Services

RPyC is oriented around the notion of services. Services are classes that derive from rpyc.core.service.Service and define “exposed methods” – normally, methods whose name explicitly begins with exposed_. Services also have a name, or a list of aliases. Normally, the name of the service is the name of its class (excluding a possible Service suffix), but you can override this behavior by specifying the ALIASES attribute in the class.

Let’s have a look at a rather basic service – a calculator (see Custom RPyC Servers for more info)

import rpyc

class CalculatorService(rpyc.Service):
    def exposed_add(self, a, b):
        return a + b
    def exposed_sub(self, a, b):
        return a - b
    def exposed_mul(self, a, b):
        return a * b
    def exposed_div(self, a, b):
        return a / b
    def foo(self):
        print "foo"

When a client connects, it can access any of the exposed members of the service

import rpyc

conn = rpyc.connect("hostname", 12345)
x = conn.root.add(4,7)
assert x == 11

try:
    conn.root.div(4,0)
except ZeroDivisionError:
    pass

As you can see, the root attribute of the connection gives you access to the service that’s exposed by the other party. For security concerns, access is only granted to exposed_ members. For instance, the foo method above is inaccessible (attempting to call it will result in an AttributeError).

Implementing Services

As previously explained, all exposed_ members of your service class will be available to the other party. This applies to methods, but in fact, it applies to any attribute. For instance, you may expose a class:

class MyService(rpyc.Service):
    class exposed_MyClass(object):
        def __init__(self, a, b):
            self.a = a
            self.b = b
        def exposed_foo(self):
            return self.a + self.b

If you wish to change the name of your service, or specify a list of aliases, set the ALIASES (class-level) attribute to a list of names. For instance:

class MyService(rpyc.Service):
    ALIASES = ["foo", "bar", "spam"]

The first name in this list is considered the “proper name” of the service, while the rest are considered aliases. This distinction is meaningless to the protocol and the registry server.

Your service class may also define two special methods: on_connect(self) and on_disconnect(self). These methods are invoked, not surprisingly, when a connection has been established, and when it’s been disconnected. Note that during on_disconnect, the connection is already dead, so you can no longer access any remote objects.

Other than that, your service instance has the _conn attribute, which represents the connection that it serves. This attribute already exists when on_connected is called.

Note

Try to avoid overriding the __init__ method of the service. Place all initialization-related code in on_connect.

Built-in Services

RPyC comes bundled with two built-in services:

  • VoidService, which is an empty “do-nothing” service. It’s useful when you want only one side of the connection to provide a service, while the other side a “consumer”.
  • SlaveService, which implements Classic Mode RPyC.

Decoupled Services

RPyC is a symmetric protocol, which means both ends of the connection can act as clients or servers – in other words – both ends may expose (possibly different) services. Normally, only the server exposes a service, while the client exposes the VoidService, but this is not constrained in any way. For instance, in the classic mode, both ends expose the SlaveService; this allows each party to execute arbitrary code on its peer. Although it’s not the most common use case, two-sides services are quite useful. Consider this client:

class ClientService(rpyc.Service):
    def exposed_foo(self):
        return "foo"

conn = rpyc.connect("hostname", 12345, service = ClientService)

And this server:

class ServerService(rpyc.Service):
    def exposed_bar(self):
        return self._conn.root.foo() + "bar"

The client can invoke conn.root.bar() on the server, which will, in turn, invoke foo back on the client. The final result would be "foobar".

Another approach is to pass callback functions. Consider this server:

class ServerService(rpyc.Service):
    def exposed_bar(self, func):
        return func() + "bar"

And this client:

def foofunc():
    return "foo"

conn = rpyc.connect("hostname", 12345)
conn.root.bar(foofunc)

See also Configuration Parameters