如何使用 autofac 注册类型化的 httpClient 服务？

Question

我正在创建 MVC Web 应用程序，它使用 .net core 2.2 调用 api，使用单独的HttpClients 来调用每个控制器（相同的 api）。

前任：

• 对于用户控制器操作：UserService (httpclient)
• 对于后控制器操作：PostService (httpclient)

在startup.cs我使用 DI 作为：

services.AddHttpClient<IUserService, UserService>();
services.AddHttpClient<IPostService, PostService>();

在我的处理程序中：

public class CommandHandler : IRequestHandler<Command, BaseResponse>
{
    private readonly IUserService _userService;

    public CommandHandler(IUserService userService)
    {
        _userService = userService;
    }

    public Task<BaseResponse> Handle(Command request, CancellationToken cancellationToken)
    {
        throw new System.NotImplementedException();
    }
}

但是在调用命令处理程序时，我收到此错误：

在类型“xxx.Application.Services.Users.UserService”上找到的带有“Autofac.Core.Activators.Reflection.DefaultConstructorFinder”的构造函数都不能用可用的服务和参数调用：无法解析参数“System.Net.Http”。构造函数 'Void .ctor(System.Net.Http.HttpClient, xxx.Application.Configurations.IApplicationConfigurations, Microsoft.Extensions.Logging.ILogger`1[xxx.Application.Services.Users.UserService])' 的 HttpClient httpClient'。

但是我已经在 autofac 模块中注册了服务：

public class ServiceModule : Module
{
    protected override void Load(ContainerBuilder builder)
    {
        builder.RegisterAssemblyTypes(typeof(ServiceModule).Assembly)
                .Where(t => t.Namespace.StartsWith("xxx.Application.Services"))
                .AsImplementedInterfaces().InstancePerLifetimeScope();
    }
}

这是我的UserService类构造函数：

public UserService (HttpClient httpClient, IApplicationConfigurations applicationConfig, ILogger<UserService> logger)
{
    _httpClient = httpClient;
    _applicationConfig = applicationConfig;
    _logger = logger;

    _remoteServiceBaseUrl = $"{_applicationConfig.WebApiBaseUrl}";
}

我有两个问题：

1. 上面的错误是什么意思？
2. 在 api 中为不同的控制器使用单独的 httpclients 是一种好习惯吗？

Answer 1

通过做

services.AddHttpClient<IUserService, UserService>();  

您将配置本机 .net 核心依赖项注入HttpClient以UserService在IUserService请求a 时注入。

然后你做

builder.RegisterAssemblyTypes(typeof(ServiceModule).Assembly)
       .Where(t => t.Namespace.StartsWith("xxx.Application.Services"))
       .AsImplementedInterfaces().InstancePerLifetimeScope();

这将删除IUserService. 将IUserService与现在注册UserService，没有任何HttpClient考虑。

添加的最简单方法HttpClient是像这样注册它：

builder.Register(c => new HttpClient())
       .As<HttpClient>();

或者

services.AddHttpClient(); // register the .net core IHttpClientFactory 
builder.Register(c => c.Resolve<IHttpClientFactory>().CreateClient())
       .As<HttpClient>(); 

如果您想为特定服务配置 httpclient，您可以创建一个 autofac 模块，该模块添加如下参数：

public class HttpClientModule<TService> : Module
{
    public HttpClientModule(Action<HttpClient> clientConfigurator)
    {
        this._clientConfigurator = clientConfigurator;
    }

    private readonly Action<HttpClient> _clientConfigurator;

    protected override void AttachToComponentRegistration(IComponentRegistry componentRegistry, IComponentRegistration registration)
    {
        base.AttachToComponentRegistration(componentRegistry, registration);

        if (registration.Activator.LimitType == typeof(TService))
        {
            registration.Preparing += (sender, e) =>
            {
                e.Parameters = e.Parameters.Union(
                  new[]
                  {
                    new ResolvedParameter(
                        (p, i) => p.ParameterType == typeof(HttpClient),
                        (p, i) => {
                            HttpClient client = i.Resolve<IHttpClientFactory>().CreateClient();
                            this._clientConfigurator(client);
                            return client;
                        }
                    )
                  });
            };
        }
    }
}

然后

builder.RegisterModule(new HttpClientModule<UserService>(client =>
{
    client.BaseAddress = new Uri("https://api.XXX.com/");
    client.DefaultRequestHeaders.Add("Accept", "application/vnd.XXX.v3+json");
    client.DefaultRequestHeaders.Add("User-Agent", "HttpClientFactory-XXX");
}));

Answer 2

Cyril 使用 Autofac 模块的实现效果非常好，但不幸的是与 Autofac 6.0+ 不兼容。

为了HttpClient在 Autofac 6.0+ 中配置特定服务，需要实现 Autofac 中间件：

public class HttpClientMiddleware<TService> : IResolveMiddleware
{
    private readonly Action<HttpClient> _clientConfigurator;

    public HttpClientMiddleware(Action<HttpClient> clientConfigurator)
    {
        _clientConfigurator = clientConfigurator;
    }

    public PipelinePhase Phase => PipelinePhase.ParameterSelection;

    public void Execute(ResolveRequestContext context, Action<ResolveRequestContext> next)
    {
        if (context.Registration.Activator.LimitType == typeof(TService))
        {
            context.ChangeParameters(context.Parameters.Union(
                new[]
                {
                    new ResolvedParameter(
                        (p, _) => p.ParameterType == typeof(HttpClient),
                        (_, i) => {
                            var client = i.Resolve<IHttpClientFactory>().CreateClient();
                            _clientConfigurator(client);
                            return client;
                        }
                    )
                }));
        }

        next(context);
    }
}

然后可以利用中间件注册服务：

builder.RegisterType<UserService>()
    .As<IUserService>()
    .ConfigurePipeline(p =>
    {
        p.Use(new HttpClientMiddleware<UserService>(client =>
        {
            client.BaseAddress = new Uri("https://api.XXX.com/");
            client.DefaultRequestHeaders.Add("Accept", "application/vnd.XXX.v3+json");
            client.DefaultRequestHeaders.Add("User-Agent", "HttpClientFactory-XXX");
        }));
    });