c# - 具有 HttpClientFactory 实现的动态代理

Question

我有 Asp.Net Core WebApi。我正在根据 HttpClientFactory pattern 发出 Http 请求.这是我的示例代码:

public void ConfigureServices(IServiceCollection services)
{
    ...
    services.AddHttpClient<IMyInterface, MyService>();
    ...
}

public class MyService: IMyInterface
{
    private readonly HttpClient _client;

    public MyService(HttpClient client)
    {
        _client = client;
    }

    public async Task CallHttpEndpoint()
    {
        var request = new HttpRequestMessage(HttpMethod.Get, "www.customUrl.com");
        var response = await _client.SendAsync(request);
        ...
    }

}

我想实现通过动态代理发送请求。这基本上意味着我可能需要为每个请求更改代理。至于现在我发现了 2 个应用程序，其中一个对我来说似乎不错:

1.有一个像这样的静态代理:

public void ConfigureServices(IServiceCollection services)
{
    ...
    services.AddHttpClient<IMyInterface, MyService>().ConfigurePrimaryHttpMessageHandler(() =>
        {
            return new HttpClientHandler
            {
                Proxy = new WebProxy("http://127.0.0.1:8888"),
                UseProxy = true
            };
        });
    ...
}

但在这种方法中，我只能为每个服务设置一个代理。

2.处理每个请求的HttpClient:

    HttpClientHandler handler = new HttpClientHandler()
    {
        Proxy = new WebProxy("http://127.0.0.1:8888"),
        UseProxy = true,
    };

    using(var client = new HttpClient(handler))
    {
        var request = new HttpRequestMessage(HttpMethod.Get, "www.customUrl.com");
        var response = await client.SendAsync(request);
        ...
    }

但以这种方式我违反了 HttpClientFactory 模式，它可能会导致应用程序性能问题，如以下 article 所述

是否有第三种方法可以在不重新创建 HttpClient 的情况下动态更改代理？

Answer 1

之后无法更改 HttpClientHandler 的任何属性或将新版本的 HttpClientHandler 分配给现有的 HttpClient它被实例化。因此，不可能为特定的 HttpClient 提供动态代理:您只能指定一个代理。

实现此目的的正确方法是使用命名客户端，并为每个代理端点定义一个客户端。然后，您需要注入(inject) IHttpClientFactory 并选择要使用的代理之一，请求实现该代理的指定客户端。

services.AddHttpClient("MyServiceProxy1").ConfigurePrimaryHttpMessageHandler(() =>
{
    return new HttpClientHandler
    {
        Proxy = new WebProxy("http://127.0.0.1:8888"),
        UseProxy = true
    };
});

services.AddHttpClient("MyServiceProxy2").ConfigurePrimaryHttpMessageHandler(() =>
{
    return new HttpClientHandler
    {
        Proxy = new WebProxy("http://127.0.0.1:8889"),
        UseProxy = true
    };
});

...

然后:

public class MyService : IMyInterface
{
    private readonly HttpClient _client;

    public MyService(IHttpClientFactory httpClientFactory)
    {
        _client = httpClientFactory.CreateClient("MyServiceProxy1");
    }

    public async Task CallHttpEndpoint()
    {
        var request = new HttpRequestMessage(HttpMethod.Get, "www.customUrl.com");
        var response = await _client.SendAsync(request);
        ...
    }
}