text: #
  # Copyright 2011 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.
  
  """Miscellaneous network utility code."""
  
  import concurrent.futures
  import errno
  import os
  import sys
  import socket
  import ssl
  import stat
  
  from tornado.concurrent import dummy_executor, run_on_executor
  from tornado import gen
  from tornado.ioloop import IOLoop
  from tornado.platform.auto import set_close_exec
  from tornado.util import Configurable, errno_from_exception
  
  import typing
  from typing import List, Callable, Any, Type, Generator, Dict, Union, Tuple
  
  if typing.TYPE_CHECKING:
      from asyncio import Future  # noqa: F401
      from typing import Awaitable  # noqa: F401
  
  # Note that the naming of ssl.Purpose is confusing; the purpose
  # of a context is to authentiate the opposite side of the connection.
  _client_ssl_defaults = ssl.create_default_context(
      ssl.Purpose.SERVER_AUTH)
  _server_ssl_defaults = ssl.create_default_context(
      ssl.Purpose.CLIENT_AUTH)
  if hasattr(ssl, 'OP_NO_COMPRESSION'):
      # See netutil.ssl_options_to_context
      _client_ssl_defaults.options |= ssl.OP_NO_COMPRESSION
      _server_ssl_defaults.options |= ssl.OP_NO_COMPRESSION
  
  # ThreadedResolver runs getaddrinfo on a thread. If the hostname is unicode,
  # getaddrinfo attempts to import encodings.idna. If this is done at
  # module-import time, the import lock is already held by the main thread,
  # leading to deadlock. Avoid it by caching the idna encoder on the main
  # thread now.
  u'foo'.encode('idna')
  
  # For undiagnosed reasons, 'latin1' codec may also need to be preloaded.
  u'foo'.encode('latin1')
  
  # These errnos indicate that a non-blocking operation must be retried
  # at a later time.  On most platforms they're the same value, but on
  # some they differ.
  _ERRNO_WOULDBLOCK = (errno.EWOULDBLOCK, errno.EAGAIN)
  
  if hasattr(errno, "WSAEWOULDBLOCK"):
      _ERRNO_WOULDBLOCK += (errno.WSAEWOULDBLOCK,)  # type: ignore
  
  # Default backlog used when calling sock.listen()
  _DEFAULT_BACKLOG = 128
  
  
  def bind_sockets(port: int, address: str=None,
                   family: socket.AddressFamily=socket.AF_UNSPEC,
                   backlog: int=_DEFAULT_BACKLOG, flags: int=None,
                   reuse_port: bool=False) -> List[socket.socket]:
      """Creates listening sockets bound to the given port and address.
  
      Returns a list of socket objects (multiple sockets are returned if
      the given address maps to multiple IP addresses, which is most common
      for mixed IPv4 and IPv6 use).
  
      Address may be either an IP address or hostname.  If it's a hostname,
      the server will listen on all IP addresses associated with the
      name.  Address may be an empty string or None to listen on all
      available interfaces.  Family may be set to either `socket.AF_INET`
      or `socket.AF_INET6` to restrict to IPv4 or IPv6 addresses, otherwise
      both will be used if available.
  
      The ``backlog`` argument has the same meaning as for
      `socket.listen() <socket.socket.listen>`.
  
      ``flags`` is a bitmask of AI_* flags to `~socket.getaddrinfo`, like
      ``socket.AI_PASSIVE | socket.AI_NUMERICHOST``.
  
      ``reuse_port`` option sets ``SO_REUSEPORT`` option for every socket
      in the list. If your platform doesn't support this option ValueError will
      be raised.
      """
      if reuse_port and not hasattr(socket, "SO_REUSEPORT"):
          raise ValueError("the platform doesn't support SO_REUSEPORT")
  
      sockets = []
      if address == "":
          address = None
      if not socket.has_ipv6 and family == socket.AF_UNSPEC:
          # Python can be compiled with --disable-ipv6, which causes
          # operations on AF_INET6 sockets to fail, but does not
          # automatically exclude those results from getaddrinfo
          # results.
          # http://bugs.python.org/issue16208
          family = socket.AF_INET
      if flags is None:
          flags = socket.AI_PASSIVE
      bound_port = None
      unique_addresses = set()  # type: set
      for res in sorted(socket.getaddrinfo(address, port, family, socket.SOCK_STREAM,
                                           0, flags), key=lambda x: x[0]):
          if res in unique_addresses:
              continue
  
