Question

So I have created a class implementing SessionhandlerInterface and set it as a session handler:

$sessionHandler = new SessionHandler();
session_set_save_handler($sessionHandler);
session_start();

The problem is, the write function is never called.

If I use the second parameter of session_set_save_handler and set it to false:

session_set_save_handler($sessionHandler, false);

Then it works properly. Can somebody explain this behaviour to me? I am using PHP 5.4.6.

In the documentation there is written:

When using objects as session save handlers, it is important to register the shutdown function with PHP to avoid unexpected side-effects from the way PHP internally destroys objects on shutdown and may prevent the write and close from being called. Typically you should register ‘session_write_close’ using the register_shutdown_function() function.

As of PHP 5.4.0 you can use session_register_shutdown() or simply use the ‘register shutdown’ flag when invoking session_set_save_handler() using the OOP method and passing an instance that implements SessionHandlerInterface.

But I don’t fully understand that.

Answer 1

The documentation states the following:

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.

This is probably why you don’t see the function being called if you use a simple echo.