1 # Protocol Buffers - Google's data interchange format
2 # Copyright 2008 Google Inc. All rights reserved.
3 # https://developers.google.com/protocol-buffers/
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31 """Contains metaclasses used to create protocol service and service stub
32 classes from ServiceDescriptor objects at runtime.
34 The GeneratedServiceType and GeneratedServiceStubType metaclasses are used to
35 inject all useful functionality into the classes output by the protocol
36 compiler at compile-time.
39 __author__ = 'petar@google.com (Petar Petrov)'
42 class GeneratedServiceType(type):
44 """Metaclass for service classes created at runtime from ServiceDescriptors.
46 Implementations for all methods described in the Service class are added here
47 by this class. We also create properties to allow getting/setting all fields
48 in the protocol message.
50 The protocol compiler currently uses this metaclass to create protocol service
51 classes at runtime. Clients can also manually create their own classes at
52 runtime, as in this example:
54 mydescriptor = ServiceDescriptor(.....)
55 class MyProtoService(service.Service):
56 __metaclass__ = GeneratedServiceType
57 DESCRIPTOR = mydescriptor
58 myservice_instance = MyProtoService()
62 _DESCRIPTOR_KEY = 'DESCRIPTOR'
64 def __init__(cls, name, bases, dictionary):
65 """Creates a message service class.
68 name: Name of the class (ignored, but required by the metaclass
70 bases: Base classes of the class being constructed.
71 dictionary: The class dictionary of the class being constructed.
72 dictionary[_DESCRIPTOR_KEY] must contain a ServiceDescriptor object
73 describing this protocol service type.
75 # Don't do anything if this class doesn't have a descriptor. This happens
76 # when a service class is subclassed.
77 if GeneratedServiceType._DESCRIPTOR_KEY not in dictionary:
79 descriptor = dictionary[GeneratedServiceType._DESCRIPTOR_KEY]
80 service_builder = _ServiceBuilder(descriptor)
81 service_builder.BuildService(cls)
84 class GeneratedServiceStubType(GeneratedServiceType):
86 """Metaclass for service stubs created at runtime from ServiceDescriptors.
88 This class has similar responsibilities as GeneratedServiceType, except that
89 it creates the service stub classes.
92 _DESCRIPTOR_KEY = 'DESCRIPTOR'
94 def __init__(cls, name, bases, dictionary):
95 """Creates a message service stub class.
98 name: Name of the class (ignored, here).
99 bases: Base classes of the class being constructed.
100 dictionary: The class dictionary of the class being constructed.
101 dictionary[_DESCRIPTOR_KEY] must contain a ServiceDescriptor object
102 describing this protocol service type.
104 super(GeneratedServiceStubType, cls).__init__(name, bases, dictionary)
105 # Don't do anything if this class doesn't have a descriptor. This happens
106 # when a service stub is subclassed.
107 if GeneratedServiceStubType._DESCRIPTOR_KEY not in dictionary:
109 descriptor = dictionary[GeneratedServiceStubType._DESCRIPTOR_KEY]
110 service_stub_builder = _ServiceStubBuilder(descriptor)
111 service_stub_builder.BuildServiceStub(cls)
114 class _ServiceBuilder(object):
116 """This class constructs a protocol service class using a service descriptor.
118 Given a service descriptor, this class constructs a class that represents
119 the specified service descriptor. One service builder instance constructs
120 exactly one service class. That means all instances of that class share the
124 def __init__(self, service_descriptor):
125 """Initializes an instance of the service class builder.
128 service_descriptor: ServiceDescriptor to use when constructing the
131 self.descriptor = service_descriptor
133 def BuildService(self, cls):
134 """Constructs the service class.
137 cls: The class that will be constructed.
140 # CallMethod needs to operate with an instance of the Service class. This
141 # internal wrapper function exists only to be able to pass the service
142 # instance to the method that does the real CallMethod work.
143 def _WrapCallMethod(srvc, method_descriptor,
144 rpc_controller, request, callback):
145 return self._CallMethod(srvc, method_descriptor,
146 rpc_controller, request, callback)
148 cls.CallMethod = _WrapCallMethod
149 cls.GetDescriptor = staticmethod(lambda: self.descriptor)
150 cls.GetDescriptor.__doc__ = "Returns the service descriptor."
