如何使用 HttpClientFactory 为命名的 HttpClient 定义 HttpClientHandler

Question

旧代码：

Client = new HttpClient(new HttpClientHandler() { DefaultProxyCredentials = CredentialCache.DefaultNetworkCredentials });

// set an default user agent string, some services does not allow emtpy user agents
if (!Client.DefaultRequestHeaders.Contains("User-Agent"))
    Client.DefaultRequestHeaders.TryAddWithoutValidation("User-Agent", "Mozilla/5.0");

尝试使用新的 ASP.NET Core 2.1 HttpClientFactory 实现相同的功能：

services.AddHttpClient("Default", client =>
        {
            client.DefaultRequestHeaders.Add("User-Agent", "Mozilla/5.0");
        }).ConfigurePrimaryHttpMessageHandler(handler => new HttpClientHandler() { DefaultProxyCredentials = CredentialCache.DefaultNetworkCredentials });          

不幸的是，我收到一个 HTTP 407（代理身份验证）错误。我做错了什么？

Answer 1

通常建议使用包含客户端名称字符串常量的静态类。

就像是：

public static class NamedHttpClients {
    public const string Default = "Default";
}

然后确保命名客户端配置正确，在您的特定情况下，它看起来像：

services
    .AddHttpClient(NamedHttpClients.Default, client => {
        client.DefaultRequestHeaders.Add("User-Agent", "Mozilla/5.0");
    })
    .ConfigurePrimaryHttpMessageHandler(() => new HttpClientHandler() { 
        DefaultProxyCredentials = CredentialCache.DefaultNetworkCredentials 
    }); 

从那里你可以从注入的客户端中获取客户端 IHttpClientFactory

var client = httpClientFactory.CreateClient(NamedHttpClients.Default);

并按预期使用。