OS/2 Shareware BBS: 10 Tools/10-Tools.zip/pyth_os2.zip/python-1.0.2/Demo/rpc/rpc.py

Text File | 1993-12-17 | 22KB | 864 lines

# Sun RPC version 2 -- RFC1057.

# XXX There should be separate exceptions for the various reasons why
# XXX an RPC can fail, rather than using RuntimeError for everything

# XXX The UDP version of the protocol resends requests when it does
# XXX not receive a timely reply -- use only for idempotent calls!

# XXX There is no provision for call timeout on TCP connections

import xdr
import socket
import os

RPCVERSION = 2

CALL = 0
REPLY = 1

AUTH_NULL = 0
AUTH_UNIX = 1
AUTH_SHORT = 2
AUTH_DES = 3

MSG_ACCEPTED = 0
MSG_DENIED = 1

SUCCESS = 0                # RPC executed successfully
PROG_UNAVAIL  = 1            # remote hasn't exported program
PROG_MISMATCH = 2            # remote can't support version #
PROC_UNAVAIL  = 3            # program can't support procedure
GARBAGE_ARGS  = 4            # procedure can't decode params

RPC_MISMATCH = 0            # RPC version number != 2
AUTH_ERROR = 1                # remote can't authenticate caller

AUTH_BADCRED      = 1            # bad credentials (seal broken)
AUTH_REJECTEDCRED = 2            # client must begin new session
AUTH_BADVERF      = 3            # bad verifier (seal broken)
AUTH_REJECTEDVERF = 4            # verifier expired or replayed
AUTH_TOOWEAK      = 5            # rejected for security reasons


class Packer(xdr.Packer):

    def pack_auth(self, auth):
        flavor, stuff = auth
        self.pack_enum(flavor)
        self.pack_opaque(stuff)

    def pack_auth_unix(self, stamp, machinename, uid, gid, gids):
        self.pack_uint(stamp)
        self.pack_string(machinename)
        self.pack_uint(uid)
        self.pack_uint(gid)
        self.pack_uint(len(gids))
        for i in gids:
            self.pack_uint(i)

    def pack_callheader(self, xid, prog, vers, proc, cred, verf):
        self.pack_uint(xid)
        self.pack_enum(CALL)
        self.pack_uint(RPCVERSION)
        self.pack_uint(prog)
        self.pack_uint(vers)
        self.pack_uint(proc)
        self.pack_auth(cred)
        self.pack_auth(verf)
        # Caller must add procedure-specific part of call

    def pack_replyheader(self, xid, verf):
        self.pack_uint(xid)
        self.pack_enum(REPLY)
        self.pack_uint(MSG_ACCEPTED)
        self.pack_auth(verf)
        self.pack_enum(SUCCESS)
        # Caller must add procedure-specific part of reply


# Exceptions
BadRPCFormat = 'rpc.BadRPCFormat'
BadRPCVersion = 'rpc.BadRPCVersion'
GarbageArgs = 'rpc.GarbageArgs'

class Unpacker(xdr.Unpacker):

    def unpack_auth(self):
        flavor = self.unpack_enum()
        stuff = self.unpack_opaque()
        return (flavor, stuff)

    def unpack_callheader(self):
        xid = self.unpack_uint(xid)
        temp = self.unpack_enum()
        if temp <> CALL:
            raise BadRPCFormat, 'no CALL but ' + `temp`
        temp = self.unpack_uint()
        if temp <> RPCVERSION:
            raise BadRPCVerspion, 'bad RPC version ' + `temp`
        prog = self.unpack_uint()
        vers = self.unpack_uint()
        proc = self.unpack_uint()
        cred = self.unpack_auth()
        verf = self.unpack_auth()
        return xid, prog, vers, proc, cred, verf
        # Caller must add procedure-specific part of call

