Skip DNS resolving if provided host is already an ip address

[lphuberdeau]

When using the AsyncResolver, there is a DNSError when trying to access a url where the host is an ip address.

This patch skips the resolver step if the host is an ip address.

An alternative would have been to move the same patch to the AsyncResolver, but other resolvers would likely have the same issue. Also, there was also a condition formatting the result properly in the TCPConnector.

[popravich]

Everybody most of their time use host names not IP addresses,
so most of time this method will raise and except ValueError what is not very efficient.

[lphuberdeau]

Anything else to suggest? The ipaddress module does not have a way to verify the format while avoiding the exception. Custom-made validation does not seem like a better route.

[kaniini]

For this, we have:

class IPAwareAsyncResolver(AsyncResolver):
    @asyncio.coroutine
    def resolve(self, host, port=0, family=socket.AF_INET):
        if not host or family not in {socket.AF_UNSPEC, socket.AF_INET, socket.AF_INET6}:
            return []

        if hasattr(socket, 'inet_pton'):
             if family == socket.AF_UNSPEC:
                 afs = [socket.AF_INET, socket.AF_INET6]
             else:
                 afs = [family]

             for af in afs:
                 # Linux's inet_pton doesn't accept an IPv6 zone index after host,
                 # like '::1%lo0', so strip it. If we happen to make an invalid
                 # address look valid, we fail later in sock.connect or sock.bind.
                 try:
                     if af == socket.AF_INET6:
                         socket.inet_pton(af, host.partition('%')[0])
                     else:
                         socket.inet_pton(af, host)
                     return [{'hostname': host, 'host': host, 'port': port, 'family': family, 'proto': 0, 'flags': socket.AI_NUMERICHOST}]
                 except OSError:
                     pass

        # ... if we reach here, this means it's not a valid IP.  try a DNS lookup.
        hosts = yield from super(IPAwareAsyncResolver, self).resolve(host, port, family)
        return hosts

[asvetlov]

Fixed by #905

[lock]

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