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+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.
+// http://code.google.com/p/protobuf/
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.protobuf;
+
+/**
+ * Abstract base interface for protocol-buffer-based RPC services.  Services
+ * themselves are abstract classes (implemented either by servers or as
+ * stubs), but they subclass this base interface.  The methods of this
+ * interface can be used to call the methods of the service without knowing
+ * its exact type at compile time (analogous to the Message interface).
+ *
+ * @author kenton@google.com Kenton Varda
+ */
+public interface Service {
+  /**
+   * Get the {@code ServiceDescriptor} describing this service and its methods.
+   */
+  Descriptors.ServiceDescriptor getDescriptorForType();
+
+  /**
+   * <p>Call a method of the service specified by MethodDescriptor.  This is
+   * normally implemented as a simple {@code switch()} that calls the standard
+   * definitions of the service's methods.
+   *
+   * <p>Preconditions:
+   * <ul>
+   *   <li>{@code method.getService() == getDescriptorForType()}
+   *   <li>{@code request} is of the exact same class as the object returned by
+   *       {@code getRequestPrototype(method)}.
+   *   <li>{@code controller} is of the correct type for the RPC implementation
+   *       being used by this Service.  For stubs, the "correct type" depends
+   *       on the RpcChannel which the stub is using.  Server-side Service
+   *       implementations are expected to accept whatever type of
+   *       {@code RpcController} the server-side RPC implementation uses.
+   * </ul>
+   *
+   * <p>Postconditions:
+   * <ul>
+   *   <li>{@code done} will be called when the method is complete.  This may be
+   *       before {@code callMethod()} returns or it may be at some point in
+   *       the future.
+   *   <li>The parameter to {@code done} is the response.  It must be of the
+   *       exact same type as would be returned by
+   *       {@code getResponsePrototype(method)}.
+   *   <li>If the RPC failed, the parameter to {@code done} will be
+   *       {@code null}.  Further details about the failure can be found by
+   *       querying {@code controller}.
+   * </ul>
+   */
+  void callMethod(Descriptors.MethodDescriptor method,
+                  RpcController controller,
+                  Message request,
+                  RpcCallback<Message> done);
+
+  /**
+   * <p>{@code callMethod()} requires that the request passed in is of a
+   * particular subclass of {@code Message}.  {@code getRequestPrototype()}
+   * gets the default instances of this type for a given method.  You can then
+   * call {@code Message.newBuilderForType()} on this instance to
+   * construct a builder to build an object which you can then pass to
+   * {@code callMethod()}.
+   *
+   * <p>Example:
+   * <pre>
+   *   MethodDescriptor method =
+   *     service.getDescriptorForType().findMethodByName("Foo");
+   *   Message request =
+   *     stub.getRequestPrototype(method).newBuilderForType()
+   *         .mergeFrom(input).build();
+   *   service.callMethod(method, request, callback);
+   * </pre>
+   */
+  Message getRequestPrototype(Descriptors.MethodDescriptor method);
+
+  /**
+   * Like {@code getRequestPrototype()}, but gets a prototype of the response
+   * message.  {@code getResponsePrototype()} is generally not needed because
+   * the {@code Service} implementation constructs the response message itself,
+   * but it may be useful in some cases to know ahead of time what type of
+   * object will be returned.
+   */
+  Message getResponsePrototype(Descriptors.MethodDescriptor method);
+}