在C#用HttpWebRequest中发送GET/HTTP/HTTPS请求

using System;
using System.Collections.Generic;
using System.Text;
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;
using System.Net;
using System.IO;

namespace Util
{
/// <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)";
#region  HttpWebResponse中获取响应字符串
/// <summary>
/// HttpWebResponse中获取响应字符串
/// </summary>
/// <param name="response">HttpWebResponse</param>
/// <returns>响应字符串</returns>
public static String GetHttpResponseStr(HttpWebResponse response)
{
Encoding encode = System.Text.Encoding.GetEncoding(response.CharacterSet);
StreamReader readStream = new StreamReader(response.GetResponseStream(), encode);
String strResponse = readStream.ReadToEnd();
return strResponse;
}
#endregion

#region 创建GET方式的HTTP请求(简化形式)
/// <summary>
/// 创建GET方式的HTTP请求
/// </summary>
/// <param name="url">请求的URL</param>
/// <returns>HttpWebResponse</returns>
public static HttpWebResponse CreateGetHttpResponse(String url)
{
return CreateGetHttpResponse(url, null, null, null);
}
#endregion

#region 创建GET方式的HTTP请求(全参数)
/// <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>HttpWebResponse</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;
}
#endregion

#region 创建POST方式的HTTP请求(简化形式)
/// <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="requestEncoding">发送HTTP请求时所用的编码</param>
/// <returns>HttpWebResponse</returns>
public static HttpWebResponse CreatePostHttpResponse(string url, IDictionary<string, string> parameters, string requestEncoding)
{
return CreatePostHttpResponse(url, parameters, requestEncoding, null, null, null);
}
#endregion

#region 创建POST方式的HTTP请求(全参数)
/// <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="requestEncoding">发送HTTP请求时所用的编码</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>HttpWebResponse</returns>
public static HttpWebResponse CreatePostHttpResponse(string url, IDictionary<string, string> parameters, string requestEncoding,
int? timeout, string userAgent, CookieCollection cookies)
{
Encoding encoding;
if (string.IsNullOrEmpty(url))
{
throw new ArgumentNullException("url");
}

if (requestEncoding == null)
{
encoding = Encoding.GetEncoding("UTF-8");
}
else
{
encoding = Encoding.GetEncoding(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 == 0))
{
StringBuilder buffer = new StringBuilder();
foreach (string key in parameters.Keys)
{
buffer.AppendFormat("{0}={1}&", key, parameters[key]);
}
String queryString = buffer.ToString();
queryString = queryString.EndsWith("&") ? queryString.Remove(queryString.LastIndexOf('&')) : queryString;

byte[] data = encoding.GetBytes(queryString);
using (Stream stream = request.GetRequestStream())
{
stream.Write(data, 0, data.Length);
}
}
return request.GetResponse() as HttpWebResponse;
}
#endregion

#region 检查验证结果
private static bool CheckValidationResult(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
{
return true; //总是接受
}
#endregion
}
}

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";
string encoding = "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", "0");
parameters.Add("username", userName);
parameters.Add("password", password);
parameters.Add("mem_pass", "1");
HttpWebResponse response = HttpWebResponseUtility.CreatePostHttpResponse(loginUrl, parameters,encoding);
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 = "userNam
c324
e";
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,"UTF-8");

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。

本文出自
“周公（周金桥）的专栏”
博客，请务必保留此出处http://zhoufoxcn.blog.51cto.com/792419/561934