| is not allowed in variable names. (yes, I know you can use it in array indexes, but $_SESSION is special in many ways)

May i ask why isn't the full session just serialized like a normal array?

It's an artifact of register_globals/session_register, could be fixed now 
that they're gone and I wrote a patch to do so a couple of years ago but 
some issues emerged and I haven't got around to addressing them yet.

If you raise a feature request someone else may get to it sooner.

I assume this is because the serialized form of sessions (as for the PHP serialization handler) contains the pipe character "|" as a separator between variable names.

The pipe example:

<?php
    $_SESSION['a|b'] = 'c';
    echo session_encode(); # '' - empty string
?>

I assume this, because other illegal variable names, like a variable starting with a number, _are_ possible, for example:

<?php
    $_SESSION['0a'] = '1a';
    echo session_encode(); # '0a|s:2:"1a";'
?>

If you change the session serialize-handler to "php_binary" (was: "php" in the exmaples above), this might already work (returns values containing the data in both cases).

Tested against PHP 5.3.8.

Can someone explain why| is not allowed in variable names but it is in array indexes.

http://us2.php.net/manual/en/session.configuration.php#ini.session.serialize-handler

As of 5.5.4, a new session serializer, "php_serialize", is available.  It uses the normal plain vanilla PHP serialize function instead of the weird pipe-delimited nonsense, thus allowing pipes to appear in session keys.

Use php_serialize save handler as previous comment.

php save handler has limitations that are originated from global session variable support. Characters that cannot be variables names cannot be used as session var names with php save handler.

rtuytuytutytutuytut

Change to a newer version