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Wait for network service to appear (Python recipe) by anatoly techtonik
ActiveState Code (http://code.activestate.com/recipes/576655/)

This script allows you to wait until specified port is opened on remote server. This can be useful in automation jobs - restarting server, wake on lan etc. It can also be used for monitoring distant service/site.

The main problem that this script solves is that you need to handle two different timeouts when opening probing socket, and it is not described in python documentation. See http://bugs.python.org/issue5293 for more information.

Python, 39 lines
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def wait_net_service(server, port, timeout=None):
    """ Wait for network service to appear 
        @param timeout: in seconds, if None or 0 wait forever
        @return: True of False, if timeout is None may return only True or
                 throw unhandled network exception
    """
    import socket
    import errno

    s = socket.socket()
    if timeout:
        from time import time as now
        # time module is needed to calc timeout shared between two exceptions
        end = now() + timeout

    while True:
        try:
            if timeout:
                next_timeout = end - now()
                if next_timeout < 0:
                    return False
                else:
            	    s.settimeout(next_timeout)
            
            s.connect((server, port))
        
        except socket.timeout, err:
            # this exception occurs only if timeout is set
            if timeout:
                return False
      
        except socket.error, err:
            # catch timeout exception from underlying network library
            # this one is different from socket.timeout
            if type(err.args) != tuple or err[0] != errno.ETIMEDOUT:
                raise
        else:
            s.close()
            return True

Examples:

wait until Samba service running on 139 port is up

wait_net_service("192.168.1.2", 139)

monitoring test if web server is responding (30 seconds timeout)

online = wait_net_service("192.168.1.2", 139, 30)

Tags: network, socket