          unique_addresses.add(res)
  
          af, socktype, proto, canonname, sockaddr = res
          if (sys.platform == 'darwin' and address == 'localhost' and
                  af == socket.AF_INET6 and sockaddr[3] != 0):
              # Mac OS X includes a link-local address fe80::1%lo0 in the
              # getaddrinfo results for 'localhost'.  However, the firewall
              # doesn't understand that this is a local address and will
              # prompt for access (often repeatedly, due to an apparent
              # bug in its ability to remember granting access to an
              # application). Skip these addresses.
              continue
          try:
              sock = socket.socket(af, socktype, proto)
          except socket.error as e:
              if errno_from_exception(e) == errno.EAFNOSUPPORT:
                  continue
              raise
          set_close_exec(sock.fileno())
          if os.name != 'nt':
              try:
                  sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
              except socket.error as e:
                  if errno_from_exception(e) != errno.ENOPROTOOPT:
                      # Hurd doesn't support SO_REUSEADDR.
                      raise
          if reuse_port:
              sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
          if af == socket.AF_INET6:
              # On linux, ipv6 sockets accept ipv4 too by default,
              # but this makes it impossible to bind to both
              # 0.0.0.0 in ipv4 and :: in ipv6.  On other systems,
              # separate sockets *must* be used to listen for both ipv4
              # and ipv6.  For consistency, always disable ipv4 on our
              # ipv6 sockets and use a separate ipv4 socket when needed.
              #
              # Python 2.x on windows doesn't have IPPROTO_IPV6.
              if hasattr(socket, "IPPROTO_IPV6"):
                  sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 1)
  
          # automatic port allocation with port=None
          # should bind on the same port on IPv4 and IPv6
          host, requested_port = sockaddr[:2]
          if requested_port == 0 and bound_port is not None:
              sockaddr = tuple([host, bound_port] + list(sockaddr[2:]))
  
          sock.setblocking(False)
          sock.bind(sockaddr)
          bound_port = sock.getsockname()[1]
          sock.listen(backlog)
          sockets.append(sock)
      return sockets
  
  
  if hasattr(socket, 'AF_UNIX'):
      def bind_unix_socket(file: str, mode: int=0o600,
                           backlog: int=_DEFAULT_BACKLOG) -> socket.socket:
          """Creates a listening unix socket.
  
          If a socket with the given name already exists, it will be deleted.
          If any other file with that name exists, an exception will be
          raised.
  
          Returns a socket object (not a list of socket objects like
          `bind_sockets`)
          """
          sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
          set_close_exec(sock.fileno())
          try:
              sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
          except socket.error as e:
              if errno_from_exception(e) != errno.ENOPROTOOPT:
                  # Hurd doesn't support SO_REUSEADDR
                  raise
          sock.setblocking(False)
          try:
              st = os.stat(file)
          except OSError as err:
              if errno_from_exception(err) != errno.ENOENT:
                  raise
          else:
              if stat.S_ISSOCK(st.st_mode):
                  os.remove(file)
              else:
                  raise ValueError("File %s exists and is not a socket", file)
          sock.bind(file)
          os.chmod(file, mode)
          sock.listen(backlog)
          return sock
  
  
  def add_accept_handler(sock: socket.socket,
                         callback: Callable[[socket.socket, Any], None]) -> Callable[[], None]:
      """Adds an `.IOLoop` event handler to accept new connections on ``sock``.
  
      When a connection is accepted, ``callback(connection, address)`` will
      be run (``connection`` is a socket object, and ``address`` is the
      address of the other end of the connection).  Note that this signature
      is different from the ``callback(fd, events)`` signature used for
      `.IOLoop` handlers.
  
      A callable is returned which, when called, will remove the `.IOLoop`
      event handler and stop processing further incoming connections.
  
      .. versionchanged:: 5.0
         The ``io_loop`` argument (deprecated since version 4.1) has been removed.
  
