content: // Protocol Buffers - Google's data interchange format
  // Copyright 2008 Google Inc.  All rights reserved.
  // https://developers.google.com/protocol-buffers/
  //
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  //     * 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
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  // in the documentation and/or other materials provided with the
  // distribution.
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  //
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  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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  package com.google.protobuf;
  
  /**
   * An {@code RpcController} mediates a single method call. The primary purpose of the controller is
   * to provide a way to manipulate settings specific to the RPC implementation and to find out about
   * RPC-level errors.
   *
   * <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.
   *
   * <p>The methods provided by the {@code RpcController} interface are intended to be a "least common
   * denominator" set of features which we expect all implementations to support. Specific
   * implementations may provide more advanced features (e.g. deadline propagation).
   *
   * @author kenton@google.com Kenton Varda
   */
  public interface RpcController {
    // -----------------------------------------------------------------
    // These calls may be made from the client side only.  Their results
    // are undefined on the server side (may throw RuntimeExceptions).
  
    /**
     * Resets the RpcController to its initial state so that it may be reused in a new call. This can
     * be called from the client side only. It must not be called while an RPC is in progress.
     */
    void reset();
  
    /**
     * After a call has finished, returns true if the call failed. The possible reasons for failure
     * depend on the RPC implementation. {@code failed()} most only be called on the client side, and
     * must not be called before a call has finished.
     */
    boolean failed();
  
    /** If {@code failed()} is {@code true}, returns a human-readable description of the error. */
    String errorText();
  
    /**
     * Advises the RPC system that the caller desires that the RPC call be canceled. The RPC system
     * may cancel it immediately, may wait awhile and then cancel it, or may not even cancel the call
     * at all. If the call is canceled, the "done" callback will still be called and the RpcController
     * will indicate that the call failed at that time.
     */
    void startCancel();
  
    // -----------------------------------------------------------------
    // These calls may be made from the server side only.  Their results
    // are undefined on the client side (may throw RuntimeExceptions).
  
    /**
     * Causes {@code failed()} to return true on the client side. {@code reason} will be incorporated
     * into the message returned by {@code errorText()}. If you find you need to return
     * machine-readable information about failures, you should incorporate it into your response
     * protocol buffer and should NOT call {@code setFailed()}.
     */
    void setFailed(String reason);
  
    /**
     * If {@code true}, indicates that the client canceled the RPC, so the server may as well give up
     * on replying to it. This method must be called on the server side only. The server should still
     * call the final "done" callback.
     */
    boolean isCanceled();
  
    /**
     * Asks that the given callback be called when the RPC is canceled. The parameter passed to the
     * callback will always be {@code null}. The callback will always be called exactly once. If the
     * RPC completes without being canceled, the callback will be called after completion. If the RPC
     * has already been canceled when NotifyOnCancel() is called, the callback will be called
     * immediately.
     *
     * <p>{@code notifyOnCancel()} must be called no more than once per request. It must be called on
     * the server side only.
     */
    void notifyOnCancel(RpcCallback<Object> callback);
  }
  