### MySqlConnector ### Couldn't connect to server

[ttosic92]

On project upgrade from 3.1.1 .NET Core version to .NET 5.0 MySqlConnector driver keeps throwing
"### MySqlConnector ### Couldn't connect to server. More information - Cannot determine the frame size or a corrupted frame was received.". But mind boggling thing was the fact that driver worked when ran from Visual Studio 19.0 but didn't work from docker container.

Base image is .NET5 is 5.0-alpine.

First i thought connection strings are wrong or maybe grants to DB but those generate different kind of exception. I checked connection strings inside container and everything matches. Tried both 1.3.1 and 1.3.9 version of MySqlConnector and same exception happens.

Thought maybe reverse proxy SSL is issue on server (Debian 10.0) but when i used curl from local network i got same error.
Also tried to host container from WSL, same issue persisted.

[bgrainger]

What's the full exception call stack with all inner exceptions?

[ttosic92]

Hello, thx for the reply. Here is full call stack. Exception persists on http calls also.

  Exception -> Source -> MySqlConnector
  Exception -> HResult -> -2147467259
  Exception -> Message -> Couldn't connect to server
  Exception -> StackTrace ->    at MySqlConnector.Core.ServerSession.ConnectAsync(ConnectionSettings cs, Int32 startTickCount, ILoadBalancer loadBalancer, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ServerSession.cs:line 530
   at MySqlConnector.Core.ConnectionPool.ConnectSessionAsync(String logMessage, Int32 startTickCount, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ConnectionPool.cs:line 376
   at MySqlConnector.Core.ConnectionPool.GetSessionAsync(MySqlConnection connection, Int32 startTickCount, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ConnectionPool.cs:line 107
   at MySqlConnector.Core.ConnectionPool.GetSessionAsync(MySqlConnection connection, Int32 startTickCount, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ConnectionPool.cs:line 137
   at MySqlConnector.MySqlConnection.CreateSessionAsync(ConnectionPool pool, Int32 startTickCount, Nullable`1 ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlConnection.cs:line 873
   at MySqlConnector.MySqlConnection.OpenAsync(Nullable`1 ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlConnection.cs:line 414
   at MySqlConnector.MySqlConnection.Open() in /_/src/MySqlConnector/MySqlConnection.cs:line 380

  InnerException -> Source -> System.Net.Security
  InnerException -> HResult -> -2146232800
  InnerException -> Message -> Cannot determine the frame size or a corrupted frame was received.
  InnerException -> StackTrace ->    at System.Net.Security.SslStream.ReceiveBlobAsync[TIOAdapter](TIOAdapter adapter)
   at System.Net.Security.SslStream.ForceAuthenticationAsync[TIOAdapter](TIOAdapter adapter, Boolean receiveFirst, Byte[] reAuthenticationData, Boolean isApm)
   at System.Net.Security.SslStream.ProcessAuthentication(Boolean isAsync, Boolean isApm, CancellationToken cancellationToken)
   at System.Net.Security.SslStream.AuthenticateAsClient(SslClientAuthenticationOptions sslClientAuthenticationOptions)
   at MySqlConnector.Core.ServerSession.InitSslAsync(ProtocolCapabilities serverCapabilities, ConnectionSettings cs, SslProtocols sslProtocols, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ServerSession.cs:line 1359
   at MySqlConnector.Core.ServerSession.ConnectAsync(ConnectionSettings cs, Int32 startTickCount, ILoadBalancer loadBalancer, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ServerSession.cs:line 470

[ttosic92]

Maybe it is old SQL server version that supports TLS 1.0 and 1.1? It wasn't issue before migrating to .NET5.

[bgrainger]

This sounds like it could be related to the known breaking changes for SSL on Linux in .NET 5.0: https://docs.microsoft.com/en-us/dotnet/core/compatibility/cryptography/5.0/default-cipher-suites-for-tls-on-linux

Given that MySqlConnector works fine under .NET 3.1 but fails under .NET 5.0, it seems like it's more likely to be a runtime issue than a MySqlConnector issue.

But mind boggling thing was the fact that driver worked when ran from Visual Studio 19.0 but didn't work from docker container.

I assume this means that the code works on Windows, but not Linux? That also points to it being a .NET runtime issue.

[ttosic92]

Thanks for help! That was exactly the issue.