      .. versionchanged:: 5.0
         A callable is returned (``None`` was returned before).
      """
      io_loop = IOLoop.current()
      removed = [False]
  
      def accept_handler(fd: socket.socket, events: int) -> None:
          # More connections may come in while we're handling callbacks;
          # to prevent starvation of other tasks we must limit the number
          # of connections we accept at a time.  Ideally we would accept
          # up to the number of connections that were waiting when we
          # entered this method, but this information is not available
          # (and rearranging this method to call accept() as many times
          # as possible before running any callbacks would have adverse
          # effects on load balancing in multiprocess configurations).
          # Instead, we use the (default) listen backlog as a rough
          # heuristic for the number of connections we can reasonably
          # accept at once.
          for i in range(_DEFAULT_BACKLOG):
              if removed[0]:
                  # The socket was probably closed
                  return
              try:
                  connection, address = sock.accept()
              except socket.error as e:
                  # _ERRNO_WOULDBLOCK indicate we have accepted every
                  # connection that is available.
                  if errno_from_exception(e) in _ERRNO_WOULDBLOCK:
                      return
                  # ECONNABORTED indicates that there was a connection
                  # but it was closed while still in the accept queue.
                  # (observed on FreeBSD).
                  if errno_from_exception(e) == errno.ECONNABORTED:
                      continue
                  raise
              set_close_exec(connection.fileno())
              callback(connection, address)
  
      def remove_handler() -> None:
          io_loop.remove_handler(sock)
          removed[0] = True
  
      io_loop.add_handler(sock, accept_handler, IOLoop.READ)
      return remove_handler
  
  
  def is_valid_ip(ip: str) -> bool:
      """Returns true if the given string is a well-formed IP address.
  
      Supports IPv4 and IPv6.
      """
      if not ip or '\x00' in ip:
          # getaddrinfo resolves empty strings to localhost, and truncates
          # on zero bytes.
          return False
      try:
          res = socket.getaddrinfo(ip, 0, socket.AF_UNSPEC,
                                   socket.SOCK_STREAM,
                                   0, socket.AI_NUMERICHOST)
          return bool(res)
      except socket.gaierror as e:
          if e.args[0] == socket.EAI_NONAME:
              return False
          raise
      return True
  
  
  class Resolver(Configurable):
      """Configurable asynchronous DNS resolver interface.
  
      By default, a blocking implementation is used (which simply calls
      `socket.getaddrinfo`).  An alternative implementation can be
      chosen with the `Resolver.configure <.Configurable.configure>`
      class method::
  
          Resolver.configure('tornado.netutil.ThreadedResolver')
  
      The implementations of this interface included with Tornado are
  
      * `tornado.netutil.DefaultExecutorResolver`
      * `tornado.netutil.BlockingResolver` (deprecated)
      * `tornado.netutil.ThreadedResolver` (deprecated)
      * `tornado.netutil.OverrideResolver`
      * `tornado.platform.twisted.TwistedResolver`
      * `tornado.platform.caresresolver.CaresResolver`
  
      .. versionchanged:: 5.0
         The default implementation has changed from `BlockingResolver` to
         `DefaultExecutorResolver`.
      """
      @classmethod
      def configurable_base(cls) -> Type['Resolver']:
          return Resolver
  
      @classmethod
      def configurable_default(cls) -> Type['Resolver']:
          return DefaultExecutorResolver
  
      def resolve(
              self, host: str, port: int, family: socket.AddressFamily=socket.AF_UNSPEC,
      ) -> 'Future[List[Tuple[int, Any]]]':
          """Resolves an address.
  
          The ``host`` argument is a string which may be a hostname or a
          literal IP address.
  
          Returns a `.Future` whose result is a list of (family,
          address) pairs, where address is a tuple suitable to pass to
          `socket.connect <socket.socket.connect>` (i.e. a ``(host,
          port)`` pair for IPv4; additional fields may be present for
          IPv6). If a ``callback`` is passed, it will be run with the
          result as an argument when it is complete.
  
          :raises IOError: if the address cannot be resolved.
  
          .. versionchanged:: 4.4
             Standardized all implementations to raise `IOError`.
  
          .. versionchanged:: 6.0 The ``callback`` argument was removed.
             Use the returned awaitable object instead.
  
          """
          raise NotImplementedError()
  
      def close(self) -> None:
          """Closes the `Resolver`, freeing any resources used.
  
