在 ASP.NET 核心中访问 HttpClientFactory 定义中的外部参数/值

Question

我有一个使用 Polly 策略的 httpclient：

services.AddHttpClient("MyClient", (serviceProvider, client) =>
        {
            var X = External_PARAMETER;
            client.BaseAddress = new Uri(settings.BaseUrl);
            .....
        })
        .AddPolicyHandler(retryPolicy)
        .AddPolicyHandler((provider, httpRequestMessage) => GetTokenPolicy(provider, httpRequestMessage));

当从这个命名的客户端创建 clienthttp 时，我想动态地传递一些参数给它，比如：

var httpClient = httpClientFactory.CreateClient("MyClient", External_PARAMETER);

我知道一种解决方案实际上是使用这样的单例服务并传递值： 据我所知，您不能在 AddHttpClient 定义中使用瞬态或范围服务。如果我使用非 sington 的，我会收到此错误（无法从根提供商解析范围服务“MyApp.IMyService”。））

services.AddHttpClient("MyClient", (serviceProvider, client) =>
        {
            var passedServer = serviceProvider.GetService<IMyService>();
            var X = passedServer.GetMyParameter();
            client.BaseAddress = new Uri(settings.BaseUrl);
            .....
        })
        .AddPolicyHandler(retryPolicy)
        .AddPolicyHandler((provider, httpRequestMessage) => GetTokenPolicy(provider, httpRequestMessage));

services.AddSingleton<IMyService, MyService>();
.
.
.
myServiceInstance.SetMyParameter("A_VALUE");
var httpClient = httpClientFactory.CreateClient("MyClient");

但是如果不使用像 MyService 这样的单例服务，我该如何实现呢？

在某些情况下，HTTP 请求应该创建一个 HttpClient 并且拥有一个 sington 服务意味着所有请求都可以访问这个不理想的单例服务。

Answer 1

据我所知，我们可以尝试为httpclient设置DelegatingHandler，这个DelegatingHandler可以注册为Transient。

更多细节，你可以参考下面的例子：

处理程序：

public class TraceLogHandler : DelegatingHandler
{
    private readonly IHttpContextAccessor _httpContextAccessor;
    private readonly ILogger<TraceLogHandler> _logger;
    private readonly bool _canLog;
    private StringValues ipAddress;

    public TraceLogHandler(IHttpContextAccessor httpContextAccessor, ILogger<TraceLogHandler> logger)
    {
        _httpContextAccessor = httpContextAccessor;
        _logger = logger;
    }

    public TraceLogHandler(IHttpContextAccessor httpContextAccessor, ILogger<TraceLogHandler> logger, bool canLog)
    {
        _httpContextAccessor = httpContextAccessor;
        _logger = logger;
        _canLog = canLog;
    }

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        // here you could modify the http request
        int i = 0;

        return new HttpResponseMessage();
        //blah blah code for custom logging
    }
}

Startup.cs：

services.AddTransient<TraceLogHandler>();
services.AddHttpClient<ICountryRepositoryClient, CountryRepositoryClientV2>()
    .ConfigureHttpClient(c => c.BaseAddress = new Uri("https://localhost"))
    .AddHttpMessageHandler((services) =>
    {
        return new TraceLogHandler(services.GetRequiredService<IHttpContextAccessor>(),
                                   services.GetRequiredService<ILogger<TraceLogHandler>>());
    });

Answer 2

您可以尝试使用 .NET 中的 Options pattern。

它允许您创建和访问一组命名的单例设置，而不是创建一个提供值的单例服务，因此您可以为每个命名的 HTTP 客户端创建一个设置：

class MyHttpClientOptions
{
    public string BaseUri { get; set; }
}

services.Configure<MyHttpClientOptions>("MyClient", opt =>
{
    opt.BaseUri = "https://url1";
});

services.Configure<MyHttpClientOptions>("MyClient2", opt =>
{
    opt.BaseUri = "https://url2";
});

您可以在创建HttpClient 时访问命名设置：

services.AddHttpClient("MyClient", (serviceProvider, client) =>
{
    var options = serviceProvider
        .GetRequiredService<IOptionsMonitor<MyHttpClientOptions>>()
        .Get("MyClient");

    client.BaseAddress = new Uri(options.BaseUri);
});

更新

如果某些值确实必须从请求的上下文中获取，并且无法设置到创建它的客户端，您可以添加一个使用 IHttpContextAccessor 的自定义构建器：

services.AddHttpClient("MyClient1");
services.AddOptions<HttpClientFactoryOptions>("MyClient1")
    .Configure<IHttpContextAccessor>((opt, httpContextAccessor) =>
    {
        opt.HttpClientActions.Add(client =>
        {
            var httpContext = httpContextAccessor.HttpContext;

            // If you have scoped service to create in the request context
            httpContext.RequestServices.GetRequiredService<MyScopedService>();

            // Shared key value pairs
            httpContext.Items["some key"]
        });
    });