The error occurs only with ReverseProxy Server. With Normal Server everything is fine. ReverseProxy Server creates proxied Instances of services and injects them in the controller. In the proxied service I got the error:

Unable to cast object of type 'd__1[NotificationMarkResultDto]' to type 'System.Collections.Generic.IReadOnlyCollection`1[NotificationMarkResultDto]'.

When I debug the Reverse Proxy Server, go to the controller, then I can see the contents of the injected service in which an error occurs:

debug screenshot Injected NotificationService

These are methods where proxy services are created.

public INotificationService GetNotificationService()
{
    return _host.Get<INotificationService>(INotificationService.NetServiceId, NetServiceFactory.Instance);
}

private sealed class NetServiceFactory : INetServiceFactory
{
    public static readonly INetServiceFactory Instance = new NetServiceFactory();

    /// <inheritdoc />
    public string ResolveServiceAddress(string serviceKey)
    {
        throw new NotSupportedException();
    }

    /// <inheritdoc />
    public TServiceContract CreateProxy<TServiceContract>(INetServiceProxy netServiceProxy)
    {
        return NetServiceDispatchProxy.Create<TServiceContract>(netServiceProxy)!;
    }
}

internal class NetServiceDispatchProxy : DispatchProxy
{
    private INetServiceProxy? _netServiceProxy;

    public static TServiceContract? Create<TServiceContract>(INetServiceProxy netServiceProxy)
    {
        object? proxy = DispatchProxy.Create<TServiceContract, NetServiceDispatchProxy>() as NetServiceDispatchProxy;
        if (proxy == null)
            return default;

        ((NetServiceDispatchProxy)proxy).Initialize(netServiceProxy);

        return (TServiceContract)proxy;
    }

    /// <inheritdoc />
    protected override object? Invoke(MethodInfo? targetMethod, object?[]? args)
    {
        var cts = new CancellationTokenSource(30000);
        return _netServiceProxy?.Invoke(targetMethod, args, cts.Token);
    }

    private void Initialize(INetServiceProxy netServiceProxy)
    {
        _netServiceProxy = netServiceProxy;
    }
}

Why does an error occur if IReadOnlyCollection appears in the inheritance chain of `List'? Maybe something strange happend in Initialization or Serialization of the proxied Service?

I get a returned object IReadOnlyCollection from this method:

public async Task<IReadOnlyCollection<NotificationMarkResultDto>> MarkNotifications(AccountId accountKey, NotificationDto[] notificationsToUpdate)
{
    var result = new List<NotificationMarkResultDto>(notificationsToUpdate.Length);
    var notificationKeys = notificationsToUpdate.Select(x => x.NotificationKey).ToHashSet();
    var notifications = await _uow.Notifications.GetNotifications(notificationKeys, accountKey);

    foreach (var updateItem in notificationsToUpdate)
    {
        var foundNotification = notifications.FirstOrDefault(x => x.NotificationKey == updateItem.NotificationKey);

        if (foundNotification != null) 
        {
            foundNotification.Status = updateItem.Status ?? foundNotification.Status;
            foundNotification.Importance = updateItem.Important switch
            {
                true => NotificationImportance.High,
                false => NotificationImportance.Low,
                _ => foundNotification.Importance,
            };

            result.Add(new NotificationMarkResultDto(updateItem.NotificationKey, foundNotification.Status, foundNotification.Importance));
        }
        else 
        {
            result.Add(new NotificationMarkResultDto(updateItem.NotificationKey, "Notificaton not found"));
        }
    }

    await _uow.SaveAsync();

    return result;
}

This method is called in the controller, controller looks like this:

[HttpPost("marks")]
[Produces(MediaTypeNames.Application.Json)]
[ProducesResponseType(StatusCodes.Status200OK)]
[ProducesResponseType(StatusCodes.Status400BadRequest, Type = typeof(ValidationProblemDetails))]
[ProducesResponseType(StatusCodes.Status401Unauthorized, Type = typeof(ProblemDetails))]
[ProducesResponseType(StatusCodes.Status500InternalServerError, Type = typeof(ProblemDetails))]
public async Task<IReadOnlyCollection<NotificationMarkResultDto>> MarkNotifications([FromBody, Required] NotificationDto[] update)
{
    return await _notificationService.MarkNotifications(params);
}

