Handle DbDataReader.GetIntXX and INT128 (#1073).

Author: cincuranet

src/FirebirdSql.Data.FirebirdClient.Tests/FbInt128SupportTests.cs

@@ -64,6 +64,15 @@ public async Task ReadsValueCorrectly(BigInteger value)
 		}
 	}
 
+	[Test]
+	public Task CanReadAsByte() => CanReadAsTypeHelper<byte>(6, r => r.GetByte(0));
+	[Test]
+	public Task CanReadAsInt16() => CanReadAsTypeHelper<short>(6, r => r.GetInt16(0));
+	[Test]
+	public Task CanReadAsInt32() => CanReadAsTypeHelper<int>(6, r => r.GetInt32(0));
+	[Test]
+	public Task CanReadAsInt64() => CanReadAsTypeHelper<long>(6, r => r.GetInt64(0));
+
 	[TestCaseSource(nameof(TestValues))]
 	public async Task PassesValueCorrectly(BigInteger value)
 	{
@@ -125,4 +134,19 @@ public async Task SimpleSelectSchemaTableTest()
 			}
 		}
 	}
+
+	async Task CanReadAsTypeHelper<T>(T value, Func<FbDataReader, T> getter)
+		where T : IFormattable
+	{
+		await using (var cmd = Connection.CreateCommand())
+		{
+			var svalue = value.ToString(null, CultureInfo.InvariantCulture);
+			cmd.CommandText = $"select cast({svalue} as int128) from rdb$database";
+			await using (var reader = await cmd.ExecuteReaderAsync())
+			{
+				await reader.ReadAsync();
+				Assert.AreEqual(value, getter(reader));
+			}
+		}
+	}
 }

src/FirebirdSql.Data.FirebirdClient/Common/DbValue.cs

@@ -184,22 +184,38 @@ public bool GetBoolean()
 
 	public byte GetByte()
 	{
-		return Convert.ToByte(_value, CultureInfo.InvariantCulture);
+		return _value switch
+		{
+			BigInteger bi => (byte)bi,
+			_ => Convert.ToByte(_value, CultureInfo.InvariantCulture),
+		};
 	}
 
 	public short GetInt16()
 	{
-		return Convert.ToInt16(_value, CultureInfo.InvariantCulture);
+		return _value switch
+		{
+			BigInteger bi => (short)bi,
+			_ => Convert.ToInt16(_value, CultureInfo.InvariantCulture),
+		};
 	}
 
 	public int GetInt32()
 	{
-		return Convert.ToInt32(_value, CultureInfo.InvariantCulture);
+		return _value switch
+		{
+			BigInteger bi => (int)bi,
+			_ => Convert.ToInt32(_value, CultureInfo.InvariantCulture),
+		};
 	}
 
 	public long GetInt64()
 	{
-		return Convert.ToInt64(_value, CultureInfo.InvariantCulture);
+		return _value switch
+		{
+			BigInteger bi => (long)bi,
+			_ => Convert.ToInt64(_value, CultureInfo.InvariantCulture),
+		};
 	}
 
 	public decimal GetDecimal()