    def unpack_replyheader(self):
        xid = self.unpack_uint()
        mtype = self.unpack_enum()
        if mtype <> REPLY:
            raise RuntimeError, 'no REPLY but ' + `mtype`
        stat = self.unpack_enum()
        if stat == MSG_DENIED:
            stat = self.unpack_enum()
            if stat == RPC_MISMATCH:
                low = self.unpack_uint()
                high = self.unpack_uint()
                raise RuntimeError, \
                  'MSG_DENIED: RPC_MISMATCH: ' + `low, high`
            if stat == AUTH_ERROR:
                stat = self.unpack_uint()
                raise RuntimeError, \
                    'MSG_DENIED: AUTH_ERROR: ' + `stat`
            raise RuntimeError, 'MSG_DENIED: ' + `stat`
        if stat <> MSG_ACCEPTED:
            raise RuntimeError, \
              'Neither MSG_DENIED nor MSG_ACCEPTED: ' + `stat`
        verf = self.unpack_auth()
        stat = self.unpack_enum()
        if stat == PROG_UNAVAIL:
            raise RuntimeError, 'call failed: PROG_UNAVAIL'
        if stat == PROG_MISMATCH:
            low = self.unpack_uint()
            high = self.unpack_uint()
            raise RuntimeError, \
                'call failed: PROG_MISMATCH: ' + `low, high`
        if stat == PROC_UNAVAIL:
            raise RuntimeError, 'call failed: PROC_UNAVAIL'
        if stat == GARBAGE_ARGS:
            raise RuntimeError, 'call failed: GARBAGE_ARGS'
        if stat <> SUCCESS:
            raise RuntimeError, 'call failed: ' + `stat`
        return xid, verf
        # Caller must get procedure-specific part of reply


# Subroutines to create opaque authentication objects

def make_auth_null():
    return ''

def make_auth_unix(seed, host, uid, gid, groups):
    p = Packer()
    p.pack_auth_unix(seed, host, uid, gid, groups)
    return p.get_buf()

def make_auth_unix_default():
    try:
        from os import getuid, getgid
        uid = getuid()
        gid = getgid()
    except ImportError:
        uid = gid = 0
    import time
    return make_auth_unix(int(time.time()), \
          socket.gethostname(), uid, gid, [])


# Common base class for clients

class Client:

    def __init__(self, host, prog, vers, port):
        self.host = host
        self.prog = prog
        self.vers = vers
        self.port = port
        self.makesocket() # Assigns to self.sock
        self.bindsocket()
        self.connsocket()
        self.lastxid = 0 # XXX should be more random?
        self.addpackers()
        self.cred = None
        self.verf = None

    def close(self):
        self.sock.close()

    def makesocket(self):
        # This MUST be overridden
        raise RuntimeError, 'makesocket not defined'

    def connsocket(self):
        # Override this if you don't want/need a connection
        self.sock.connect((self.host, self.port))

    def bindsocket(self):
        # Override this to bind to a different port (e.g. reserved)
        self.sock.bind(('', 0))

    def addpackers(self):
        # Override this to use derived classes from Packer/Unpacker
        self.packer = Packer()
        self.unpacker = Unpacker('')

    def make_call(self, proc, args, pack_func, unpack_func):
        # Don't normally override this (but see Broadcast)
        if pack_func is None and args is not None:
            raise TypeError, 'non-null args with null pack_func'
        self.start_call(proc)
        if pack_func:
            pack_func(args)
        self.do_call()
        if unpack_func:
            result = unpack_func()
        else:
            result = None
        self.unpacker.done()
        return result

    def start_call(self, proc):
        # Don't override this
        self.lastxid = xid = self.lastxid + 1
        cred = self.mkcred()
        verf = self.mkverf()
        p = self.packer
        p.reset()
        p.pack_callheader(xid, self.prog, self.vers, proc, cred, verf)

    def do_call(self):
        # This MUST be overridden
        raise RuntimeError, 'do_call not defined'

    def mkcred(self):
        # Override this to use more powerful credentials
        if self.cred == None:
            self.cred = (AUTH_NULL, make_auth_null())
        return self.cred

    def mkverf(self):
        # Override this to use a more powerful verifier
        if self.verf == None:
            self.verf = (AUTH_NULL, make_auth_null())
        return self.verf

    def call_0(self):        # Procedure 0 is always like this
        return self.make_call(0, None, None, None)


# Record-Marking standard support

def sendfrag(sock, last, frag):
    x = len(frag)
    if last: x = x | 0x80000000L
    header = (chr(int(x>>24 & 0xff)) + chr(int(x>>16 & 0xff)) + \
          chr(int(x>>8 & 0xff)) + chr(int(x & 0xff)))
    sock.send(header + frag)

def sendrecord(sock, record):
    sendfrag(sock, 1, record)

def recvfrag(sock):
    header = sock.recv(4)
    if len(header) < 4:
        raise EOFError
    x = long(ord(header[0]))<<24 | ord(header[1])<<16 | \
        ord(header[2])<<8 | ord(header[3])
    last = ((x & 0x80000000) != 0)
    n = int(x & 0x7fffffff)
    frag = ''
    while n > 0:
        buf = sock.recv(n)
        if not buf: raise EOFError
        n = n - len(buf)
        frag = frag + buf
    return last, frag

def recvrecord(sock):
    record = ''
    last = 0
    while not last:
        last, frag = recvfrag(sock)
        record = record + frag
    return record


