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// Protocol Buffers - Google's data interchange format

// Copyright 2008 Google Inc.  All rights reserved.

// http://code.google.com/p/protobuf/

//

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// modification, are permitted provided that the following conditions are

// met:

//

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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).

 *

 * <p>Starting with version 2.3.0, RPC implementations should not try to build

 * on this, but should instead provide code generator plugins which generate

 * code specific to the particular RPC implementation.  This way the generated

 * code can be more appropriate for the implementation in use and can avoid

 * unnecessary layers of indirection.

 *

 * @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);

}