python中网络相关的包和函数

一些概念

• 文件描述符
  • 可以是一个整数形式的文件描述符，比如 sys.stdin.fileno() 的返回结果，或为 io.IOBase 对象，比如 sys.stdin 提供一个 fileno()，可返回一个真正的文件描述符。

常用包

socket

• 比较底层的API接口，该模块提供对 BSD套接字接口的访问。它适用于所有现代 Unix 系统、Windows、MacOS 以及可能的其他平台。
• 每一个socket name都是一个地址族(address family) ，常用的地址族就是AF_INET(host,port) 以及 AF_UNIX(string形式返回的bytes-like object) [其他的AF还有很多… 比如AF_INET6 ]

  reference: 官方API：address family

  • 所以说有时候会看到sock.getsockname()[1]，如果采用的是AF_INET，[0] 就是host ip ( in string format )，[1]就是port ( in int format )
    • 但，也可能采用的是AF_UNIX地址，这个是在socket创建的时候指定的

fcntl

• 用于操控文件描述符，实际上是系统的API，python中有对应的包

• python 使用ioctl() 获得网卡IP 和MAC地址

  • 代码

  from fcntl import ioctl 
  import socket
  import struct
  import sys
   
  sock=socket.socket(socket.AF_INET,socket.SOCK_DGRAM)
  	try:
  		ip=ioctl(sock.fileno(),0x8915,struct.pack('64s','eth0'))
  		ip=socket.inet_ntoa(ip[20:24])
  		print ip
  except:
  		print sys.exc_info()
  

  • 我理解SIOCGIFADDR的意思是 socket IO get Interface Address

  more reference about ioctl : 知乎的函数API讲解

struct

• 用于格式化/解析字符串

  • struct.pack(fmt,v1,v2,…) --> a packed string
  • struct.unpack(fmt,string) --> a tuple of string
  • reference : 这个blog不错的

some demo codes

• extras/sflow.py in sflow-rt 居然还可以显示拓扑

  from mininet.net import Mininet
  from mininet.log import info
  from mininet.util import quietRun
  from os import listdir, environ
  from json import dumps
  from re import match
  from fcntl import ioctl
  from array import array
  from struct import pack, unpack
  from sys import maxsize
  import socket
  import sys
  
  try:
    from urllib.request import build_opener, HTTPHandler, Request
  except ImportError:
    from urllib2 import build_opener, HTTPHandler, Request
  
  
  def wrapper(fn):
    def getIfInfo(dst):
        is_64bits = maxsize > 2**32
        struct_size = 40 if is_64bits else 32
        s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)  # AF and stream type
        max_possible = 8  # initial value
        while True:
            bytes = max_possible * struct_size
            names = array('B')  #!
            for i in range(0, bytes):
                names.append(0)
            outbytes = unpack(  # struct.unpack(format, buffer) 
                'iL', # 目前猜测是是 integer long
                ioctl(  # 根据命令(2nd para)，对fd执行操作(1st para)，读写缓冲区((3rd para)) --> return buffer
                    s.fileno(), # 返回文件描述符fd，which可以做select()等
                    0x8912,  # SIOCGIFCONF 对应的值
                    pack('iL', bytes,
                          names.buffer_info()[0])))[0]
            if outbytes == bytes:
                max_possible *= 2
            else:
                break
  
        s.connect((dst, 0))
        ip = s.getsockname()[0]
        for i in range(0, outbytes, struct_size):
            addr = socket.inet_ntoa(names[i + 20:i + 24])
            if addr == ip:
                name = names[i:i + 16]
                try:
                    name = name.tobytes().decode('utf-8')
                except AttributeError:
                    name = name.tostring()
                name = name.split('\0', 1)[0]
                return (name, addr)
  
    def configSFlow(net, collector, ifname, sampling, polling):
      """ 创建sflow设置的命令行，调用 进行执行
      Args:
          net ([type]): [description]
          collector ([type]): [description]
          ifname ([type]): [description]
          sampling ([type]): [description]
          polling ([type]): [description]
      """
      info("*** Enabling sFlow:\n")
      sflow = 'ovs-vsctl -- --id=@sflow create sflow agent=%s target=%s sampling=%s polling=%s --' % (ifname, collector, sampling, polling)
      for s in net.switches:
          sflow += ' -- set bridge %s sflow=@sflow' % s
      info(' '.join([s.name for s in net.switches]) + "\n")
      quietRun(sflow) # TODO 立刻and后台执行？
  
    def sendTopology(net, agent, collector):
      info("*** Sending topology\n")
      topo = {
        
        'nodes': {
        
        }, 'links': {
        
        }}
      for s in net.switches:
          topo['nodes'][s.name] = {
        
        'agent': agent, 'ports': {
        
        }}
      path = '/sys/devices/virtual/net/'
      for child in listdir(path):
          parts = match('(^.+)-(.+)', child)
          if parts == None: continue
          if parts.group(1) in topo['nodes']:
              ifindex = open(path + child + '/ifindex').read().split('\n', 1)[0]
              topo['nodes'][parts.group(1)]['ports'][child] = {
        
        'ifindex': ifindex}
      i = 0
      for s1 in net.switches:
          j = 0
          for s2 in net.switches:
              if j > i:
                  intfs = s1.connectionsTo(s2)
                  for intf in intfs:
                      s1ifIdx = topo['nodes'][s1.name]['ports'][intf[0].name]['ifindex']
                      s2ifIdx = topo['nodes'][s2.name]['ports'][intf[1].name]['ifindex']
                      linkName = '%s-%s' % (s1.name, s2.name)
                      topo['links'][linkName] = {
        
        'node1': s1.name, 'port1': intf[0].name, 'node2': s2.name, 'port2': intf[1].name}
              j += 1
          i += 1
  
      opener = build_opener(HTTPHandler)
      request = Request('http://%s:8008/topology/json' % collector, data=dumps(topo).encode('utf-8')) # TODO
      request.add_header('Content-Type', 'application/json')
      request.get_method = lambda: 'PUT'
      url = opener.open(request)
  
    def result(*args, **kwargs):
        res = fn(*args, **kwargs)
        net = args[0]
        collector = environ.get('COLLECTOR', '127.0.0.1')  #! 环境变量
        sampling = environ.get('SAMPLING', '10')
        polling = environ.get('POLLING', '10')
        (ifname, agent) = getIfInfo(collector)
        configSFlow(net, collector, ifname, sampling, polling)
        sendTopology(net, agent, collector)
        return res
  
    return result
  
  
  setattr(Mininet, 'start', wrapper(Mininet.__dict__['start']))