# Try to bind to a reserved port (must be root)

last_resv_port_tried = None
def bindresvport(sock, host):
    global last_resv_port_tried
    FIRST, LAST = 600, 1024 # Range of ports to try
    if last_resv_port_tried == None:
        import os
        last_resv_port_tried = FIRST + os.getpid() % (LAST-FIRST)
    for i in range(last_resv_port_tried, LAST) + \
          range(FIRST, last_resv_port_tried):
        last_resv_port_tried = i
        try:
            sock.bind((host, i))
            return last_resv_port_tried
        except socket.error, (errno, msg):
            if errno <> 114:
                raise socket.error, (errno, msg)
    raise RuntimeError, 'can\'t assign reserved port'


# Client using TCP to a specific port

class RawTCPClient(Client):

    def makesocket(self):
        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

    def do_call(self):
        call = self.packer.get_buf()
        sendrecord(self.sock, call)
        reply = recvrecord(self.sock)
        u = self.unpacker
        u.reset(reply)
        xid, verf = u.unpack_replyheader()
        if xid <> self.lastxid:
            # Can't really happen since this is TCP...
            raise RuntimeError, 'wrong xid in reply ' + `xid` + \
                ' instead of ' + `self.lastxid`


# Client using UDP to a specific port

class RawUDPClient(Client):

    def makesocket(self):
        self.sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

    def do_call(self):
        call = self.packer.get_buf()
        self.sock.send(call)
        try:
            from select import select
        except ImportError:
            print 'WARNING: select not found, RPC may hang'
            select = None
        BUFSIZE = 8192 # Max UDP buffer size
        timeout = 1
        count = 5
        while 1:
            r, w, x = [self.sock], [], []
            if select:
                r, w, x = select(r, w, x, timeout)
            if self.sock not in r:
                count = count - 1
                if count < 0: raise RuntimeError, 'timeout'
                if timeout < 25: timeout = timeout *2
##                print 'RESEND', timeout, count
                self.sock.send(call)
                continue
            reply = self.sock.recv(BUFSIZE)
            u = self.unpacker
            u.reset(reply)
            xid, verf = u.unpack_replyheader()
            if xid <> self.lastxid:
##                print 'BAD xid'
                continue
            break


# Client using UDP broadcast to a specific port

class RawBroadcastUDPClient(RawUDPClient):

    def __init__(self, bcastaddr, prog, vers, port):
        RawUDPClient.__init__(self, bcastaddr, prog, vers, port)
        self.reply_handler = None
        self.timeout = 30

    def connsocket(self):
        # Don't connect -- use sendto
        self.sock.allowbroadcast(1)

    def set_reply_handler(self, reply_handler):
        self.reply_handler = reply_handler

    def set_timeout(self, timeout):
        self.timeout = timeout # Use None for infinite timeout

    def make_call(self, proc, args, pack_func, unpack_func):
        if pack_func is None and args is not None:
            raise TypeError, 'non-null args with null pack_func'
        self.start_call(proc)
        if pack_func:
            pack_func(args)
        call = self.packer.get_buf()
        self.sock.sendto(call, (self.host, self.port))
        try:
            from select import select
        except ImportError:
            print 'WARNING: select not found, broadcast will hang'
            select = None
        BUFSIZE = 8192 # Max UDP buffer size (for reply)
        replies = []
        if unpack_func is None:
            def dummy(): pass
            unpack_func = dummy
        while 1:
            r, w, x = [self.sock], [], []
            if select:
                if self.timeout is None:
                    r, w, x = select(r, w, x)
                else:
                    r, w, x = select(r, w, x, self.timeout)
            if self.sock not in r:
                break
            reply, fromaddr = self.sock.recvfrom(BUFSIZE)
            u = self.unpacker
            u.reset(reply)
            xid, verf = u.unpack_replyheader()
            if xid <> self.lastxid:
##                print 'BAD xid'
                continue
            reply = unpack_func()
            self.unpacker.done()
            replies.append((reply, fromaddr))
            if self.reply_handler:
                self.reply_handler(reply, fromaddr)
        return replies


