First cut at new layout

1 files changed, 150 insertions, 0 deletions

diff --git a/src/ProtocolBuffers/MessageStreamIterator.cs b/src/ProtocolBuffers/MessageStreamIterator.cs
new file mode 100644
index 00000000..61dbf840
--- /dev/null
+++ b/src/ProtocolBuffers/MessageStreamIterator.cs
@@ -0,0 +1,150 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Collections;
+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;
+
+    /// <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", Type.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.
+    /// This will check 
+    /// </summary>
+    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;
+    }
+
+    /// <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();
+    }
+    
+    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;
+    }
+
+    /// <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);
+    }
+
+    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);
+        uint tag;
+        while ((tag = input.ReadTag()) != 0) {
+          if (tag != ExpectedTag) {
+            throw InvalidProtocolBufferException.InvalidMessageStreamTag();
+          }
+          yield return messageReader(input, extensionRegistry);
+        }
+      }
+    }
+
+    IEnumerator IEnumerable.GetEnumerator() {
+      return GetEnumerator();
+    }
+  }
+}