.NET 使用 HttpClient 从 URL 下载任何类型的文件数据

使用 HttpClient 类从 Internet URL/URI 下载文件；用 C# 编写。
本文与.NET Core 3.1、.NET 5、.NET 6和.NET 8兼容。此代码与ASP.NET Core Web 服务器应用程序同样有效。

以下代码将从 Internet URL 下载任何类型的数据，如果已压缩则解压缩，然后将其写入控制台。请参阅本文以获取有关如何从控制台应用程序（例如此应用程序）读取数据（包括二进制数据）的示例。

另请参阅：使用 WebClient 下载比 HttpClient 更简单的客户端；从端点获取请求和向端点发送 POST 请求，以使用带有REST API端点的 HttpClient。

using System;
using System.IO.Compression;
using System.IO;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
   class Program
   {
       // NOTE: must specify that Main() be an async method
       static async Task Main(string[] args)
       {
           if(args.Length == 0)
           {
               Console.WriteLine("Must specify a URL to download");
               return;
           }

using(var httpClient = new System.Net.Http.HttpClient())
{

               // NOTE: to save bandwidth, request compressed content
               httpClient.DefaultRequestHeaders.AcceptEncoding.Clear();
               httpClient.DefaultRequestHeaders.AcceptEncoding.Add(new System.Net.Http.Headers.StringWithQualityHeaderValue("gzip"));
               httpClient.DefaultRequestHeaders.AcceptEncoding.Add(new System.Net.Http.Headers.StringWithQualityHeaderValue("deflate"));
               httpClient.DefaultRequestHeaders.AcceptEncoding.Add(new System.Net.Http.Headers.StringWithQualityHeaderValue("br"));

               // NOTE: accept all languages
               httpClient.DefaultRequestHeaders.AcceptLanguage.Clear();
               httpClient.DefaultRequestHeaders.AcceptLanguage.Add(new System.Net.Http.Headers.StringWithQualityHeaderValue("*"));

               // NOTE: accept all media types
               httpClient.DefaultRequestHeaders.Accept.Clear();
               httpClient.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("*/*"));

               System.Net.Http.HttpResponseMessage response;
               try
               {
                   // NOTE: argument zero may be a URL to text, like HTML, or a zip file, image file, PDF file or any other binary data
                   response = await httpClient.GetAsync(args[0]);
                   using (var ms = new MemoryStream())
                   {
                       var contentType = response.Content.Headers.ContentType.ToString().ToLower();

                       // NOTE: this block of code may be omitted; it simply writes the URL along with the content-type
                       if (contentType.StartsWith("text/"))
                       {
                           var line = args[0] + " => " + contentType;
                           Console.WriteLine(line);
                           Console.WriteLine(new string('=', line.Length));
                       }

                       await response.Content.CopyToAsync(ms);
                       byte[] data;
                       switch (response.Content.Headers.ContentEncoding.FirstOrDefault())
                       {
                           case "br":
                               data = await Decompressor.Brotli(ms);
                               break;
                           case "gzip":
                               data = await Decompressor.GZip(ms);
                               break;
                           case "deflate":
                               data = await Decompressor.Deflate(ms);
                               break;
                           default: // NOTE: not compressed
                               data = ms.ToArray();
                               break;
                       }
                       using (var msData = new MemoryStream(data))
                       {
                           msData.WriteTo(Console.OpenStandardOutput());
                       }
                   }
               }
               catch (Exception ex)
               {
                   Console.WriteLine(ex.Message);
                   return;
               }
           }
       }
   }
   // NOTE: this class is used to decompress data that is sent compressed, saving bandwidth
   internal class Decompressor
   {
       public static async Task<byte[]> GZip(MemoryStream inputStream, CancellationToken cancel = default)
       {
           inputStream.Position = 0;
           using (var outputStream = new MemoryStream())
           {
               using (var compressionStream = new GZipStream(inputStream, CompressionMode.Decompress))
               {
                   await compressionStream.CopyToAsync(outputStream, cancel);
               }
               return outputStream.ToArray();
           }
       }
       public static async Task<byte[]> Brotli(MemoryStream inputStream, CancellationToken cancel = default)
       {
           inputStream.Position = 0;
           using (var outputStream = new MemoryStream())
           {
               using (var compressionStream = new BrotliStream(inputStream, CompressionMode.Decompress))
               {
                   await compressionStream.CopyToAsync(outputStream, cancel);
               }
               return outputStream.ToArray();
           }
       }
       public static async Task<byte[]> Deflate(MemoryStream inputStream, CancellationToken cancel = default)
       {
           inputStream.Position = 0;
           using (var outputStream = new MemoryStream())
           {
               using (var compressionStream = new DeflateStream(inputStream, CompressionMode.Decompress))
               {
                   await compressionStream.CopyToAsync(outputStream, cancel);
               }
               return outputStream.ToArray();
           }
       }
   }
}