Using non-singleton service in transform

[leoshusar]

Hi, I need to proxy login request and transform the response:

• take the session header
• generate random token
• save the session to the database with the new token
• remove the session header from response
• modify the response body, append the new token to the JSON response sent from the server

I have been successful with the ITransformProvider with just IMemoryCache, everything worked perfectly.
But when I wanted to inject my DbContext, I realized that transform providers are registered as singleton and thus injecting DbContext won't work here.

What is my best option here?

• create middleware - but the docs discourage from using middleware for what I am trying to do and say transforms are better fit for it
• inject IServiceProvider into ITransformProvider and get the DbContext manually in each transform func call
• any better idea?

[karelz]

Triage: This looks like general DI scoping problem -- can happen even if you have middleware and you need DbContext there.
We think that getting it manually is probably best. It should be documented somewhere in ASP.NET docs.
@halter73 @davidfowl any thoughts here?

[leoshusar]

Thank you!

Just an idea, wouldn't it be possible to add functionality that would inject dependencies like new minimal APIs do?

Something like:

context.AddResponseTransform(async (ResponseTransformContext transformContext, MyDbContext dbContext) =>
{
});

[halter73]

@leoshusar Make sure you use transformContext.HttpContext.RequestServices.GetRequiredService<MyDbContext>() instead of an IServiceProvider injected into your ITransformProvider. Using an IServiceProvider injected into a singleton service to get another service has the exact same problems as directly injecting the other service. You could manually create a scope, but using RequestServices is easier.

The minimal API like suggestion in a cool one, but at least right now, it's not as easy to inject services into Delegates as it is to do with constructors and DI. I do like the idea though. We should make it easier to create APIs like that.

[leoshusar]

@halter73 thank you for the DI tip!

Yeah, I think since I'm probably the first to request this, I think minimal API like injection can wait.
Maybe in the future there will be some simple universal API for enabling injections into Delegates for everyone to use.

[samsp-msft]

Possible, yes, but there is a lot behind the minimal APIs required to make it work. I'm not sure if that is worth it for this scenario.