From d8800ae2f3699964363cc23f6f31f77a8e3a83b5 Mon Sep 17 00:00:00 2001
From: James Newton-King <james@newtonking.com>
Date: Fri, 13 Nov 2020 12:11:31 +1300
Subject: [PATCH 1/2] Fix parsing negative Int32Value that crosses segment
 boundary

---
 .../CodedInputStreamTest.cs                   | 19 +++++++++++++++++++
 .../ParsingPrimitivesWrappers.cs              | 10 ++++++----
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/csharp/src/Google.Protobuf.Test/CodedInputStreamTest.cs b/csharp/src/Google.Protobuf.Test/CodedInputStreamTest.cs
index 1fb3bb503908..0ad286f3787f 100644
--- a/csharp/src/Google.Protobuf.Test/CodedInputStreamTest.cs
+++ b/csharp/src/Google.Protobuf.Test/CodedInputStreamTest.cs
@@ -343,6 +343,25 @@ public void ReadWholeMessage_VaryingBlockSizes_FromSequence()
             }
         }
 
+        [Test]
+        public void ReadInt32Wrapper_VariableBlockSizes()
+        {
+            byte[] rawBytes = new byte[] { 202, 1, 11, 8, 254, 255, 255, 255, 255, 255, 255, 255, 255, 1 };
+
+            for (int blockSize = 1; blockSize <= rawBytes.Length; blockSize++)
+            {
+                ReadOnlySequence<byte> data = ReadOnlySequenceFactory.CreateWithContent(rawBytes, blockSize);
+                AssertReadFromParseContext(data, (ref ParseContext ctx) =>
+                {
+                    ctx.ReadTag();
+
+                    var value = ParsingPrimitivesWrappers.ReadInt32Wrapper(ref ctx);
+
+                    Assert.AreEqual(-2, value);
+                }, true);
+            }
+        }
+
         [Test]
         public void ReadHugeBlob()
         {
diff --git a/csharp/src/Google.Protobuf/ParsingPrimitivesWrappers.cs b/csharp/src/Google.Protobuf/ParsingPrimitivesWrappers.cs
index 126306490a09..629ec32bd81e 100644
--- a/csharp/src/Google.Protobuf/ParsingPrimitivesWrappers.cs
+++ b/csharp/src/Google.Protobuf/ParsingPrimitivesWrappers.cs
@@ -160,8 +160,11 @@ internal static class ParsingPrimitivesWrappers
 
         internal static uint? ReadUInt32Wrapper(ref ReadOnlySpan<byte> buffer, ref ParserInternalState state)
         {
-            // length:1 + tag:1 + value:5(varint32-max) = 7 bytes
-            if (state.bufferPos + 7 <= state.bufferSize)
+            // field=1, type=varint = tag of 8
+            const int expectedTag = 8;
+            // length:1 + tag:1 + value:10(varint64-max) = 12 bytes
+            // Value can be 64 bits for negative integers
+            if (state.bufferPos + 12 <= state.bufferSize)
             {
                 // The entire wrapper message is already contained in `buffer`.
                 int pos0 = state.bufferPos;
@@ -177,8 +180,7 @@ internal static class ParsingPrimitivesWrappers
                     return ReadUInt32WrapperSlow(ref buffer, ref state);
                 }
                 int finalBufferPos = state.bufferPos + length;
-                // field=1, type=varint = tag of 8
-                if (buffer[state.bufferPos++] != 8)
+                if (buffer[state.bufferPos++] != expectedTag)
                 {
                     state.bufferPos = pos0;
                     return ReadUInt32WrapperSlow(ref buffer, ref state);

From fdf4ef62a56e4c628aeda3921da1f11b68fd2d71 Mon Sep 17 00:00:00 2001
From: James Newton-King <james@newtonking.com>
Date: Fri, 13 Nov 2020 12:17:24 +1300
Subject: [PATCH 2/2] Additional test

---
 .../WellKnownTypes/WrappersTest.cs            | 22 +++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/csharp/src/Google.Protobuf.Test/WellKnownTypes/WrappersTest.cs b/csharp/src/Google.Protobuf.Test/WellKnownTypes/WrappersTest.cs
index 94c4746a80dc..5b0e5e8fc1cb 100644
--- a/csharp/src/Google.Protobuf.Test/WellKnownTypes/WrappersTest.cs
+++ b/csharp/src/Google.Protobuf.Test/WellKnownTypes/WrappersTest.cs
@@ -87,6 +87,28 @@ public void NonDefaultSingleValues()
             });
         }
 
+        [Test]
+        public void NegativeSingleValues()
+        {
+            var message = new TestWellKnownTypes
+            {
+                FloatField = -12.5f,
+                DoubleField = -12.25d,
+                Int32Field = -1,
+                Int64Field = -2
+            };
+
+            MessageParsingHelpers.AssertWritingMessage(message);
+
+            MessageParsingHelpers.AssertRoundtrip(TestWellKnownTypes.Parser, message, parsed =>
+            {
+                Assert.AreEqual(-12.5f, parsed.FloatField);
+                Assert.AreEqual(-12.25d, parsed.DoubleField);
+                Assert.AreEqual(-1, parsed.Int32Field);
+                Assert.AreEqual(-2L, parsed.Int64Field);
+            });
+        }
+
         [Test]
         public void NonNullDefaultIsPreservedThroughSerialization()
         {