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/.python_keyfile 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 $PYTHON_KEYFILE).

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. z**x mod y).