Configure/register depdency injection scoped service from within the scope - dependency-injection

Question

I have a stateless service in Azure Service Fabric, and I'm using Microsoft.Extensions.DependencyInjection, although the same issue exists for any other DI frameworks. In my Program.cs, I create a ServiceCollection, add all (but one) of my registrations, create the service provider, and pass it to my service's constructor. Any service method with external entry will create a new service scope and call the main business logic class. The issue is that one of the classes I want to have scoped lifetime needs a value that is an input parameter on the request itself. Here's a code snippet of what I would like to achieve.
internal sealed class MyService : StatelessService, IMyService
{
private IServiceProvider _serviceProvider;
private IServiceScopeFactory _scopeFactory;
public MyService(StatelessServiceContext context, IServiceProvider serviceProvider)
: base(context)
{
_serviceProvider = serviceProvider;
_scopeFactory = _serviceProvider.GetRequiredService<IServiceScopeFactory>();
}
public async Task<MyResponse> ProcessAsync(MyRequest request, string correlationId, CancellationToken cancellationToken)
{
using (var scope = _scopeFactory.CreateScope())
{
var requestContext = new RequestContext(correlationId);
//IServiceCollection serviceCollection = ??;
//serviceCollection.AddScoped<RequestContext>(di => requestContext);
var businessLogic = scope.ServiceProvider.GetRequiredService<BusinessLogic>();
return await businessLogic.ProcessAsync(request, cancellationToken);
}
}
}
The cancellation token is already passed around everywhere, including to classes that don't use it directly, just so it can be passed to dependencies that do use it, and I want to avoid doing the same with the request context.
The same issue exists in my MVC APIs. I can create middle-ware which will extract the correlation id from the HTTP headers, so the API controller doesn't need to deal with it like my service fabric service does. One way I can make it work is by giving RequestContext a default constructor, and have a mutable correlation id. However, it's absolutely critical that the correlation id doesn't get changed during a request, so I'd really like the safety of having get-only property on the context class.
My best idea at the moment is to have a scoped RequestContextFactory which has a SetCorrelationId method, and the RequestContext registration simply calls the factory to get an instance. The factory can throw an exception if a new instance is requested before the id is set, to ensure no id-less contexts are created, but it doesn't feel like a good solution.
How can I cleanly register read-only objects with a dependency injection framework, where the value depends on the incoming request?

Answer 1

I only had the idea for a RequestContextFactory as I was writing the original question, and I finally made time to test the idea out. It actually was less code than I expected, and worked well, so this will be my go-to solution now. But, the name factory is wrong. I'm not sure what to call it though.
First, define the context and factory classes. I even added some validation checks into the factory to ensure it worked the way I expect:
public class RequestContext
{
public RequestContext(string correlationId)
{
CorrelationId = correlationId;
}
public string CorrelationId { get; }
}
public class RequestContextFactory
{
private RequestContext _requestContext;
private bool _used = false;
public void SetContext(RequestContext requestContext)
{
if (_requestContext != null || requestContext == null)
{
throw new InvalidOperationException();
}
_requestContext = requestContext;
}
public RequestContext GetContext()
{
if (_used || _requestContext == null)
{
throw new InvalidOperationException();
}
_used = true;
return _requestContext;
}
}
Then, add registrations to your DI container:
services.AddScoped<RequestContextFactory>();
services.AddScoped<RequestContext>(di => di.GetRequiredService<RequestContextFactory>().GetContext());
Finally, the Service Fabric service method looks something like this
public async Task<MyResponse> ProcessAsync(MyRequest request, string correlationId, CancellationToken cancellationToken)
{
using (var scope = _scopeFactory.CreateScope())
{
var requestContext = new RequestContext(correlationId);
var requestContextFactory = scope.ServiceProvider.GetRequiredService<RequestContextFactory>();
requestContextFactory.SetContext(requestContext);
var businessLogic = scope.ServiceProvider.GetRequiredService<BusinessLogic>();
return await businessLogic.ProcessAsync(request, cancellationToken);
}
}
Kestrel middleware could look something like this
public async Task Invoke(HttpContext httpContext)
{
RequestContext requestContext = new RequestContext(Guid.NewGuid().ToString());
var factory = httpContext.RequestServices.GetRequiredService<RequestContextFactory>();
factory.SetContext(requestContext);
httpContext.Response.Headers["X-CorrelationId"] = requestContext.CorrelationId;
await _next(httpContext);
}
Then just do the normal thing and add a RequestContext parameter to the constructor of any class that needs to get the correlation id (or any other info you put in the request context)