151 cls.GetRequestClass = self._GetRequestClass
152 cls.GetResponseClass = self._GetResponseClass
153 for method in self.descriptor.methods:
154 setattr(cls, method.name, self._GenerateNonImplementedMethod(method))
156 def _CallMethod(self, srvc, method_descriptor,
157 rpc_controller, request, callback):
158 """Calls the method described by a given method descriptor.
161 srvc: Instance of the service for which this method is called.
162 method_descriptor: Descriptor that represent the method to call.
163 rpc_controller: RPC controller to use for this method's execution.
164 request: Request protocol message.
165 callback: A callback to invoke after the method has completed.
167 if method_descriptor.containing_service != self.descriptor:
169 'CallMethod() given method descriptor for wrong service type.')
170 method = getattr(srvc, method_descriptor.name)
171 return method(rpc_controller, request, callback)
173 def _GetRequestClass(self, method_descriptor):
174 """Returns the class of the request protocol message.
177 method_descriptor: Descriptor of the method for which to return the
178 request protocol message class.
181 A class that represents the input protocol message of the specified
184 if method_descriptor.containing_service != self.descriptor:
186 'GetRequestClass() given method descriptor for wrong service type.')
187 return method_descriptor.input_type._concrete_class
189 def _GetResponseClass(self, method_descriptor):
190 """Returns the class of the response protocol message.
193 method_descriptor: Descriptor of the method for which to return the
194 response protocol message class.
197 A class that represents the output protocol message of the specified
200 if method_descriptor.containing_service != self.descriptor:
202 'GetResponseClass() given method descriptor for wrong service type.')
203 return method_descriptor.output_type._concrete_class
205 def _GenerateNonImplementedMethod(self, method):
206 """Generates and returns a method that can be set for a service methods.
209 method: Descriptor of the service method for which a method is to be
213 A method that can be added to the service class.
215 return lambda inst, rpc_controller, request, callback: (
216 self._NonImplementedMethod(method.name, rpc_controller, callback))
218 def _NonImplementedMethod(self, method_name, rpc_controller, callback):
219 """The body of all methods in the generated service class.
222 method_name: Name of the method being executed.
223 rpc_controller: RPC controller used to execute this method.
224 callback: A callback which will be invoked when the method finishes.
226 rpc_controller.SetFailed('Method %s not implemented.' % method_name)
230 class _ServiceStubBuilder(object):
232 """Constructs a protocol service stub class using a service descriptor.
234 Given a service descriptor, this class constructs a suitable stub class.
235 A stub is just a type-safe wrapper around an RpcChannel which emulates a
236 local implementation of the service.
238 One service stub builder instance constructs exactly one class. It means all
239 instances of that class share the same service stub builder.
242 def __init__(self, service_descriptor):
243 """Initializes an instance of the service stub class builder.
246 service_descriptor: ServiceDescriptor to use when constructing the
249 self.descriptor = service_descriptor
251 def BuildServiceStub(self, cls):
252 """Constructs the stub class.
255 cls: The class that will be constructed.
258 def _ServiceStubInit(stub, rpc_channel):
259 stub.rpc_channel = rpc_channel
261 cls.__init__ = _ServiceStubInit
262 for method in self.descriptor.methods:
263 setattr(cls, method.name, self._GenerateStubMethod(method))
265 def _GenerateStubMethod(self, method):
266 return (lambda inst, rpc_controller, request, callback=None:
267 self._StubMethod(inst, method, rpc_controller, request, callback))
269 def _StubMethod(self, stub, method_descriptor,
270 rpc_controller, request, callback):
271 """The body of all service methods in the generated stub class.
275 method_descriptor: Descriptor of the invoked method.
276 rpc_controller: Rpc controller to execute the method.
277 request: Request protocol message.
278 callback: A callback to execute when the method finishes.
280 Response message (in case of blocking call).
282 return stub.rpc_channel.CallMethod(
283 method_descriptor, rpc_controller, request,
284 method_descriptor.output_type._concrete_class, callback)