Recipe15.5.Implementing SimpleXMLRPCServer Niceties

Recipe 15.5. Implementing SimpleXMLRPCServer Niceties

Credit: Rune Hansen

Problem

You are coding XML-RPC servers with the Python Standard Library SimpleXMLRPCServer class and want to ensure you're using the simple but useful idioms that can ease your coding, or give your servers more flexibility at no substantial cost to you.

Solution

Here are a few tweaks I generally use, to enhance my servers' usability, when I'm developing servers based on SimpleXMLRPCServer:

# give the base class a short, readable nickname from SimpleXMLRPCServer import SimpleXMLRPCServer as BaseServer class Server(BaseServer):     def _ _init_ _(self, host, port):         # accept separate hostname and portnumber and group them         BaseServer._ _init_ _(self, (host, port))     def server_bind(self):         # allow fast restart of the server after it's killed         import socket         self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)         BaseServer.server_bind(self)     allowedClientHosts = '127.0.0.1', '192.168.0.15',     def verify_request(self, request, client_address):         # forbid requests except from specific client hosts         return client_address[0] in self.allowedClientHosts

Discussion

The recipe begins with a statement of the form from module import name as nickname, a Python idiom that is often handy for importing something under a short and usable nickname. It's certainly miles better than having to repeatedly write SimpleXMLRPCServer.SimpleXMLRPCServer after a simple import statement, or using the ill-advised construct from module import *, which mixes up all the namespaces and can often cause subtle and hard-to-find bugs.

The sole purpose of the _ _init_ _ statement of class Server is to accept host and port as separate parameters and group them into the required tuple. I find myself often writing such statements with the many Python functions and classes that require this address tuple grouping (your tastes, of course, may be different).

By default, a server socket belonging to a process that dies is kept busy for quite a while. Particularly during development, it is handy to kill such a process, edit the script, and restart immediately. For such an immediate restart to work, you must ensure the code of your server sets the SO_REUSEADDR option on the relevant socket, as the recipe's code does in its overridden method server_bind.

Last but not least, the recipe overrides verify_request in order to apply a simple check that refuses service except to requests coming from client hosts on a predefined list. This approach doesn't provide rock-solid security, but nevertheless, it is potentially useful. Again, it's particularly useful during development, to help avoid those cases where some other developer on the same LAN accidentally connects his client to the server I'm just developing, and we both experience puzzling problems until we figure out what's happened!

See Also

The SimpleXMLRPCServer module is part of the Python Standard Library and is documented in a chapter of the Library Reference portion of Python's online documentation.