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);
        ...
    }

}

我想通过动态代理实现发送请求。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 approuces，其中没有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.Dispose HttpClient 处理每个请求：

    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);
        ...
    }

但是这样我就违反了 HttpClientFactory 模式，它可能会导致应用程序性能出现问题，如下面的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

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

实现这一点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 IHttpClientFactory 并选择要使用的代理之一，请求实现它的命名客户端。

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);
        ...
    }
}

Answer 2

我可以通过继承 HttpClientHandler 来做到这一点：

public class ProxyHttpHandler : HttpClientHandler
{
    private int currentProxyIndex = 0;

private ProxyOptions proxyOptions;

public ProxyHttpHandler(IOptions<ProxyOptions> options)
{
    proxyOptions = options != null ? options.Value : throw new ArgumentNullException(nameof(options));
    UseProxy = true;
}

protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
    var proxy = proxyOptions.Proxies[currentProxyIndex];
    var proxyResolver = new WebProxy(proxy.Host, proxy.Port)
    {
        Credentials = proxy.Credentials
    };

    Proxy = proxyResolver;

    currentProxyIndex++;
    if(currentProxyIndex >= proxyOptions.Proxies.Count)
        currentProxyIndex = 0;

    return base.SendAsync(request, cancellationToken);
}

}

然后我在 IoC 中注册我的 ProxyHttpHandler 和 ProxyOptions：

public IForksCoreConfigurationBuilder ConfigureProxy(Action<ProxyOptions> options)
{
    Services.AddOptions<ProxyOptions>().Configure(options);
    Services.AddTransient<ProxyHttpHandler>();
    Services.AddHttpClient<IService, MyService>()
            .ConfigurePrimaryHttpMessageHandler<ProxyHttpHandler>();

    return this;
}