Programming PHP

When a session is completed, the destroy handler is called. It is responsible for cleaning
up anything created during the open handler’s call. In the case of the database
storage system, we must remove that session’s entry in the table:
function destroy($session_id) {
global $table;
mysql_query( "DELETE FROM $table WHERE session_id = '$session_id'";
return true;
}
The final handler, the garbage-collection handler, is called at intervals to clean up
expired session data. The function should check for data that has not been used in
longer than the lifetime given by the call to the handler. Our database garbagecollection
handler removes entries from the table whose last-modified timestamp
exceeds the maximum time:
function gc($max_time) {
global $table;
mysql_query(
"DELETE FROM $table WHERE UNIX_TIMESTAMP(expiration)
< UNIX_TIMESTAMP()-$max_time")
or error_log("gc: ".mysql_error( )."\n",3,"/tmp/errors.log");
return true;
}
After creating all the handler functions, install them by calling session_set_save_
handler() with the appropriate function names. With the preceding examples, call:
session_set_save_handler('open', 'close', 'read', 'write', 'destroy', 'gc');
You must call session_set_save_handler() before starting a session with session_
start(). This is normally accomplished by putting the store functions and call to
session_set_save_handler() in a file that’s included in every page that needs the custom
session handler. For example:
Because the handlers are called after output for the script is sent, no function that
generates output can be called. If errors occur, log them into a file using error_log(),
as we did earlier.
Combining Cookies and Sessions
Using a combination of cookies and your own session handler, you can preserve
state across visits. Any state that should be forgotten when a user leaves the site,
such as which page the user is on, can be left up to PHP’s built-in sessions. Any state
that should persist between user visits, such as a unique user ID, can be stored in a
cookie. With the user’s ID, you can retrieve the user’s more permanent state, such as
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