[CSharp C#] Verifier fails for valid messages for resized buffers(even with disabled alignment check)

[wonbinkanglg]

Here is full minimally reproducible code:

Test.cs

        public static void Main(string[] args)
        {
            var b0 = TestFbs(1); // This fails both VerifyTableStart, TestTableVerify.Verify
            var b1 = TestFbs(512);  // both Succeeds
        }

        static private ByteBuffer TestFbs(int startingSize)
        {
            // Start parsing fbs.
            var fbsBuilder = new FlatBufferBuilder(startingSize);
            var childrenOffset = new List<Offset<TestTableChild>>();

            for (int i = 0; i < 4; i++)
            {
                TestTableChild.StartChildrenVector(fbsBuilder, 2);
                var off1 = TestStruct.CreateTestStruct(fbsBuilder, [1, 2]);
                var off2 = TestStruct.CreateTestStruct(fbsBuilder, [1, 2]);
                var structChildrenOffset = fbsBuilder.EndVector();
                var  testTableChildOffset = TestTableChild.CreateTestTableChild(fbsBuilder, 1, structChildrenOffset);
                childrenOffset.Add(testTableChildOffset);
            }
            var childrenVectorOffset = TestTable.CreateChildrenVector(fbsBuilder, childrenOffset.ToArray());
            var offset = TestTable.CreateTestTable(fbsBuilder, 1, childrenVectorOffset);
            fbsBuilder.Finish(offset.Value);

            Verifier verifier = new Verifier(fbsBuilder.DataBuffer, new Options {alignmentCheck = false  });
            var ok = verifier.VerifyTableStart((uint)offset.Value);
            var totalOk = TestTableVerify.Verify(verifier, (uint)offset.Value);
            return fbsBuilder.DataBuffer;
        }

Message.fbs

struct TestStruct{
  index:[uint32:2];
}
table TestTableChild{
  index:uint32;
  children:[TestStruct];
}

table TestTable{
  index:uint32;
  children:[TestTableChild];
}

I don't understand why resizing buffer causes different results. Funny thing is both buffers result in same Table data.

[legokangpalla]

Could somebody comment on this at least if I'm using verifier incorrectly?

[mustiikhalil]

Hello,

It seems that the usage of the verifier is incorrect, there should be a function within the generated code that should verify the code for you. so in your case it should be something like Verify.TestTable and try using the SizedByteArray instead

public static bool VerifyMonster(ByteBuffer _bb) {
   Google.FlatBuffers.Verifier verifier = new Google.FlatBuffers.Verifier(_bb); 
   return verifier.VerifyBuffer("MONS", false, MonsterVerify.Verify);
 }

https://github.com/google/flatbuffers/blob/master/tests/MyGame/Example/Monster.cs#L51