The whole error contains these lines:

{
    "type": ";,
    "title": "Unable to cast object of type '<Enumerate>d__1[Acp.Domain.Queries.Dtos.Notifications.NotificationMarkResultDto]' to type 'System.Collections.Generic.IReadOnlyCollection`1[Notifications.NotificationMarkResultDto]'.",
    "status": 500,
    "detail": "System.InvalidCastException: Unable to cast object of type '<Enumerate>d__1[NotificationMarkResultDto]' to type 'System.Collections.Generic.IReadOnlyCollection`1[Notifications.NotificationMarkResultDto]'.\n 
at Net.NetCommHost.NetServiceProxy.TaskWrapper`1.<>c.<Wrap>b__0_0(Task`1 x)
\n at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2.InnerInvoke()\n 
at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)\n--- End of stack trace from previous location ---\n 
at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)\n 
at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)\n--- End of stack trace from previous location ---\n 
at Controllers.NotificationController.MarkNotifications(NotificationDto[] update) in /source/src/Controllers/NotificationController.cs:line 101\n at lambda_method305(Closure, Object)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(ActionContext actionContext, IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextExceptionFilterAsync>g__Awaited|26_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)"
}

In the IDE, the compiler highlights explicit type conversion for service method in gray color as unnecessary code: "IDE0004 Cast is redudant"

return (IReadOnlyCollection<NotificationMarkResultDto>)result;

The error occurs only with ReverseProxy Server. With Normal Server everything is fine. ReverseProxy Server creates proxied Instances of services and injects them in the controller. In the proxied service I got the error:

Unable to cast object of type 'd__1[NotificationMarkResultDto]' to type 'System.Collections.Generic.IReadOnlyCollection`1[NotificationMarkResultDto]'.

When I debug the Reverse Proxy Server, go to the controller, then I can see the contents of the injected service in which an error occurs:

debug screenshot Injected NotificationService

These are methods where proxy services are created.

public INotificationService GetNotificationService()
{
    return _host.Get<INotificationService>(INotificationService.NetServiceId, NetServiceFactory.Instance);
}

private sealed class NetServiceFactory : INetServiceFactory
{
    public static readonly INetServiceFactory Instance = new NetServiceFactory();

    /// <inheritdoc />
    public string ResolveServiceAddress(string serviceKey)
    {
        throw new NotSupportedException();
    }

    /// <inheritdoc />
    public TServiceContract CreateProxy<TServiceContract>(INetServiceProxy netServiceProxy)
    {
        return NetServiceDispatchProxy.Create<TServiceContract>(netServiceProxy)!;
    }
}

internal class NetServiceDispatchProxy : DispatchProxy
{
    private INetServiceProxy? _netServiceProxy;

    public static TServiceContract? Create<TServiceContract>(INetServiceProxy netServiceProxy)
    {
        object? proxy = DispatchProxy.Create<TServiceContract, NetServiceDispatchProxy>() as NetServiceDispatchProxy;
        if (proxy == null)
            return default;

        ((NetServiceDispatchProxy)proxy).Initialize(netServiceProxy);

        return (TServiceContract)proxy;
    }

    /// <inheritdoc />
    protected override object? Invoke(MethodInfo? targetMethod, object?[]? args)
    {
        var cts = new CancellationTokenSource(30000);
        return _netServiceProxy?.Invoke(targetMethod, args, cts.Token);
    }

    private void Initialize(INetServiceProxy netServiceProxy)
    {
        _netServiceProxy = netServiceProxy;
    }
}

Why does an error occur if IReadOnlyCollection appears in the inheritance chain of `List'? Maybe something strange happend in Initialization or Serialization of the proxied Service?

