How to init 'MySocket' object with standart socket object?

I want to write my own socket class for server-client talking with RSA and AES encryption, and for server side I need to overload accept() function to return not (socket, address) pair, but (MySocket, address). So that's why I need MySocket class to be initializable with another socket.

This is simplified version of my code:

import socket as sock

class MySocket(sock.socket):
def __init__(self, socket_obj = None):
if socket_obj == None:
sock.socket.__init__(self, family = sock.AF_INET, type = sock.SOCK_STREAM)
else:
assert(socket_obj.family == sock.AF_INET and socket_obj.type == sock.SOCK_STREAM)
self = socket_obj

self.key = 'value'

my_socket = MySocket() # works fine

print('First worked')

my_socket = MySocket(socket_obj = sock.socket()) # falls with error

print('Second also worked')


And after executing this code, I get an error:

Traceback (most recent call last):
File "./pyoverflow.py", line 19, in <module>
my_socket = MySocket(socket_obj = sock.socket()) # falls with error
File "./pyoverflow.py", line 13, in __init__
self.key = 'value'
AttributeError: 'socket' object has no attribute 'key'


As I understand, the problem is in the #9 string self = socket_obj, but googling the error didn't give anything.

self = socket_obj

self

self

self.key = value

MySocket

self

1 Answer
1

If MySocket is a subclass of socket, then a MySocket instance is a socket instance; it can't become a different socket instance, nor can you change another socket instance into a MySocket if it wasn't one already.¹

MySocket

socket

MySocket

socket

socket

socket

MySocket

There are two possible things that do make sense here, however.

First, instead of being a socket, your MySocket can own a socket, and provide the same interface as the socket type by delegating calls to its owned socket. Then, you can easily choose whether to own a newly-created socket, or one that was passed in. Something like this:

socket

MySocket

socket

socket

socket

class MySocket:
def __init__(self, socket_obj = None):
if socket_obj is None:
socket_obj = socket.socket(self, family = sock.AF_INET, type = sock.SOCK_STREAM)
self._socket_obj = socket_obj
self.key = 'value'
def accept(self):
addr, sock = self._socket_obj.accept()
return addr, MySocket(sock)
def __getattr__(self, name):
if name.startswith('_'):
raise AttributeError(name)
return getattr(self._socket_obj, name)


Writing explicit delegators (whether manually, or by looping over inspect.getmembers(socket.socket) and creating them programmatically) is probably a better design here than __getattr__, but this gets the idea across.

inspect.getmembers(socket.socket)

__getattr__

The other option is to to do effectively what ssl.SSLSocket does.

ssl.SSLSocket

Socket objects are basically just a thin wrapper around a file descriptor. You can call detach on a socket to steal its fd, and then you can pass that fd into the socket constructor:

detach

socket

class MySocket(sock.socket):
def __init__(self, socket_obj=None):
if socket_obj is None:
super().__init__(family=sock.AF_INET, type=sock.SOCK_STREAM)
else:
super().__init__(fileno=socket_obj.detach())
self.key = 'value'


_{1. Actually, in Python, you can sometimes change the type of a live object, by setting its __class__ attribute. But this is almost always a bad idea, and wanting to do so is usually a sign that your design has gone very wrong somewhere.}

__class__

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