Implement MySqlException.IsTransient. Fixes #849

Author: bgrainger

src/MySqlConnector/MySqlException.cs

@@ -40,6 +40,15 @@ public sealed class MySqlException : DbException
 		public override string? SqlState { get; }
 #endif
 
+		/// <summary>
+		/// Returns <c>true</c> if this exception could indicate a transient error condition (that could succeed if retried); otherwise, <c>false</c>.
+		/// </summary>
+#if NET45 || NET461 || NET471 || NETSTANDARD1_3 || NETSTANDARD2_0 || NETSTANDARD2_1 || NETCOREAPP2_1 || NETCOREAPP3_1
+		public bool IsTransient => IsErrorTransient(ErrorCode);
+#else
+		public override bool IsTransient => IsErrorTransient(ErrorCode);
+#endif
+
 #if !NETSTANDARD1_3
 		private MySqlException(SerializationInfo info, StreamingContext context)
 			: base(info, context)
@@ -115,7 +124,15 @@ internal MySqlException(MySqlErrorCode errorCode, string? sqlState, string messa
 		internal static MySqlException CreateForTimeout() => CreateForTimeout(null);
 
 		internal static MySqlException CreateForTimeout(Exception? innerException) =>
-			new MySqlException(MySqlErrorCode.CommandTimeoutExpired, "The Command Timeout expired before the operation completed.", innerException);
+			new(MySqlErrorCode.CommandTimeoutExpired, "The Command Timeout expired before the operation completed.", innerException);
+
+		private static bool IsErrorTransient(MySqlErrorCode errorCode) =>
+			errorCode is MySqlErrorCode.CommandTimeoutExpired
+				or MySqlErrorCode.ConnectionCountError
+				or MySqlErrorCode.LockDeadlock
+				or MySqlErrorCode.LockWaitTimeout
+				or MySqlErrorCode.UnableToConnectToHost
+				or MySqlErrorCode.XARBDeadlock;
 
 		IDictionary? m_data;
 	}

tests/MySqlConnector.Tests/CancellationTests.cs

@@ -215,6 +215,7 @@ public void Test(int step, int method)
 				var ex = Assert.Throws<MySqlException>(() => s_executeMethods[method](command));
 				Assert.InRange(stopwatch.ElapsedMilliseconds, 2900, 3500);
 				Assert.Equal(MySqlErrorCode.CommandTimeoutExpired, ex.ErrorCode);
+				Assert.True(ex.IsTransient);
 
 				// connection is unusable
 				Assert.Equal(ConnectionState.Closed, connection.State);

tests/SideBySide/ConnectSync.cs

@@ -30,6 +30,9 @@ public void ConnectBadHost()
 			using var connection = new MySqlConnection(csb.ConnectionString);
 			Assert.Equal(ConnectionState.Closed, connection.State);
 			var ex = Assert.Throws<MySqlException>(connection.Open);
+#if !BASELINE
+			Assert.True(ex.IsTransient);
+#endif
 			Assert.Equal((int) MySqlErrorCode.UnableToConnectToHost, ex.Number);
 			Assert.Equal((int) MySqlErrorCode.UnableToConnectToHost, ex.Data["Server Error Code"]);
 			Assert.Equal(ConnectionState.Closed, connection.State);