/thirdparty/breakpad/third_party/protobuf/protobuf/java/src/main/java/com/google/protobuf/RpcUtil.java

  1// Protocol Buffers - Google's data interchange format
  2// Copyright 2008 Google Inc.  All rights reserved.
  3// http://code.google.com/p/protobuf/
  4//
  5// Redistribution and use in source and binary forms, with or without
  6// modification, are permitted provided that the following conditions are
  7// met:
  8//
  9//     * Redistributions of source code must retain the above copyright
 10// notice, this list of conditions and the following disclaimer.
 11//     * Redistributions in binary form must reproduce the above
 12// copyright notice, this list of conditions and the following disclaimer
 13// in the documentation and/or other materials provided with the
 14// distribution.
 15//     * Neither the name of Google Inc. nor the names of its
 16// contributors may be used to endorse or promote products derived from
 17// this software without specific prior written permission.
 18//
 19// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 20// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 21// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 22// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 23// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 24// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 25// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 26// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 27// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 28// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 29// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 30
 31package com.google.protobuf;
 32
 33/**
 34 * Grab-bag of utility functions useful when dealing with RPCs.
 35 *
 36 * @author kenton@google.com Kenton Varda
 37 */
 38public final class RpcUtil {
 39  private RpcUtil() {}
 40
 41  /**
 42   * Take an {@code RpcCallback<Message>} and convert it to an
 43   * {@code RpcCallback} accepting a specific message type.  This is always
 44   * type-safe (parameter type contravariance).
 45   */
 46  @SuppressWarnings("unchecked")
 47  public static <Type extends Message> RpcCallback<Type>
 48  specializeCallback(final RpcCallback<Message> originalCallback) {
 49    return (RpcCallback<Type>)originalCallback;
 50    // The above cast works, but only due to technical details of the Java
 51    // implementation.  A more theoretically correct -- but less efficient --
 52    // implementation would be as follows:
 53    //   return new RpcCallback<Type>() {
 54    //     public void run(Type parameter) {
 55    //       originalCallback.run(parameter);
 56    //     }
 57    //   };
 58  }
 59
 60  /**
 61   * Take an {@code RpcCallback} accepting a specific message type and convert
 62   * it to an {@code RpcCallback<Message>}.  The generalized callback will
 63   * accept any message object which has the same descriptor, and will convert
 64   * it to the correct class before calling the original callback.  However,
 65   * if the generalized callback is given a message with a different descriptor,
 66   * an exception will be thrown.
 67   */
 68  public static <Type extends Message>
 69  RpcCallback<Message> generalizeCallback(
 70      final RpcCallback<Type> originalCallback,
 71      final Class<Type> originalClass,
 72      final Type defaultInstance) {
 73    return new RpcCallback<Message>() {
 74      public void run(final Message parameter) {
 75        Type typedParameter;
 76        try {
 77          typedParameter = originalClass.cast(parameter);
 78        } catch (ClassCastException ignored) {
 79          typedParameter = copyAsType(defaultInstance, parameter);
 80        }
 81        originalCallback.run(typedParameter);
 82      }
 83    };
 84  }
 85
 86  /**
 87   * Creates a new message of type "Type" which is a copy of "source".  "source"
 88   * must have the same descriptor but may be a different class (e.g.
 89   * DynamicMessage).
 90   */
 91  @SuppressWarnings("unchecked")
 92  private static <Type extends Message> Type copyAsType(
 93      final Type typeDefaultInstance, final Message source) {
 94    return (Type)typeDefaultInstance.newBuilderForType()
 95                                    .mergeFrom(source)
 96                                    .build();
 97  }
 98
 99  /**
100   * Creates a callback which can only be called once.  This may be useful for
101   * security, when passing a callback to untrusted code:  most callbacks do
102   * not expect to be called more than once, so doing so may expose bugs if it
103   * is not prevented.
104   */
105  public static <ParameterType>
106    RpcCallback<ParameterType> newOneTimeCallback(
107      final RpcCallback<ParameterType> originalCallback) {
108    return new RpcCallback<ParameterType>() {
109      private boolean alreadyCalled = false;
110
111      public void run(final ParameterType parameter) {
112        synchronized(this) {
113          if (alreadyCalled) {
114            throw new AlreadyCalledException();
115          }
116          alreadyCalled = true;
117        }
118
119        originalCallback.run(parameter);
120      }
121    };
122  }
123
124  /**
125   * Exception thrown when a one-time callback is called more than once.
126   */
127  public static final class AlreadyCalledException extends RuntimeException {
128    private static final long serialVersionUID = 5469741279507848266L;
129
130    public AlreadyCalledException() {
131      super("This RpcCallback was already called and cannot be called " +
132            "multiple times.");
133    }
134  }
135}