from __future__ import absolute_import, division, print_function, with_statement import pycares import socket from tornado import gen from tornado.ioloop import IOLoop from tornado.netutil import Resolver, is_valid_ip class CaresResolver(Resolver): """Name resolver based on the c-ares library. This is a non-blocking and non-threaded resolver. It may not produce the same results as the system resolver, but can be used for non-blocking resolution when threads cannot be used. c-ares fails to resolve some names when ``family`` is ``AF_UNSPEC``, so it is only recommended for use in ``AF_INET`` (i.e. IPv4). This is the default for ``tornado.simple_httpclient``, but other libraries may default to ``AF_UNSPEC``. """ def initialize(self, io_loop=None): self.io_loop = io_loop or IOLoop.current() self.channel = pycares.Channel(sock_state_cb=self._sock_state_cb) self.fds = {} def _sock_state_cb(self, fd, readable, writable): state = ((IOLoop.READ if readable else 0) | (IOLoop.WRITE if writable else 0)) if not state: self.io_loop.remove_handler(fd) del self.fds[fd] elif fd in self.fds: self.io_loop.update_handler(fd, state) self.fds[fd] = state else: self.io_loop.add_handler(fd, self._handle_events, state) self.fds[fd] = state def _handle_events(self, fd, events): read_fd = pycares.ARES_SOCKET_BAD write_fd = pycares.ARES_SOCKET_BAD if events & IOLoop.READ: read_fd = fd if events & IOLoop.WRITE: write_fd = fd self.channel.process_fd(read_fd, write_fd) @gen.coroutine def resolve(self, host, port, family=0): if is_valid_ip(host): addresses = [host] else: # gethostbyname doesn't take callback as a kwarg self.channel.gethostbyname(host, family, (yield gen.Callback(1))) callback_args = yield gen.Wait(1) assert isinstance(callback_args, gen.Arguments) assert not callback_args.kwargs result, error = callback_args.args if error: raise Exception('C-Ares returned error %s: %s while resolving %s' % (error, pycares.errno.strerror(error), host)) addresses = result.addresses addrinfo = [] for address in addresses: if '.' in address: address_family = socket.AF_INET elif ':' in address: address_family = socket.AF_INET6 else: address_family = socket.AF_UNSPEC if family != socket.AF_UNSPEC and family != address_family: raise Exception('Requested socket family %d but got %d' % (family, address_family)) addrinfo.append((address_family, (address, port))) raise gen.Return(addrinfo)