Python 使用指定的网卡发送HTTP请求的实例

需求: 一台机器上有多个网卡, 如何访问指定的 URL 时使用指定的网卡发送数据呢?

$ curl --interface eth0 www.baidu.com # curl interface 可以指定网卡

阅读 urllib.py 的源码, 追述到 open_http ?> httplib.HTTP ?> httplib.HTTP._connection_class = HTTPConnection

HTTPConnection 在创建的时候会指定一个 source_address.

HTTPConnection.connect 时调用 HTTPConnection._create_connection = socket.create_connection

# 先看一下本地网卡信息
$ ifconfig
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
  options=3<RXCSUM,TXCSUM>
  inet6 ::1 prefixlen 128 
  inet 127.0.0.1 netmask 0xff000000 
  inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1 
  nd6 options=1<PERFORMNUD>
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
  ether c8:e0:eb:17:3a:73 
  inet6 fe80::cae0:ebff:fe17:3a73%en0 prefixlen 64 scopeid 0x4 
  inet 192.168.20.2 netmask 0xffffff00 broadcast 192.168.20.255
  nd6 options=1<PERFORMNUD>
  media: autoselect
  status: active
en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
  options=4<VLAN_MTU>
  ether 0c:5b:8f:27:9a:64 
  inet6 fe80::e5b:8fff:fe27:9a64%en8 prefixlen 64 scopeid 0xa 
  inet 192.168.8.100 netmask 0xffffff00 broadcast 192.168.8.255
  nd6 options=1<PERFORMNUD>
  media: autoselect (100baseTX <full-duplex>)
  status: active

可以看到en0和en1, 这两块网卡都可以访问公网. lo0是本地回环.

直接修改 socket.py 做测试.

def create_connection(address, timeout=_GLOBAL_DEFAULT_TIMEOUT,
           source_address=None):
  """If *source_address* is set it must be a tuple of (host, port)
  for the socket to bind as a source address before making the connection.
  An host of '' or port 0 tells the OS to use the default.
  source_address 如果设置, 必须是传递元组 (host, port), 默认是 ("", 0) 
  """

  host, port = address
  err = None
  for res in getaddrinfo(host, port, 0, SOCK_STREAM):
    af, socktype, proto, canonname, sa = res
    sock = None
    try:
      sock = socket(af, socktype, proto)
      # sock.bind(("192.168.20.2", 0)) # en0
      # sock.bind(("192.168.8.100", 0)) # en1
      # sock.bind(("127.0.0.1", 0)) # lo0
      if timeout is not _GLOBAL_DEFAULT_TIMEOUT:
        sock.settimeout(timeout)
      if source_address:
        print "socket bind source_address: %s" % source_address
        sock.bind(source_address)
      sock.connect(sa)
      return sock

    except error as _:
      err = _
      if sock is not None:
        sock.close()
  if err is not None:
    raise err
  else:
    raise error("getaddrinfo returns an empty list")

参考说明文档, 直接分三次绑定不通网卡的 IP 地址, 端口设置为0.

# 测试 en0
$ python -c 'import urllib as u;print u.urlopen("http://ip.haschek.at").read()'
.148.245.16

# 测试 en1
$ python -c 'import urllib as u;print u.urlopen("http://ip.haschek.at").read()'
.94.115.227

# 测试 lo0
$ python -c 'import urllib as u;print u.urlopen("http://ip.haschek.at").read()'
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.py", line 87, in urlopen
  return opener.open(url)
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.py", line 213, in open
  return getattr(self, name)(url)
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.py", line 350, in open_http
  h.endheaders(data)
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.py", line 1049, in endheaders
  self._send_output(message_body)
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.py", line 893, in _send_output
  self.send(msg)
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.py", line 855, in send
  self.connect()
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.py", line 832, in connect
  self.timeout, self.source_address)
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/socket.py", line 578, in create_connection
  raise err
IOError: [Errno socket error] [Errno 49] Can't assign requested address

测试通过, 说明在多网卡情况下, 创建 socket 时绑定某块网卡的 IP 就可以, 端口需要设置为0. 如果端口不设置为0, 第二次请求时, 可以看到抛异常, 端口被占用.

Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.py", line 87, in urlopen
  return opener.open(url)
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.py", line 213, in open
  return getattr(self, name)(url)
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.py", line 350, in open_http
  h.endheaders(data)
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.py", line 1049, in endheaders
  self._send_output(message_body)
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.py", line 893, in _send_output
  self.send(msg)
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.py", line 855, in send
  self.connect()
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.py", line 832, in connect
  self.timeout, self.source_address)
 File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/socket.py", line 577, in create_connection
  raise err
IOError: [Errno socket error] [Errno 48] Address already in use

如果是在项目中, 只需要把 socket.create_connection 这个函数的形参 source_address 设置为对应网卡的 (IP, 0) 就可以.

