability to disable this setting in php.ini, you are using mod_php (or
                    equivalent), and the setting is already enabled in <code>php.ini</code>, then
                    add the following to your <code>.htaccess</code> file (usually in your
                    <acronym>HTML</acronym> document root directory):
                    <programlisting language="httpd.conf"><![CDATA[
php_value session.auto_start 0
]]></programlisting>
                </para>
            </listitem>

            <listitem>
                <para>
                    Wrong: Do not use <acronym>PHP</acronym>'s <ulink
                        url="http://www.php.net/session_start"><methodname>session_start()</methodname></ulink>
                    function directly. If you use <methodname>session_start()</methodname> directly,
                    and then start using <classname>Zend_Session_Namespace</classname>, an exception
                    will be thrown by <methodname>Zend_Session::start()</methodname> ("session has
                    already been started"). If you call <methodname>session_start()</methodname>
                    after using <classname>Zend_Session_Namespace</classname> or calling
                    <methodname>Zend_Session::start()</methodname>, an error of level
                    <constant>E_NOTICE</constant> will be generated, and the call will be ignored.
                </para>
            </listitem>

            <listitem>
                <para>
                    Correct: Use <methodname>Zend_Session::start()</methodname>. If you want all
                    requests to have and use sessions, then place this function call early and
                    unconditionally in your bootstrap code. Sessions have some overhead. If some
                    requests need sessions, but other requests will not need to use sessions, then:
                </para>

                <itemizedlist mark="opencircle">
                    <listitem>
                        <para>
                            Unconditionally set the <code>strict</code> option to
                            <constant>TRUE</constant> using
                            <methodname>Zend_Session::setOptions()</methodname> in your bootstrap.
                        </para>
                    </listitem>

                    <listitem>
                        <para>
                            Call <methodname>Zend_Session::start()</methodname> only for requests
                            that need to use sessions and before any
                            <classname>Zend_Session_Namespace</classname> objects are instantiated.
                        </para>
                    </listitem>

                    <listitem>
                        <para>
                            Use "<code>new Zend_Session_Namespace()</code>" normally, where needed,
                            but make sure <methodname>Zend_Session::start()</methodname> has been
                            called previously.
                        </para>
                    </listitem>
                </itemizedlist>

                <para>
                    The <code>strict</code> option prevents
                    <code>new Zend_Session_Namespace()</code> from automatically starting the
                    session using <methodname>Zend_Session::start()</methodname>. Thus, this option
                    helps application developers enforce a design decision to avoid using sessions
                    for certain requests, since it causes an exception to be thrown when
                    <classname>Zend_Session_Namespace</classname> is instantiated before
                    <methodname>Zend_Session::start()</methodname> is called. Developers should
                    carefully consider the impact of using
                    <methodname>Zend_Session::setOptions()</methodname>, since these options have
                    global effect, owing to their correspondence to the underlying options for
                    ext/session.
                </para>
            </listitem>

            <listitem>
                <para>
                    Correct: Just instantiate <classname>Zend_Session_Namespace</classname> whenever
                    needed, and the underlying <acronym>PHP</acronym> session will be automatically
                    started. This offers extremely simple usage that works well in most situations.
                    However, you then become responsible for ensuring that the first
                    <code>new Zend_Session_Namespace()</code> happens <emphasis>before</emphasis>
                    any output (e.g., <ulink url="http://www.php.net/headers_sent">HTTP
                        headers</ulink>) has been sent by <acronym>PHP</acronym> to the client, if
                    you are using the default, cookie-based sessions (strongly recommended). See
                    <xref linkend="zend.session.global_session_management.headers_sent" /> for more
                    information.
                </para>
            </listitem>
        </orderedlist>
    </sect2>

    <sect2 id="zend.session.advanced_usage.locking">
        <title>Locking Session Namespaces</title>

        <para>
            Session namespaces can be locked, to prevent further alterations to the data in that
            namespace. Use <methodname>lock()</methodname> to make a specific namespace read-only,
            <methodname>unLock()</methodname> to make a read-only namespace read-write, and
            <methodname>isLocked()</methodname> to test if a namespace has been previously locked.
            Locks are transient and do not persist from one request to the next. Locking the
            namespace has no effect on setter methods of objects stored in the namespace, but does
            prevent the use of the namespace's setter method to remove or replace objects stored
            directly in the namespace. Similarly, locking
            <classname>Zend_Session_Namespace</classname> instances does not prevent the use of
            symbol table aliases to the same data (see <ulink
                url="http://www.php.net/references">PHP references</ulink>).
        </para>

