抓取百万知乎用户信息之HttpHelper的迭代之路

什么是Httphelper？

httpelpers是一个封装好拿来获取网络上资源的工具类。因为是用http协议，故取名httphelper。

httphelper出现的背景

使用WebClient可以很方便获取网络上的资源，例如

              WebClient client = new WebClient();
            string html=   client.DownloadString("https://www.baidu.com/");

这样就可以拿到百度首页的的源代码，由于WebClient封装性太强，有时候不大灵活，需要对底层有更细致的把控，这个时候就需要打造自己的网络资源获取工具了；

HttpHelper初级

现在着手打造自己的下载工具，刚开始时候长这样

public class HttpHelp
  {
        public static string DownLoadString(string url)
        {

               string Source = string.Empty;

         HttpWebRequest request= (HttpWebRequest)WebRequest.Create(url);         using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())         {             using (Stream stream = response.GetResponseStream())            {                using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))                       {                          Source = reader.ReadToEnd();                         }              }         }        return  Source;      } }程序总会出现各种异常的，这个时候加个Try catch语句

public class HttpHelp
  {
        public static string DownLoadString(string url)
        {

           string Source = string.Empty;
           try{
                HttpWebRequest request= (HttpWebRequest)WebRequest.Create(url);
                using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
                {
                    using (Stream stream = response.GetResponseStream())
                     {
                        using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))
                       {
                          Source = reader.ReadToEnd();
                       }
                    }
                }
           }
          catch          {
              Console.WriteLine("出错了，请求的URL为{0}", url);
          }
        return  Source;
      }
 }

请求资源是I/O密集型，特别耗时，这个时候需要异步

 public static async Task<string> DownLoadString(string url)
        {
            return await Task<string>.Run(() =>
            {
                string Source = string.Empty;
                try
                {
                    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
                    using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
                    {
                        using (Stream stream = response.GetResponseStream())
                        {
                            using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))
                            {
                                Source = reader.ReadToEnd();
                            }
                        }
                    }
                }
                catch
                {
                    Console.WriteLine("出错了，请求的URL为{0}", url);
                }
                return Source;
            });

        }

 HttpHelper完善       
为了欺骗服务器，让服务器认为这个请求是浏览器发出的

   request.UserAgent = "Mozilla/5.0 (Windows NT 10.0; WOW64; rv:49.0) Gecko/20100101 Firefox/49.0";

有些资源是需要权限的，这个时候要伪装成某个用户，http协议是无状态的，标记信息都在cookie上面，给请求加上cookie

    request.Headers.Add("Cookie", "这里填cookie，从浏览器上面拷贝")

再完善下，设定个超时吧

   request.Timeout = 5000;

有些网站提供资源是GZIP压缩，这样可以节省带宽，所以请求头再加个

request.Headers.Add("Accept-Encoding", " gzip, deflate, br");

相应的得到相应流要有相对应的解压，这个时候httphelper变成这样了

           public static string DownLoadString(string url)            {                 string Source = string.Empty;                 try{                     HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
                request.UserAgent = "Mozilla/5.0 (Windows NT 10.0; WOW64; rv:49.0) Gecko/20100101 Firefox/49.0";

                request.Headers.Add("Cookie", "这里是Cookie");

                request.Headers.Add("Accept-Encoding", " gzip, deflate, br");
                request.KeepAlive = true;//启用长连接

                using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
                {

                    using (Stream dataStream = response.GetResponseStream())
                    {

                        if (response.ContentEncoding.ToLower().Contains("gzip"))//解压
                        {
                            using (GZipStream stream = new GZipStream(response.GetResponseStream(), CompressionMode.Decompress))
                            {
                                using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))
                                {
                                    Source = reader.ReadToEnd();
                                }
                            }
                        }
                        else if (response.ContentEncoding.ToLower().Contains("deflate"))//解压
                        {
                            using (DeflateStream stream = new DeflateStream(response.GetResponseStream(), CompressionMode.Decompress))
                            {
                                using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))
                                {
                                    Source = reader.ReadToEnd();
                                }

                            }
                        }
                        else
                        {
                            using (Stream stream = response.GetResponseStream())//原始
                            {
                                using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))
                                {

                                    Source = reader.ReadToEnd();
                                }
                            }
                        }

                    }
                }
                request.Abort();
            }
            catch
            {
                Console.WriteLine("出错了，请求的URL为{0}", url);

            }
            return Source;}

请求态度会被服务器拒绝，返回429。这个时候需要设置代理，我们的请求会提交到代理服务器，代理服务器会向目标服务器请求，得到的响应由代理服务器返回给我们。只要不断切换代理，服务器不会因为请求太频繁而拒绝掉程序的请求

   var proxy = new WebProxy(“Adress”,8080);//后面是端口号
   request.Proxy = proxy;//为httpwebrequest设置代理

至于如何获取代理，请见后面的博客