Warn user of lost external database connection

[Sprooty]

Fileflows running with external database (mariaDB)

Killing database results in no useful feedback on GUI

Suggest

• database connection is monitored and relevant action is taken to pause/stop FF processing etc and warn user.
• Consider if FF should auto recover from database loss if DB comes back online without restarting FF and how that is presented to the user; is it automated or is user action required etc?

Trace noted in FF logs when DB is killed.

Error -> ExceptionMiddleware: Unable to connect to any of the specified MySQL hosts.REQUEST [GET] [200]: /api/library-file/status

   at MySqlConnector.Core.ServerSession.ConnectAsync(ConnectionSettings cs, MySqlConnection connection, Int32 startTickCount, ILoadBalancer loadBalancer, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ServerSession.cs:line 432

   at MySqlConnector.Core.ConnectionPool.ConnectSessionAsync(MySqlConnection connection, String logMessage, Int32 startTickCount, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ConnectionPool.cs:line 422

   at MySqlConnector.Core.ConnectionPool.GetSessionAsync(MySqlConnection connection, Int32 startTickCount, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ConnectionPool.cs:line 126

   at MySqlConnector.Core.ConnectionPool.GetSessionAsync(MySqlConnection connection, Int32 startTickCount, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ConnectionPool.cs:line 126

   at MySqlConnector.MySqlConnection.CreateSessionAsync(ConnectionPool pool, Int32 startTickCount, Nullable`1 ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlConnection.cs:line 940

   at MySqlConnector.MySqlConnection.OpenAsync(Nullable`1 ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlConnection.cs:line 445

   at MySqlConnector.MySqlConnection.Open() in /_/src/MySqlConnector/MySqlConnection.cs:line 369

   at NPoco.Database.OpenSharedConnectionImp(Boolean isInternal)

   at NPoco.Database.QueryAsync[T](T instance, Expression`1 listExpression, Func`2 idFunc, Sql Sql, PocoData pocoData)+MoveNext()

   at NPoco.Database.QueryAsync[T](T instance, Expression`1 listExpression, Func`2 idFunc, Sql Sql, PocoData pocoData)+System.Threading.Tasks.Sources.IValueTaskSource<System.Boolean>.GetResult()

   at System.Linq.AsyncEnumerable.<ToListAsync>g__Core|620_0[TSource](IAsyncEnumerable`1 source, CancellationToken cancellationToken) in /_/Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToList.cs:line 36

   at System.Linq.AsyncEnumerable.<ToListAsync>g__Core|620_0[TSource](IAsyncEnumerable`1 source, CancellationToken cancellationToken) in /_/Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToList.cs:line 36

   at FileFlows.Server.Database.Managers.MySqlDbManager.GetLibraryFileOverview() in /src/Server/Database/Managers/MySqlDbManager.cs:line 198

   at FileFlows.Server.Controllers.LibraryFileController.GetStatus() in /src/Server/Controllers/LibraryFileController.cs:line 473

   at lambda_method66(Closure , Object )

   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)

   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)

   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)

   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)

   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)

   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()

--- End of stack trace from previous location ---