How to define a global error handler in gRPC python

Question

Im trying to catch any exception that is raised in any servicer so I can make sure that I only propagate known exceptions and not unexpected ones like ValueError, TypeError etc.

Answer 1

As some of the previous comments suggested, I tried the meta-class approach which works quite well.

Attached is a simple example to demonstrate how to intercept the grpc calls. You could extend this by providing the metaclass a list of decorators which you could apply on each function.

Also, it would be wise to be more selective regarding the methods you apply the wrapper to. A good option would be to list the methods of the autogenerated base class and only wrap those.

from types import FunctionType
from functools import wraps


def wrapper(method):
    @wraps(method)
    def wrapped(*args, **kwargs):
        # do stuff here
        return method(*args, **kwargs)

    return wrapped


class ServicerMiddlewareClass(type):
    def __new__(meta, classname, bases, class_dict):
        new_class_dict = {}

        for attribute_name, attribute in class_dict.items():
            if isinstance(attribute, FunctionType):
                # replace it with a wrapped version
                attribute = wrapper(attribute)

            new_class_dict[attribute_name] = attribute

        return type.__new__(meta, classname, bases, new_class_dict)


# In order to use
class MyGrpcService(grpc.MyGrpcServicer, metaclass=ServicerMiddlewareClass):
   ...