跟进网站使用cookies的C#下载文件

using System;
using System.IO;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;

class Program
{
    static async System.Threading.Tasks.Task Main(string[] args)
    {
        // 创建一个HttpClient实例
        HttpClient httpClient = new HttpClient();

        // 创建一个CookieContainer实例，用于存储cookies
        CookieContainer cookieContainer = new CookieContainer();
        httpClient.BaseAddress = new Uri("https://example.com");

        // 将HttpClient的默认请求头设置为使用CookieContainer
        httpClient.DefaultRequestHeaders.Accept.Clear();
        httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
        httpClient.DefaultRequestHeaders.Add("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.3");
        httpClient.DefaultRequestHeaders.Add("Connection", "keep-alive");

        // 创建一个HttpClientHandler，并设置它的CookieContainer属性为之前创建的CookieContainer
        HttpClientHandler handler = new HttpClientHandler();
        handler.CookieContainer = cookieContainer;

        // 使用HttpClientHandler来创建一个新的HttpClient实例
        HttpClient client = new HttpClient(handler);

        // 发送GET请求，获取包含cookies的响应
        HttpResponseMessage response = await client.GetAsync("https://example.com/login");

        // 确保响应成功
        response.EnsureSuccessStatusCode();

        // 获取响应中的cookies，并将它们添加到CookieContainer中
        foreach (Cookie cookie in cookieContainer.GetCookies(new Uri("https://example.com")))
        {
            cookieContainer.Add(new Uri("https://example.com"), cookie);
        }

        // 创建一个新的GET请求，将之前获取的cookies包含在请求中
        HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Get, "https://example.com/download");
        request.Headers.Add("Cookie", cookieContainer.GetCookieHeader(new Uri("https://example.com")));

        // 发送GET请求，获取文件
        HttpResponseMessage fileResponse = await client.SendAsync(request);

        // 确保响应成功
        fileResponse.EnsureSuccessStatusCode();

        // 将文件保存到本地
        using (Stream fileStream = await fileResponse.Content.ReadAsStreamAsync())
        {
            using (FileStream outputStream = File.Create("downloaded_file.txt"))
            {
                fileStream.CopyTo(outputStream);
            }
        }

        Console.WriteLine("文件下载完成！");
    }
}