3 files changed, 65 insertions, 2 deletions
diff --git a/src/ProtocolBuffers/ByteString.cs b/src/ProtocolBuffers/ByteString.cs
index 53811205..0d67a539 100644
--- a/src/ProtocolBuffers/ByteString.cs
+++ b/src/ProtocolBuffers/ByteString.cs
@@ -184,7 +184,7 @@ namespace Google.ProtocolBuffers {
         output = CodedOutputStream.CreateInstance(buffer);
       }
 
-      public ByteString Build() {
+      internal ByteString Build() {
         output.CheckNoSpaceLeft();
 
         // We can be confident that the CodedOutputStream will not modify the
@@ -193,7 +193,7 @@ namespace Google.ProtocolBuffers {
         return new ByteString(buffer);
       }
 
-      public CodedOutputStream CodedOutput {
+      internal CodedOutputStream CodedOutput {
         get {
           return output;
         }
diff --git a/src/ProtocolBuffers/MessageUtil.cs b/src/ProtocolBuffers/MessageUtil.cs
new file mode 100644
index 00000000..d53af9c5
--- /dev/null
+++ b/src/ProtocolBuffers/MessageUtil.cs
@@ -0,0 +1,62 @@
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+using System.Text;
+
+namespace Google.ProtocolBuffers {
+  /// <summary>
+  /// Utilities for arbitrary messages of an unknown type. This class does not use
+  /// generics precisely because it is designed for dynamically discovered types.
+  /// </summary>
+  public static class MessageUtil {
+
+    /// <summary>
+    /// Returns the default message for the given type. If an exception is thrown
+    /// (directly from this code), the message will be suitable to be displayed to a user.
+    /// </summary>
+    /// <param name="type"></param>
+    /// <exception cref="ArgumentNullException">The type parameter is null.</exception>
+    /// <exception cref="ArgumentException">The type doesn't implement IMessage, or doesn't
+    /// have a static DefaultMessage property of the same type, or is generic or abstract.</exception>
+    /// <returns></returns>
+    public static IMessage GetDefaultMessage(Type type) {
+      if (type == null) {
+        throw new ArgumentNullException("type", "No type specified.");
+      }
+      if (type.IsAbstract || type.IsGenericTypeDefinition) {
+        throw new ArgumentException("Unable to get a default message for an abstract or generic type (" + type.FullName + ")");
+      }
+      if (!typeof(IMessage).IsAssignableFrom(type)) {
+        throw new ArgumentException("Unable to get a default message for non-message type (" + type.FullName + ")");
+      }
+      PropertyInfo property = type.GetProperty("DefaultInstance", BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic);
+      if (property == null) {
+        throw new ArgumentException(type.FullName + " doesn't have a static DefaultInstance property");
+      }
+      if (property.PropertyType != type) {
+        throw new ArgumentException(type.FullName + ".DefaultInstance property is of the wrong type");
+      }
+      return (IMessage) property.GetValue(null, null);
+    }
+
+    /// <summary>
+    /// Returns the default message for the type with the given name. This is just
+    /// a convenience wrapper around calling Type.GetType and then GetDefaultMessage.
+    /// If an exception is thrown, the message will be suitable to be displayed to a user.
+    /// </summary>
+    /// <param name="typeName"></param>
+    /// <exception cref="ArgumentNullException">The typeName parameter is null.</exception>
+    /// <exception cref="ArgumentException">The type doesn't implement IMessage, or doesn't
+    /// have a static DefaultMessage property of the same type, or can't be found.</exception>
+    public static IMessage GetDefaultMessage(string typeName) {
+      if (typeName == null) {
+        throw new ArgumentNullException("typeName", "No type name specified.");
+      }
+      Type type = Type.GetType(typeName);
+      if (type == null) {
+        throw new ArgumentException("Unable to load type " + typeName);
+      }
+      return GetDefaultMessage(type);
+    }
+  }
+}
diff --git a/src/ProtocolBuffers/ProtocolBuffers.csproj b/src/ProtocolBuffers/ProtocolBuffers.csproj
index 6a746cc9..520594f5 100644
--- a/src/ProtocolBuffers/ProtocolBuffers.csproj
+++ b/src/ProtocolBuffers/ProtocolBuffers.csproj
@@ -97,6 +97,7 @@
     <Compile Include="IService.cs" />
     <Compile Include="MessageStreamIterator.cs" />
     <Compile Include="MessageStreamWriter.cs" />
+    <Compile Include="MessageUtil.cs" />
     <Compile Include="NameHelpers.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="RpcUtil.cs" />