Add named and typed clients section

[peter-csala]

This PR is basically a follow up of my other PR against the dotnet/docs repository.

It extends the Make HTTP requests using IHttpClientFactory in ASP.NET Core page with named and typed client capability.

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aspnetcore/fundamentals/http-requests.md	Make HTTP requests using IHttpClientFactory in ASP.NET Core

[Rick-Anderson]

@IEvangelist I'll do the edit review after you do the technical review.

[peter-csala]

@IEvangelist Hi David, can I ask you to please review my PR?

[IEvangelist]

I had a look, seems ok - but let's please have @CarnaViire review this for technical accuracy instead.

[CarnaViire]

In general, I believe this is the case where you should use just an ordinary Transient service instead of a typed client.

That service could either

1. use IHttpClientFactory and incapsulate multiple named clients inside

service.UseNamedClient();
service.UseOtherClient();

/* Output:
Name=NamedClient, BaseAddress=https://some-uri/
Name=OtherNamedClient, BaseAddress=https://other-uri/
*/

class Service(IHttpClientFactory _httpClientFactory /*, ... */)
{
    private void UseHttpClient(string name) => Console.WriteLine($"Name={name}, BaseAddress={_httpClientFactory.CreateClient(name).BaseAddress}");
    public void UseNamedClient() => UseHttpClient("NamedClient");
    public void UseOtherClient() => UseHttpClient("OtherNamedClient");
}

-OR-

2. Have an instance of HttpClient passed as a parameter to the method each time

foreach (var name in new[] {"NamedClient", "OtherNamedClient" })
{
    service.UseHttpClient(name, _httpClientFactory.CreateClient(name));
}

/* Output:
Name=NamedClient, BaseAddress=https://some-uri/
Name=OtherNamedClient, BaseAddress=https://other-uri/
*/

class Service(/* ... */)
{
    private void UseHttpClient(string name, HttpClient client) => Console.WriteLine($"Name={name}, BaseAddress={client.BaseAddress}");
}

-OR-

3. Leverage Keyed Services DI Pattern (and it can even be non-transient in such case):

using Microsoft.Extensions.DependencyInjection;

var services = new ServiceCollection();

services.AddHttpClient("NamedClient", c => c.BaseAddress = new Uri("https://some-uri"));
services.AddHttpClient("OtherNamedClient", c => c.BaseAddress = new Uri("https://other-uri"));

services.AddKeyedSingleton<Service>(KeyedService.AnyKey); // instead of a typed client
services.AddSingleton<TwoNamesDependentService>();

var provider = services.BuildServiceProvider();

var dependentService = provider.GetRequiredService<TwoNamesDependentService>();
dependentService.UseServices();

/* Output:
Name=NamedClient, BaseAddress=https://some-uri/
Name=OtherNamedClient, BaseAddress=https://other-uri/
*/

class Service([ServiceKey] string _name, IHttpClientFactory _httpClientFactory)
{
    private HttpClient Client => _httpClientFactory.CreateClient(_name);
    public void UseHttpClient() => Console.WriteLine($"Name={_name}, BaseAddress={Client.BaseAddress}");
}

class TwoNamesDependentService([FromKeyedServices("NamedClient")] Service _service, [FromKeyedServices("OtherNamedClient")] Service _otherService)
{
    public void UseServices()
    {
        _service.UseHttpClient();
        _otherService.UseHttpClient();
    }
}

[CarnaViire]

This exact scenario should be handled not by multiple clients, but by resilience strategies applied via Polly

[CarnaViire]

Thanks for tagging me @IEvangelist!

While I appreciate your contribution @peter-csala I believe this is not a good guidance, see my comment #32456 (comment). If you strongly believe using multiple named clients should be highlighted in the docs, I'd propose to change the guidance to the one I provided in the comment.

I see that dotnet/docs#40359 was merged but I missed it -- @IEvangelist I think we would need to either revert it or substitute it with the guidance from #32456 (comment).

On a side note:
I also keep thinking that we need to make some effort to reduce duplications between the docs -- as HttpClientFactory belongs to BCL now, it would be better to have the conceptual docs there, and only leave ASP.NET Core related stuff here, and redirect to .NET docs otherwise. But this needs to be done carefully, not to disrupt the users flow. Let's discuss it later @IEvangelist

[peter-csala]

Thank you @CarnaViire for the review. I agree that my made up example is not the best. I wanted to create a simple example to showcase the usage of named and typed clients because (for some unknown reason) they are not listed on any of the documentation pages. Neither here nor on the dotnet docs.

Do you have any idea what would be an ideal sample scenario for this?