.NET下透過HttpListener實現簡單的Http服務

HttpListener提供一個簡單的、可透過程式控制的 HTTP 協定偵聽器。使用它可以很容易的提供一些Http服務，而無需啟動IIS這類大型服務程式。使用HttpListener的方法流程很簡單：主要分為以下幾個步驟

#1.建立一個HTTP偵聽器物件並初始化

2.加入需要監聽的URI 前綴

#3.開始偵聽來自客戶端的請求

4.處理客戶端的Http請求

#5.關閉HTTP偵聽器

例如：我們要實作一個簡單Http服務，進行文件的下載，或進行一些其他的操作，例如要發送郵件，使用HttpListener監聽，處理郵件佇列，避免在網站上的同步等待。以及獲取一些快取的資料等等行為

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading;
using System.Web;
using System.IO;
using Newtonsoft.Json;

namespace HttpListenerApp
{
 /// <summary>
 /// HttpRequest逻辑处理
 /// </summary>
 public class HttpProvider
 {

  private static HttpListener httpFiledownload; //文件下载处理请求监听
  private static HttpListener httOtherRequest; //其他超做请求监听

  /// <summary>
  /// 开启HttpListener监听
  /// </summary>
  public static void Init()
  {
   httpFiledownload = new HttpListener(); //创建监听实例
   httpFiledownload.Prefixes.Add("http://10.0.0.217:20009/FileManageApi/Download/"); //添加监听地址 注意是以/结尾。
   httpFiledownload.Start(); //允许该监听地址接受请求的传入。
   Thread ThreadhttpFiledownload = new Thread(new ThreadStart(GethttpFiledownload)); //创建开启一个线程监听该地址得请求
   ThreadhttpFiledownload.Start();

   httOtherRequest = new HttpListener();
   httOtherRequest.Prefixes.Add("http://10.0.0.217:20009/BehaviorApi/EmailSend/"); //添加监听地址 注意是以/结尾。
   httOtherRequest.Start(); //允许该监听地址接受请求的传入。
   Thread ThreadhttOtherRequest = new Thread(new ThreadStart(GethttOtherRequest));
   ThreadhttOtherRequest.Start();
  }

  /// <summary>
  /// 执行文件下载处理请求监听行为
  /// </summary>
  public static void GethttpFiledownload()
  {
   while (true)
   {
    HttpListenerContext requestContext = httpFiledownload.GetContext(); //接受到新的请求
    try
    {
     //reecontext 为开启线程传入的 requestContext请求对象
     Thread subthread = new Thread(new ParameterizedThreadStart((reecontext) =>  
     {
      Console.WriteLine("执行文件处理请求监听行为");

      var request = (HttpListenerContext)reecontext;
      var image = HttpUtility.UrlDecode(request.Request.QueryString["imgname"]); //接受GET请求过来的参数；
      string filepath = AppDomain.CurrentDomain.BaseDirectory + image;
      if (!File.Exists(filepath))
      {
       filepath = AppDomain.CurrentDomain.BaseDirectory + "default.jpg";  //下载默认图片
      }
      using (FileStream fs = new FileStream(filepath, FileMode.Open, FileAccess.Read))
      {
       byte[] buffer = new byte[fs.Length];
       fs.Read(buffer, 0, (int)fs.Length); //将文件读到缓存区
       request.Response.StatusCode = 200;
       request.Response.Headers.Add("Access-Control-Allow-Origin", "*");
       request.Response.ContentType = "image/jpg"; 
       request.Response.ContentLength64 = buffer.Length;
       var output = request.Response.OutputStream; //获取请求流
       output.Write(buffer, 0, buffer.Length);  //将缓存区的字节数写入当前请求流返回
       output.Close();
      }
     }));
     subthread.Start(requestContext); //开启处理线程处理下载文件
    }
    catch (Exception ex)
    {
     try
     {
      requestContext.Response.StatusCode = 500;
      requestContext.Response.ContentType = "application/text";
      requestContext.Response.ContentEncoding = Encoding.UTF8;
      byte[] buffer = System.Text.Encoding.UTF8.GetBytes("System Error");
      //对客户端输出相应信息.
      requestContext.Response.ContentLength64 = buffer.Length;
      System.IO.Stream output = requestContext.Response.OutputStream;
      output.Write(buffer, 0, buffer.Length);
      //关闭输出流，释放相应资源
      output.Close();
     }
     catch { }
    }
   }
  }

  /// <summary>
  /// 执行其他超做请求监听行为
  /// </summary>
  public static void GethttOtherRequest()
  {
   while (true)
   {
    HttpListenerContext requestContext = httOtherRequest.GetContext(); //接受到新的请求
    try
    {
     //reecontext 为开启线程传入的 requestContext请求对象
     Thread subthread = new Thread(new ParameterizedThreadStart((reecontext) =>
     {
      Console.WriteLine("执行其他超做请求监听行为");
      var request = (HttpListenerContext)reecontext;
      var msg = HttpUtility.UrlDecode(request.Request.QueryString["behavior"]); //接受GET请求过来的参数；
      //在此处执行你需要进行的操作>>比如什么缓存数据读取，队列消息处理，邮件消息队列添加等等。

      request.Response.StatusCode = 200;
      request.Response.Headers.Add("Access-Control-Allow-Origin", "*");
      request.Response.ContentType = "application/json";
      requestContext.Response.ContentEncoding = Encoding.UTF8;
      byte[] buffer = System.Text.Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(new { success = true, behavior = msg }));
      request.Response.ContentLength64 = buffer.Length;
      var output = request.Response.OutputStream;
      output.Write(buffer, 0, buffer.Length);
      output.Close();
     }));
     subthread.Start(requestContext); //开启处理线程处理下载文件
    }
    catch (Exception ex)
    {
     try
     {
      requestContext.Response.StatusCode = 500;
      requestContext.Response.ContentType = "application/text";
      requestContext.Response.ContentEncoding = Encoding.UTF8;
      byte[] buffer = System.Text.Encoding.UTF8.GetBytes("System Error");
      //对客户端输出相应信息.
      requestContext.Response.ContentLength64 = buffer.Length;
      System.IO.Stream output = requestContext.Response.OutputStream;
      output.Write(buffer, 0, buffer.Length);
      //关闭输出流，释放相应资源
      output.Close();
     }
     catch { }
    }
   }
  }
 }
}

呼叫方式：注意這裡啟動程式必須以管理員身份運行，因為上午的監聽需要開啟端口，所有需要以管理員身份執行。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace HttpListenerApp
{
 class Program
 {
  static void Main(string[] args)
  {
   //开启请求监听
   HttpProvider.Init();
  }
 }
}

執行後的結果為：



這裡透過一個簡單的控製程式在裡面使用HttpListener實作了簡單的Http服務程式。裡面有少量的線程和和非同步處理，例如收到行為訊息請求可以先回傳給用戶，讓用戶不用同步等待，就可以執行下一步操作，又例如實作的簡單郵件伺服器，將請求傳送給HttpListener接收到請求後就立即返回，交給隊列去發送郵件。郵件的發送會出現延遲等待等狀況出現，這樣就不用等待。

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