Work around server bug reading BIT column. Fixes #713

Author: bgrainger

src/MySqlConnector/Core/BinaryRow.cs

@@ -87,7 +87,7 @@ protected override object GetValueCore(ReadOnlySpan<byte> data, ColumnDefinition
 				return isUnsigned ? (object) MemoryMarshal.Read<ulong>(data) : MemoryMarshal.Read<long>(data);
 
 			case ColumnType.Bit:
-				return ReadBit(data, columnDefinition.ColumnFlags);
+				return ReadBit(data, columnDefinition);
 
 			case ColumnType.String:
 				if (Connection.GuidFormat == MySqlGuidFormat.Char36 && columnDefinition.ColumnLength / ProtocolUtility.GetBytesPerCharacter(columnDefinition.CharacterSet) == 36)

src/MySqlConnector/Core/Row.cs

@@ -433,16 +433,22 @@ protected static Guid CreateGuidFromBytes(MySqlGuidFormat guidFormat, ReadOnlySp
 #endif
 		}
 
-		protected static object ReadBit(ReadOnlySpan<byte> data, ColumnFlags columnFlags)
+		protected static object ReadBit(ReadOnlySpan<byte> data, ColumnDefinitionPayload columnDefinition)
 		{
-			if ((columnFlags & ColumnFlags.Binary) == 0)
+			if ((columnDefinition.ColumnFlags & ColumnFlags.Binary) == 0)
 			{
 				// when the Binary flag IS NOT set, the BIT column is transmitted as MSB byte array
 				ulong bitValue = 0;
 				for (int i = 0; i < data.Length; i++)
 					bitValue = bitValue * 256 + data[i];
 				return bitValue;
 			}
+			else if (columnDefinition.ColumnLength <= 5 && data.Length == 1 && data[0] < (byte) (1 << (int) columnDefinition.ColumnLength))
+			{
+				// a server bug may return the data as binary even when we expect text: https://github.com/mysql-net/MySqlConnector/issues/713
+				// in this case, the data can't possibly be an ASCII digit, so assume it's the binary serialisation of BIT(n) where n <= 5
+				return (ulong) data[0];
+			}
 			else
 			{
 				// when the Binary flag IS set, the BIT column is transmitted as text

src/MySqlConnector/Core/TextRow.cs

@@ -50,7 +50,7 @@ protected override object GetValueCore(ReadOnlySpan<byte> data, ColumnDefinition
 				return isUnsigned ? (object) ParseUInt64(data) : ParseInt64(data);
 
 			case ColumnType.Bit:
-				return ReadBit(data, columnDefinition.ColumnFlags);
+				return ReadBit(data, columnDefinition);
 
 			case ColumnType.String:
 				if (Connection.GuidFormat == MySqlGuidFormat.Char36 && columnDefinition.ColumnLength / ProtocolUtility.GetBytesPerCharacter(columnDefinition.CharacterSet) == 36)

tests/SideBySide/QueryTests.cs

@@ -1093,6 +1093,61 @@ public void NoBackslashEscapes()
 		}
 #endif
 
+		[SkippableFact(Baseline = "https://bugs.mysql.com/bug.php?id=97067")]
+		public async Task QueryBit()
+		{
+			using var connection = new MySqlConnection(AppConfig.ConnectionString);
+			await connection.OpenAsync();
+			await connection.ExecuteAsync(@"
+DROP TABLE IF EXISTS query_bit;
+CREATE TABLE query_bit(name TEXT, value BIT(1));
+INSERT INTO query_bit VALUES('a', 1);
+");
+
+			using var command = new MySqlCommand(@"
+SELECT value FROM query_bit;
+
+SELECT MAX(value) FROM query_bit;
+
+SELECT COALESCE(value, 0) FROM query_bit;
+
+SELECT CASE
+    WHEN name IS NOT NULL THEN value
+    ELSE NULL
+END AS value
+FROM query_bit;", connection);
+			using var reader = await command.ExecuteReaderAsync();
+
+			Assert.True(await reader.ReadAsync());
+			Assert.Equal(1ul, reader.GetValue(0));
+			Assert.False(await reader.ReadAsync());
+
+			Assert.True(await reader.NextResultAsync());
+
+			Assert.True(await reader.ReadAsync());
+			Assert.Equal(1ul, reader.GetValue(0));
+			Assert.False(await reader.ReadAsync());
+
+			Assert.True(await reader.NextResultAsync());
+
+			Assert.True(await reader.ReadAsync());
+			var value = reader.GetValue(0);
+			if (value is byte[] byteArray)
+				Assert.Equal(new byte[] { 49 }, byteArray); // server bug returns '1' as a blob
+			else
+				Assert.Equal(1m, value);
+			Assert.False(await reader.ReadAsync());
+
+			Assert.True(await reader.NextResultAsync());
+
+			Assert.True(await reader.ReadAsync());
+			// MySQL returns ulong, MariaDB returns decimal; GetBoolean will coerce both
+			Assert.True(reader.GetBoolean(0));
+			Assert.False(await reader.ReadAsync());
+
+			Assert.False(await reader.NextResultAsync());
+		}
+
 		class BoolTest
 		{
 			public int Id { get; set; }