#!/usr/bin/env python # # Copyright 2014 Facebook # # Licensed under the Apache License, Version 2.0 (the "License"); you may # not use this file except in compliance with the License. You may obtain # a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the # License for the specific language governing permissions and limitations # under the License. """A non-blocking TCP connection factory. """ from __future__ import absolute_import, division, print_function, with_statement import functools import socket from tornado.concurrent import Future from tornado.ioloop import IOLoop from tornado.iostream import IOStream from tornado import gen from tornado.netutil import Resolver _INITIAL_CONNECT_TIMEOUT = 0.3 class _Connector(object): """A stateless implementation of the "Happy Eyeballs" algorithm. "Happy Eyeballs" is documented in RFC6555 as the recommended practice for when both IPv4 and IPv6 addresses are available. In this implementation, we partition the addresses by family, and make the first connection attempt to whichever address was returned first by ``getaddrinfo``. If that connection fails or times out, we begin a connection in parallel to the first address of the other family. If there are additional failures we retry with other addresses, keeping one connection attempt per family in flight at a time. http://tools.ietf.org/html/rfc6555 """ def __init__(self, addrinfo, io_loop, connect): self.io_loop = io_loop self.connect = connect self.future = Future() self.timeout = None self.last_error = None self.remaining = len(addrinfo) self.primary_addrs, self.secondary_addrs = self.split(addrinfo) @staticmethod def split(addrinfo): """Partition the ``addrinfo`` list by address family. Returns two lists. The first list contains the first entry from ``addrinfo`` and all others with the same family, and the second list contains all other addresses (normally one list will be AF_INET and the other AF_INET6, although non-standard resolvers may return additional families). """ primary = [] secondary = [] primary_af = addrinfo[0][0] for af, addr in addrinfo: if af == primary_af: primary.append((af, addr)) else: secondary.append((af, addr)) return primary, secondary def start(self, timeout=_INITIAL_CONNECT_TIMEOUT): self.try_connect(iter(self.primary_addrs)) self.set_timout(timeout) return self.future def try_connect(self, addrs): try: af, addr = next(addrs) except StopIteration: # We've reached the end of our queue, but the other queue # might still be working. Send a final error on the future # only when both queues are finished. if self.remaining == 0 and not self.future.done(): self.future.set_exception(self.last_error or IOError("connection failed")) return future = self.connect(af, addr) future.add_done_callback(functools.partial(self.on_connect_done, addrs, af, addr)) def on_connect_done(self, addrs, af, addr, future): self.remaining -= 1 try: stream = future.result() except Exception as e: if self.future.done(): return # Error: try again (but remember what happened so we have an # error to raise in the end) self.last_error = e self.try_connect(addrs) if self.timeout is not None: # If the first attempt failed, don't wait for the # timeout to try an address from the secondary queue. self.on_timeout() return self.clear_timeout() if self.future.done(): # This is a late arrival; just drop it. stream.close() else: self.future.set_result((af, addr, stream)) def set_timout(self, timeout): self.timeout = self.io_loop.add_timeout(self.io_loop.time() + timeout, self.on_timeout) def on_timeout(self): self.timeout = None self.try_connect(iter(self.secondary_addrs)) def clear_timeout(self): if self.timeout is not None: self.io_loop.remove_timeout(self.timeout) class TCPClient(object): """A non-blocking TCP connection factory. """ def __init__(self, resolver=None, io_loop=None): self.io_loop = io_loop or IOLoop.current() if resolver is not None: self.resolver = resolver self._own_resolver = False else: self.resolver = Resolver(io_loop=io_loop) self._own_resolver = True def close(self): if self._own_resolver: self.resolver.close() @gen.coroutine def connect(self, host, port, af=socket.AF_UNSPEC, ssl_options=None, max_buffer_size=None): """Connect to the given host and port. Asynchronously returns an `.IOStream` (or `.SSLIOStream` if ``ssl_options`` is not None). """ addrinfo = yield self.resolver.resolve(host, port, af) connector = _Connector( addrinfo, self.io_loop, functools.partial(self._create_stream, max_buffer_size)) af, addr, stream = yield connector.start() # TODO: For better performance we could cache the (af, addr) # information here and re-use it on subsequent connections to # the same host. (http://tools.ietf.org/html/rfc6555#section-4.2) if ssl_options is not None: stream = yield stream.start_tls(False, ssl_options=ssl_options, server_hostname=host) raise gen.Return(stream) def _create_stream(self, max_buffer_size, af, addr): # Always connect in plaintext; we'll convert to ssl if necessary # after one connection has completed. stream = IOStream(socket.socket(af), io_loop=self.io_loop, max_buffer_size=max_buffer_size) return stream.connect(addr)