        <example id="zend.session.advanced_usage.locking.example.basic">
            <title>Locking Session Namespaces</title>

            <programlisting language="php"><![CDATA[
$userProfileNamespace = new Zend_Session_Namespace('userProfileNamespace');

// marking session as read only locked
$userProfileNamespace->lock();

// unlocking read-only lock
if ($userProfileNamespace->isLocked()) {
    $userProfileNamespace->unLock();
}
]]></programlisting>
        </example>
    </sect2>

    <sect2 id="zend.session.advanced_usage.expiration">
        <title>Namespace Expiration</title>

        <para>
            Limits can be placed on the longevity of both namespaces and individual keys in
            namespaces. Common use cases include passing temporary information between requests, and
            reducing exposure to certain security risks by removing access to potentially sensitive
            information some time after authentication occurred. Expiration can be based on either
            elapsed seconds or the number of "hops", where a hop occurs for each successive request.
        </para>

        <example id="zend.session.advanced_usage.expiration.example">
            <title>Expiration Examples</title>

            <programlisting language="php"><![CDATA[
$s = new Zend_Session_Namespace('expireAll');
$s->a = 'apple';
$s->p = 'pear';
$s->o = 'orange';

$s->setExpirationSeconds(5, 'a'); // expire only the key "a" in 5 seconds

// expire entire namespace in 5 "hops"
$s->setExpirationHops(5);

$s->setExpirationSeconds(60);
// The "expireAll" namespace will be marked "expired" on
// the first request received after 60 seconds have elapsed,
// or in 5 hops, whichever happens first.
]]></programlisting>
        </example>

        <para>
            When working with data expiring from the session in the current request, care should be
            used when retrieving them. Although the data are returned by reference, modifying the
            data will not make expiring data persist past the current request. In order to "reset"
            the expiration time, fetch the data into temporary variables, use the namespace to unset
            them, and then set the appropriate keys again.
        </para>
    </sect2>

    <sect2 id="zend.session.advanced_usage.controllers">
        <title>Session Encapsulation and Controllers</title>

        <para>
            Namespaces can also be used to separate session access by controllers to protect
            variables from contamination. For example, an authentication controller might keep its
            session state data separate from all other controllers for meeting security
            requirements.
        </para>

        <example id="zend.session.advanced_usage.controllers.example">
            <title>Namespaced Sessions for Controllers with Automatic Expiration</title>

            <para>
                The following code, as part of a controller that displays a test question, initiates
                a boolean variable to represent whether or not a submitted answer to the test
                question should be accepted. In this case, the application user is given 300 seconds
                to answer the displayed question.
            </para>

            <programlisting language="php"><![CDATA[
// ...
// in the question view controller
$testSpace = new Zend_Session_Namespace('testSpace');
// expire only this variable
$testSpace->setExpirationSeconds(300, 'accept_answer');
$testSpace->accept_answer = true;
//...
]]></programlisting>

            <para>
                Below, the controller that processes the answers to test questions determines
                whether or not to accept an answer based on whether the user submitted the answer
                within the allotted time:
            </para>

            <programlisting language="php"><![CDATA[
// ...
// in the answer processing controller
$testSpace = new Zend_Session_Namespace('testSpace');
if ($testSpace->accept_answer === true) {
    // within time
}
else {
    // not within time
}
// ...
]]></programlisting>
        </example>
    </sect2>

    <sect2 id="zend.session.advanced_usage.single_instance">
        <title>Preventing Multiple Instances per Namespace</title>

        <para>
            Although <link linkend="zend.session.advanced_usage.locking">session locking</link>
            provides a good degree of protection against unintended use of namespaced session data,
            <classname>Zend_Session_Namespace</classname> also features the ability to prevent the
            creation of multiple instances corresponding to a single namespace.
        </para>

        <para>
            To enable this behavior, pass <constant>TRUE</constant> to the second constructor
            argument when creating the last allowed instance of
            <classname>Zend_Session_Namespace</classname>. Any subsequent attempt to instantiate the
            same namespace would result in a thrown exception.
        </para>

        <example id="zend.session.advanced_usage.single_instance.example">
            <title>Limiting Session Namespace Access to a Single Instance</title>

            <programlisting language="php"><![CDATA[
// create an instance of a namespace
$authSpaceAccessor1 = new Zend_Session_Namespace('Zend_Auth');

