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Kotlin core Protocol Buffers library. Protocol Buffers are a way of encoding structured data in an efficient yet extensible format.
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// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

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).
 *
 * 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 [email protected] Kenton Varda
 */
public interface Service {
  /** Get the {@code ServiceDescriptor} describing this service and its methods. */
  Descriptors.ServiceDescriptor getDescriptorForType();

  /**
   * 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.
   *
   * 
Preconditions:
   *
   * 

   *   {@code method.getService() == getDescriptorForType()}
   *   
{@code request} is of the exact same class as the object returned by {@code
   *       getRequestPrototype(method)}.
   *   
{@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.
   * 
   *
   * Postconditions:
   *
   * 

   *   {@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.
   *   
The parameter to {@code done} is the response. It must be of the exact same type as would
   *       be returned by {@code getResponsePrototype(method)}.
   *   
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}.
   * 
   */
  void callMethod(
      Descriptors.MethodDescriptor method,
      RpcController controller,
      Message request,
      RpcCallback done);

  /**
   * {@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()}.
   *
   * Example:
   *
   * 
   *   MethodDescriptor method =
   *     service.getDescriptorForType().findMethodByName("Foo");
   *   Message request =
   *     stub.getRequestPrototype(method).newBuilderForType()
   *         .mergeFrom(input).build();
   *   service.callMethod(method, request, callback);
   * 
   */
  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);
}