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Diffstat (limited to 'java/src/main/java/com/google/protobuf/RpcUtil.java')
-rw-r--r-- | java/src/main/java/com/google/protobuf/RpcUtil.java | 135 |
1 files changed, 135 insertions, 0 deletions
diff --git a/java/src/main/java/com/google/protobuf/RpcUtil.java b/java/src/main/java/com/google/protobuf/RpcUtil.java new file mode 100644 index 0000000..b1b959a --- /dev/null +++ b/java/src/main/java/com/google/protobuf/RpcUtil.java @@ -0,0 +1,135 @@ +// 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."); + } + } +} |