// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
// https://developers.google.com/protocol-buffers/
//
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// 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.
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//
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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>() {
@
Override
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;
@
Override
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.");
}
}
}