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Asp.net – How to use "TypedHttpClientFactory" with "AddHttpMessageHandler"?

I have some AuthorizationHandler that I register with a typed client:

    var clientFactory = services.BuildServiceProvider().GetRequiredService<IHttpClientFactory>();
    services.AddHttpClient<TypedClient>()
        .AddHttpMessageHandler(() =>
        {
            var authorization = new BearerAuthorization(clientFactory, clientId, clientSecret, authHost, token);
            return new AuthorizationHandler(authorization);
        });

When I get the "TypedClient" directly through the DI container, everything works fine and the AuthorizationHandler handler is called before the request, for example, like this:

    _typedClient = serviceProvider.GetRequiredService<TypedClient>();
    await _typedClient.SendRequest(); // OK

BUT. When trying to get this client from the ITypedHttpClientFactory factory, the handler stops being called, which gives an authorization error:

    _httpClientFactory = serviceProvider.GetRequiredService<IHttpClientFactory>();
    _typedClientFactory = serviceProvider.GetRequiredService<ITypedHttpClientFactory<TypedClient>>();
    using var client = _httpClientFactory.CreateClient();
    using var typedClient = _typedClientFactory.CreateClient(client);

    await typedClient.SendRequest(); // Fail

How do I get a typed client from the factory that will have the added handler called before the request?

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2

Answers


  1. 0

    This is expected, as the ITypedHttpClientFactory documentation states:

    The default ITypedHttpClientFactory<TClient> uses type activation to create typed client instances. Typed client types are not retrieved directly from the IServiceProvider. See CreateInstance(IServiceProvider, Type, Object[]) for details.

    So, here’s answer to your question:

    Typed client types are not retrieved directly from the IServiceProvider.

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  2. 0

    One way to solve this problem is to inject a named client into the typed client via the ITypedHttpClientFactory‘s CreateClient method. Whenever you fetch a named HttpClient then it will retrieve it from the DI with all of its DelegatingHandlers.

    Here you can find a working example: https://dotnetfiddle.net/wC4Neg

    Service registrations

    ServiceCollection collection  = new();
collection.AddTransient<TestDelegatingHandler>();
collection.AddHttpClient();
collection.AddHttpClient<ITypedClient, TypedClient>("test")
    .AddHttpMessageHandler(sp => sp.GetService<TestDelegatingHandler>());
    • Here we register a dummy DelegatingHandler into the DI container first
    • Then we register the default HttpClient factories
    • Finally we register a typed client which is named test
      • Here we add the MessageHandler to the named client

    Client creations

    ServiceProvider provider = collection.BuildServiceProvider();
IHttpClientFactory namedFactory = provider.GetRequiredService<IHttpClientFactory>();
ITypedHttpClientFactory<TypedClient> typedFactory  = provider.GetRequiredService<ITypedHttpClientFactory<TypedClient>>();

HttpClient namedClient = namedFactory.CreateClient("test");
TypedClient typedClient = typedFactory.CreateClient(namedClient);
    • First we build the ServiceCollection
    • Then we retrieve an IHttpClientFactory and an ITypedHttpClientFactory service
    • Thirdly we fetch the named client .CreateClient("test")
      • This client is decorated with the dummy DelegatingHandler
    • Finally we create a TypedClient instance via the ITypedHttpClientFactory by injecting the previously fetched named HttpClient

    Supporting structures

    public interface ITypedClient
{
    Task GetAsync();
}

public class TypedClient: ITypedClient
{
    private readonly HttpClient _client;
    public TypedClient(HttpClient client) => _client = client;
    
    public async Task GetAsync() => await _client.GetAsync("http://stackoverflow.com");
}

public class TestDelegatingHandler: DelegatingHandler
{
    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        "Hello".Dump();
        return await base.SendAsync(request, cancellationToken);
    }
}
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