Multiple submissions for the same nation cause server to return error

[lifehackerhansol]

It is possible for multiple users to join as one country. This can cause race conditions as seen in the following game input: https://pastebin.com/9TZqtdXh

(thanks to penteract for the script: https://gist.github.com/penteract/54cdae72e4cf3dc9316a2f68b4feb884)

In the above log, Vienna managed to get two events happening at once, effectively ending the game (the game ID will return 500 forever) and causing the following stack trace:

backend-1  | fail: Microsoft.AspNetCore.Server.Kestrel[13]
backend-1  |       Connection id "0HNAABBHDFSNS", Request id "0HNAABBHDFSNS:00000003": An unhandled exception was thrown by the application.
backend-1  |       System.ArgumentException: An item with the same key has already been added. Key: Vie
backend-1  |          at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)
backend-1  |          at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](List`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
backend-1  |          at Mappers.EntityMapper.MapBoard(Board board, List`1 builds)
backend-1  |          at System.Linq.Enumerable.SelectListIterator`2.MoveNext()
backend-1  |          at System.Collections.Generic.List`1.AddRange(IEnumerable`1 collection)
backend-1  |          at Mappers.EntityMapper.MapWorld(World world, Nullable`1 player) in /app/Mappers/EntityMapper.cs:line 15
backend-1  |          at Controllers.GameController.GetWorld(Int32 gameId, Nation player) in /app/Controllers/GameController.cs:line 90
backend-1  |          at lambda_method461(Closure, Object)
backend-1  |          at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(ActionContext actionContext, IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
backend-1  |          at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)
backend-1  |          at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
backend-1  |          at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
backend-1  |          at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
backend-1  |          at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
backend-1  |          at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|20_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
backend-1  |          at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
backend-1  |          at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
backend-1  |          at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
backend-1  |          at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
backend-1  |          at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication`1 application)

As far as I can tell, there seems to be no mechanism to block multiple users submitting as one country. Could something like that be configured? (such as a keepalive ping?)

[Oliveriver]

I changed the title slightly since it's not joining as the same nation that causes the error, but submitting as the same nation.

I believe I've fixed the most likely crash with 0484f64, but I thought it through and there is still a minor potential for race conditions in the way submission is handled. I think it's unlikely enough that it's not worth thinking too hard about though.

I will close this for now, but will reopen it if anyone reports experiencing race conditions even after this fix.