/src/ProtocolBuffers/MessageStreamIterator.cs
C# | 244 lines | 144 code | 23 blank | 77 comment | 17 complexity | 3d168377184aa0b22d55bca9271d2539 MD5 | raw file
Possible License(s): BSD-3-Clause, Apache-2.0, GPL-2.0
- #region Copyright notice and license
-
- // Protocol Buffers - Google's data interchange format
- // Copyright 2008 Google Inc. All rights reserved.
- // http://github.com/jskeet/dotnet-protobufs/
- // Original C++/Java/Python code:
- // 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.
-
- #endregion
-
- using System;
- using System.Collections;
- using System.Collections.Generic;
- using System.IO;
- using System.Reflection;
-
- namespace Google.ProtocolBuffers
- {
- /// <summary>
- /// Iterates over data created using a <see cref="MessageStreamWriter{T}" />.
- /// Unlike MessageStreamWriter, this class is not usually constructed directly with
- /// a stream; instead it is provided with a way of opening a stream when iteration
- /// is started. The stream is closed when the iteration is completed or the enumerator
- /// is disposed. (This occurs naturally when using <c>foreach</c>.)
- /// </summary>
- public class MessageStreamIterator<TMessage> : IEnumerable<TMessage>
- where TMessage : IMessage<TMessage>
- {
- private readonly StreamProvider streamProvider;
- private readonly ExtensionRegistry extensionRegistry;
- private readonly int sizeLimit;
-
- // Type.EmptyTypes isn't present on the compact framework
- private static readonly Type[] EmptyTypes = new Type[0];
-
- /// <summary>
- /// Delegate created via reflection trickery (once per type) to create a builder
- /// and read a message from a CodedInputStream with it. Note that unlike in Java,
- /// there's one static field per constructed type.
- /// </summary>
- private static readonly Func<CodedInputStream, ExtensionRegistry, TMessage> messageReader = BuildMessageReader();
-
- /// <summary>
- /// Any exception (within reason) thrown within messageReader is caught and rethrown in the constructor.
- /// This makes life a lot simpler for the caller.
- /// </summary>
- private static Exception typeInitializationException;
-
- /// <summary>
- /// Creates the delegate later used to read messages. This is only called once per type, but to
- /// avoid exceptions occurring at confusing times, if this fails it will set typeInitializationException
- /// to the appropriate error and return null.
- /// </summary>
- private static Func<CodedInputStream, ExtensionRegistry, TMessage> BuildMessageReader()
- {
- try
- {
- Type builderType = FindBuilderType();
-
- // Yes, it's redundant to find this again, but it's only the once...
- MethodInfo createBuilderMethod = typeof (TMessage).GetMethod("CreateBuilder", EmptyTypes);
- Delegate builderBuilder = Delegate.CreateDelegate(
- typeof (Func<>).MakeGenericType(builderType), null, createBuilderMethod);
-
- MethodInfo buildMethod = typeof (MessageStreamIterator<TMessage>)
- .GetMethod("BuildImpl", BindingFlags.Static | BindingFlags.NonPublic)
- .MakeGenericMethod(typeof (TMessage), builderType);
-
- return (Func<CodedInputStream, ExtensionRegistry, TMessage>) Delegate.CreateDelegate(
- typeof (Func<CodedInputStream, ExtensionRegistry, TMessage>), builderBuilder, buildMethod);
- }
- catch (ArgumentException e)
- {
- typeInitializationException = e;
- }
- catch (InvalidOperationException e)
- {
- typeInitializationException = e;
- }
- catch (InvalidCastException e)
- {
- // Can't see why this would happen, but best to know about it.
- typeInitializationException = e;
- }
- return null;
- }
-
- /// <summary>
- /// Works out the builder type for TMessage, or throws an ArgumentException to explain why it can't.
