allow message parsing from an array slice

csharp/src/Google.Protobuf/MessageExtensions.cs

@@ -53,6 +53,22 @@ namespace Google.Protobuf
             input.CheckReadEndOfStreamTag();
         }
 
+        /// <summary>
+        /// Merges data from the given byte array slice into an existing message.
+        /// </summary>
+        /// <param name="message">The message to merge the data into.</param>
+        /// <param name="data">The data containing the slice to merge, which must be protobuf-encoded binary data.</param>
+        /// <param name="offset">The offset of the slice to merge.</param>
+        /// <param name="length">The length of the slice to merge.</param>
+        public static void MergeFrom(this IMessage message, byte[] data, int offset, int length)
+        {
+            ProtoPreconditions.CheckNotNull(message, "message");
+            ProtoPreconditions.CheckNotNull(data, "data");
+            CodedInputStream input = new CodedInputStream(data, offset, length);
+            message.MergeFrom(input);
+            input.CheckReadEndOfStreamTag();
+        }
+
         /// <summary>
         /// Merges data from the given byte string into an existing message.
         /// </summary>

csharp/src/Google.Protobuf/MessageParser.cs

@@ -70,6 +70,21 @@ namespace Google.Protobuf
             return message;
         }
 
+        /// <summary>
+        /// Parses a message from a byte array slice.
+        /// </summary>
+        /// <param name="data">The byte array containing the message. Must not be null.</param>
+        /// <param name="offset">The offset of the slice to parse.</param>
+        /// <param name="length">The length of the slice to parse.</param>
+        /// <returns>The newly parsed message.</returns>
+        public IMessage ParseFrom(byte[] data, int offset, int length)
+        {
+            ProtoPreconditions.CheckNotNull(data, "data");
+            IMessage message = factory();
+            message.MergeFrom(data, offset, length);
+            return message;
+        }
+
         /// <summary>
         /// Parses a message from the given byte string.
         /// </summary>