# Port mapper interface

# Program number, version and (fixed!) port number
PMAP_PROG = 100000
PMAP_VERS = 2
PMAP_PORT = 111

# Procedure numbers
PMAPPROC_NULL = 0            # (void) -> void
PMAPPROC_SET = 1            # (mapping) -> bool
PMAPPROC_UNSET = 2            # (mapping) -> bool
PMAPPROC_GETPORT = 3            # (mapping) -> unsigned int
PMAPPROC_DUMP = 4            # (void) -> pmaplist
PMAPPROC_CALLIT = 5            # (call_args) -> call_result

# A mapping is (prog, vers, prot, port) and prot is one of:

IPPROTO_TCP = 6
IPPROTO_UDP = 17

# A pmaplist is a variable-length list of mappings, as follows:
# either (1, mapping, pmaplist) or (0).

# A call_args is (prog, vers, proc, args) where args is opaque;
# a call_result is (port, res) where res is opaque.


class PortMapperPacker(Packer):

    def pack_mapping(self, mapping):
        prog, vers, prot, port = mapping
        self.pack_uint(prog)
        self.pack_uint(vers)
        self.pack_uint(prot)
        self.pack_uint(port)

    def pack_pmaplist(self, list):
        self.pack_list(list, self.pack_mapping)

    def pack_call_args(self, ca):
        prog, vers, proc, args = ca
        self.pack_uint(prog)
        self.pack_uint(vers)
        self.pack_uint(proc)
        self.pack_opaque(args)


class PortMapperUnpacker(Unpacker):

    def unpack_mapping(self):
        prog = self.unpack_uint()
        vers = self.unpack_uint()
        prot = self.unpack_uint()
        port = self.unpack_uint()
        return prog, vers, prot, port

    def unpack_pmaplist(self):
        return self.unpack_list(self.unpack_mapping)

    def unpack_call_result(self):
        port = self.unpack_uint()
        res = self.unpack_opaque()
        return port, res


class PartialPortMapperClient:

    def addpackers(self):
        self.packer = PortMapperPacker()
        self.unpacker = PortMapperUnpacker('')

    def Set(self, mapping):
        return self.make_call(PMAPPROC_SET, mapping, \
            self.packer.pack_mapping, \
            self.unpacker.unpack_uint)

    def Unset(self, mapping):
        return self.make_call(PMAPPROC_UNSET, mapping, \
            self.packer.pack_mapping, \
            self.unpacker.unpack_uint)

    def Getport(self, mapping):
        return self.make_call(PMAPPROC_GETPORT, mapping, \
            self.packer.pack_mapping, \
            self.unpacker.unpack_uint)

    def Dump(self):
        return self.make_call(PMAPPROC_DUMP, None, \
            None, \
            self.unpacker.unpack_pmaplist)

    def Callit(self, ca):
        return self.make_call(PMAPPROC_CALLIT, ca, \
            self.packer.pack_call_args, \
            self.unpacker.unpack_call_result)


class TCPPortMapperClient(PartialPortMapperClient, RawTCPClient):

    def __init__(self, host):
        RawTCPClient.__init__(self, \
            host, PMAP_PROG, PMAP_VERS, PMAP_PORT)


class UDPPortMapperClient(PartialPortMapperClient, RawUDPClient):

    def __init__(self, host):
        RawUDPClient.__init__(self, \
            host, PMAP_PROG, PMAP_VERS, PMAP_PORT)


class BroadcastUDPPortMapperClient(PartialPortMapperClient, \
                   RawBroadcastUDPClient):

    def __init__(self, bcastaddr):
        RawBroadcastUDPClient.__init__(self, \
            bcastaddr, PMAP_PROG, PMAP_VERS, PMAP_PORT)


