使用工厂方法创建类型化的HTTP客户端ASP.NET Core 2.1

Question

I'm following guides/docs on registering HTTP client within my application. There are couple of services I need to call so I decided to go with "Typed clients".

In order to call another service I need to use OAuth - since this is service-to-service call, when I obtain access token, I cache it + I have setup periodical refresh of token. This means there's another component IAccessTokenCache which gives me access token for service.

Thing I'm struggling to figure out is how to register and configure my typed HTTP client providing it also dependency on IAccessTokenCache .

I'm using ASP.NET Core 2.1 (crucial detail, read on).

HTTP client wrapper looks like this (from: HttpClientFactory in ASP.NET Core 2.1 (Part 2) ):

public class ServiceFooClient
{
    public ServiceFooClient(HttpClient client)
    {
        Client = client;
    }

    public HttpClient Client { get; }
}

And this is how I register and configure client:

services
    .AddHttpClient<ServiceFooClient>(
        c =>
        {
            c.BaseAddress = new Uri("https://www.foo.svc");

            // TODO: grab particular access token from cache
            c.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", "...");
        })
    .AddHttpMessageHandler<ResponseMonitorHandler>()
    .ConfigureHttpMessageHandlerBuilder(
        b =>
        {
            var handler =
                b.AdditionalHandlers.OfType<ResponseMonitorHandler>().FirstOrDefault();

            if (handler != null)
            {
                handler.ServiceName = "Foo Service";
            }
        });

... I'm already configuring HTTP client and even adding my custom HTTP handler. You can see exact point where I want to access IAccessTokenCache , but I can't.

Possible solutions I can think of:

Configure underlying HttpClient in ServiceFooClient wrapper, like:

// ctor
public ServiceFooClient(HttpClient httpClient, IAccessTokenCache tokenCache)
{
    Client = httpClient;
    Client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", tokenCache.GetToken("Foo"));
}

This could work nicely, except I don't configuration decoupling - suddenly dedicated HTTP client has part of configuration in Startup (base URI, additional HTTP handler) and another part in wrapping class (setting authorization header).

Not using AddHttpClient extension method (and others)

I don't really need to call HttpClientFactoryServiceCollectionExtensions.AddHttpClient<T>(...) - I could do all that stuff myself. But as lazy developer... I don't even want to finish this sentence. There's quite a lot of registering inside, so this is just big no no for me.

Upgrade to ASP.NET Core 2.2

Related to previous point - in 2.1, there's no overload of AddHttpClient (2.2: AddHttpClient<TClient>(this IServiceCollection services, Action<IServiceProvider, HttpClient> configureClient) ) which would accept callback with service provider. Upgrading to 2.2 would be probably the best solution, yet I will have to be pretty sure that nothing else gets broken (and I already know that there is/was BC break with getting/setting request tracing ID on HTTP context). This could be potentially risky, so I'm trying first to solve my issue in scope of 2.1.

Compare branch of 2.1 with 2.2: HttpClientFactoryServiceCollectionExtensions

Custom HTTP handler setting request headers

Same way as I now register ResponseMonitorHandler , I could register HTTP handler which has access to IAccessTokenCache and sets request authorization header.

But again, as in first case, this decouples configuration of HTTP client. Also if I had several different access tokens, I would either need to implement several HTTP handlers or do some logic deciding what token from cache to use based on request properties.

Finally, question : is there any other way I didn't consider? Is there easy solution of this in ASP.NET 2.1? (... apart of just copy-pasting method from 2.2 of course)

Answer 1

显然，在2.1 ConfigureHttpClient(IHttpClientBuilder, Action<IServiceProvider,HttpClient>)中还有另一种扩展方法，它完全ConfigureHttpClient(IHttpClientBuilder, Action<IServiceProvider,HttpClient>)我的需要！