Filesystem, RCS and CVS client and server classes

*** See the security warning at the end of this file! ***

This directory contains various modules and classes that support remote file system operations.

CVS stuff

rcvs Script to put in your bin directory rcvs.py Remote CVS client command line interface

cvslib.py CVS admin files classes (used by rrcs) cvslock.py CVS locking algorithms

RCS stuff

rrcs Script to put in your bin directory rrcs.py Remote RCS client command line interface

rcsclient.py Return an RCSProxyClient instance (has reasonable default server/port/directory)

RCSProxy.py RCS proxy and server classes (on top of rcslib.py)

rcslib.py Local-only RCS base class (affects stdout & local work files)

FSProxy stuff

sumtree.py Old demo for FSProxy cmptree.py First FSProxy client (used to sync from the Mac) FSProxy.py Filesystem interface classes

Generic client/server stuff

client.py Client class server.py Server class

security.py Security mix-in class (not very secure I think)

Other generic stuff

cmdfw.py CommandFrameWork class (used by rcvs, should be used by rrcs as well)

Client/Server operation

The Client and Server classes implement a simple-minded RPC protocol, using Python's pickle module to transfer arguments, return values and exceptions with the most generality. The Server class is instantiated with a port number on which it should listen for requests; the Client class is instantiated with a host name and a port number where it should connect to. Once a client is connected, a TCP connection is maintained between client and server.

The Server class currently handles only one connection at a time; however it could be rewritten to allow various modes of operations, using multiple threads or processes or the select() system call as desired to serve multiple clients simultaneously (when using select(), still handling one request at a time). This would not require rewriting of the Client class. It may also be possible to adapt the code to use UDP instead of TCP, but then both classes will have to be rewritten (and unless extensive acknowlegements and request serial numbers are used, the server should handle duplicate requests, so its semantics should be idempotent -- shrudder).

Even though the FSProxy and RCSProxy modules define client classes, the client class is fully generic -- what methods it supports is determined entirely by the server. The server class, however, must be derived from. This is generally done as follows:

from server import Server
from client import Client

# Define a class that performs the operations locally
class MyClassLocal:
    def __init__(self): ...
    def _close(self): ...

# Derive a server class using multiple inheritance
class MyClassServer(MyClassLocal, Server):
    def __init__(self, address):
        # Must initialize MyClassLocal as well as Server
        MyClassLocal.__init__(self)
        Server.__init__(self, address)
    def _close(self):
        Server._close()
        MyClassLocal._close()

# A dummy client class
class MyClassClient(Client): pass

Note that because MyClassLocal isn't used in the definition of MyClassClient, it would actually be better to place it in a separate module so the definition of MyClassLocal isn't executed when we only instantiate a client.

The modules client and server should probably be renamed to Client and Server in order to match the class names.

* Security warning: this version requires that you have a file $HOME/.pythonkeyfile at the server and client side containing two comma- separated numbers. The security system at the moment makes no guarantees of actuallng being secure -- however it requires that the key file exists and contains the same numbers at both ends for this to work. (You can specify an alternative keyfile in $PYTHONKEYFILE). Have a look at the Security class in security.py for details; basically, if the key file contains (x, y), then the security server class chooses a random number z (the challenge) in the range 10..100000 and the client must be able to produce pow(z, x, y) (i.e. zx mod y).