@rpyc.service and subclasses

[random-developer]

It seems that @rpyc.service is not smart enough to detect that a method has already been exposed. For example:

import rpyc
@rpyc.service
class BaseService(rpyc.Service):
    @rpyc.exposed
    def foo(self): ...

@rpyc.service
class ExtendedService(BaseService):
    @rpyc.exposed
    def bar(self): ...

service = ExtendedService()
for attr in dir(service):
    if attr.startswith('exposed_'):
        print(attr)

The output of this is:

exposed_bar
exposed_exposed_foo
exposed_foo
exposed_get_service_aliases
exposed_get_service_name

Notice the ExtendedService's foo method is exposed twice.

Clearly I can avoid this by removing @rpyc.service from either class, but that doesn't seem to be the right solution. If I remove it from ExtendedService then bar disappears from exposure. If I remove it from BaseService then I can no longer use BaseService without having some @rpyc.service extend it.

I don't know if this will have negative side effects, but I find that if I change @rpyc.service to the following, this problem is resolved:

def service(cls):
    """find and rename exposed decorated attributes"""
    # NOTE: inspect.getmembers invokes getattr for each attribute-name. Descriptors may raise AttributeError.
    # Only the AttributeError exception is caught when raised. This decorator will fail if a descriptor raises
    # any exception other than AttributeError when getattr is called.

    # Track already exposed attributes from base classes
    inherited_exposed = {
        attr_name
        for base in cls.__bases__
        for attr_name, attr_obj in inspect.getmembers(base)
        if getattr(attr_obj, '__exposed__', False)
    }

    for attr_name, attr_obj in inspect.getmembers(cls):  # rebind exposed decorated attributes
        exposed_prefix = getattr(attr_obj, '__exposed__', False)
        if exposed_prefix and not inspect.iscode(attr_obj):  # exclude the implementation
            # Skip if the attribute is already exposed in a parent class
            if attr_name in inherited_exposed:
                continue
            renamed = exposed_prefix + attr_name
            if inspect.isclass(attr_obj):  # recurse exposed objects such as a class
                attr_obj = service(attr_obj)
            setattr(cls, attr_name, attr_obj)
            setattr(cls, renamed, attr_obj)
    return cls
    ```