/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * license agreements; and to You under the Apache License, version 2.0:
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * This file is part of the Apache Pekko project, which was derived from Akka.
 */

/*
 * Copyright (C) 2018-2022 Lightbend Inc. <https://www.lightbend.com>
 */

// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// http://code.google.com/p/protobuf/
//
// 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,
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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package org.apache.pekko.protobuf;

/**
 * <p>Abstract interface for an RPC channel.  An {@code RpcChannel} represents a
 * communication line to a {@link Service} which can be used to call that
 * {@link Service}'s methods.  The {@link Service} may be running on another
 * machine.  Normally, you should not call an {@code RpcChannel} directly, but
 * instead construct a stub {@link Service} wrapping it.  Example:
 *
 * <pre>
 *   RpcChannel channel = rpcImpl.newChannel("remotehost.example.com:1234");
 *   RpcController controller = rpcImpl.newController();
 *   MyService service = MyService.newStub(channel);
 *   service.myMethod(controller, request, callback);
 * </pre>
 *
 * <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 RpcChannel {
  /**
   * Call the given method of the remote service.  This method is similar to
   * {@code Service.callMethod()} with one important difference:  the caller
   * decides the types of the {@code Message} objects, not the callee.  The
   * request may be of any type as long as
   * {@code request.getDescriptor() == method.getInputType()}.
   * The response passed to the callback will be of the same type as
   * {@code responsePrototype} (which must have
   * {@code getDescriptor() == method.getOutputType()}).
   */
  void callMethod(Descriptors.MethodDescriptor method,
                  RpcController controller,
                  Message request,
                  Message responsePrototype,
                  RpcCallback<Message> done);
}
