C# HttpWebRequest GET HTTP HTTPS 请求

下面是我编写的一个辅助类，在这个类中采用了HttpWebRequest中发送GET/HTTP/HTTPS请求，因为有的时候需要获取认证信息（如Cookie），所以返回的是HttpWebResponse对象，有了返回的HttpWebResponse实例，可以获取登录过程中返回的会话信息，也可以获取响应流。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;
using System.DirectoryServices.Protocols;
using System.ServiceModel.Security;
using System.Net;
using System.IO;
using System.IO.Compression;
using System.Text.RegularExpressions;  

namespace BaiduCang
{
   /// <summary>
   /// 有关HTTP请求的辅助类
   /// </summary>
   public class HttpWebResponseUtility
   {
       private static readonly string DefaultUserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)";
       /// <summary>
       /// 创建GET方式的HTTP请求
       /// </summary>
       /// <param name="url">请求的URL</param>
       /// <param name="timeout">请求的超时时间</param>
       /// <param name="userAgent">请求的客户端浏览器信息，可以为空</param>
       /// <param name="cookies">随同HTTP请求发送的Cookie信息，如果不需要身份验证可以为空</param>
       /// <returns></returns>
       public static HttpWebResponse CreateGetHttpResponse(string url,int? timeout, string userAgent,CookieCollection cookies)
       {
           if (string.IsNullOrEmpty(url))
           {
               throw new ArgumentNullException("url");
           }
           HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
           request.Method = "GET";
           request.UserAgent = DefaultUserAgent;
           if (!string.IsNullOrEmpty(userAgent))
           {
               request.UserAgent = userAgent;
           }
           if (timeout.HasValue)
           {
               request.Timeout = timeout.Value;
           }
           if (cookies != null)
           {
               request.CookieContainer = new CookieContainer();
               request.CookieContainer.Add(cookies);
           }
           return request.GetResponse() as HttpWebResponse;
       }
       /// <summary>
       /// 创建POST方式的HTTP请求
       /// </summary>
       /// <param name="url">请求的URL</param>
       /// <param name="parameters">随同请求POST的参数名称及参数值字典</param>
       /// <param name="timeout">请求的超时时间</param>
       /// <param name="userAgent">请求的客户端浏览器信息，可以为空</param>
       /// <param name="requestEncoding">发送HTTP请求时所用的编码</param>
       /// <param name="cookies">随同HTTP请求发送的Cookie信息，如果不需要身份验证可以为空</param>
       /// <returns></returns>
       public static HttpWebResponse CreatePostHttpResponse(string url,IDictionary<string,string> parameters,int? timeout, string userAgent,Encoding requestEncoding,CookieCollection cookies)
       {
           if (string.IsNullOrEmpty(url))
           {
               throw new ArgumentNullException("url");
           }
           if(requestEncoding==null)
           {
               throw new ArgumentNullException("requestEncoding");
           }
           HttpWebRequest request=null;
           //如果是发送HTTPS请求
           if(url.StartsWith("https",StringComparison.OrdinalIgnoreCase))
           {
               ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);
               request = WebRequest.Create(url) as HttpWebRequest;
               request.ProtocolVersion=HttpVersion.Version10;
           }
           else
           {
               request = WebRequest.Create(url) as HttpWebRequest;
           }
           request.Method = "POST";
           request.ContentType = "application/x-www-form-urlencoded";  

           if (!string.IsNullOrEmpty(userAgent))
           {
               request.UserAgent = userAgent;
           }
           else
           {
               request.UserAgent = DefaultUserAgent;
           }  

