Python, wait until network interface is up?

Question

I have a python script which opens a port and listens to it on Raspberry. I added it to /etc/rc.local and everything is working properly. But my problem is the socket which is not created when the process is being executed.

s = socket.socket()      
s.bind((host_ip,port)) #e.g. host_ip='192.168.1.32' , port=12345
s.listen(5)
while True:
    c,addr = s.accept()
    c.send('ACK')
    c.close()

the above code is not executed because there is no 'eth0' connection available. What should I do? Should I loop scan the socket status until connection is being available? Is there any other more sophisticated solution?

Answer 1

Like this:

import urllib2,thread
from time import sleep
import netifaces


class _check:
    def __init__(self):
        self.uri="http://www.google.com"
        self.period = 5
        self.status = False
        self.ifaces()
    def check(self):
        try:
            answ = urllib2.urlopen(self.uri)
            if answ:
                self.status = True
                #Now can run your awesome code !
                print "okay go take a beer"
        except Exception,e : print e

    def timer(self,pass_arg) :
        while True :
            if   self.status != True :
                self.check()
                sleep(self.period)
                print "running"
            elif   self.status == True :
                print "thread ending"
                break
    def ifaces(self):
        for i in netifaces.interfaces() :
            try:
                print i,netifaces.ifaddresses(i)[2]
            except:
                print i, "iface not up !"


check = _check()
thread.start_new_thread(check.timer,(None,))

so this answer equal to my comment answer.

Answer 2

accept()方法会阻塞线程，当没有检测到设备连接服务器时，它会阻塞，表示accept()之后的代码不会被执行。

Answer 3

I don't know anything about Python but generally speaking of socket programming.

1. When you listen you don't need any host ( s.bind(('',port)) ).

2. You have to determine a function or an event handler that raises when a connection is established (maybe handle_connect in Python).

3. In the handler function you connect the client on a port other than the port you are currently listening.