Session handling functionsSessions
Session support in PHP consists of a way to preserve certain data
across subsequent accesses. This enables you to build more
customized applications and increase the appeal of your web site.
If you are familiar with the session management of PHPLIB, you
will notice that some concepts are similar to PHP's session
support.
A visitor accessing your web site is assigned an unique id, the
so-called session id. This is either stored in a cookie on the
user side or is propagated in the URL.
The session support allows you to register arbitrary numbers of
variables to be preserved across requests. When a visitor accesses
your site, PHP will check automatically (if session.auto_start is
set to 1) or on your request (explicitly through
session_start or implicitly through
session_register) whether a specific session
id has been sent with the request. If this is the case, the prior
saved environment is recreated.
All registered variables are serialized after the request
finishes. Registered variables which are undefined are marked as
being not defined. On subsequent accesses, these are not defined
by the session module unless the user defines them later.
The track_vars and
register_globals
configuration settings influence how the session variables get
stored and restored.
As of PHP 4.0.3, track_vars is
always turned on.
As of PHP 4.1.0, $_SESSION is available as
global variable just like $_POST,
$_GET, $_REQUEST and so on.
Not like $HTTP_SESSION_VARS,
$_SESSION is always global. Therefore,
global should not be used for
$_SESSION.
If track_vars is
enabled and register_globals
is disabled, only members of the global associative array
$HTTP_SESSION_VARS can be registered as session
variables. The restored session variables will only be available
in the array $HTTP_SESSION_VARS.
Registering a variable with <link
linkend="ini.track-vars"><literal>track_vars</literal></link>
enabled
]]>
Use of $_SESSION (or
$HTTP_SESSION_VARS with PHP 4.0.6 or less) is
recommended for security and code readablity. With
$_SESSION or
$HTTP_SESSION_VARS, there is no need to use
session_register()/session_unregister()/session_is_registered()
functions. Users can access session variable like a normal
variable.
Registering a variable with $_SESSION.
]]>
Unregistering a variable with $_SESSION.
]]>
If register_globals
is enabled, then all global variables can be registered as session
variables and the session variables will be restored to
corresponding global variables. Since PHP must know which global
variables are registered as session variables, users must register
variables with session_register() function while
$HTTP_SESSION_VARS/$_SESSION
does not need to use session_register().
If you are using
$HTTP_SESSION_VARS/$_SESSION
and disable register_globals,
do not use session_register,
session_is_registered and
session_unregister.
If you enable register_globals,
session_unregister should be used since
session variables are registered as global variables when
session data is deserialized. Disabling register_globals
is recommended for both security and performance reason.
Registering a variable with <link
linkend="ini.register-globals"><literal>register_globals</literal></link>
enabled
]]>
If both track_vars and
register_globals
are enabled, then the globals variables and the
$HTTP_SESSION_VARS/$_SESSION
entries will reference the same value for already registered
variables.
If user use session_register() to register session variable,
$HTTP_SESSION_VARS/$_SESSION
will not have these variable in array until it is loaded from
session storage. (i.e. until next request)
There are two methods to propagate a session id:
Cookies
URL parameter
The session module supports both methods. Cookies are optimal, but
since they are not reliable (clients are not bound to accept
them), we cannot rely on them. The second method embeds the
session id directly into URLs.
PHP is capable of doing this transparently when compiled with
--enable-trans-sid. If you enable this option,
relative URIs will be changed to contain the session id
automatically. Alternatively, you can use the constant
SID which is defined, if the client did not
send the appropriate cookie. SID is either of
the form session_name=session_id or is an empty
string.
The following example demonstrates how to register a variable, and
how to link correctly to another page using SID.
Counting the number of hits of a single user
Hello visitor, you have seen this page times.
;
( can be used if short tag is enabled)
# is necessary to preserve the session id
# in the case that the user has disabled cookies
?>
To continue, click here
]]>
The <?=SID?> is not necessary, if
--enable-trans-sid was used to compile PHP.