           if (timeout.HasValue)
           {
               request.Timeout = timeout.Value;
           }
           if (cookies != null)
           {
               request.CookieContainer = new CookieContainer();
               request.CookieContainer.Add(cookies);
           }
           //如果需要POST数据
           if(!(parameters==null||parameters.Count==))
           {
               StringBuilder buffer = new StringBuilder();
               int i = ;
               foreach (string key in parameters.Keys)
               {
                   if (i > )
                   {
                       buffer.AppendFormat("&{0}={1}", key, parameters[key]);
                   }
                   else
                   {
                       buffer.AppendFormat("{0}={1}", key, parameters[key]);
                   }
                   i++;
               }
               byte[] data = requestEncoding.GetBytes(buffer.ToString());
               using (Stream stream = request.GetRequestStream())
               {
                   stream.Write(data, , data.Length);
               }
           }
           return request.GetResponse() as HttpWebResponse;
       }  

       private static bool CheckValidationResult(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
       {
           return true; //总是接受
       }
   }
}

从上面的代码中可以看出POST数据到HTTP和HTTPS站点不同，POST数据到HTTPS站点的时候需要设置ServicePointManager类的ServerCertificateValidationCallback属性，并且在POST到https://passport.baidu.com/?login时还需要将HttpWebResquest实例的ProtocolVersion属性设置为HttpVersion.Version10（这个未验证是否所有的HTTPS站点都需要设置），否则在调用GetResponse()方法时会抛出“基础连接已经关闭: 连接被意外关闭。”的异常。

用法举例
这个类用起来也很简单：
（1）POST数据到HTTPS站点，用它来登录百度：

string loginUrl = "https://passport.baidu.com/?login";
string userName = "userName";
string password = "password";
string tagUrl = "http://cang.baidu.com/"+userName+"/tags";
Encoding encoding = Encoding.GetEncoding("gb2312");  

IDictionary<string, string> parameters = new Dictionary<string, string>();
parameters.Add("tpl", "fa");
parameters.Add("tpl_reg", "fa");
parameters.Add("u", tagUrl);
parameters.Add("psp_tt", "");
parameters.Add("username", userName);
parameters.Add("password", password);
parameters.Add("mem_pass", "");
HttpWebResponse response = HttpWebResponseUtility.CreatePostHttpResponse(loginUrl, parameters, null, null, encoding, null);
string cookieString = response.Headers["Set-Cookie"];

（2）发送GET请求到HTTP站点
在cookieString中包含了服务器端返回的会话信息数据，从中提取了之后可以设置Cookie下次登录时带上这个Cookie就可以以认证用户的信息，假设我们已经登录成功并且获取了Cookie，那么发送GET请求的代码如下：

string userName = "userName";
string tagUrl = "http://cang.baidu.com/"+userName+"/tags";
CookieCollection cookies = new CookieCollection();//如何从response.Headers["Set-Cookie"];中获取并设置CookieCollection的代码略
response = HttpWebResponseUtility.CreateGetHttpResponse(tagUrl, null, null, cookies);  

(3)发送POST请求到HTTP站点
以登录51CTO为例：

string loginUrl = "http://home.51cto.com/index.php?s=/Index/doLogin";
string userName = "userName";
string password = "password";  

IDictionary<string, string> parameters = new Dictionary<string, string>();
parameters.Add("email", userName);
parameters.Add("passwd", password);  

HttpWebResponse response = HttpWebResponseUtility.CreatePostHttpResponse(loginUrl, parameters, null, null, Encoding.UTF8, null);

在这里说句题外话，CSDN的登录处理是由http://passport.csdn.net/ajax/accounthandler.ashx这个Handler来处理的。

总结
在本文只是讲解了在C#中发送请求到HTTP和HTTPS的用法，分GET/POST两种方式，为减少一些繁琐和机械的编码，周公将其封装为一个类，发送数据之后返回HttpWebResponse对象实例，利用这个实例我们可以获取服务器端返回的Cookie以便用认证用户的身份继续发送请求，或者读取服务器端响应的内容，不过在读取响应内容时要注意响应格式和编码，本来在这个类中还有读取HTML和WML内容的方法（包括服务器使用压缩方式传输的数据），但限于篇幅和其它方面的原因，此处省略掉了。如有机会，在以后的文章中会继续讲述这方面的内容。