Python 从特定源接收UDP数据包

我试图测量DNS服务器的响应。对小于512字节的典型DNS响应进行嗅探并不是什么大问题。我的问题是接收3000多字节的大响应—在某些情况下是5000多字节。我还没有找到一个能可靠接收数据的套接字。pythonsockets有没有办法从特定的源地址接收数据

以下是我到目前为止的情况：

import socket
import struct


def craft_dns(Qdns):

    iden = struct.pack('!H', randint(0, 65535))
    QR_thru_RD = chr(int('00000001', 2)) # '\x01'
    RA_thru_RCode = chr(int('00100000', 2)) # '\x00'
    Qcount = '\x00\x01' # question count is 1
    ANcount = '\x00\x00'
    NScount = '\x00\x00'
    ARcount = '\x00\x01' # additional resource count is 1
    pad = '\x00' #
    Rtype_ANY = '\x00\xff' # Request ANY record
    PROtype = '\x00\x01' # Protocol IN || '\x00\xff' # Protocol ANY
    DNSsec_do = chr(int('10000000', 2)) # flips DNSsec bit to enable
    edns0 = '\x00\x00\x29\x10\x00\x00\x00\x00\x00\x00\x00' # DNSsec disabled
    domain = Qdns.split('.')
    quest = ''

    for x in domain:
        quest += struct.pack('!B', len(x)) + x

    packet = (iden+QR_thru_RD+RA_thru_RCode+Qcount+ANcount+NScount+ARcount+
            quest+pad+Rtype_ANY+PROtype+edns0) # remove pad if asking <root>

    return packet

def craft_ip(target, resolv):

    ip_ver_len = int('01000101', 2) # IPvers: 4, 0100 | IP_hdr len: 5, 0101 = 69
    ipvers = 4
    ip_tos  = 0
    ip_len = 0 # socket will put in the right length
    iden = randint(0, 65535)
    ip_frag = 0 # off
    ttl = 255
    ip_proto = socket.IPPROTO_UDP # dns, brah
    chksm = 0 # socket will do the checksum
    s_addr = socket.inet_aton(target)
    d_addr = socket.inet_aton(resolv)

    ip_hdr = struct.pack('!BBHHHBBH4s4s', ip_ver_len, ip_tos, ip_len, iden, 
                    ip_frag, ttl, ip_proto, chksm, s_addr, d_addr)
    return ip_hdr

def craft_udp(sport, dest_port, packet): 

    #sport = randint(0, 65535) # not recommended to do a random port generation
    udp_len = 8 + len(packet) # calculate length of UDP frame in bytes.
    chksm = 0 # socket fills in
    udp_hdr = struct.pack('!HHHH', sport, dest_port, udp_len, chksm)

    return udp_hdr

def get_len(resolv, domain):

    target = "10.0.0.3"
    d_port = 53
    s_port = 5353

    ip_hdr = craft_ip(target, resolv)
    dns_payload = craft_dns(domain) # '\x00' for root
    udp_hdr = craft_udp(s_port, d_port, dns_payload)
    packet = ip_hdr + udp_hdr + dns_payload
    buf = bytearray("-" * 60000)

    recvSock = socket.socket(socket.PF_PACKET, socket.SOCK_RAW, socket.ntohs(0x0800))
    recvSock.settimeout(1)

    sendSock = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_RAW)
    sendSock.settimeout(1)

    sendSock.connect((resolv, d_port))
    sendSock.send(packet)

    msglen = 0
    while True:
        try:

            pkt = recvSock.recvfrom(65535)
            msglen += len(pkt[0])
            print repr(pkt[0])

        except socket.timeout as e:

            break

    sendSock.close()
    recvSock.close()    

    return msglen

result = get_len('75.75.75.75', 'isc.org')
print result

一无所获。因为我使用的是SOCK_RAW，所以上面的代码不太理想，但它可以正常工作。如果套接字非常嘈杂（比如在WLAN上），我最终可能会收到远远超出DNS数据包的数据包，因为我无法知道在接收多数据包DNS应答时何时停止接收数据包。对于一个安静的网络，如实验室虚拟机，它可以工作

在这种情况下，有没有更好的方法使用接收插座？ 显然，从代码来看，我对Python套接字没有那么强。
我必须使用SOCK_RAW发送，因为我正在以原始格式构造数据包。如果使用SOCK_DGRAM，则在发送到DNS解析程序时，自定义数据包的格式将不正确

---

我能看到的唯一方法是使用原始套接字接收器（recvSock.recv或recvfrom）并解压缩每个数据包，查看源地址和目标地址是否在get_len（）中提供的内容内匹配，然后查看片段位是否翻转。然后用len（）记录每个数据包的字节长度。我宁愿不那样做。似乎有更好的办法

好吧，我很愚蠢，没有查看接收套接字的协议。当您试图通过IPPROTO_原始协议接收数据包时，套接字会变得有点不稳定，所以我们确实需要两个套接字。通过更改为IPPROTO_UDP并绑定它，套接字能够跟踪多个请求的完整DNS响应。我去掉了try/catch和while循环，因为它不再是必需的，并且我能够用这个块拉取响应长度：

recvSock = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_UDP)
recvSock.settimeout(.3)
recvSock.bind((target, s_port))

sendSock = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_RAW)
#sendSock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sendSock.settimeout(.3)    
sendSock.bind((target, s_port))

sendSock.connect((resolv, d_port))
sendSock.send(packet)

pkt = recvSock.recvfrom(65535)
msglen = len(pkt[0])

现在，该方法将返回从DNS查询接收的确切字节。我将保留此选项，以防其他人需要执行类似操作：）

recvSock = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_UDP)
recvSock.settimeout(.3)
recvSock.bind((target, s_port))

sendSock = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_RAW)
#sendSock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sendSock.settimeout(.3)    
sendSock.bind((target, s_port))

sendSock.connect((resolv, d_port))
sendSock.send(packet)

pkt = recvSock.recvfrom(65535)
msglen = len(pkt[0])