使用python的socket发送http(s)请求

摘要：结果总是重定向，状态码找了好久都不知道什么原因，而且直接在浏览器网址栏输入网址，用抓包也没有抓到状态为的包。其实状态码的时候应答部分的可以观察到，但是一个太不显眼了所以我没有注意到，导致卡了很久接下来只要知道如何发送请求就好了。

这是个在写计算机网络课设的时候碰到的问题，卡了我一天，所以总结一下。

其实在之前就有用requests写过python爬虫，但是计算机网络要求更底层的实现，刚好我看到了[这篇文章]1结果发现他就是用socket来实现的请求，所以就学习了。

本来也觉得应该不难，毕竟就是建立tcp连接。原网站的例子如下：

  def fetch(url):
  sock = socket.socket()   # 建立socket
  sock.connect(("xkcd.com", 80))    # 远程连接
  request = "GET {} HTTP/1.0
Host: xkcd.com

".format(url)  # 构建请求
  sock.send(request.encode("ascii"))  # 向socket发送数据
  response = b""   
  chunk = sock.recv(4096)    # 从socket接收数据
  while chunk:
      response += chunk
      chunk = sock.recv(4096)

  # Page is now downloaded.
  links = parse_links(response)
  q.add(links)

我选择爬取的网站是链家，当然也看了很多其他例子,还用fiddler抓包，把headers整个放了上去，首先是参考了这个文章，写出如下代码。

s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
s.connect(("www.baidu.com",80))
s.send("""GET / HTTP/1.1
Host: zh.lianjia.com
Connection: keep-alive
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.139 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
Referer: https://www.baidu.com/link?url=4J5Kx--GLdLFESJhkfRePU8Ac_0agnTcOtB-b3kfnX8VNdZ_6TPqOyJGKVXkTczg&ck=6140.3.83.296.315.287.208.155&shh=www.baidu.com&sht=94886267_hao_pg&wd=&eqid=af98b98700060b77000000065aef0524
Accept-Encoding: gzip, deflate, br
Accept-Language: zh-CN,zh;q=0.9,en-CA;q=0.8,en;q=0.7
Cookie: lianjia_uuid=ce61c41c-25b0-46d6-a0a0-d57a75ee8706; UM_distinctid=1631f588055f9-0286722badd3ec-b34356b-1fa400-1631f58805657f; _ga=GA1.2.43397143.1525239286; _smt_uid=5ae94e02.558be516; _jzqx=1.1525248800.1525335927.1.jzqsr=zh%2Elianjia%2Ecom|jzqct=/ershoufang/xiangzhouqu/.-; _jzqc=1; _jzqckmp=1; _gid=GA1.2.1028411676.1525594529; select_city=440400; all-lj=c60bf575348a3bc08fb27ee73be8c666; _qzjc=1; CNZZDATA1254525948=963210960-1525238218-https%253A%252F%252Fwww.lianjia.com%252F%7C1525608956; CNZZDATA1255633284=1054798284-1525238580-https%253A%252F%252Fwww.lianjia.com%252F%7C1525608969; lianjia_ssid=c046ddb3-3e66-4809-998a-52ade335fdfc; _qzja=1.1070225156.1525239298260.1525603274282.1525613866775.1525609113492.1525613866775.0.0.0.92.9; _qzjto=29.3.0; _jzqa=1.3750161754444366000.1525239284.1525603274.1525613867.9; _jzqy=1.1525239284.1525613867.3.jzqsr=baidu.jzqsr=baidu; Hm_lvt_9152f8221cb6243a53c83b956842be8a=1525607433,1525607626,1525609113,1525613867; Hm_lpvt_9152f8221cb6243a53c83b956842be8a=1525613867; _qzjb=1.1525613866775.1.0.0.0; _jzqb=1.1.10.1525613867.1; CNZZDATA1255604082=964175865-1525237915-https%253A%252F%252Fwww.lianjia.com%252F%7C1525612833
""")

结果总是报400(Bad Request)，这个地方卡了很久，最后解决办法是一条一条发送，每一条后面加 。

        sock = socket.socket()
        sock.connect(("zh.lianjia.com", 80))
        sock.send("GET /ershoufang/ HTTP/1.1
".encode())
        sock.send("Host: zh.lianjia.com
".encode())
        sock.send("Connection: keep-alive
".encode())
        sock.send("Cache-Control: no-cache
".encode())
        sock.send("Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
".encode())
        sock.send("Upgrade-Insecure-Requests: 1
".encode())
        sock.send("User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.139 Safari/537.36
".encode())
        sock.send("Accept-Encoding: gzip, deflate, br
".encode())
        sock.send("Cookie: lianjia_uuid=ce61c41c-25b0-46d6-a0a0-d57a75ee8706; UM_distinctid=1631f588055f9-0286722badd3ec-b34356b-1fa400-1631f58805657f; _ga=GA1.2.43397143.1525239286; _smt_uid=5ae94e02.558be516; _jzqx=1.1525248800.1525335927.1.jzqsr=zh%2Elianjia%2Ecom|jzqct=/ershoufang/xiangzhouqu/.-; _jzqc=1; _jzqy=1.1525239284.1525594526.2.jzqsr=baidu.jzqsr=baidu|jzqct=%E9%93%BE%E5%AE%B6; _jzqckmp=1; _gid=GA1.2.1028411676.1525594529; Hm_lvt_9152f8221cb6243a53c83b956842be8a=1525594526,1525594536,1525594804,1525595210; select_city=440400; all-lj=c60bf575348a3bc08fb27ee73be8c666; _qzjc=1; lianjia_ssid=99306d63-8ee5-a53c-a740-2d3021f3db2f; CNZZDATA1255604082=964175865-1525237915-https%253A%252F%252Fwww.lianjia.com%252F%7C1525602095; _jzqa=1.3750161754444366000.1525239284.1525594526.1525603274.8; CNZZDATA1254525948=963210960-1525238218-https%253A%252F%252Fwww.lianjia.com%252F%7C1525603556; CNZZDATA1255633284=1054798284-1525238580-https%253A%252F%252Fwww.lianjia.com%252F%7C1525603557; Hm_lpvt_9152f8221cb6243a53c83b956842be8a=1525606057; _jzqb=1.9.10.1525603274.1; _qzja=1.1070225156.1525239298260.1525597069547.1525603274282.1525605398368.1525606071025.0.0.0.86.8; _qzjb=1.1525603274282.9.0.0.0; _qzjto=23.2.0

".encode())

结果总是重定向，状态码301！找了好久都不知道什么原因，而且直接在浏览器网址栏输入网址，用fiddler抓包也没有抓到状态为301的包。最后使用fiddler的composer输入http://zh.lianjia.com/ershoufang 就抓到了301和200，其中200的地址就是https://zh.lianjia.com/ershoufang，如下图所示。

这下知道原因了，是http和https的区别。(其实301状态码的时候应答部分的Location可以观察到，但是一个s太不显眼了所以我没有注意到，导致卡了很久)

接下来只要知道如何发送https请求就好了。下面是代码，主要是更改建立socket和连接的部分。注意端口号为443。参考文章在这里

        sock = ssl.wrap_socket(socket.socket())
        sock.connect(("zh.lianjia.com", 443))

感觉自己很多地方了解的不够深入，暂时学校也没有讲到应用层。到时候再研究研究，如有错漏欢迎指出。