使用HttpClient设置多部分/表单数据文件上传权限的MultipartFormDataContent

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

class Program
{
    static async System.Threading.Tasks.Task Main(string[] args)
    {
        using (var httpClient = new HttpClient())
        {
            var content = new MultipartFormDataContent();

            // 添加表单字段
            content.Add(new StringContent("value"), "key");

            // 添加文件
            var fileContent = new ByteArrayContent(await File.ReadAllBytesAsync("path/to/file"));
            fileContent.Headers.ContentType = MediaTypeHeaderValue.Parse("multipart/form-data");
            content.Add(fileContent, "file", "filename");

            // 发送请求
            var response = await httpClient.PostAsync("https://example.com/upload", content);

            // 处理响应
            if (response.IsSuccessStatusCode)
            {
                Console.WriteLine("文件上传成功");
            }
            else
            {
                Console.WriteLine("文件上传失败");
            }
        }
    }
}