远程服务库

此模块包含对构建符合标准请求和响应模式的远程服务有用的类。为了符合该模式，服务必须提供以下类：

# Each service instance only handles a single request and is then discarded.
# Make these objects light weight.
class Service(object):

    # It must be possible to construct service objects without any parameters.
    # If your constructor needs extra information you should provide a
    # no-argument factory function to create service instances.
    def __init__(self):
        ...

    # Each remote method must use the 'remote' decorator, passing the request
    # and response message types.  The remote method itself must take a single
    # parameter which is an instance of RequestMessage and return an instance
    # of ResponseMessage.
    @method(RequestMessage, ResponseMessage)
    def remote_method(self, request):
        # Return an instance of ResponseMessage.

    # A service object may optionally implement a 'initialize_request_state'
    # method that takes as a parameter a single instance of a RequestState.  If
    # a service does not implement this method it will not receive the request
    # state.
    def initialize_request_state(self, state):
        ...

服务类是一个可以提供上述功能的便捷基类。它实现了服务的所有必需的和可选的方法。它还提供了创建工厂函数的简便方法，可将永久性全局状态传递给新的服务实例。

远程装饰器用于声明哪些类方法属于服务 RPC。但请注意，这个修饰器不负责处理套接字和各种底层 RPC 协议。虽然该修饰器会确保您能够使用正确的请求类型，但它不会检查是否进行了初始化。

在将远程修饰器用于某个方法时，被封装的方法会具有与该修饰器相关的“远程”属性。此属性包含方法实现所需的 request_type 和 response_type。

远程修饰器本身并没有为子类远程方法提供任何支持。为了扩展服务，请使用子类方法进行重新修饰。例如：

class MyService(Service):

    @method(DoSomethingRequest, DoSomethingResponse)
    def do_something(self, request):
        ... implement do-something ...

class MyBetterService(MyService):

    @method(DoSomethingRequest, DoSomethingResponse)
    def do_something(self, request):
        response = super(MyBetterService, self).do_something.remote.method(request)
        ... do something with response ...
        return response