walkingonions/network.py

#!/usr/bin/env python3

class NetAddr:
    """A class representing a network address"""
    nextaddr = 1

    def __init__(self):
        """Generate a fresh network address"""
        self.addr = NetAddr.nextaddr
        NetAddr.nextaddr += 1

    def __eq__(self, other):
        return (isinstance(other, self.__class__)
            and self.__dict__ == other.__dict__)

    def __hash__(self):
        return hash(self.addr)

    def __str__(self):
        return self.addr.__str__()

class Network:
    """A class representing a simulated network.  Servers can bind()
    to the network, yielding a NetAddr (network address), and clients
    can connect() to a NetAddr yielding a Connection."""

    def __init__(self):
        self.servers = dict()
        self.epoch = 1
        self.epochcallbacks = []

    def printservers(self):
        """Print the list of NetAddrs bound to something."""
        print("Servers:")
        for a in self.servers.keys():
            print(a)

    def getepoch(self):
        """Return the current epoch."""
        return self.epoch

    def nextepoch(self):
        """Increment the current epoch, and return it."""
        self.epoch += 1
        for c in self.epochcallbacks:
            c.newepoch(self.epoch)
        return self.epoch

    def wantepochticks(self, callback, want):
        """Register or deregister an object from receiving epoch change
        callbacks.  If want is True, the callback object's newepoch()
        method will be called at each epoch change, with an argument of
        the new epoch.  If want if False, the callback object will be
        deregistered."""
        if want:
            self.epochcallbacks.append(callback)
        else:
            self.epochcallbacks.remove(callback)

    def bind(self, server):
        """Bind a server to a newly generated NetAddr, returning the
        NetAddr.  The server's bound() callback will also be invoked."""
        addr = NetAddr()
        self.servers[addr] = server
        server.bound(addr, lambda: self.servers.pop(addr))
        return addr

    def connect(self, client, srvaddr):
        """Connect the given client to the server bound to addr.  Throw
        an exception if there is no server bound to that address."""
        server = self.servers[srvaddr]
        return server.connected(client)

# The singleton instance of Network
thenetwork = Network()

class NetMsg:
    """The parent class of network messages.  Subclass this class to
    implement specific kinds of network messages."""

class StringNetMsg(NetMsg):
    """Send an arbitratry string as a NetMsg."""
    def __init__(self, str):
        self.data = str

    def __str__(self):
        return self.data.__str__()

class Connection:
    def __init__(self, peer = None):
        """Create a Connection object with the given peer."""
        self.peer = peer

    def closed(self):
        print("connection closed with", self.peer)
        self.peer = None

    def close(self):
        print("closing connection with", self.peer)
        self.peer.closed()
        self.peer = None

class ClientConnection(Connection):
    """The parent class of client-side network connections.  Subclass
    this class to do anything more elaborate than just passing arbitrary
    NetMsgs, which then get ignored."""
    
    def __init__(self, peer):
        """Create a ClientConnection object with the given peer.  The
        peer must have a received(client, msg) method."""
        self.peer = peer

    def sendmsg(self, netmsg):
        assert(isinstance(netmsg, NetMsg))
        self.peer.received(self, netmsg)

    def received(self, netmsg):
        print("received", netmsg, "from server")


class ServerConnection(Connection):
    """The parent class of server-side network connections."""

    def __init__(self):
        self.peer = None

    def sendmsg(self, netmsg):
        assert(isinstance(netmsg, NetMsg))
        self.peer.received(netmsg)

    def received(self, client, netmsg):
        print("received", netmsg, "from client", client)

class Server:
    """The parent class of network servers.  Subclass this class to
    implement servers of different kinds.  You will probably only need
    to override the implementation of connected()."""

    def __init__(self, name):
        self.name = name

    def __str__(self):
        return self.name.__str__()

    def bound(self, netaddr, closer):
        """Callback invoked when the server is successfully bound to a
        NetAddr.  The parameters are the netaddr to which the server is
        bound and closer (as in a thing that causes something to close)
        is a callback function that should be used when the server
        wishes to stop listening for new connections."""
        self.closer = closer

    def close(self):
        """Stop listening for new connections."""
        self.closer()

    def connected(self, client):
        """Callback invoked when a client connects to this server.
        This callback must create the Connection object that will be
        returned to the client."""
        print("server", self, "conected to client", client)
        serverconnection = ServerConnection()
        clientconnection = ClientConnection(serverconnection)
        serverconnection.peer = clientconnection
        return clientconnection

if __name__ == '__main__':
    n1 = NetAddr()
    n2 = NetAddr()
    assert(n1 == n1)
    assert(not (n1 == n2))
    assert(n1 != n2)
    print(n1, n2)

    srv = Server("hello world server")

    thenetwork.printservers()
    a = thenetwork.bind(srv)
    thenetwork.printservers()
    print("in main", a)

    conn = thenetwork.connect("hello world client", a)
    conn.sendmsg(StringNetMsg("hi"))
    conn.close()

    srv.close()
    thenetwork.printservers()