Could not contact DNS servers after a connection outage and re-establishment

[mberdyshev]

I changed the example from the repository description to provide infinite query retries until a successful answer:

import asyncio
import aiodns

loop = asyncio.SelectorEventLoop()
resolver = aiodns.DNSResolver(loop=loop)

async def query(name, query_type):
    while True:
        try:
            return await resolver.query(name, query_type)
        except aiodns.error.DNSError as err:
            print(err)
            await asyncio.sleep(1)

coro = query('google.com', 'A')
result = loop.run_until_complete(coro)
print(result)
loop.close()

Let's assume my Windows machine has some network problems before the script run - I mockup this with the following cmd command:

netsh wlan add filter permission=block ssid="<Wi-Fi ssid>" networktype=infrastructure

When the script starts it constantly outputs (11, 'Could not contact DNS servers') as expected. But even if the network connection is re-established (netsh wlan delete filter <...>) during the script run, it still outputs the error. I can get the answer only if I stop and rerun the script.

I have also opened the issue on pycares tracker - saghul/pycares#203 .

[bdraco]

The channel is probably being initialized with no nameservers, and then the connection comes online the nameservers are populated, but the channel isn't being recreated

[bdraco]

When the system config changes, https://c-ares.org/docs/ares_reinit.html needs to be called on the channel

[bdraco]

To fix this

area_reinit needs to be exposed in pycares and than aiodns.DNSResolver needs a reinit method.

Then you need to call that method when the network changes

[Dreamsorcerer]

Is there a possibility this can be done automatically? Seems like a bit of an issue if we expect every developer to implement this themselves in order to have a robust application.

[saghul]

Not sure how TBH. THat's a question for the c-ares project likely...

[bdraco]

Is there a possibility this can be done automatically? Seems like a bit of an issue if we expect every developer to implement this themselves in order to have a robust application.

Every operating system is different on how it knows the network has changed. I'm not aware of any python library that can abstract that away and watch for network changes on all or even most systems