// create another instance of the same namespace, but disallow any
// new instances
$authSpaceAccessor2 = new Zend_Session_Namespace('Zend_Auth', true);

// making a reference is still possible
$authSpaceAccessor3 = $authSpaceAccessor2;

$authSpaceAccessor1->foo = 'bar';

assert($authSpaceAccessor2->foo, 'bar');

try {
    $aNamespaceObject = new Zend_Session_Namespace('Zend_Auth');
} catch (Zend_Session_Exception $e) {
    echo 'Cannot instantiate this namespace since ' .
         '$authSpaceAccessor2 was created\n';
}
]]></programlisting>
        </example>

        <para>
            The second parameter in the constructor above tells
            <classname>Zend_Session_Namespace</classname> that any future instances with the
            "<classname>Zend_Auth</classname>" namespace are not allowed. Attempting to create such
            an instance causes an exception to be thrown by the constructor. The developer therefore
            becomes responsible for storing a reference to an instance object
            (<varname>$authSpaceAccessor1</varname>, <varname>$authSpaceAccessor2</varname>, or
            <varname>$authSpaceAccessor3</varname> in the example above) somewhere, if access to the
            session namespace is needed at a later time during the same request. For example, a
            developer may store the reference in a static variable, add the reference to a <ulink
                url="http://www.martinfowler.com/eaaCatalog/registry.html">registry</ulink> (see
            <xref linkend="zend.registry" />), or otherwise make it available to other methods that
            may need access to the session namespace.
        </para>
    </sect2>

    <sect2 id="zend.session.advanced_usage.arrays">
        <title>Working with Arrays</title>

        <para>
            Due to the implementation history of <acronym>PHP</acronym> magic methods, modifying an
            array inside a namespace may not work under <acronym>PHP</acronym> versions before
            5.2.1. If you will only be working with <acronym>PHP</acronym> 5.2.1 or later, then you
            may <link linkend="zend.session.advanced_usage.objects">skip to the next section</link>.
        </para>

        <example id="zend.session.advanced_usage.arrays.example.modifying">
            <title>Modifying Array Data with a Session Namespace</title>

            <para>
                The following illustrates how the problem may be reproduced:
            </para>

            <programlisting language="php"><![CDATA[
$sessionNamespace = new Zend_Session_Namespace();
$sessionNamespace->array = array();

// may not work as expected before PHP 5.2.1
$sessionNamespace->array['testKey'] = 1;
echo $sessionNamespace->array['testKey'];
]]></programlisting>
        </example>

        <example id="zend.session.advanced_usage.arrays.example.building_prior">
            <title>Building Arrays Prior to Session Storage</title>

            <para>
                If possible, avoid the problem altogether by storing arrays into a session namespace
                only after all desired array values have been set.
            </para>

            <programlisting language="php"><![CDATA[
$sessionNamespace = new Zend_Session_Namespace('Foo');
$sessionNamespace->array = array('a', 'b', 'c');
]]></programlisting>
        </example>

        <para>
            If you are using an affected version of <acronym>PHP</acronym> and need to modify the
            array after assigning it to a session namespace key, you may use either or both of the
            following workarounds.
        </para>

        <example id="zend.session.advanced_usage.arrays.example.workaround.reassign">
            <title>Workaround: Reassign a Modified Array</title>

            <para>
                In the code that follows, a copy of the stored array is created, modified, and
                reassigned to the location from which the copy was created, overwriting the original
                array.
            </para>

            <programlisting language="php"><![CDATA[
$sessionNamespace = new Zend_Session_Namespace();

// assign the initial array
$sessionNamespace->array = array('tree' => 'apple');

// make a copy of the array
$tmp = $sessionNamespace->array;

// modfiy the array copy
$tmp['fruit'] = 'peach';

// assign a copy of the array back to the session namespace
$sessionNamespace->array = $tmp;

echo $sessionNamespace->array['fruit']; // prints "peach"
]]></programlisting>
        </example>

        <example id="zend.session.advanced_usage.arrays.example.workaround.reference">
            <title>Workaround: store array containing reference</title>

            <para>
                Alternatively, store an array containing a reference to the desired array, and then
                access it indirectly.
            </para>

            <programlisting language="php"><![CDATA[
$myNamespace = new Zend_Session_Namespace('myNamespace');
$a = array(1, 2, 3);
$myNamespace->someArray = array( &$a );
$a['foo'] = 'bar';
echo $myNamespace->someArray['foo']; // prints "bar"
]]></programlisting>
        </example>
    </sect2>

