1 files changed, 109 insertions, 0 deletions
diff --git a/csharp/src/ProtocolBuffers/MessageUtil.cs b/csharp/src/ProtocolBuffers/MessageUtil.cs
new file mode 100644
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+++ b/csharp/src/ProtocolBuffers/MessageUtil.cs
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+#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.Reflection;
+
+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);
+        }
+    }
+}
+\ No newline at end of file