Non-relative URLs are assumed to point to external sites and
hence don't append the SID, as it would be a security risk to
leak the SID to a different server.
To implement database storage, or any other storage method, you
will need to use session_set_save_handler to
create a set of user-level storage functions.
The session management system supports a number of configuration
options which you can place in your &php.ini; file. We will give a
short overview.
session.save_handler defines the name of the
handler which is used for storing and retrieving data
associated with a session. Defaults to
files.
session.save_path defines the argument which
is passed to the save handler. If you choose the default files
handler, this is the path where the files are created.
Defaults to /tmp. If
session.save_path's path depth is more than
2, garbage collection will not be performed.
If you leave this set to a world-readable directory, such as
/tmp (the default), other users on the
server may be able to hijack sessions by getting the list of
files in that directory.
session.name specifies the name of the
session which is used as cookie name. It should only contain
alphanumeric characters. Defaults to
PHPSESSID.
session.auto_start specifies whether the
session module starts a session automatically on request
startup. Defaults to 0 (disabled).
session.cookie_lifetime specifies the lifetime of
the cookie in seconds which is sent to the browser. The value 0
means "until the browser is closed." Defaults to
0.
session.serialize_handler defines the name
of the handler which is used to serialize/deserialize
data. Currently, a PHP internal format (name
php) and WDDX is supported (name
wddx). WDDX is only available, if PHP is
compiled with WDDX
support. Defaults to php.
session.gc_probability specifies the
probability that the gc (garbage collection) routine is started
on each request in percent. Defaults to 1.
session.gc_maxlifetime specifies the number
of seconds after which data will be seen as 'garbage' and
cleaned up.
session.referer_check contains the substring you
want to check each HTTP Referer for. If the Referer was sent by the
client and the substring was not found, the embedded session id will
be marked as invalid. Defaults to the empty string.
session.entropy_file gives a path to an
external resource (file) which will be used as an additional
entropy source in the session id creation process. Examples are
/dev/random or
/dev/urandom which are available on many
Unix systems.
session.entropy_length specifies the number
of bytes which will be read from the file specified
above. Defaults to 0 (disabled).
session.use_cookies specifies whether the
module will use cookies to store the session id on the client
side. Defaults to 1 (enabled).
session.cookie_path specifies path to set
in session_cookie. Defaults to /.
session.cookie_domain specifies domain to
set in session_cookie. Default is none at all.
session.cache_limiter specifies cache
control method to use for session pages
(none/nocache/private/private_no_expire/public). Defaults to
nocache.
session.cache_expire specifies time-to-live
for cached session pages in minutes, this has no effect for
nocache limiter. Defaults to 180.
session.use_trans_sid whether transparent sid support
is enabled or not if enabled by compiling with
--enable-trans-sid.
Defaults to 1 (enabled).
url_rewriter.tags spefifies which html tags are
rewritten to include session id if transparent sid support is enabled.
Defaults to a=href,area=href,frame=src,input=src,form=fakeentry
Session handling was added in PHP 4.0.
session_startInitialize session dataDescriptionboolsession_startsession_start creates a session (or resumes
the current one based on the session id being passed via a GET
variable or a cookie).
If you want to use a named session, you must call
session_name before calling
session_start.
This function always returns &true;.
If you are using cookie-based sessions, you must call
session_start before anything is output to the
browser.
session_start will register internal output
handler for URL rewriting when trans-sid is
enabled. If a user uses ob_gzhandler or like
with ob_start, the order of output handler
is important for proper output. For example, user must register
ob_gzhandler before session start.
Use of zlib.output_compression is recommended
rather than ob_gzhandlersession_destroyDestroys all data registered to a sessionDescriptionboolsession_destroysession_destroy destroys all of the data
associated with the current session. It does not unset any of
the global variables associated with the session, or unset the
session cookie.
This function returns &true; on success and
&false; on failure to destroy
the session data.