    <sect2 id="zend.session.advanced_usage.objects">
        <title>Using Sessions with Objects</title>

        <para>
            If you plan to persist objects in the <acronym>PHP</acronym> session, know that they
            will be <ulink
                url="http://www.php.net/manual/en/language.oop.serialization.php">serialized</ulink>
            for storage. Thus, any object persisted with the <acronym>PHP</acronym> session must be
            unserialized upon retrieval from storage. The implication is that the developer must
            ensure that the classes for the persisted objects must have been defined before the
            object is unserialized from session storage. If an unserialized object's class is not
            defined, then it becomes an instance of <code>stdClass</code>.
        </para>
    </sect2>

    <sect2 id="zend.session.advanced_usage.testing">
        <title>Using Sessions with Unit Tests</title>

        <para>
            Zend Framework relies on PHPUnit to facilitate testing of itself. Many developers extend
            the existing suite of unit tests to cover the code in their applications. The exception
            "<emphasis>Zend_Session is currently marked as read-only</emphasis>" is thrown while
            performing unit tests, if any write-related methods are used after ending the session.
            However, unit tests using <classname>Zend_Session</classname> require extra attention,
            because closing (<methodname>Zend_Session::writeClose()</methodname>), or destroying a
            session (<methodname>Zend_Session::destroy()</methodname>) prevents any further setting
            or unsetting of keys in any instance of <classname>Zend_Session_Namespace</classname>.
            This behavior is a direct result of the underlying ext/session mechanism and
            <acronym>PHP</acronym>'s <methodname>session_destroy()</methodname> and
            <methodname>session_write_close()</methodname>, which have no "undo" mechanism to
            facilitate setup/teardown with unit tests.
        </para>

        <para>
            To work around this, see the unit test
            <methodname>testSetExpirationSeconds()</methodname> in <code>SessionTest.php</code> and
            <code>SessionTestHelper.php</code>, both located in <code>tests/Zend/Session</code>,
            which make use of <acronym>PHP</acronym>'s <methodname>exec()</methodname> to launch a
            separate process. The new process more accurately simulates a second, successive request
            from a browser. The separate process begins with a "clean" session, just like any
            <acronym>PHP</acronym> script execution for a web request. Also, any changes to
            <varname>$_SESSION</varname> made in the calling process become available to the child
            process, provided the parent closed the session before using
            <methodname>exec()</methodname>.
        </para>

        <example id="zend.session.advanced_usage.testing.example">
            <title>PHPUnit Testing Code Dependent on Zend_Session</title>

            <programlisting language="php"><![CDATA[
// testing setExpirationSeconds()
$script = 'SessionTestHelper.php';
$s = new Zend_Session_Namespace('space');
$s->a = 'apple';
$s->o = 'orange';
$s->setExpirationSeconds(5);

Zend_Session::regenerateId();
$id = Zend_Session::getId();
session_write_close(); // release session so process below can use it
sleep(4); // not long enough for things to expire
exec($script . "expireAll $id expireAll", $result);
$result = $this->sortResult($result);
$expect = ';a === apple;o === orange;p === pear';
$this->assertTrue($result === $expect,
    "iteration over default Zend_Session namespace failed; " .
    "expecting result === '$expect', but got '$result'");

sleep(2); // long enough for things to expire (total of 6 seconds
          // waiting, but expires in 5)
exec($script . "expireAll $id expireAll", $result);
$result = array_pop($result);
$this->assertTrue($result === '',
    "iteration over default Zend_Session namespace failed; " .
    "expecting result === '', but got '$result')");
session_start(); // resume artificially suspended session

// We could split this into a separate test, but actually, if anything
// leftover from above contaminates the tests below, that is also a
// bug that we want to know about.
$s = new Zend_Session_Namespace('expireGuava');
$s->setExpirationSeconds(5, 'g'); // now try to expire only 1 of the
                                  // keys in the namespace
$s->g = 'guava';
$s->p = 'peach';
$s->p = 'plum';

session_write_close(); // release session so process below can use it
sleep(6); // not long enough for things to expire
exec($script . "expireAll $id expireGuava", $result);
$result = $this->sortResult($result);
session_start(); // resume artificially suspended session
$this->assertTrue($result === ';p === plum',
    "iteration over named Zend_Session namespace failed (result=$result)");
]]></programlisting>
        </example>
    </sect2>
</sect1>