Injecting Service in Middleware in ASP.NET Core

Question

I want to inject a service based on the HTTP header value. So I have 2 classes - DbDataProvider and InMemDataProvider, both are implemented from IDataProvider. Whenever an API call is made, a header is passed by the client which determines whether DbDataProvider is required or InMemDataProvider is required. How do I achieve that? So in short I need to inject service in the ServiceCollection in one of the middlewares. Is that possible?

The problem is that in the ConfigureService method in Startup class I cannot get the HttpContext. I have written a middleware using which I am able to get the HTTP Context but how do I inject a Service there?

Answer 1

You can achieve this in your DI config in Startup.cs.

They key is services.AddHttpContextAccessor() which allows you to get access to the HttpContext.

services.AddHttpContextAccessor();

services.AddScoped<DbDataProvider>();
services.AddScoped<InMemDataProvider>();
services.AddScoped<IDataProvider>(ctx =>
{
    var contextAccessor = ctx.GetService<IHttpContextAccessor>();
    var httpContext = contextAccessor.HttpContext;

    // Whatever the header is that you are looking for
    if (httpContext.Request.Headers.TryGetValue("Synthetic", out var syth))
    {
        return ctx.GetService<InMemDataProvider>();
    }
    else
    {
        return ctx.GetService<DbDataProvider>();
    }
});