Ensure there is adequate space in the output buffer. Fixes #520

Author: bgrainger

src/MySqlConnector/Protocol/Serialization/ByteBufferWriter.cs

@@ -148,7 +148,7 @@ public void Write(ReadOnlySpan<char> chars)
 				m_encoder = Encoding.UTF8.GetEncoder();
 			while (chars.Length > 0)
 			{
-				if (m_output.Length == 0)
+				if (m_output.Length < 4)
 					Reallocate();
 				m_encoder.Convert(chars, m_output.Span, true, out var charsUsed, out var bytesUsed, out var completed);
 				chars = chars.Slice(charsUsed);

tests/MySqlConnector.Tests/ByteBufferWriterTests.cs

@@ -0,0 +1,29 @@
+using MySqlConnector.Protocol.Serialization;
+using Xunit;
+
+namespace MySqlConnector.Tests
+{
+	public class ByteBufferWriterTests
+	{
+		[Theory]
+		[InlineData(1)]
+		[InlineData(10)]
+		[InlineData(100)]
+		public void WriteString(int length)
+		{
+			var expected = new byte[length * 3];
+			for (var i = 0; i < length; i++)
+			{
+				expected[i * 3] = 0xEE;
+				expected[i * 3 + 1] = 0x80;
+				expected[i * 3 + 2] = 0x81;
+			}
+
+			var writer = new ByteBufferWriter();
+			var input = char.ConvertFromUtf32(0xE001);
+			for (var i = 0; i < length; i++)
+				writer.Write(input);
+			Assert.Equal(expected, writer.ArraySegment);
+		}
+	}
+}

tests/MySqlConnector.Tests/MySqlConnector.Tests.csproj

@@ -32,7 +32,7 @@
 
   <ItemGroup Condition=" '$(Configuration)' == 'Baseline' ">
     <PackageReference Include="MySql.Data" Version="8.0.11" />
-    <Compile Remove="ConnectionTests.cs;FakeMySqlServer.cs;FakeMySqlServerConnection.cs;LoadBalancerTests.cs;NormalizeTests.cs;StatementPreparerTests.cs;TypeMapperTests.cs;UtilityTests.cs" />
+    <Compile Remove="ByteBufferWriterTests.cs;ConnectionTests.cs;FakeMySqlServer.cs;FakeMySqlServerConnection.cs;LoadBalancerTests.cs;NormalizeTests.cs;StatementPreparerTests.cs;TypeMapperTests.cs;UtilityTests.cs" />
   </ItemGroup>
 
   <ItemGroup Condition=" '$(TargetFramework)' == 'net462' ">