IHttpClientFactory in ASP.NET Core Typed Clients

Question

I receive an error when I try to use a typed client for HttpClient as documented here: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/http-requests?view=aspnetcore-2.2

Here is my setup:

Startup.cs:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

    services.AddDefaultAWSOptions(Configuration.GetAWSOptions());

    services.AddHttpClient<IPStackService>(c =>
    {
        c.BaseAddress = new Uri(Configuration["IPStackURL"]);
    });

    services.AddHttpContextAccessor();

    services.AddTransient<IIPStackService, IPStackService>();
}

Controller:

[Route("api/[controller]")]
    [ApiController]
    public class RenderController : ControllerBase
    {
        private IConfiguration _configuration;
        private readonly ILogger _logger;
        private IIPStackService _ipMetaDataService;

        public RenderController(IConfiguration configuration,
                                ILogger<RenderController> logger,
                                IIPStackService ipStackService)
        {
            _configuration = configuration;
            _ipStackService = ipStackService;
            _logger = logger;
        }

        [HttpGet]
        [ProducesResponseType(StatusCodes.Status200OK)]
        [Produces("text/plain")]
        public async Task<ActionResult> GetAsync(string hostId, string clientUtc)
        {
            var ip = Common.ResolveIPAddress(HttpContext);

            var ipMetaData = await _ipStackService.GetByIPAsync(ip, _configuration["AccessKey"]);

            // removed for clarity

            return allowed ? Ok(true) : Ok(null);
        }
    }

Service:

public class IPStackService : IIPStackService
{
    private readonly ILogger _logger;
    private readonly HttpClient _httpClient;

    public IPStackService(ILogger<IPStackService> logger, HttpClient client)
    {
        _logger = logger;
        _httpClient = client;
    }

    public async Task<IPMetaDataModel> GetByIPAsync(string ip, string accessKey)
    {
        var ipMetaData = new IPMetaDataModel();

        var response = await _httpClient.GetAsync($"/{ip}?access_key={accessKey}");
        response.EnsureSuccessStatusCode();

        // removed for clarity

        return ipMetaData;
    }
}

Error received:

An unhandled exception occurred while processing the request. InvalidOperationException: Unable to resolve service for type 'System.Net.Http.HttpClient' while attempting to activate 'WebScreen.Gate.Services.IPStackService'. Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateArgumentCallSites(Type serviceType, Type implementationType, CallSiteChain callSiteChain, ParameterInfo[] parameters, bool throwIfCallSiteNotFound)

How do I setup typed clients properly for HttpClient?

Answer 1

The Activator for IPStackService (code reflection) cannot find the HttpClient in the DI collection, that's why you got the exception (specifically for the services.AddTransient<IIPStackService, IPStackService>()).

BTW, you a added the service IPStackService twice in your DI collection:

1. services.AddHttpClient<IPStackService>(...);.
2. services.AddTransient<IIPStackService, IPStackService>();

You only need one, and since you are using typed client you can solve your issue by removing the second one and keep the first, and alter the first one a tiny bit by adding the contract to the implementation, as follow:

services.AddHttpClient<IIPStackService, IPStackService>(c =>
{
     c.BaseAddress = new Uri(Configuration["IPStackURL"]);
});

The AddHttpClient will take care of binding the HttpClinet to your service.

---

And in case you want to use services.AddTransient<IIPStackService, IPStackService>(); instead of services.AddHttpClient, then you need to add the HttpClinet to your DI Collection as:

services.AddTransient<HttpClient>();