How can I return a complex object type (python-ldap connection) from a Pyro4 Daemon?

Question

I've got a Pyro4 daemon going which I would like to have return a connection to LDAP (instantiated by the python-ldap module). The code is short and simple, but I run into an error with (I believe) serialization of the connection object upon my attempt to return the connection to the client script.

class LDAPDaemon(object):
   def get_ldap_connection(self):
      conn = ldap.initialize("ldap://ds1")
      conn.simple_bind_s("cn=Directory Manager", "abc123")
      return conn

daemon = Pyro4.Daemon(unixsocket="/tmp/ldap_unix.sock")
os.system("chmod 700 /tmp/ldap_unix.sock")
uri=daemon.register(LDAPDaemon(), "LDAPDaemon")
daemon.requestLoop()

Then in my driver script, I have the following (assume uri is known, cut all that out for brevity's sake):

with Pyro4.Proxy(uri) as ldap_daemon:
   conn = ldap_daemon.get_ldap_connection()

This results in the following error:

Traceback (most recent call last):
  File "./tester.py", line 14, in <module>
    conn = ldap_daemon.get_ldap_connection()
  File "/opt/csw/lib/python2.6/site-packages/Pyro4/core.py", line 160, in __call__
    return self.__send(self.__name, args, kwargs)
  File "/opt/csw/lib/python2.6/site-packages/Pyro4/core.py", line 318, in _pyroInvoke
    raise data
AttributeError: __class__

I tried changing the Pyro4 configuration to accept different serializers, i.e.:

Pyro4.config.SERIALIZERS_ACCEPTED = set(['json', 'marshal', 'serpent', 'pickle'])

but that didn't change anything.

Please ignore the glaring security holes as this was dumbed down to the most basic code to produce the error.

Answer 1

You guessed right. The LDAPOject is not serializable. Arguments passed to a remote object and the return values of its methods are serialized and then sent through a socket. Not serializable objects will cause errors. You should consider User's comment, create a proxy for the connection instead of sending it to the other process or you have to find a way to serialize it.