1 files changed, 52 insertions, 14 deletions

diff --git a/csharp/src/Google.Protobuf/MessageParser.cs b/csharp/src/Google.Protobuf/MessageParser.cs
index 66d44135..4d35554a 100644
--- a/csharp/src/Google.Protobuf/MessageParser.cs
+++ b/csharp/src/Google.Protobuf/MessageParser.cs
@@ -42,10 +42,13 @@ namespace Google.Protobuf
     public class MessageParser
     {
         private Func<IMessage> factory;
+        // TODO: When we use a C# 7.1 compiler, make this private protected.
+        internal bool DiscardUnknownFields { get; }
 
-        internal MessageParser(Func<IMessage> factory)
+        internal MessageParser(Func<IMessage> factory, bool discardUnknownFields)
         {
             this.factory = factory;
+            DiscardUnknownFields = discardUnknownFields;
         }
 
         /// <summary>
@@ -65,7 +68,7 @@ namespace Google.Protobuf
         public IMessage ParseFrom(byte[] data)
         {
             IMessage message = factory();
-            message.MergeFrom(data);
+            message.MergeFrom(data, DiscardUnknownFields);
             return message;
         }
 
@@ -79,7 +82,7 @@ namespace Google.Protobuf
         public IMessage ParseFrom(byte[] data, int offset, int length)
         {
             IMessage message = factory();
-            message.MergeFrom(data, offset, length);
+            message.MergeFrom(data, offset, length, DiscardUnknownFields);
             return message;
         }
 
@@ -91,7 +94,7 @@ namespace Google.Protobuf
         public IMessage ParseFrom(ByteString data)
         {
             IMessage message = factory();
-            message.MergeFrom(data);
+            message.MergeFrom(data, DiscardUnknownFields);
             return message;
         }
 
@@ -103,7 +106,7 @@ namespace Google.Protobuf
         public IMessage ParseFrom(Stream input)
         {
             IMessage message = factory();
-            message.MergeFrom(input);
+            message.MergeFrom(input, DiscardUnknownFields);
             return message;
         }
 
@@ -119,7 +122,7 @@ namespace Google.Protobuf
         public IMessage ParseDelimitedFrom(Stream input)
         {
             IMessage message = factory();
-            message.MergeDelimitedFrom(input);
+            message.MergeDelimitedFrom(input, DiscardUnknownFields);
             return message;
         }
 
@@ -131,7 +134,7 @@ namespace Google.Protobuf
         public IMessage ParseFrom(CodedInputStream input)
         {
             IMessage message = factory();
-            message.MergeFrom(input);
+            MergeFrom(message, input);
             return message;
         }
 
@@ -148,6 +151,29 @@ namespace Google.Protobuf
             JsonParser.Default.Merge(message, json);
             return message;
         }
+
+        // TODO: When we're using a C# 7.1 compiler, make this private protected.
+        internal void MergeFrom(IMessage message, CodedInputStream codedInput)
+        {
+            bool originalDiscard = codedInput.DiscardUnknownFields;
+            try
+            {
+                codedInput.DiscardUnknownFields = DiscardUnknownFields;
+                message.MergeFrom(codedInput);
+            }
+            finally
+            {
+                codedInput.DiscardUnknownFields = originalDiscard;
+            }
+        }
+
+        /// <summary>
+        /// Creates a new message parser which optionally discards unknown fields when parsing.
+        /// </summary>
+        /// <param name="discardUnknownFields">Whether or not to discard unknown fields when parsing.</param>
+        /// <returns>A newly configured message parser.</returns>
+        public MessageParser WithDiscardUnknownFields(bool discardUnknownFields) =>
+            new MessageParser(factory, discardUnknownFields);
     }
 
     /// <summary>
@@ -182,7 +208,11 @@ namespace Google.Protobuf
         /// to require a parameterless constructor: delegates are significantly faster to execute.
         /// </remarks>
         /// <param name="factory">Function to invoke when a new, empty message is required.</param>
-        public MessageParser(Func<T> factory) : base(() => factory())
+        public MessageParser(Func<T> factory) : this(factory, false)
+        {
+        }
+
+        internal MessageParser(Func<T> factory, bool discardUnknownFields) : base(() => factory(), discardUnknownFields)
         {
             this.factory = factory;
         }
@@ -204,7 +234,7 @@ namespace Google.Protobuf
         public new T ParseFrom(byte[] data)
         {
             T message = factory();
-            message.MergeFrom(data);
+            message.MergeFrom(data, DiscardUnknownFields);
             return message;
         }
 
@@ -218,7 +248,7 @@ namespace Google.Protobuf
         public new T ParseFrom(byte[] data, int offset, int length)
         {
             T message = factory();
-            message.MergeFrom(data, offset, length);
+            message.MergeFrom(data, offset, length, DiscardUnknownFields);
             return message;
         }
 
@@ -230,7 +260,7 @@ namespace Google.Protobuf
         public new T ParseFrom(ByteString data)
         {
             T message = factory();
-            message.MergeFrom(data);
+            message.MergeFrom(data, DiscardUnknownFields);
             return message;
         }
 
@@ -242,7 +272,7 @@ namespace Google.Protobuf
         public new T ParseFrom(Stream input)
         {
             T message = factory();
-            message.MergeFrom(input);
+            message.MergeFrom(input, DiscardUnknownFields);
             return message;
         }
 
@@ -258,7 +288,7 @@ namespace Google.Protobuf
         public new T ParseDelimitedFrom(Stream input)
         {
             T message = factory();
-            message.MergeDelimitedFrom(input);
+            message.MergeDelimitedFrom(input, DiscardUnknownFields);
             return message;
         }
 
@@ -270,7 +300,7 @@ namespace Google.Protobuf
         public new T ParseFrom(CodedInputStream input)
         {
             T message = factory();
-            message.MergeFrom(input);
+            MergeFrom(message, input);
             return message;
         }
 
@@ -287,5 +317,13 @@ namespace Google.Protobuf
             JsonParser.Default.Merge(message, json);
             return message;
         }
+
+        /// <summary>
+        /// Creates a new message parser which optionally discards unknown fields when parsing.
+        /// </summary>
+        /// <param name="discardUnknownFields">Whether or not to discard unknown fields when parsing.</param>
+        /// <returns>A newly configured message parser.</returns>
+        public new MessageParser<T> WithDiscardUnknownFields(bool discardUnknownFields) =>
+            new MessageParser<T>(factory, discardUnknownFields);
     }
 }