Resolves #170

What is the feature

Implement support for a custom Inversion of Control (IoC) container by integrating the .NET method HostBuilder.UseServiceProviderFactory. This feature introduces a custom service provider factory that allows the application to use a tailor-made IoC container, aligning with standards from established IoC libraries without relying on external dependencies.

Why we need the feature

Our current service registry lacks support for UseServiceProviderFactory, limiting our flexibility in dependency management and service configuration. By implementing a custom IoC container, we can:

• Enhance Dependency Management: Provide advanced techniques for managing dependencies, including modular registrations and custom lifecycles.
• Increase Flexibility: Allow developers to customize how services are registered and resolved, accommodating complex scenarios.
• Align with Best Practices: Follow established patterns from well-known IoC containers, improving code maintainability and scalability.
• Avoid External Dependencies: Achieve the benefits of popular IoC libraries without adding external library dependencies to the project.

How to implement and why

Step 1: Design a Custom IoC Container

• Create Core Functionality:

  • Implement classes for dependency registration, resolution, and lifecycle management (singleton, scoped, transient).
  • Ensure the container supports generic type registration and open generic types.

• Adhere to Standards:

  • Follow design patterns from libraries like Autofac and Castle Windsor, such as fluent interfaces for registration and support for advanced scenarios.
  • Implement service interception and decorators if necessary.

Step 2: Implement the UseServiceProviderFactory Method

• Create the Service Provider Factory:

  • Implement the IServiceProviderFactory<TContainerBuilder> interface with our custom container builder.
  • Example:

    public class CustomServiceProviderFactory : IServiceProviderFactory<CustomContainerBuilder>
    {
        public CustomContainerBuilder CreateBuilder(IServiceCollection services)
        {
            var builder = new CustomContainerBuilder();
            builder.Populate(services);
            return builder;
        }
    
        public IServiceProvider CreateServiceProvider(CustomContainerBuilder containerBuilder)
        {
            return containerBuilder.BuildServiceProvider();
        }
    }

• Integrate with HostBuilder:

  • Modify the application's entry point to use the custom service provider factory.

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .UseServiceProviderFactory(new CustomServiceProviderFactory())
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });

Step 3: Extend Service Registration Capabilities

• Implement Registration Methods:

  • Provide methods for registering services with different lifetimes and options.

    public class CustomContainerBuilder
    {
        public void RegisterTransient<TService, TImplementation>() where TImplementation : TService
        {
            // Implementation
        }
    
        public void RegisterScoped<TService, TImplementation>() where TImplementation : TService
        {
            // Implementation
        }
    
        public void RegisterSingleton<TService, TImplementation>() where TImplementation : TService
        {
            // Implementation
        }
    
        public void Populate(IServiceCollection services)
        {
            // Transfer registrations from IServiceCollection to the custom container
        }
    
        public IServiceProvider BuildServiceProvider()
        {
            // Build and return the IServiceProvider
        }
    }

• Support Advanced Features:

  • Enable open generic registrations, conditional registrations, and constructor injection.

Step 4: Test the Integration Thoroughly

• Unit Testing:

  • Write unit tests to verify that services are registered and resolved correctly.
  • Test different lifecycles and ensure that scoped services behave as expected.

• Integration Testing:

  • Validate that the application starts up correctly using the custom IoC container.
  • Ensure that middleware and other framework integrations work without issues.

Step 5: Documentation and Examples

• Provide Clear Documentation:

  • Explain how to register and resolve services using the new IoC container.
  • Include examples of common scenarios and best practices.

• Update Existing Documentation:

  • Modify any existing documentation to reflect the new options available for dependency injection.

About backward compatibility

The introduction of the custom IoC container is designed to be fully backward compatible:

• Optional Adoption: Existing applications can continue using the default service provider without any changes. The custom IoC container is an opt-in feature.
• Non-Intrusive Changes: The implementation does not alter existing service registrations or resolutions unless the custom service provider factory is explicitly used.
• Compatibility Layer: The custom container will respect the registrations made in IServiceCollection, ensuring that services behave as before unless overridden.
• Gradual Migration: Developers can migrate to the custom IoC container at their own pace, testing and verifying functionality in stages.

By ensuring backward compatibility, we allow current users to benefit from the new feature without disrupting existing functionality.

Test these changes locally

git checkout -b gitauto/issue-#170-eb0577d7-c1a9-4900-b082-96a8cc77ee04
git pull origin gitauto/issue-#170-eb0577d7-c1a9-4900-b082-96a8cc77ee04