I get a returned object IReadOnlyCollection from this method:

public async Task<IReadOnlyCollection<NotificationMarkResultDto>> MarkNotifications(AccountId accountKey, NotificationDto[] notificationsToUpdate)
{
    var result = new List<NotificationMarkResultDto>(notificationsToUpdate.Length);
    var notificationKeys = notificationsToUpdate.Select(x => x.NotificationKey).ToHashSet();
    var notifications = await _uow.Notifications.GetNotifications(notificationKeys, accountKey);

    foreach (var updateItem in notificationsToUpdate)
    {
        var foundNotification = notifications.FirstOrDefault(x => x.NotificationKey == updateItem.NotificationKey);

        if (foundNotification != null) 
        {
            foundNotification.Status = updateItem.Status ?? foundNotification.Status;
            foundNotification.Importance = updateItem.Important switch
            {
                true => NotificationImportance.High,
                false => NotificationImportance.Low,
                _ => foundNotification.Importance,
            };

            result.Add(new NotificationMarkResultDto(updateItem.NotificationKey, foundNotification.Status, foundNotification.Importance));
        }
        else 
        {
            result.Add(new NotificationMarkResultDto(updateItem.NotificationKey, "Notificaton not found"));
        }
    }

    await _uow.SaveAsync();

    return result;
}

This method is called in the controller, controller looks like this:

[HttpPost("marks")]
[Produces(MediaTypeNames.Application.Json)]
[ProducesResponseType(StatusCodes.Status200OK)]
[ProducesResponseType(StatusCodes.Status400BadRequest, Type = typeof(ValidationProblemDetails))]
[ProducesResponseType(StatusCodes.Status401Unauthorized, Type = typeof(ProblemDetails))]
[ProducesResponseType(StatusCodes.Status500InternalServerError, Type = typeof(ProblemDetails))]
public async Task<IReadOnlyCollection<NotificationMarkResultDto>> MarkNotifications([FromBody, Required] NotificationDto[] update)
{
    return await _notificationService.MarkNotifications(params);
}

The whole error contains these lines:

{
    "type": "https://httpstatuses/500",
    "title": "Unable to cast object of type '<Enumerate>d__1[Acp.Domain.Queries.Dtos.Notifications.NotificationMarkResultDto]' to type 'System.Collections.Generic.IReadOnlyCollection`1[Notifications.NotificationMarkResultDto]'.",
    "status": 500,
    "detail": "System.InvalidCastException: Unable to cast object of type '<Enumerate>d__1[NotificationMarkResultDto]' to type 'System.Collections.Generic.IReadOnlyCollection`1[Notifications.NotificationMarkResultDto]'.\n 
at Net.NetCommHost.NetServiceProxy.TaskWrapper`1.<>c.<Wrap>b__0_0(Task`1 x)
\n at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2.InnerInvoke()\n 
at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)\n--- End of stack trace from previous location ---\n 
at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)\n 
at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)\n--- End of stack trace from previous location ---\n 
at Controllers.NotificationController.MarkNotifications(NotificationDto[] update) in /source/src/Controllers/NotificationController.cs:line 101\n at lambda_method305(Closure, Object)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(ActionContext actionContext, IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)\n 
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextExceptionFilterAsync>g__Awaited|26_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)"
}

In the IDE, the compiler highlights explicit type conversion for service method in gray color as unnecessary code: "IDE0004 Cast is redudant"

return (IReadOnlyCollection<NotificationMarkResultDto>)result;

• c#
• -core
• casting
• asp-core-mvc
• reverse-proxy

• 1 "the compiler highlights explicit type conversion in gray color as unnecessary code." What are you referring to and where is that in your code ? Like NotificationMarkResultDto is in the service and the controller isn't the same class and you expecting some type conversion somewhere occurring? – Ralf Commented Mar 13 at 14:16
• Are you make sure the runtime for different environment is the same? – Brando Zhang Commented Mar 14 at 6:14
• @BrandoZhang Update information: deployed the same version in docker, the error is still not reproducible in there. I checked the file history in git, the error has been appearing since the method began to return the IReadOnlyCollection type (previously the method was void) – Taya Commented Mar 14 at 8:25
• Consider either adding an Answer yourself, or closing the question. At the moment nobody except you might be able to write an Answer. – Peter B Commented Mar 17 at 21:06

1 Answer 1

Problem was solved, when I set return value of MarkNotifications from IReadOnlyCollection<NotificationMarkResultDto> to NotificationMarkResult[] and in NotificationMarkResultDto were no setters written before (because I wanted to do that for the immutable response), but now they have been added.