// 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,
// 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;
/**
* Grab-bag of utility functions useful when dealing with RPCs.
*
* @author kenton@google.com Kenton Varda
*/
public final class RpcUtil {
private RpcUtil() {}
/**
* Take an {@code RpcCallback<Message>} and convert it to an
* {@code RpcCallback} accepting a specific message type. This is always
* type-safe (parameter type contravariance).
*/
@SuppressWarnings("unchecked")
public static <Type extends Message> RpcCallback<Type>
specializeCallback(final RpcCallback<Message> originalCallback) {
return (RpcCallback<Type>)originalCallback;
// The above cast works, but only due to technical details of the Java
// implementation. A more theoretically correct -- but less efficient --
// implementation would be as follows:
// return new RpcCallback<Type>() {
// public void run(Type parameter) {
// originalCallback.run(parameter);
// }
// };
}
/**
* Take an {@code RpcCallback} accepting a specific message type and convert
* it to an {@code RpcCallback<Message>}. The generalized callback will
* accept any message object which has the same descriptor, and will convert
* it to the correct class before calling the original callback. However,
* if the generalized callback is given a message with a different descriptor,
* an exception will be thrown.
*/
public static <Type extends Message>
RpcCallback<Message> generalizeCallback(
final RpcCallback<Type> originalCallback,
final Class<Type> originalClass,
final Type defaultInstance) {
return new RpcCallback<Message>() {
public void run(final Message parameter) {
Type typedParameter;
try {
typedParameter = originalClass.cast(parameter);
} catch (ClassCastException ignored) {
typedParameter = copyAsType(defaultInstance, parameter);
}
originalCallback.run(typedParameter);
}
};
}
/**
* Creates a new message of type "Type" which is a copy of "source". "source"
* must have the same descriptor but may be a different class (e.g.
* DynamicMessage).
*/
@SuppressWarnings("unchecked")
private static <Type extends Message> Type copyAsType(
final Type typeDefaultInstance, final Message source) {
return (Type)typeDefaultInstance.newBuilderForType()
.mergeFrom(source)
.build();
}
/**
* Creates a callback which can only be called once. This may be useful for
* security, when passing a callback to untrusted code: most callbacks do
* not expect to be called more than once, so doing so may expose bugs if it
* is not prevented.
*/
public static <ParameterType>
RpcCallback<ParameterType> newOneTimeCallback(
final RpcCallback<ParameterType> originalCallback) {
return new RpcCallback<ParameterType>() {
private boolean alreadyCalled = false;
public void run(final ParameterType parameter) {
synchronized(this) {
if (alreadyCalled) {
throw new AlreadyCalledException();
}
alreadyCalled = true;
}
originalCallback.run(parameter);
}
};
}
/**
* Exception thrown when a one-time callback is called more than once.
*/
public static final class AlreadyCalledException extends RuntimeException {
private static final long serialVersionUID = 5469741279507848266L;
public AlreadyCalledException() {
super("This RpcCallback was already called and cannot be called " +
"multiple times.");
}
}
}