python调用tcpdump抓包过滤

之前在linux用python脚本写一个抓包分析小工具，实在不想用什么libpcap、pypcap所以，简单来了个tcpdump加grep搞定。基本思路是分别起tcpdump和grep两个进程，进程直接通过pipe交换数据，简单代码如下：

#! /usr/bin/python  

def tcpdump():
    import subprocess, fcntl, os
    # sudo tcpdump -i eth0 -n -s 0 -w - | grep -a -o -E "Host: .*|GET /.*"
    cmd1 = ['tcpdump', '-i', 'eth0', '-n','-B', '4096','-s', '0', '-w', '-']
    cmd2 = ['grep', '--line-buffered', '-a', '-o', '-E', 'Host: .*|GET /.*']
    p1 = subprocess.Popen(cmd1, stdout=subprocess.PIPE)
    p2 = subprocess.Popen(cmd2, stdout=subprocess.PIPE, stdin=p1.stdout)  

    flags = fcntl.fcntl(p2.stdout.fileno(), fcntl.F_GETFL)
    fcntl.fcntl(p2.stdout.fileno(), fcntl.F_SETFL, (flags | os.O_NDELAY | os.O_NONBLOCK))
    return p2  

def poll_tcpdump(proc):
    #print 'poll_tcpdump....'
    import select
    txt = None
    while True:
        # wait 1/10 second
        readReady, _, _ = select.select([proc.stdout.fileno()], [], [], 0.1)
        if not len(readReady):
            break
        try:
            for line in iter(proc.stdout.readline, ""):
                if txt is None:
                    txt = ''
                txt += line
        except IOError:
            print 'data empty...'
            pass
        break
    return txt  

proc = tcpdump()
while True:
    text = poll_tcpdump(proc)
    if text:
        print '>>>> ' + text

　　运行效果：

其中值得注意tcpdump中'-B', '4096'这个参数，官方文档貌似没有明确提及，但是它是你解决丢包的关键地方之一，当然还有-s这个参数也得好好利用！其他的大家可以自由发挥！