摘要：結果總是重定向，狀態碼找了好久都不知道什么原因，而且直接在瀏覽器網址欄輸入網址，用抓包也沒有抓到狀態為的包。其實狀態碼的時候應答部分的可以觀察到，但是一個太不顯眼了所以我沒有注意到，導致卡了很久接下來只要知道如何發送請求就好了。

這是個在寫計算機網絡課設的時候碰到的問題，卡了我一天，所以總結一下。

其實在之前就有用requests寫過python爬蟲，但是計算機網絡要求更底層的實現，剛好我看到了[這篇文章]1結果發現他就是用socket來實現的請求，所以就學習了。

本來也覺得應該不難，畢竟就是建立tcp連接。原網站的例子如下：

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

".format(url)  # 構建請求
  sock.send(request.encode("ascii"))  # 向socket發送數據
  response = b""   
  chunk = sock.recv(4096)    # 從socket接收數據
  while chunk:
      response += chunk
      chunk = sock.recv(4096)

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

我選擇爬取的網站是鏈家，當然也看了很多其他例子,還用fiddler抓包，把headers整個放了上去，首先是參考了這個文章，寫出如下代碼。

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
""")

結果總是報400(Bad Request)，這個地方卡了很久，最后解決辦法是一條一條發送，每一條后面加 。

        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())

結果總是重定向，狀態碼301！找了好久都不知道什么原因，而且直接在瀏覽器網址欄輸入網址，用fiddler抓包也沒有抓到狀態為301的包。最后使用fiddler的composer輸入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，如下圖所示。

這下知道原因了，是http和https的區別。(其實301狀態碼的時候應答部分的Location可以觀察到，但是一個s太不顯眼了所以我沒有注意到，導致卡了很久)

接下來只要知道如何發送https請求就好了。下面是代碼，主要是更改建立socket和連接的部分。注意端口號為443。參考文章在這里

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

感覺自己很多地方了解的不夠深入，暫時學校也沒有講到應用層。到時候再研究研究，如有錯漏歡迎指出。