# Generic clients that find their server through the Port mapper

class TCPClient(RawTCPClient):

    def __init__(self, host, prog, vers):
        pmap = TCPPortMapperClient(host)
        port = pmap.Getport((prog, vers, IPPROTO_TCP, 0))
        pmap.close()
        if port == 0:
            raise RuntimeError, 'program not registered'
        RawTCPClient.__init__(self, host, prog, vers, port)


class UDPClient(RawUDPClient):

    def __init__(self, host, prog, vers):
        pmap = UDPPortMapperClient(host)
        port = pmap.Getport((prog, vers, IPPROTO_UDP, 0))
        pmap.close()
        if port == 0:
            raise RuntimeError, 'program not registered'
        RawUDPClient.__init__(self, host, prog, vers, port)


class BroadcastUDPClient(Client):

    def __init__(self, bcastaddr, prog, vers):
        self.pmap = BroadcastUDPPortMapperClient(bcastaddr)
        self.pmap.set_reply_handler(self.my_reply_handler)
        self.prog = prog
        self.vers = vers
        self.user_reply_handler = None
        self.addpackers()

    def close(self):
        self.pmap.close()

    def set_reply_handler(self, reply_handler):
        self.user_reply_handler = reply_handler

    def set_timeout(self, timeout):
        self.pmap.set_timeout(timeout)

    def my_reply_handler(self, reply, fromaddr):
        port, res = reply
        self.unpacker.reset(res)
        result = self.unpack_func()
        self.unpacker.done()
        self.replies.append((result, fromaddr))
        if self.user_reply_handler is not None:
            self.user_reply_handler(result, fromaddr)

    def make_call(self, proc, args, pack_func, unpack_func):
        self.packer.reset()
        if pack_func:
            pack_func(args)
        if unpack_func is None:
            def dummy(): pass
            self.unpack_func = dummy
        else:
            self.unpack_func = unpack_func
        self.replies = []
        packed_args = self.packer.get_buf()
        dummy_replies = self.pmap.Callit( \
            (self.prog, self.vers, proc, packed_args))
        return self.replies


# Server classes

# These are not symmetric to the Client classes
# XXX No attempt is made to provide authorization hooks yet

class Server:

    def __init__(self, host, prog, vers, port):
        self.host = host # Should normally be '' for default interface
        self.prog = prog
        self.vers = vers
        self.port = port # Should normally be 0 for random port
        self.makesocket() # Assigns to self.sock and self.prot
        self.bindsocket()
        self.host, self.port = self.sock.getsockname()
        self.addpackers()

    def register(self):
        mapping = self.prog, self.vers, self.prot, self.port
        p = TCPPortMapperClient(self.host)
        if not p.Set(mapping):
            raise RuntimeError, 'register failed'

    def unregister(self):
        mapping = self.prog, self.vers, self.prot, self.port
        p = TCPPortMapperClient(self.host)
        if not p.Unset(mapping):
            raise RuntimeError, 'unregister failed'

    def handle(self, call):
        # Don't use unpack_header but parse the header piecewise
        # XXX I have no idea if I am using the right error responses!
        self.unpacker.reset(call)
        self.packer.reset()
        xid = self.unpacker.unpack_uint()
        self.packer.pack_uint(xid)
        temp = self.unpacker.unpack_enum()
        if temp <> CALL:
            return None # Not worthy of a reply
        self.packer.pack_uint(REPLY)
        temp = self.unpacker.unpack_uint()
        if temp <> RPCVERSION:
            self.packer.pack_uint(MSG_DENIED)
            self.packer.pack_uint(RPC_MISMATCH)
            self.packer.pack_uint(RPCVERSION)
            self.packer.pack_uint(RPCVERSION)
            return self.packer.get_buf()
        self.packer.pack_uint(MSG_ACCEPTED)
        self.packer.pack_auth((AUTH_NULL, make_auth_null()))
        prog = self.unpacker.unpack_uint()
        if prog <> self.prog:
            self.packer.pack_uint(PROG_UNAVAIL)
            return self.packer.get_buf()
        vers = self.unpacker.unpack_uint()
        if vers <> self.vers:
            self.packer.pack_uint(PROG_MISMATCH)
            self.packer.pack_uint(self.vers)
            self.packer.pack_uint(self.vers)
            return self.packer.get_buf()
        proc = self.unpacker.unpack_uint()
        methname = 'handle_' + `proc`
        try:
            meth = getattr(self, methname)
        except AttributeError:
            self.packer.pack_uint(PROC_UNAVAIL)
            return self.packer.get_buf()
        cred = self.unpacker.unpack_auth()
        verf = self.unpacker.unpack_auth()
        try:
            meth() # Unpack args, call turn_around(), pack reply
        except (EOFError, GarbageArgs):
            # Too few or too many arguments
            self.packer.reset()
            self.packer.pack_uint(xid)
            self.packer.pack_uint(REPLY)
            self.packer.pack_uint(MSG_ACCEPTED)
            self.packer.pack_auth((AUTH_NULL, make_auth_null()))
            self.packer.pack_uint(GARBAGE_ARGS)
        return self.packer.get_buf()