- /// </summary>
- private static Type FindBuilderType()
- {
- MethodInfo createBuilderMethod = typeof (TMessage).GetMethod("CreateBuilder", EmptyTypes);
- if (createBuilderMethod == null)
- {
- throw new ArgumentException("Message type " + typeof (TMessage).FullName +
- " has no CreateBuilder method.");
- }
- if (createBuilderMethod.ReturnType == typeof (void))
- {
- throw new ArgumentException("CreateBuilder method in " + typeof (TMessage).FullName +
- " has void return type");
- }
- Type builderType = createBuilderMethod.ReturnType;
- Type messageInterface = typeof (IMessage<,>).MakeGenericType(typeof (TMessage), builderType);
- Type builderInterface = typeof (IBuilder<,>).MakeGenericType(typeof (TMessage), builderType);
- if (Array.IndexOf(typeof (TMessage).GetInterfaces(), messageInterface) == -1)
- {
- throw new ArgumentException("Message type " + typeof (TMessage) + " doesn't implement " +
- messageInterface.FullName);
- }
- if (Array.IndexOf(builderType.GetInterfaces(), builderInterface) == -1)
- {
- throw new ArgumentException("Builder type " + typeof (TMessage) + " doesn't implement " +
- builderInterface.FullName);
- }
- return builderType;
- }
-
- // This is only ever fetched by reflection, so the compiler may
- // complain that it's unused
- #pragma warning disable 0169
- /// <summary>
- /// Method we'll use to build messageReader, with the first parameter fixed to TMessage.CreateBuilder. Note that we
- /// have to introduce another type parameter (TMessage2) as we can't constrain TMessage for just a single method
- /// (and we can't do it at the type level because we don't know TBuilder). However, by constraining TMessage2
- /// to not only implement IMessage appropriately but also to derive from TMessage2, we can avoid doing a cast
- /// for every message; the implicit reference conversion will be fine. In practice, TMessage2 and TMessage will
- /// be the same type when we construct the generic method by reflection.
- /// </summary>
- private static TMessage BuildImpl<TMessage2, TBuilder>(Func<TBuilder> builderBuilder, CodedInputStream input,
- ExtensionRegistry registry)
- where TBuilder : IBuilder<TMessage2, TBuilder>
- where TMessage2 : TMessage, IMessage<TMessage2, TBuilder>
- {
- TBuilder builder = builderBuilder();
- input.ReadMessage(builder, registry);
- return builder.Build();
- }
- #pragma warning restore 0414
-
- private static readonly uint ExpectedTag = WireFormat.MakeTag(1, WireFormat.WireType.LengthDelimited);
-
- private MessageStreamIterator(StreamProvider streamProvider, ExtensionRegistry extensionRegistry, int sizeLimit)
- {
- if (messageReader == null)
- {
- throw typeInitializationException;
- }
- this.streamProvider = streamProvider;
- this.extensionRegistry = extensionRegistry;
- this.sizeLimit = sizeLimit;
- }
-
- private MessageStreamIterator(StreamProvider streamProvider, ExtensionRegistry extensionRegistry)
- : this(streamProvider, extensionRegistry, CodedInputStream.DefaultSizeLimit)
- {
- }
-
- /// <summary>
- /// Creates a new instance which uses the same stream provider as this one,
- /// but the specified extension registry.
- /// </summary>
- public MessageStreamIterator<TMessage> WithExtensionRegistry(ExtensionRegistry newRegistry)
- {
- return new MessageStreamIterator<TMessage>(streamProvider, newRegistry, sizeLimit);
- }
-
- /// <summary>
- /// Creates a new instance which uses the same stream provider and extension registry as this one,
- /// but with the specified size limit. Note that this must be big enough for the largest message
- /// and the tag and size preceding it.
- /// </summary>
- public MessageStreamIterator<TMessage> WithSizeLimit(int newSizeLimit)
- {
- return new MessageStreamIterator<TMessage>(streamProvider, extensionRegistry, newSizeLimit);
- }
-
- public static MessageStreamIterator<TMessage> FromFile(string file)
- {
- return new MessageStreamIterator<TMessage>(() => File.OpenRead(file), ExtensionRegistry.Empty);
- }
-
- public static MessageStreamIterator<TMessage> FromStreamProvider(StreamProvider streamProvider)
- {
- return new MessageStreamIterator<TMessage>(streamProvider, ExtensionRegistry.Empty);
- }
-
- public IEnumerator<TMessage> GetEnumerator()
- {
- using (Stream stream = streamProvider())
- {
- CodedInputStream input = CodedInputStream.CreateInstance(stream);
- input.SetSizeLimit(sizeLimit);
- uint tag;
- string name;
- while (input.ReadTag(out tag, out name))
- {
- if ((tag == 0 && name == "item") || (tag == ExpectedTag))
- {
- yield return messageReader(input, extensionRegistry);
- }
- else
- {
- throw InvalidProtocolBufferException.InvalidMessageStreamTag();
- }
-
- input.ResetSizeCounter();
- }
- }
- }
-
- IEnumerator IEnumerable.GetEnumerator()
- {
- return GetEnumerator();
- }
- }
- }