Support of DI

[ycrumeyrolle]

Check may support DI on ctor.

[bradwilson]

@ycrumeyrolle Please take a look at PR #50, as this makes significant changes in support of DI. I hope based on our previous discussions you will probably be happier with the post-DI design than the pre-DI design. :) Thanks!

[ycrumeyrolle]

@bradwilson It is much better, but... I am wondering how to implement an HealthCheck with an existing registered transient service, requiring parameters to check.

services.AddTransient<IWonderfulService, WonderfulService>();

where IWonderfulService looks like

public interface IWonderfulService
{
  void DoSomething(string someValue);
}

I would like to avoid to wrap existing services into a HealthCheckAdapter or something similar.

Adding a HealthCheckContext parameter to the IHealthCheck.CheckHealthAsync() would allow to pass values. Maybe something similar to the AuthZ service ?

[bradwilson]

I'm not sure what you're after here. You should just be able to ask for the IWonderService constructor argument to get it for DI. What is the purpose of the context?

[ycrumeyrolle]

What I would like to do :

healthCheckBuilder.AddMyService(testingValue: "special value for test purpose")

I have this kind of interface (basically, a method with value parameter)

// This interface is an existing interface and should not be modified. 
public interface IMyService 
{
  void DoSomething(string someValue);
}

I see two ways to implement a IHealthCheck for this service. With a DI-friendly HealthCheck :

public class MyServiceHealthCheckByDI : IHealthCheck
{
  private readonly IMyService _myService;
  public MyServiceHealthCheck(IMyService service)
  {
    _myService = service;
  }

  public async ValueTask<IHealthCheckResult> CheckAsync(CancellationToken cancellationToken = default(CancellationToken))
  {
    try
    {
      // How can set this value with the HealthCheckBuilder? 
      var testingValue = "special value for test purpose";
      _myService.DoSomething(testingValue);
      return HealthCheckResult.Healthy("OK");
    }
    catch(Exception e)
    {
      return HealthCheckResult.Unhealthy(e.ToString());
    }
  }
}

I do not know how to pass the required value to the HealthCheck.

With a non DI-Friendly HealthCheck :

public class MyServiceHealthCheckWithoutDI : IHealthCheck
{
  private readonly IMyService _myService;
  private readonly string _testingValue;
  public MyServiceHealthCheck(string testingValue)
  {
    _testingValue = testingValue;
    // Not DI Friendly
    _myService = new MyServiceImplementation(new MyServiceImplementationDependency(new MyServiceImplementationDependencyDependency(...)));
  }

  public async ValueTask<IHealthCheckResult> CheckAsync(CancellationToken cancellationToken = default(CancellationToken))
  {
    try
    {
      _myService.DoSomething(_testingValue);
      return HealthCheckResult.Healthy("OK");
    }
    catch(Exception e)
    {
      return HealthCheckResult.Unhealthy(e.ToString());
    }
  }
}

I can pass the value parameter with the HealthCheck constructor, but it is not DI-compliant anymore...

[bradwilson]

Registration of services is outside the scope of health checks.

That said, there are lambda versions of DI registration that do what you want:

public static IServiceCollection RegisterMyService(this IServiceCollection serviceCollection, string testingValue)
    => serviceCollection.AddSingleton<IMyService>(serviceProvider => new MyServiceImplementation(testingValue));