如何在 .NET Core 中使用 HttpClientHandler 和 HttpClientFactory

Question

我想使用 .NET Core 2.1 中可用的 HttpClientFactory，但我还想使用 HttpClientHandler 在创建时利用 AutomaticDecompression 属性 HttpClients.

我很挣扎，因为 .AddHttpMessageHandler<> 需要 DelegatingHandler 而不是 HttpClientHandler。

有人知道如何让它工作吗？

谢谢， 吉姆

Answer 1

其实我并没有使用自动解压，但是实现这个的方法是正确注册http客户端

services.AddHttpClient<MyCustomHttpClient>()
   .ConfigureHttpMessageHandlerBuilder((c) =>
     new HttpClientHandler()
     {
        AutomaticDecompression = System.Net.DecompressionMethods.GZip
     }
   )
   .AddHttpMessageHandler((s) => s.GetService<MyCustomDelegatingHandler>())

Answer 2

通过 HttpClientBuilder 的 ConfigurePrimaryHttpMessageHandler() 方法定义主 HttpMessageHandler 更合适。请参阅下面的示例以配置类型化客户端。

services.AddHttpClient<TypedClient>()
    .ConfigureHttpClient((sp, httpClient) =>
    {
        var options = sp.GetRequiredService<IOptions<SomeOptions>>().Value;
        httpClient.BaseAddress = options.Url;
        httpClient.Timeout = options.RequestTimeout;
    })
    .SetHandlerLifetime(TimeSpan.FromMinutes(5))
    .ConfigurePrimaryHttpMessageHandler(x => new HttpClientHandler() 
    {
        AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate;
    })
    .AddHttpMessageHandler(sp => sp.GetService<SomeCustomHandler>().CreateAuthHandler())
    .AddPolicyHandlerFromRegistry(PollyPolicyName.HttpRetry)
    .AddPolicyHandlerFromRegistry(PollyPolicyName.HttpCircuitBreaker);

您还可以通过使用 Polly 库的特殊构建器方法来定义错误处理策略。在此示例中，应预定义策略并将其存储到策略注册表服务中。

public static IServiceCollection AddPollyPolicies(
    this IServiceCollection services, 
    Action<PollyPoliciesOptions> setupAction = null)
{
    var policyOptions = new PollyPoliciesOptions();
    setupAction?.Invoke(policyOptions);

    var policyRegistry = services.AddPolicyRegistry();

    policyRegistry.Add(
        PollyPolicyName.HttpRetry,
        HttpPolicyExtensions
            .HandleTransientHttpError()
            .WaitAndRetryAsync(
                policyOptions.HttpRetry.Count,
                retryAttempt => TimeSpan.FromSeconds(Math.Pow(policyOptions.HttpRetry.BackoffPower, retryAttempt))));

    policyRegistry.Add(
        PollyPolicyName.HttpCircuitBreaker,
        HttpPolicyExtensions
            .HandleTransientHttpError()
            .CircuitBreakerAsync(
                handledEventsAllowedBeforeBreaking: policyOptions.HttpCircuitBreaker.ExceptionsAllowedBeforeBreaking,
                    durationOfBreak: policyOptions.HttpCircuitBreaker.DurationOfBreak));

    return services;
}