          .. versionadded:: 3.1
  
          """
          pass
  
  
  def _resolve_addr(
          host: str, port: int, family: socket.AddressFamily=socket.AF_UNSPEC,
  ) -> List[Tuple[int, Any]]:
      # On Solaris, getaddrinfo fails if the given port is not found
      # in /etc/services and no socket type is given, so we must pass
      # one here.  The socket type used here doesn't seem to actually
      # matter (we discard the one we get back in the results),
      # so the addresses we return should still be usable with SOCK_DGRAM.
      addrinfo = socket.getaddrinfo(host, port, family, socket.SOCK_STREAM)
      results = []
      for fam, socktype, proto, canonname, address in addrinfo:
          results.append((fam, address))
      return results
  
  
  class DefaultExecutorResolver(Resolver):
      """Resolver implementation using `.IOLoop.run_in_executor`.
  
      .. versionadded:: 5.0
      """
      @gen.coroutine
      def resolve(
              self, host: str, port: int, family: socket.AddressFamily=socket.AF_UNSPEC,
      ) -> Generator[Any, Any, List[Tuple[int, Any]]]:
          result = yield IOLoop.current().run_in_executor(
              None, _resolve_addr, host, port, family)
          return result
  
  
  class ExecutorResolver(Resolver):
      """Resolver implementation using a `concurrent.futures.Executor`.
  
      Use this instead of `ThreadedResolver` when you require additional
      control over the executor being used.
  
      The executor will be shut down when the resolver is closed unless
      ``close_resolver=False``; use this if you want to reuse the same
      executor elsewhere.
  
      .. versionchanged:: 5.0
         The ``io_loop`` argument (deprecated since version 4.1) has been removed.
  
      .. deprecated:: 5.0
         The default `Resolver` now uses `.IOLoop.run_in_executor`; use that instead
         of this class.
      """
      def initialize(self, executor: concurrent.futures.Executor=None,
                     close_executor: bool=True) -> None:
          self.io_loop = IOLoop.current()
          if executor is not None:
              self.executor = executor
              self.close_executor = close_executor
          else:
              self.executor = dummy_executor
              self.close_executor = False
  
      def close(self) -> None:
          if self.close_executor:
              self.executor.shutdown()
          self.executor = None  # type: ignore
  
      @run_on_executor
      def resolve(
              self, host: str, port: int, family: socket.AddressFamily=socket.AF_UNSPEC,
      ) -> List[Tuple[int, Any]]:
          return _resolve_addr(host, port, family)
  
  
  class BlockingResolver(ExecutorResolver):
      """Default `Resolver` implementation, using `socket.getaddrinfo`.
  
      The `.IOLoop` will be blocked during the resolution, although the
      callback will not be run until the next `.IOLoop` iteration.
  
      .. deprecated:: 5.0
         The default `Resolver` now uses `.IOLoop.run_in_executor`; use that instead
         of this class.
      """
      def initialize(self) -> None:  # type: ignore
          super(BlockingResolver, self).initialize()
  
  
  class ThreadedResolver(ExecutorResolver):
      """Multithreaded non-blocking `Resolver` implementation.
  
      Requires the `concurrent.futures` package to be installed
      (available in the standard library since Python 3.2,
      installable with ``pip install futures`` in older versions).
  
      The thread pool size can be configured with::
  
          Resolver.configure('tornado.netutil.ThreadedResolver',
                             num_threads=10)
  
      .. versionchanged:: 3.1
         All ``ThreadedResolvers`` share a single thread pool, whose
         size is set by the first one to be created.
  
      .. deprecated:: 5.0
         The default `Resolver` now uses `.IOLoop.run_in_executor`; use that instead
         of this class.
      """
      _threadpool = None  # type: ignore
      _threadpool_pid = None  # type: int
  
      def initialize(self, num_threads: int=10) -> None:  # type: ignore
          threadpool = ThreadedResolver._create_threadpool(num_threads)
          super(ThreadedResolver, self).initialize(
              executor=threadpool, close_executor=False)
  
      @classmethod
      def _create_threadpool(cls, num_threads: int) -> concurrent.futures.ThreadPoolExecutor:
          pid = os.getpid()
          if cls._threadpool_pid != pid:
              # Threads cannot survive after a fork, so if our pid isn't what it
              # was when we created the pool then delete it.
              cls._threadpool = None
          if cls._threadpool is None:
              cls._threadpool = concurrent.futures.ThreadPoolExecutor(num_threads)
              cls._threadpool_pid = pid
          return cls._threadpool
  
  
  class OverrideResolver(Resolver):
      """Wraps a resolver with a mapping of overrides.
  
      This can be used to make local DNS changes (e.g. for testing)
      without modifying system-wide settings.
  
