Best strategy for overcoming excessive gethostbyname timeout.

[r0g]

Gabriel Genellina wrote:
> En Fri, 27 Nov 2009 22:35:36 -0300, r0g <aioe.org at technicalbloke.com>
> escribió:
> 
>> gethostbyname ignores setdefaulttimeout.
>>
>> How big a job is it to use non-blocking sockets to write a DNS lookup
>> function with a customisable timeout? A few lines? A few hundred? I'd
>> only need to  resolve v4 addresses for the foreseeable.
> 
> This guy reports good results using GNU adns to perform asynchronous
> queries:
> http://www.catonmat.net/blog/asynchronous-dns-resolution/
> 
> Also, look for pydns. Don't be afraid of its age; it always worked fine
> for me.
> 

Thanks Gabriel, that worked a treat when combined with John's SIGALARM
solution :)

For posterity here's the code...

import signal, socket
try:
    import DNS
except:
    DNS = False


def DNSResolve( s ):
    if DNS:
        DNS.ParseResolvConf() # Windows?
        r = DNS.DnsRequest(name=s,qtype='A')
        a = r.req()
        return a.answers[0]['data']
    else:
        return socket.gethostbyname( s )


def dns_timeout(a,b):
    raise Exception("Oh Noes! a DNS lookup timeout!")


def canIHasIP( domain_name, timeout=3 ):
    signal.signal(signal.SIGALRM, dns_timeout)
    signal.alarm( timeout )
    try:
        ip = DNSResolve( domain_name )
    except Exception, exc:
        print exc
        return False
    signal.alarm(0)
    return ip

usage: canIHasIP( domain_name, timeout_in_seconds) i.e.
canIHasIP("google.com",5)


Thanks guys! :D

Roger.