# test-interface_urllib.py
import socket
import urllib, urllib2

_create_socket = socket.create_connection

SOURCE_ADDRESS = ("127.0.0.1", 0)
#SOURCE_ADDRESS = ("172.28.153.121", 0)
#SOURCE_ADDRESS = ("172.16.30.41", 0)

def create_connection(*args, **kwargs):
  in_args = False
  if len(args) >=3:
    args = list(args)
    args[2] = SOURCE_ADDRESS
    args = tuple(args)
    in_args = True
  if not in_args:
    kwargs["source_address"] = SOURCE_ADDRESS
  print "args", args
  print "kwargs", str(kwargs)
  return _create_socket(*args, **kwargs)

socket.create_connection = create_connection

print urllib.urlopen("http://ip.haschek.at").read()

通过测试, 可以发现已经可以通过制定的网卡发送数据, 并且 IP 地址对应网卡分配的 IP.

问题, 爬虫经常使用 requests, requests 是否支持呢. 通过测试, 可以发现, requests 并没有使用 python 内置的 socket 模块.

看源码, requests 是如果创建的 socket 连接呢. 方法和查看 urllib 创建socket 的方式一样. 具体就不写了.

因为我用的是 python 2.7, 所以可以定位到 requests 使用的 socket 模块是 urllib3.utils.connection 的.

修改方法和 urllib 相差不大.

import urllib3.connection
_create_socket = urllib3.connection.connection.create_connection
# pass

urllib3.connection.connection.create_connection = create_connection
# pass

运行后, 可能会抛出异常. requests.exceptions.ConnectionError: Max retries exceeded with .. Invalid argument

这个异常不是每次出现, 跟 IP 段有关系, 跳转递归层数太多导致, 只需要将 kwargs 中的 socket_options去掉即可. 127.0.0.1肯定会出异常.

import socket
import urllib
import urllib2
import urllib3.connection

import requests as req

_default_create_socket = socket.create_connection
_urllib3_create_socket = urllib3.connection.connection.create_connection


SOURCE_ADDRESS = ("127.0.0.1", 0)
#SOURCE_ADDRESS = ("172.28.153.121", 0)
#SOURCE_ADDRESS = ("172.16.30.41", 0)

def default_create_connection(*args, **kwargs):
  try:
    del kwargs["socket_options"]
  except:
    pass
  in_args = False
  if len(args) >=3:
    args = list(args)
    args[2] = SOURCE_ADDRESS
    args = tuple(args)
    in_args = True
  if not in_args:
    kwargs["source_address"] = SOURCE_ADDRESS
  print "args", args
  print "kwargs", str(kwargs)
  return _default_create_socket(*args, **kwargs)

def urllib3_create_connection(*args, **kwargs):
  in_args = False
  if len(args) >=3:
    args = list(args)
    args[2] = SOURCE_ADDRESS
    in_args = True
    args = tuple(args)
  if not in_args:
    kwargs["source_address"] = SOURCE_ADDRESS
  print "args", args
  print "kwargs", str(kwargs)
  return _urllib3_create_socket(*args, **kwargs)

socket.create_connection = default_create_connection
# 因为偶尔会出问题, 所以使用默认的 socket.create_connection
# urllib3.connection.connection.create_connection = urllib3_create_connection
urllib3.connection.connection.create_connection = default_create_connection

print " *** test requests: " + req.get("http://ip.haschek.at").content
print " *** test urllib: " + urllib.urlopen("http://ip.haschek.at").read()
print " *** test urllib2: " + urllib2.urlopen("http://ip.haschek.at").read()

注意: 使用 urllib3.utils.connection 好像不起作用

稍微再完善一下, 就是把根据网卡名自动获取 IP.

import subprocess

def get_all_net_devices():
  sub = subprocess.Popen("ls /sys/class/net", shell=True, stdout=subprocess.PIPE)
  sub.wait()
  net_devices = sub.stdout.read().strip().splitlines()
  # ['eth0', 'eth1', 'lo']
  # 这里简单过滤一下网卡名字, 根据需求改动
  net_devices = [i for i in net_devices if "ppp" in i]
  return net_devices
ALL_DEVICES = get_all_net_devices()

def get_local_ip(device_name):
  sub = subprocess.Popen("/sbin/ifconfig en0 | grep '%s ' | awk '{print $2}'" % device_name, shell=True, stdout=subprocess.PIPE)
  sub.wait()
  ip = sub.stdout.read().strip()
  return ip

def random_local_ip():
  return get_local_ip(random.choice(ALL_DEVICES))

# code ...

只需要把 args[2] = SOURCE_ADDRESS 和 kwargs["source_address"] = SOURCE_ADDRESS改成 random_local_ip() 或者 get_local_ip("eth0")

至于有什么用途, 就全凭想象了.

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