using System;
using System.Collections.Generic;
using System.Collections;
using System.IO;
using System.Reflection;
namespace Google.ProtocolBuffers {
///
/// Iterates over data created using a .
/// 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 foreach.)
///
public class MessageStreamIterator : IEnumerable
where TMessage : IMessage {
private readonly StreamProvider streamProvider;
private readonly ExtensionRegistry extensionRegistry;
///
/// 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.
///
private static readonly Func messageReader = BuildMessageReader();
///
/// Any exception (within reason) thrown within messageReader is caught and rethrown in the constructor.
/// This makes life a lot simpler for the caller.
///
private static Exception typeInitializationException;
///
/// 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.
///
private static Func 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", Type.EmptyTypes);
Delegate builderBuilder = Delegate.CreateDelegate(
typeof(Func<>).MakeGenericType(builderType), null, createBuilderMethod);
MethodInfo buildMethod = typeof(MessageStreamIterator)
.GetMethod("BuildImpl", BindingFlags.Static | BindingFlags.NonPublic)
.MakeGenericMethod(typeof(TMessage), builderType);
return (Func)Delegate.CreateDelegate(
typeof(Func), 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;
}
///
/// Works out the builder type for TMessage, or throws an ArgumentException to explain why it can't.
/// This will check
///
private static Type FindBuilderType() {
MethodInfo createBuilderMethod = typeof(TMessage).GetMethod("CreateBuilder", Type.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;
}
///
/// 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.
///
private static TMessage BuildImpl(Func builderBuilder, CodedInputStream input, ExtensionRegistry registry)
where TBuilder : IBuilder
where TMessage2 : TMessage, IMessage {
TBuilder builder = builderBuilder();
input.ReadMessage(builder, registry);
return builder.Build();
}
private static readonly uint ExpectedTag = WireFormat.MakeTag(1, WireFormat.WireType.LengthDelimited);
private MessageStreamIterator(StreamProvider streamProvider, ExtensionRegistry extensionRegistry) {
if (messageReader == null) {
throw typeInitializationException;
}
this.streamProvider = streamProvider;
this.extensionRegistry = extensionRegistry;
}
///
/// Creates a new instance which uses the same stream provider as this one,
/// but the specified extension registry.
///
public MessageStreamIterator WithExtensionRegistry(ExtensionRegistry newRegistry) {
return new MessageStreamIterator(streamProvider, newRegistry);
}
public static MessageStreamIterator FromFile(string file) {
return new MessageStreamIterator(() => File.OpenRead(file), ExtensionRegistry.Empty);
}
public static MessageStreamIterator FromStreamProvider(StreamProvider streamProvider) {
return new MessageStreamIterator(streamProvider, ExtensionRegistry.Empty);
}
public IEnumerator GetEnumerator() {
using (Stream stream = streamProvider()) {
CodedInputStream input = CodedInputStream.CreateInstance(stream);
uint tag;
while ((tag = input.ReadTag()) != 0) {
if (tag != ExpectedTag) {
throw InvalidProtocolBufferException.InvalidMessageStreamTag();
}
yield return messageReader(input, extensionRegistry);
}
}
}
IEnumerator IEnumerable.GetEnumerator() {
return GetEnumerator();
}
}
}