How can a depending class know if IServiceProvider is Scoped, in order to safely resolve a scoped service if available?

[FrankBakkerNl]

Sometimes a scoped service needs to be injected into a depending class that is sometimes used inside a scope and sometimes outside a scope. An example would be a Log Enrichter that wants to access data that is only available within a Scope.

When used inside a scope it wants to receive the instance of that specific scope. If the depending class is created from the root scope it is illegal to resolve a scoped service. One way resolve the service from a 'root' IServiceProvider` is to create a new scope on the fly and resolve teh scoped service from that. However the depending class then needs a way of knowing if it needs to create a new scope or not. If it would always create a new scope, it will not receive the correct instance if it was already in a scope.

As far as I can tell, there is currenlty no public API that allowes a consumer of an IServiceProvider to dertermine if it is scoped or not, Except for trying to create the scoped service and catch an exception if it fails, which seems unreliable.

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[julealgon]

Scopes can be arbitrarily nested... how would you know which scope is "correct"?

I know this is not what you asked here, but I think it should also be taken into consideration. Knowing whether or not "you are in a scope" only answers part of the possible questions a consumer could have.

Also, can you provide a more concrete example of why you need this? Usually, the class creating the scope is responsible for creating the dependent object using that scope, and all dependencies are then resolved from the container at that moment in time. If you need to pass along the IServiceProvider to further resolve other services, maybe you could change your implementation to avoid that need and resolve the services upfront?

[FrankBakkerNl]

The way I understand it is that scopes are not really, 'nested'. Yes you can create a new scope from an exisisting one, but that does not have anything in common with its 'parent' it is really just a new blank scope with a separated lifetime. The real distiction made by the DI framework is between the root and scopes. Where for the root it is not allowed to resolve scoped services while for a scope it is allowed.

Some services are sometimes created inside a scope and sometimes from the root without my own code controlling it. An example is Serilog, which I do not control but while logging, it creates Enrichers or LogSinks that I do implement myself and configure serilog to use. Inside my own Enricher I want to access scoped services that belong to the same scope which created the ILogger in the first place. So that it can provide information related to objects in that scope, if available. This all works fine, as long as I use the logger that is created from a scope, all of itys dependencies are also created from that scope. It fails with an exception however when the logger is used outside of a scope because the Scoped service is not allowed to be resolved.

[julealgon]

@FrankBakkerNl ok, fair enough.

The only suggestion I have for this situation you describe is to avoid scoped registrations and use ambient data with AsyncLocal to store the data, like how IHttpContextAccessor works: it is a singleton instance, that provides the current request.

I've had a similar situation as yours recently and went with that approach with good success. When outside of a request, this abstraction would return null (instead of crashing) and I can conditionally skip the logic.

I believe this is actually why IHttpContextAccessor was coded this way, so that it could work seamlessly regardless of the container lifetime.

[FrankBakkerNl]

Unfortunately there is no async excution context directly related to the scope in our scenario. It is not asp.net handling webrequests.

Out platform is NetDaemon We built it so that users of the platform can create classes we will load as 'apps' . For each such app we create a ServiceScope and then use that to instantiate the app and all its dependencies. Each app then gets its own version of any scoped services. When the app is stopped, we dispose the service scope so all injected scoped services will then also be disposed. This model looks a bit like ASP.NET actually, an app works a bit like a controller in ASP.NET, it is just that there will not be a single logical execution context associated with it.

We might be able to create a new execution context and then within that execution context create the app and the scope etc. The app can however also respond to other external events which might then not run in the same context.

[FrankBakkerNl]

Aside from the specific scenario, to me it is like having a Parse() method without a TryParse(). The only way to find out if resolving a service is allowed is by doing it and catching the exception if it fails. It would be usefull to be able to avoid that by eg making IsRootScope available via a public interface

[wvpm]

First of all, try not to depend on dependency injection. Request desired services in your constructor instead of requesting IServiceProvider to resolve them on the fly. The first approach makes code clearer, easier to test and usable in a context without DI.

As for a TryResolve, you can call IServiceProvider.GetService(). It returns your service if registered or null if not. (It can be confusing when you registered null as the service.)

As for your original post, I don't understand why you would create a new scope. You can resolve scoped registrations even via the root serviceprovider. Note only the most recent registration is used to resolve an instance. Singleton/Scoped/Transient does not play a role in this. See this example.

using Microsoft.Extensions.DependencyInjection; //.NET 8

int i = 0;
ServiceCollection serviceCollection = new();
serviceCollection.AddSingleton("Singleton"); //only resolvable via GetServices
serviceCollection.AddScoped(_ => i++.ToString());
using ServiceProvider serviceProvider = serviceCollection.BuildServiceProvider();
string? rootString = serviceProvider.GetService<string>(); //not allowed to resolve scoped services in root when building service provider with validate scopes
Console.WriteLine(rootString); //0
using IServiceScope scope = serviceProvider.CreateScope();
string? scopedString = scope.ServiceProvider.GetService<string>();
Console.WriteLine(scopedString); //1

I understand you want to provide context data to a logger. You could register a scoped context (ConcurrentDictionary?) and add data into it for your log enricher to resolve. To ensure you get the log context and not just any ConcurrentDictionary, you can use key scoped services or better a custom type.

Edit:
There is a dirty way to access an internal bool IsRootScope.

using System.Reflection;
using Microsoft.Extensions.DependencyInjection;

Type serviceProviderEngineScope = typeof(ServiceProvider).Assembly.GetType("Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope")!;
PropertyInfo propertyInfo = serviceProviderEngineScope.GetProperty("IsRootScope")!;

string key = "root";
int i = 0;
ServiceCollection serviceCollection = new();
serviceCollection.AddTransient<object>(p => ((bool)propertyInfo.GetValue(p)! ? p.GetKeyedService<string>(key) : p.GetService<string>()) ?? "Nope");
serviceCollection.AddScoped(_ => i++.ToString());
serviceCollection.AddKeyedSingleton(key, "singleton");
using ServiceProvider serviceProvider = serviceCollection.BuildServiceProvider(true);
string? rootString = serviceProvider.GetRequiredService<object>().ToString();
Console.WriteLine(rootString); //singleton
using IServiceScope scope = serviceProvider.CreateScope();
string? scopedString = scope.ServiceProvider.GetRequiredService<object>().ToString();
Console.WriteLine(scopedString); //0
Console.WriteLine(scope.ServiceProvider.GetRequiredService<object>().ToString()); //0

[julealgon]

As for your original post, I don't understand why you would create a new scope. You can resolve scoped registrations even via the root serviceprovider. Note only the most recent registration is used to resolve an instance. Singleton/Scoped/Transient does not play a role in this. See this example.

@wvpm you are only partially correct here.

Your example is too simplistic. When the container is used with Microsoft.Extensions.Hosting, the validateScopes setting is set to true by default, which in turn causes an exception when attempting to resolve a scoped service from the root container:

ServiceCollection services = new();
services.AddScoped<MyClass>();
var provider = services.BuildServiceProvider(validateScopes: true);

var service = provider.GetService<MyClass>();

[wvpm]

@julealgon I am aware of this limitation. That's why I added this comment.

string? rootString = serviceProvider.GetService<string>(); //not allowed to resolve scoped services in root when building service provider with validate scopes

You can specify your service provider to not validate the scopes.
For aspnetcore, see UseDefaultServiceProvider.
For Microsoft.Extensions.Hosting, see UseDefaultServiceProvider.

Note this is a workaround, just like the reflection of internals.
I much prefer (and normally use) the AsyncLocal approach.