      The mapping can be in three formats::
  
          {
              # Hostname to host or ip
              "example.com": "127.0.1.1",
  
              # Host+port to host+port
              ("login.example.com", 443): ("localhost", 1443),
  
              # Host+port+address family to host+port
              ("login.example.com", 443, socket.AF_INET6): ("::1", 1443),
          }
  
      .. versionchanged:: 5.0
         Added support for host-port-family triplets.
      """
      def initialize(self, resolver: Resolver, mapping: dict) -> None:  # type: ignore
          self.resolver = resolver
          self.mapping = mapping
  
      def close(self) -> None:
          self.resolver.close()
  
      def resolve(
              self, host: str, port: int, family: socket.AddressFamily=socket.AF_UNSPEC,
      ) -> 'Future[List[Tuple[int, Any]]]':
          if (host, port, family) in self.mapping:
              host, port = self.mapping[(host, port, family)]
          elif (host, port) in self.mapping:
              host, port = self.mapping[(host, port)]
          elif host in self.mapping:
              host = self.mapping[host]
          return self.resolver.resolve(host, port, family)
  
  
  # These are the keyword arguments to ssl.wrap_socket that must be translated
  # to their SSLContext equivalents (the other arguments are still passed
  # to SSLContext.wrap_socket).
  _SSL_CONTEXT_KEYWORDS = frozenset(['ssl_version', 'certfile', 'keyfile',
                                     'cert_reqs', 'ca_certs', 'ciphers'])
  
  
  def ssl_options_to_context(ssl_options: Union[Dict[str, Any], ssl.SSLContext]) -> ssl.SSLContext:
      """Try to convert an ``ssl_options`` dictionary to an
      `~ssl.SSLContext` object.
  
      The ``ssl_options`` dictionary contains keywords to be passed to
      `ssl.wrap_socket`.  In Python 2.7.9+, `ssl.SSLContext` objects can
      be used instead.  This function converts the dict form to its
      `~ssl.SSLContext` equivalent, and may be used when a component which
      accepts both forms needs to upgrade to the `~ssl.SSLContext` version
      to use features like SNI or NPN.
      """
      if isinstance(ssl_options, ssl.SSLContext):
          return ssl_options
      assert isinstance(ssl_options, dict)
      assert all(k in _SSL_CONTEXT_KEYWORDS for k in ssl_options), ssl_options
      # Can't use create_default_context since this interface doesn't
      # tell us client vs server.
      context = ssl.SSLContext(
          ssl_options.get('ssl_version', ssl.PROTOCOL_SSLv23))
      if 'certfile' in ssl_options:
          context.load_cert_chain(ssl_options['certfile'], ssl_options.get('keyfile', None))
      if 'cert_reqs' in ssl_options:
          context.verify_mode = ssl_options['cert_reqs']
      if 'ca_certs' in ssl_options:
          context.load_verify_locations(ssl_options['ca_certs'])
      if 'ciphers' in ssl_options:
          context.set_ciphers(ssl_options['ciphers'])
      if hasattr(ssl, 'OP_NO_COMPRESSION'):
          # Disable TLS compression to avoid CRIME and related attacks.
          # This constant depends on openssl version 1.0.
          # TODO: Do we need to do this ourselves or can we trust
          # the defaults?
          context.options |= ssl.OP_NO_COMPRESSION
      return context
  
  
  def ssl_wrap_socket(socket: socket.socket, ssl_options: Union[Dict[str, Any], ssl.SSLContext],
                      server_hostname: str=None, **kwargs: Any) -> ssl.SSLSocket:
      """Returns an ``ssl.SSLSocket`` wrapping the given socket.
  
      ``ssl_options`` may be either an `ssl.SSLContext` object or a
      dictionary (as accepted by `ssl_options_to_context`).  Additional
      keyword arguments are passed to ``wrap_socket`` (either the
      `~ssl.SSLContext` method or the `ssl` module function as
      appropriate).
      """
      context = ssl_options_to_context(ssl_options)
      if ssl.HAS_SNI:
          # In python 3.4, wrap_socket only accepts the server_hostname
          # argument if HAS_SNI is true.
          # TODO: add a unittest (python added server-side SNI support in 3.4)
          # In the meantime it can be manually tested with
          # python3 -m tornado.httpclient https://sni.velox.ch
          return context.wrap_socket(socket, server_hostname=server_hostname,
                                     **kwargs)
      else:
          return context.wrap_socket(socket, **kwargs)
  