如何将 RateLimiter 的 HttpClient DelegatingHandler 与依赖注入一起使用？

Question

我已经在我的项目中成功使用RateLimiter (github) 有一段时间了。我最近发现了依赖注入，并试图按原样迁移我的代码以使用它，但我被困在 RateLimiter 上。

文档中的正常用法是

var handler = TimeLimiter
        .GetFromMaxCountByInterval(25, TimeSpan.FromMinutes(1))
        .AsDelegatingHandler();
var Client = new HttpClient(handler)

但是，如果我尝试在依赖注入期间复制它

    public override void Configure(IFunctionsHostBuilder builder)
    {
        builder.Services.AddHttpClient<IMyApiClient, MyApiClient>(client => client.BaseAddress = new Uri("https://api.myapi.com/"))
               .AddPolicyHandler(GetRetryPolicy())
               .AddHttpMessageHandler(() => TimeLimiter.GetFromMaxCountByInterval(25, TimeSpan.FromMinutes(1)).AsDelegatingHandler());
     }

我收到错误：

[2021-05-17T21:58:00.116Z] Microsoft.Extensions.Http: The 'InnerHandler' property must be null. 'DelegatingHandler' instances provided to 'HttpMessageHandlerBuilder' must not be reused or cached.
[2021-05-17T21:58:00.117Z] Handler: 'ComposableAsync.DispatcherDelegatingHandler'.
[2021-05-17T21:58:00.122Z] An unhandled host error has occurred.

我的类客户端结构（主要是为了单元测试）如下所示：

using System.Net.Http;
using System.Threading.Tasks;

public class MyApiClient : HumbleHttpClient, IMyApiClient
{
    public MyApiClient(HttpClient client)
        : base(client)
    {
    }
}

public class HumbleHttpClient : IHttpClient
{
    public HumbleHttpClient(HttpClient httpClient)
    {
        this.Client = httpClient;
    }

    public HttpClient Client { get; }

    public Task<HttpResponseMessage> GetAsync(string requestUri)
    {
        return this.Client.GetAsync(requestUri);
    }

    public Task<HttpResponseMessage> PostAsync(string requestUri, HttpContent content)
    {
        return this.Client.PostAsync(requestUri, content);
    }
}

public interface IHttpClient
{
    Task<HttpResponseMessage> GetAsync(string requestUri);
    Task<HttpResponseMessage> PostAsync(string requestUri, HttpContent content);
    HttpClient Client { get; }
}

这些是我一直在努力关注的文档： https://docs.microsoft.com/en-us/dotnet/architecture/microservices/implement-resilient-applications/use-httpclientfactory-to-implement-resilient-http-requests

Answer 1

我不知道这是错误还是功能，但要解决此问题，我相信您还需要将委托处理程序添加为 Transient。

因此，在典型情况下，您会这样设置DelegatingHandler：

public sealed class MyDelegatingHandler : DelegatingHandler
{
    // ...
}

然后你需要注册它；但问题是……您还需要将处理程序注册为 Transient：

public override void Configure(IFunctionsHostBuilder builder)
{
    builder.Services.AddHttpClient<IMyHttpService, MyHttpService>()
        .AddHttpMessageHandler<MyDelegatingHandler>();

    // this needs to be added:
    builder.Services.AddTransient<MyDelegatingHandler>();
}

话虽如此，您处于一种独特的情况，因为您要使用的处理程序是在运行时从第 3 方创建的。你可以让这个工作......如果它是正确的，不是 100%，但它应该工作：

public override void Configure(IFunctionsHostBuilder builder)
{
    var handler = TimeLimiter
        .GetFromMaxCountByInterval(25, TimeSpan.FromMinutes(1))
        .AsDelegatingHandler();

    builder.Services.AddHttpClient<IMyApiClient, MyApiClient>(
            client => client.BaseAddress = new Uri("https://api.myapi.com/"))
        .AddPolicyHandler(GetRetryPolicy())
        .AddHttpMessageHandler(() => handler);

    builder.Services.AddTransient(_ => handler);
}

编辑添加...

您看到的问题与ComposableAsync Nuget 包有关。特别是this line。代码不应设置此属性。 ASP.NET Core 应该/将会这样做。幸运的是，这只是一个简单的扩展方法。

让我们编写自己的扩展程序，以正确的方式完成：

using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

namespace YourNamespace
{
    public static class DispatcherExtension
    {
        private sealed class DispatcherDelegatingHandler : DelegatingHandler
        {
            private readonly ComposableAsync.IDispatcher _Dispatcher;

            public DispatcherDelegatingHandler(ComposableAsync.IDispatcher dispatcher)
            {
                _Dispatcher = dispatcher;
            }

            protected override Task<HttpResponseMessage> SendAsync(
                HttpRequestMessage request,
                CancellationToken cancellationToken)
            {
                return _Dispatcher.Enqueue(() =>
                    base.SendAsync(request, cancellationToken), cancellationToken);
            }
        }

        public static DelegatingHandler AsDelegatingHandler(
            this ComposableAsync.IDispatcher dispatcher)
        {
            return new DispatcherDelegatingHandler(dispatcher);
        }
    }
}

确保将您的代码更改为我在上面注册处理程序时的代码。此外，请确保它使用的是 new 扩展而不是库中的扩展。

我对其进行了测试，您可以看到它设置正确：

我还会考虑在 ComposableAsync github 页面中打开一个错误。