Destroying a session
]]>
Destroying a session with $_SESSION
]]>
session_nameGet and/or set the current session nameDescriptionstringsession_namestringnamesession_name returns the name of the current
session. If name is specified, the name of
the current session is changed to its value.
The session name references the session id in cookies and
URLs. It should contain only alphanumeric characters; it should
be short and descriptive (i.e. for users with enabled cookie
warnings). The session name is reset to the default value
stored in session.name at request startup
time. Thus, you need to call session_name
for every request (and before session_start
or session_register are called).
<function>session_name</function> examples
";
?>
]]>
session_module_nameGet and/or set the current session moduleDescriptionstringsession_module_namestringmodulesession_module_name returns the name of the
current session module. If module is
specified, that module will be used instead.
session_save_pathGet and/or set the current session save pathDescriptionstringsession_save_pathstringpathsession_save_path returns the path of the current
directory used to save session data. If path
is specified, the path to which data is saved will be changed.
On some operating systems, you may want to specify a path on a
filesystem that handles lots of small files efficiently. For
example, on Linux, reiserfs may provide better performance than
ext2fs.
session_idGet and/or set the current session idDescriptionstringsession_idstringidsession_id returns the session id for the
current session. If id is specified, it
will replace the current session id.
The constant SID can also be used to
retrieve the current name and session id as a string suitable for
adding to URLs.
session_register
Register one or more variables with the current session
Descriptionboolsession_registermixednamemixed...session_register accepts a variable number of
arguments, any of which can be either a string holding the name of a
variable or an array consisting of variable names or other arrays. For
each name, session_register registers the global
variable with that name in the current session.
This registers a global variable. If you want to
register a session variable inside a function, you need to make sure to
make it global using global or use the session
arrays as noted below.
If you are using
$HTTP_SESSION_VARS/$_SESSION,
do not use session_register,
session_is_registered and
session_unregister.
This function returns &true; when all of the variables are successfully
registered with the session.
If session_start was not called before this function
is called, an implicit call to session_start with no
parameters will be made.
You can also create a session variable by simply setting the
appropriate member of the $HTTP_SESSION_VARS
or $_SESSION (PHP >= 4.1.0) array.
It is not currently possible to register resource variables in a
session. For example, you can not create a connection to a
database and store the connection id as a session variable and
expect the connection to still be valid the next time the
session is restored. PHP functions that return a resource are
identified by having a return type of
resource in their function definitions. A
list of functions that return resources are available in the
resource types appendix.
If $_SESSION (or
$HTTP_SESSION_VARS for PHP 4.0.6 or less) is
used, assign variable to
$_SESSION. i.e. $_SESSION['var'] = 'ABC';
See also session_is_registered and
session_unregister.
session_unregister
Unregister a variable from the current session
Descriptionboolsession_unregisterstringnamesession_unregister unregisters (forgets)
the global variable named name from the
current session.
This function returns &true; when the variable is successfully
unregistered from the session.
If $_SESSION (or
$HTTP_SESSION_VARS for PHP 4.0.6 or less) is
used, use unset to unregister a session
variable.
This function doesn't unset the corresponding global variable for
name, it only prevents the variable from being
saved as part of the session. You must call unset
to remove the corresponding global variable.
If you are using
$HTTP_SESSION_VARS/$_SESSION,
do not use session_register,
session_is_registered and
session_unregister.
session_unset
Free all session variables
Descriptionvoidsession_unset
The session_unset function free's all session variables
currently registered.
If $_SESSION (or
$HTTP_SESSION_VARS for PHP 4.0.6 or less) is
used, use unset to unregister session
variable. i.e. $_SESSION = array();
session_is_registered
Find out if a variable is registered in a session
Descriptionboolsession_is_registeredstringnamesession_is_registered returns &true; if there
is a variable with the name name
registered in the current session.
