Why should I inject IHttpContextAccessor as a Singleton

Question

In all examples that i've seen of IHttpContextAccessor injection, it is set as a Singleton.

Examples:

How to add IHttpContextAccessor in the Startup class in the DI in ASP.NET Core 1.0? Injecting IHttpContextAccessor into ApplicationDbContext ASP.NET Core 1.0 .NET Core IHttpContextAccessor issue

I find it kinda weird, since HttpContext really looks like something that maps to requests. Wouldn't AddScoped be more appropriate in this case?

Is Singleton really the recomended way? Am I not seeeing something?

Answer 1

Is Singleton really the recomended way?

Yes

According to comments associated with an issue raised on GitHub

https://github.com/aspnet/Hosting/issues/793#issuecomment-224828588

In that sample, you are registering it as a singleton. Shouldn't it be a scoped instance?

It's fine being a singleton because the backing store is async local.

Which got a later reply

https://github.com/aspnet/Hosting/issues/793#issuecomment-224924030

Actually if you register it as a Transient on .NET Core then it doesn't work properly since the implementation for .NET Core is using a AsyncLocal which relies upon the instance variable to track the thread local storage slot. So it has to be registered as a singleton on .NET Core.