Why there is no value for unable to connect error in MySqlErrorCode

[vanbukin]

As I see there are two places (here and here) in a whole codebase where that exception could be thrown. So the problem there is no error code for that exception types. And when we want to handle situation when there is no connecton to MySQL database, we need to check the error code (it should be 0) and additionaly check exception message. I think it would be better to add additional enum value into MySqlErrorCode to handle that situation (specially with when clauses).

[bgrainger]

The "why" is mostly oversight and backwards-compatibility with Connector/NET (which also does't have a specific error code for this situation AFAIK).

It seems like we could safely add a new negative enum value, as was done for CommandTimeoutExpired:

MySqlConnector/src/MySqlConnector/MySql.Data.MySqlClient/MySqlErrorCode.g.cs

Lines 9 to 12 in 717c3ec

	/// <summary>
	/// The timeout period specified by <see cref="MySqlCommand.CommandTimeout"/> elapsed before the operation completed.
	/// </summary>
	CommandTimeoutExpired = -1,

[vanbukin]

@bgrainger Maybe we can reuse that one? https://github.com/mysql-net/MySqlConnector/blob/0.48.2/src/MySqlConnector/MySql.Data.MySqlClient/MySqlErrorCode.g.cs#L229

Looks like it doesn’t used now

[bgrainger]

The defined error codes are generally expected to be returned by the server in an error packet.

It's possible that that particular one is reserved for clients to signal connection failure; if so, it would be appropriate to reuse. (Thanks for the pointer.)

[bgrainger]

MySqlErrorCode.UnableToConnectToHost is used by Connector/NET for failure to connect.

[bgrainger]

I wonder if Connector/NET may have co-opted ER_BAD_HOST_ERROR (1042) to mean "can't connect to server"? The "right" client-side error code might be CR_CONNECTION_ERROR (2002) or CR_CONN_HOST_ERROR (2003). Nevertheless, the precedent for .NET is set now.

[bgrainger]

Fixed in 0.49.0.