If $_SESSION (or
$HTTP_SESSION_VARS for PHP 4.0.6 or less) is
used, use isset to check a variable is
registered in $_SESSION.
If you are using
$HTTP_SESSION_VARS/$_SESSION,
do not use session_register,
session_is_registered and
session_unregister.
session_get_cookie_params
Get the session cookie parameters
Descriptionarraysession_get_cookie_params
The session_get_cookie_params function returns an
array with the current session cookie information, the array contains
the following items:
"lifetime" - The lifetime of the cookie.
"path" - The path where information is stored.
"domain" - The domain of the cookie.
"secure" - The cookie should only be sent over secure connections.
(This item was added in PHP 4.0.4.)
session_set_cookie_params
Set the session cookie parameters
Descriptionvoidsession_set_cookie_paramsintlifetimestringpathstringdomainboolsecure
Set cookie parameters defined in the &php.ini; file. The effect of this
function only lasts for the duration of the script.
The secure parameter was added in PHP
4.0.4.
session_decodeDecodes session data from a stringDescriptionboolsession_decodestringdatasession_decode decodes the session data in
data, setting variables stored in the
session.
session_encode
Encodes the current session data as a string
Descriptionstringsession_encodesession_encode returns a string with the
contents of the current session encoded within.
session_set_save_handler
Sets user-level session storage functions
Descriptionvoidsession_set_save_handlerstringopenstringclosestringreadstringwritestringdestroystringgcsession_set_save_handler sets the user-level
session storage functions which are used for storing and
retrieving data associated with a session. This is most useful
when a storage method other than those supplied by PHP sessions
is preferred. i.e. Storing the session data in a local database.
You must set the configuration option
session.save_handler to
user in your &php.ini; file for
session_set_save_handler to take effect.
The "write" handler is not executed until after the output
stream is closed. Thus, output from debugging statements in the
"write" handler will never be seen in the browser. If debugging
output is necessary, it is suggested that the debug output be
written to a file instead.
The following example provides file based session
storage similar to the PHP sessions default save handler
files. This example could easily be
extended to cover database storage using your favorite PHP
supported database engine.
Read function must return string value always to make save
handler work as expected. Return empty string if there is no data
to read. Return values from other handlers are converted to
boolean expression. TRUE for success, FALSE for failure.
<function>session_set_save_handler</function> example
]]>
session_cache_limiterGet and/or set the current cache limiterDescriptionstringsession_cache_limiterstringcache_limitersession_cache_limiter returns the name of the
current cache limiter. If cache_limiter is
specified, the name of the current cache limiter is changed to the
new value.
The cache limiter controls the cache control HTTP headers sent to the
client. These headers determine the rules by which the page content
may be cached. Setting the cache limiter to nocache,
for example, would disallow any client-side caching. A value of
public, however, would permit caching. It can also
be set to private, which is slightly more restrictive
than public.
In private mode, Expire header sent to the
client, may cause confusion for some browser including Mozilla.
You can avoid this problem with
private_no_expire mode. Expire header is never
sent to the client in this mode.
private_no_expire was added in PHP 4.2.0dev.
The cache limiter is reset to the default value stored in
session.cache_limiter at request startup time. Thus,
you need to call session_cache_limiter for every
request (and before session_start is called).
<function>session_cache_limiter</function> examples
";
?>
]]>
session_cache_expireReturn current cache expireDescriptionintsession_cache_expireintnew_cache_expiresession_cache_expire returns current cache expire.
If new_cache_expire is given, the current
cache expire is replaced with new_cache_expire.
session_write_closeWrite session data and end sessionDescriptionvoidsession_write_close
End the current session and store session data.
Session data is usually stored after your script terminated
without the need to call session_write_close, but as
session data is locked to prevent concurrent writes only one
script may operate on a session at any time. When using framesets
together with sessions you will experience the frames loading one
by one due to this locking. You can reduce the time needed to
load all the frames by ending the session as soon as all changes
to session variables are done.