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