type enforcement on _ssl.sslwrap function params

Question

The _ssl.sslwrap function appears to check to see if the sock passed in is a subclass of _socket.socket. I am passing in a class that implements the interface of _socket.socket.

It gets mad because my socket isn't a subclass. Is this something I should fix on my side, or is this something that I should ask about from the python-dev guys?

Here is the code from ssl.SSLSocket.init that is giving me grief:

self._sslobj = _ssl.sslwrap(self._sock, server_side,
                                    keyfile, certfile,
                                    cert_reqs, ssl_version, ca_certs,
                                    ciphers)

In my case, self._sock is an instance of my custom socket class.

UPDATE:

I am going to look into how twisted does some of this stuff. My fake socket is getting too complicated. However, I am still curious why the _ssl module is enforcing the socket type the way it is.

Answer 1

I agree that explicitly enforcing the type hierarchy seems un-Pythonic and that you might want to ask the developers about that.

OTOH, I wonder if it has to do with _ssl and _socket being the implementation modules for ssl and socket. I haven't used ssl, and I've barely used socket, but is it actually routinely necessary when using them to directly use _ssl or _socket?

Anyway, in the meantime, one workaround might be a proxy object that:

(a) inherits from _socket.socket (and thus does claim that it isinstance of _socket.socket), yet

(b) passes all its messages on to your actual "socket interface" compliant object.

I haven't tested this code, so I hope it is not an ignoble contribution:

def socketify( socket_protocol_compliant_object ):
    import _socket
    class proxy( _socket.socket ):
        def __init__( self ): pass
        def __getattribute__( self, attr_name ):
            return getattr( socket_protocol_compliant_object, attr_name )
        def __setattribute__( self, attr_name, new_value ):
            setattr( socket_protocol_compliant_object, attr_name, new_value )
    return proxy()

self._sslobj = _ssl.sslwrap( socketify(self._sock), server_side, keyfile, ... )

What do other Pythonists think? Is this a good idea?