    def turn_around(self):
        try:
            self.unpacker.done()
        except RuntimeError:
            raise GarbageArgs
        self.packer.pack_uint(SUCCESS)

    def handle_0(self): # Handle NULL message
        self.turn_around()

    def makesocket(self):
        # This MUST be overridden
        raise RuntimeError, 'makesocket not defined'

    def bindsocket(self):
        # Override this to bind to a different port (e.g. reserved)
        self.sock.bind((self.host, self.port))

    def addpackers(self):
        # Override this to use derived classes from Packer/Unpacker
        self.packer = Packer()
        self.unpacker = Unpacker('')


class TCPServer(Server):

    def makesocket(self):
        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.prot = IPPROTO_TCP

    def loop(self):
        self.sock.listen(0)
        while 1:
            self.session(self.sock.accept())

    def session(self, connection):
        sock, (host, port) = connection
        while 1:
            try:
                call = recvrecord(sock)
            except EOFError:
                break
            except socket.error, msg:
                print 'socket error:', msg
                break
            reply = self.handle(call)
            if reply is not None:
                sendrecord(sock, reply)

    def forkingloop(self):
        # Like loop but uses forksession()
        self.sock.listen(0)
        while 1:
            self.forksession(self.sock.accept())

    def forksession(self, connection):
        # Like session but forks off a subprocess
        import os
        # Wait for deceased children
        try:
            while 1:
                pid, sts = os.waitpid(0, 1)
        except os.error:
            pass
        pid = None
        try:
            pid = os.fork()
            if pid: # Parent
                connection[0].close()
                return
            # Child
            self.session(connection)
        finally:
            # Make sure we don't fall through in the parent
            if pid == 0:
                os._exit(0)


class UDPServer(Server):

    def makesocket(self):
        self.sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
        self.prot = IPPROTO_UDP

    def loop(self):
        while 1:
            self.session()

    def session(self):
        call, host_port = self.sock.recvfrom(8192)
        reply = self.handle(call)
        if reply <> None:
            self.sock.sendto(reply, host_port)


# Simple test program -- dump local portmapper status

def test():
    pmap = UDPPortMapperClient('')
    list = pmap.Dump()
    list.sort()
    for prog, vers, prot, port in list:
        print prog, vers,
        if prot == IPPROTO_TCP: print 'tcp',
        elif prot == IPPROTO_UDP: print 'udp',
        else: print prot,
        print port


# Test program for broadcast operation -- dump everybody's portmapper status

def testbcast():
    import sys
    if sys.argv[1:]:
        bcastaddr = sys.argv[1]
    else:
        bcastaddr = '<broadcast>'
    def rh(reply, fromaddr):
        host, port = fromaddr
        print host + '\t' + `reply`
    pmap = BroadcastUDPPortMapperClient(bcastaddr)
    pmap.set_reply_handler(rh)
    pmap.set_timeout(5)
    replies = pmap.Getport((100002, 1, IPPROTO_UDP, 0))


# Test program for server, with corresponding client
# On machine A: python -c 'import rpc; rpc.testsvr()'
# On machine B: python -c 'import rpc; rpc.testclt()' A
# (A may be == B)

def testsvr():
    # Simple test class -- proc 1 doubles its string argument as reply
    class S(UDPServer):
        def handle_1(self):
            arg = self.unpacker.unpack_string()
            self.turn_around()
            print 'RPC function 1 called, arg', `arg`
            self.packer.pack_string(arg + arg)
    #
    s = S('', 0x20000000, 1, 0)
    try:
        s.unregister()
    except RuntimeError, msg:
        print 'RuntimeError:', msg, '(ignored)'
    s.register()
    print 'Service started...'
    try:
        s.loop()
    finally:
        s.unregister()
        print 'Service interrupted.'


def testclt():
    import sys
    if sys.argv[1:]: host = sys.argv[1]
    else: host = ''
    # Client for above server
    class C(UDPClient):
        def call_1(self, arg):
            return self.make_call(1, arg, \
                self.packer.pack_string, \
                self.unpacker.unpack_string)
    c = C(host, 0x20000000, 1)
    print 'making call...'
    reply = c.call_1('hello, world, ')
    print 'call returned', `reply`