I dont get HTTP answer with sr function. Just an A

2019-09-09 20:13发布

站内问答 / 后端开发
1907 1 4

I am trying to send an HTTP GET request to google.com, but the answer I get is an ACK and not the HTML file. Here is the code:

def Make_Get():
        synR = IP(dst = 'www.google.com', ttl = 64)/TCP(dport = 80,sport = randint(1024,65535), flags = 'S')
        synAckAN = sr1(synR)
        req = (IP(dst='www.google.com') / TCP(dport=80, sport=synAckAN[TCP].dport, seq=synAckAN[TCP].ack, ack=synAckAN[TCP].seq + 1, flags='A')/"GET / HTTP/1.0 \n\n")

        ans, a = sr(req)
        return ans

and this are the two packets I got in return of this function:

###[ IP ]###
  version   = 4
  ihl       = None
  tos       = 0x0
  len       = None
  id        = 1
  flags     = 
  frag      = 0
  ttl       = 64
  proto     = tcp
  chksum    = None
  src       = 192.168.233.128
  dst       = 216.58.214.100
  \options   \
###[ TCP ]###
     sport     = 35534
     dport     = http
     seq       = 1
     ack       = 1964930533
     dataofs   = None
     reserved  = 0
     flags     = A
     window    = 8192
     chksum    = None
     urgptr    = 0
     options   = {}
###[ Raw ]###
        load      = 'GET / HTTP/1.0 \n\n'
None


###[ IP ]###
  version   = 4L
  ihl       = 5L
  tos       = 0x0
  len       = 40
  id        = 32226
  flags     = 
  frag      = 0L
  ttl       = 128
  proto     = tcp
  chksum    = 0x6425
  src       = 216.58.214.100
  dst       = 192.168.233.128
  \options   \
###[ TCP ]###
     sport     = http
     dport     = 35534
     seq       = 1964930533
     ack       = 18
     dataofs   = 5L
     reserved  = 0L
     flags     = A
     window    = 64240
     chksum    = 0xe5e6
     urgptr    = 0
     options   = {}
###[ Padding ]###
        load      = '\x00\x00\x00\x00\x00\x00'
None

When I sniffed the traffic while I sent this packet, I got this:

###[ Ethernet ]###
  dst= 00:0c:29:bb:8e:79
  src= 00:50:56:e9:b8:b1
  type= 0x800
###[ IP ]###
     version= 4L
     ihl= 5L
     tos= 0x0
     len= 517
     id= 32136
     flags= 
     frag= 0L
     ttl= 128
     proto= tcp
     chksum= 0x5004
     src= 172.217.20.100
     dst= 192.168.233.128
     \options\
###[ TCP ]###
        sport= http
        dport= 1928
        seq= 1828330545
        ack= 18
        dataofs= 5L
        reserved= 0L
        flags= FPA
        window= 64240
        chksum= 0x8b5f
        urgptr= 0
        options= []
###[ HTTP ]###
###[ HTTP Response ]###
              Status-Line= u'HTTP/1.0 302 Found'
              Accept-Ranges= None
              Age= None
              E-Tag= None
              Location= u'http://www.google.co.il/?gfe_rd=cr&ei=9fiTV6P6FuWg8weei7rQDA'
              Proxy-Authenticate= None
              Retry-After= None
              Server= None
              Vary= None
              WWW-Authenticate= None
              Cache-Control= u'private'
              Connection= None
              Date= u'Sat, 23 Jul 2016 23:08:37 GMT'
              Pragma= None
              Trailer= None
              Transfer-Encoding= None
              Upgrade= None
              Via= None
              Warning= None
              Keep-Alive= None
              Allow= None
              Content-Encoding= None
              Content-Language= None
              Content-Length= u'261'
              Content-Location= None
              Content-MD5= None
              Content-Range= None
              Content-Type= u'text/html; charset=UTF-8'
              Expires= None
              Last-Modified= None
              Headers= u'Date: Sat, 23 Jul 2016 23:08:37 GMT\r\nContent-Length: 261\r\nContent-Type: text/html; charset=UTF-8\r\nLocation: http://www.google.co.il/?gfe_rd=cr&ei=9fiTV6P6FuWg8weei7rQDA\r\nCache-Control: private'
              Additional-Headers= None
###[ Raw ]###
                 load= '<HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">\n<TITLE>302 Moved</TITLE></HEAD><BODY>\n<H1>302 Moved</H1>\nThe document has moved\n<A HREF="http://www.google.co.il/?gfe_rd=cr&amp;ei=9fiTV6P6FuWg8weei7rQDA">here</A>.\r\n</BODY></HTML>\r\n'

As you can see, the last layer in this one, contain the code I need.

my question is:

Why don't I get the packet with sr() and how can I obtain it to collect the HTML code?

EDIT:

The call to the function:

print Make_Get('www.google.com')[0][Raw]

The function:

def Make_Get(ipp):
        ip = DNS_Req(ipp)
        synR = IP(dst = ip)/TCP(dport = 80,sport = randint(1024,65535), flags = 'S')
        syn_ack = sr1(synR)
        getStr = "GET / HTTP/1.1\r\nHost: {}\r\n\r\n".format(ip)
        request = (IP(dst= ip) / TCP(dport=80, sport=syn_ack[TCP].dport, seq=syn_ack[TCP].ack, ack=syn_ack[TCP].seq + 1, flags='A')/getStr)
        an = sr(request)
        return an

The resuls:

    Begin emission:
.Finished to send 1 packets.
*
Received 2 packets, got 1 answers, remaining 0 packets
Begin emission:
*Finished to send 1 packets.

Received 1 packets, got 1 answers, remaining 0 packets
[]

标签： http get scapy
举报
1条回答
SAY GOODBYE
2楼-- · 2019-09-09 20:47

First, in HTTP, a correct newline is "\r\n", not "\n".

Second, is there any reason why you use HTTP/1.0 and not HTTP/1.1? If not, you should change your request to:

GET / HTTP/1.1\r\n
Host: www.google.com\r\n
\r\n

Third, the ACK you are getting is usually sent by the server before sending the actual HTTP response to acknowledge your request faster. A second segment is then sent with the HTTP response. You are missing this one in your first show() example.

Have a look here.

To catch this segment, you can use sr() function with its parameter timeout and multi:

ans, unans = sr(request, timeout=2, multi=True)

for c, s in ans:
    if s.haslayer(Raw):
        print b[Raw]
    print("-----------") # just a delimiter

timeout is used to ensure that sr() will stop (value 2 is arbitrary). multi mean "accept multiple answers for the same stimulus" unless it is there, sr() will stop sniffing after one answer to the request sent.

查看更多
0人赞 添加讨论(0) 举报
登录 后发表回答
相关问题
查看全部
相关文章
查看全部
收藏的人(4)