Manager Service API (MSA)

MSA is not part of etm.wccoa.manager. It is the separate import package etm.wccoa.msa, installed with the distribution package etm-wccoa-msa. It builds on a running Manager. Applications import the vrpc module:

from etm.wccoa.msa import vrpc

vrpc contains everything an application needs. The API reference describes etm.wccoa.msa.vrpc and the protocol-neutral types in etm.wccoa.msa.base.

A service derives from vrpc.ServiceBase and registers its methods in __init__. A vrpc.ServiceContainer announces the service and runs it until the container is closed.

from etm.wccoa.datatypes import OaValueLike, OaVariant
from etm.wccoa.manager import Manager
from etm.wccoa.msa import vrpc


class GreeterService(vrpc.ServiceBase):
    def __init__(self) -> None:
        super().__init__("Greeter")
        self.register_function("SayHello", self.say_hello)

    def say_hello(self, context: vrpc.ServerContext, request: OaVariant) -> OaValueLike:
        if not request.value:
            raise vrpc.RpcError(vrpc.Status(vrpc.StatusCode.INVALID_ARGUMENT, "Name cannot be empty"))
        return f"Hello {request.value}"


with Manager() as manager, vrpc.ServiceContainer(manager) as container:
    container.register_service(GreeterService())
    container.start_all_services()
    manager.wait()

The handlers of a service run on a thread of their own, one request after another. A handler answers by returning a value, or by raising vrpc.RpcError to return an error status. A handler that takes a third parameter receives a vrpc.Responder and may send the answer later, from any thread.

A vrpc.Stub calls the methods of a service by name.

from etm.wccoa.manager import Manager
from etm.wccoa.msa import vrpc

with Manager() as manager, vrpc.Stub.create_and_initialize(manager, "Greeter") as stub:
    try:
        greeting = stub.call_function("SayHello", "Python")
        print(greeting.value)
    except vrpc.RpcError as error:
        print(error.status)

call_function() blocks until the response arrives. call_function_async() returns a vrpc.AsyncUnaryCall at once. It gives access to the response and trailing headers and allows the call to be canceled.