Mocking the connection to the server

You may mock the connection to the server by passing in host=None when you instantiate Client64. Also, the Server32 may need to decide which library to load.

When the connection is mocked, both Client64 and Server32 instances will run in the same Python interpreter, therefore the server must load a library that is the same bitness as the Python interpreter that the client is running in. The pickle module is not used when the connection is mocked, so there is no overhead of using a file as a middle step to process requests and responses (which has a side effect that a mocked connection can return objects in a server's response that are not pickleable).

One reason that you may want to mock the connection is that you wrote a lot of code that had to load a 32-bit library but now a 64-bit version of the library is available. You may also need to support the 32-bit and 64-bit libraries at the same time. Instead of making a relatively large change to your code, or managing different code bases, you can simply specify a keyword argument when instantiating your client class to decide whether to use the 32-bit library or the 64-bit library and the client class behaves exactly the same.

Here is an example on how a client (running within 64-bit Python) can have a Server32 subclass load a 32-bit library or a 64-bit library.

from msl.loadlib import Client64, Server32

class MockableServer(Server32):

    def __init__(self, host, port, **kwargs):
        # Decide which library to load on the server.
        # `host` is `None` when the connection is mocked.
        if host is None:
            path = "path/to/64bit/c/library.so"
        else:
            path = "path/to/32bit/c/library.so"
        super().__init__(path, "cdll", host, port)

class MockableClient(Client64):

    def __init__(self, **kwargs):
        super().__init__(__file__, **kwargs)

if __name__ == "__main__":
    client_uses_32bit_library = MockableClient()
    client_uses_64bit_library = MockableClient(host=None)