ASP.NET Core 2.1 - Memory cache - value set in middleware cannot be accessed by controller

Question

I am using IMemoryCache in Asp.Net Core 2.1 Webapi project to temporarily store some data received from RabbitMq channel. I have a channel listener in a customised middleware. But when I try to access the data in the cache from controller, there is no data in it. I am using Autofac as my DI framework.

If I set a value to memory cache in a controller, I can get it from other classes, such as a service (also registered in Autofac DI) associated with this controller.

My implementation is as follow:

1. In Startup.cs, I have

services.AddMemoryCache();

and then use the middleware as

app.UseMiddleware<RabbitMqConsumerMiddleware>();
app.UseCors("default")
    .UseAuthentication()
    .UseMvc();`

My Autofac registration is as follow:

Here is my Autofac registration

public IServiceProvider ConfigureServices(IServiceCollection services)
{
RabbitMqConfiguration rabbitMqConfiguration = new RabbitMqConfiguration();
        Configuration.GetSection("RabbitMq").Bind(rabbitMqConfiguration);
        services.AddSingleton(rabbitMqConfiguration);

        services.AddMvcCore()
            .AddAuthorization()
            .AddJsonFormatters()
            .SetCompatibilityVersion(CompatibilityVersion.Version_2_1)
            .AddViewLocalization(LanguageViewLocationExpanderFormat.Suffix)
            .AddDataAnnotationsLocalization()
            .AddControllersAsServices()
            .AddApiExplorer();

        services.AddRabbitMq(rabbitMqConfiguration);
        services.AddMemoryCache();


        ContainerBuilder builder = new ContainerBuilder();

        builder.Populate(services);
        IContainer container = builder.Build();
        return new AutofacServiceProvider(container);
    }

2. In the middleware, I have

    public RabbitMqConsumerMiddleware(RequestDelegate next, IMemoryCache memoryCache, RabbitMqConfiguration configuration, IModel messageBodyReceiverChannel) { _next = next; _memoryCache = memoryCache; _configuration = configuration; _messageBodyReceiverChannel = messageBodyReceiverChannel; } public async Task Invoke(HttpContext context) { bool isMessageBodyReceiverConsumerExist = _memoryCache.TryGetValue("message-body-receiver-consumer", out EventingBasicConsumer messageBodyReceiverConsumer); if (!isMessageBodyReceiverConsumerExist) { var messageBodyReceiverConsumer = new EventingBasicConsumer(_messageBodyReceiverChannel); messageBodyReceiverConsumer.Received += (ch, ea) => { MessageBody messageBody = JsonConvert.DeserializeObject<MessageBody>(Encoding.Default.GetString(ea.Body)); if (_memoryCache.TryGetValue("Message Body", out List<MessageBody> cacheMessageBodies)) { cacheMessageBodies.Add(messageBody); } else { _memoryCache.Set("Message Body", new List<MessageBody> { messageBody }); } }; _memoryCache.Set("message-body-receiver-consumer", messageBodyReceiverConsumer); } _messageBodyReceiverChannel.BasicConsume(_configuration.MessageReceiverQueue, false, messageBodyReceiverConsumer); await _next(context); } 

where messageBody comes from RabbitMq

3. In controller I have

    [Authorize] [Route("[controller]")] [ApiController] public class MessageBodyController : ControllerBase { private readonly IApplicationService<Dto.MessageBody> _messageBodyPresenter; private readonly IMemoryCache _memoryCache; public MessageBodyController(IApplicationService<Dto.MessageBody> messageBodyPresenter, IMemoryCache memoryCache) { _messageBodyPresenter = messageBodyPresenter; _memoryCache = memoryCache; } [HttpGet] [Route("Stop")] public IActionResult Stop() { ((MessageBodyPresenter)_messageBodyPresenter).Stop(); return Ok(); } } 

But _memoryCache is always empty.

I put a breakpoint in my middleware and confirm that data has been set to the cache.

Do I use memory cache in a wrong way? Thanks

Answer 1

Without knowing your full configuration, I guess one issue could be that you have registered the new middleware after the Mvc middleware.
Your registration should look like this:

app.UseMiddleware<RabbitMqConsumerMiddleware>();
app.UseMvc();