text: #!/usr/bin/env python
  # -*- coding: utf-8 -*-
  #
  # 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."""
  
  from __future__ import absolute_import, division, \
      print_function, with_statement
  
  import errno
  import os
  import sys
  import socket
  import stat
  
  from tornado.concurrent import dummy_executor, run_on_executor
  from tornado.ioloop import IOLoop
  from tornado.platform.auto import set_close_exec
  from tornado.util import u, Configurable, errno_from_exception
  
  try:
      import ssl
  except ImportError:
      # ssl is not available on Google App Engine
      ssl = None
  
  try:
      import certifi
  except ImportError:
      # certifi is optional as long as we have ssl.create_default_context.
      if ssl is None or hasattr(ssl, 'create_default_context'):
          certifi = None
      else:
          raise
  
  try:
      xrange  # py2
  except NameError:
      xrange = range  # py3
  
  if hasattr(ssl, 'match_hostname') and \
          hasattr(ssl, 'CertificateError'):  # python 3.2+
      ssl_match_hostname = ssl.match_hostname
      SSLCertificateError = ssl.CertificateError
  elif ssl is None:
      ssl_match_hostname = SSLCertificateError = None
  else:
      import backports.ssl_match_hostname
      ssl_match_hostname = backports.ssl_match_hostname.match_hostname
      SSLCertificateError = backports.ssl_match_hostname.CertificateError
  
  if hasattr(ssl, 'SSLContext'):
      if hasattr(ssl, 'create_default_context'):
          # Python 2.7.9+, 3.4+
          # 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)
      else:
          # Python 3.2-3.3
          _client_ssl_defaults = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
          _client_ssl_defaults.verify_mode = ssl.CERT_REQUIRED
          _client_ssl_defaults.load_verify_locations(certifi.where())
          _server_ssl_defaults = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
          if hasattr(ssl, 'OP_NO_COMPRESSION'):
              # Disable TLS compression to avoid CRIME and related attacks.
              # This constant wasn't added until python 3.3.
              _client_ssl_defaults.options |= ssl.OP_NO_COMPRESSION
              _server_ssl_defaults.options |= ssl.OP_NO_COMPRESSION
  
  elif ssl:
      # Python 2.6-2.7.8
      _client_ssl_defaults = dict(cert_reqs=ssl.CERT_REQUIRED,
                                  ca_certs=certifi.where())
      _server_ssl_defaults = {}
  else:
      # Google App Engine
      _client_ssl_defaults = dict(cert_reqs=None,
                                  ca_certs=None)
      _server_ssl_defaults = {}
  
  # 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')
  
  # 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,)
  
  # Default backlog used when calling sock.listen()
  _DEFAULT_BACKLOG = 128
  
  
  def bind_sockets(port, address=None, family=socket.AF_UNSPEC,
                   backlog=_DEFAULT_BACKLOG, flags=None, reuse_port=False):
      """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``.
  
      ``resuse_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 之所以是数组，是因为一台机器可能有多块实体、虚拟网卡，并且网卡可能同时
      # 支持 IPv4 与 IPv6，这样服务器要监听的 socket 就不止一个了。
      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:
          # 如果没有指定 flags，则默认让产生的 socket 是可以监听请求的。
          flags = socket.AI_PASSIVE
      bound_port = None
      for res in set(socket.getaddrinfo(address, port,
                                        family, socket.SOCK_STREAM,
                                        0, flags)):
          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':
              sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
          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(0)
          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, mode=0o600, backlog=_DEFAULT_BACKLOG):
          """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())
          sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
          sock.setblocking(0)
          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, callback, io_loop=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.
  
      .. versionchanged:: 4.1
         The ``io_loop`` argument is deprecated.
      """
      if io_loop is None:
          io_loop = IOLoop.current()
  
      def accept_handler(fd, events):
          # 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 xrange(_DEFAULT_BACKLOG):
              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
              callback(connection, address)
      io_loop.add_handler(sock, accept_handler, IOLoop.READ)
  
  
  def is_valid_ip(ip):
      """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.BlockingResolver`
      * `tornado.netutil.ThreadedResolver`
      * `tornado.netutil.OverrideResolver`
      * `tornado.platform.twisted.TwistedResolver`
      * `tornado.platform.caresresolver.CaresResolver`
      """
      @classmethod
      def configurable_base(cls):
          return Resolver
  
      @classmethod
      def configurable_default(cls):
          return BlockingResolver
  
      def resolve(self, host, port, family=socket.AF_UNSPEC, callback=None):
          """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.
          """
          raise NotImplementedError()
  
      def close(self):
          """Closes the `Resolver`, freeing any resources used.
  
          .. versionadded:: 3.1
  
          """
          pass
  
  
  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:: 4.1
         The ``io_loop`` argument is deprecated.
      """
      def initialize(self, io_loop=None, executor=None, close_executor=True):
          self.io_loop = io_loop or 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):
          if self.close_executor:
              self.executor.shutdown()
          self.executor = None
  
      @run_on_executor
      def resolve(self, host, port, family=socket.AF_UNSPEC):
          # 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 family, socktype, proto, canonname, address in addrinfo:
              results.append((family, address))
          return results
  
  
  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.
      """
      def initialize(self, io_loop=None):
          super(BlockingResolver, self).initialize(io_loop=io_loop)
  
  
  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.
      """
      _threadpool = None
      _threadpool_pid = None
  
      def initialize(self, io_loop=None, num_threads=10):
          threadpool = ThreadedResolver._create_threadpool(num_threads)
          super(ThreadedResolver, self).initialize(
              io_loop=io_loop, executor=threadpool, close_executor=False)
  
      @classmethod
      def _create_threadpool(cls, num_threads):
          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:
              from concurrent.futures import ThreadPoolExecutor
              cls._threadpool = 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 contain either host strings or host-port pairs.
      """
      def initialize(self, resolver, mapping):
          self.resolver = resolver
          self.mapping = mapping
  
      def close(self):
          self.resolver.close()
  
      def resolve(self, host, port, *args, **kwargs):
          if (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, *args, **kwargs)
  
  
  # 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):
      """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, dict):
          assert all(k in _SSL_CONTEXT_KEYWORDS
                     for k in ssl_options), ssl_options
      if (not hasattr(ssl, 'SSLContext') or
              isinstance(ssl_options, ssl.SSLContext)):
          return ssl_options
      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 wasn't added until python 3.3.
          context.options |= ssl.OP_NO_COMPRESSION
      return context
  
  
  def ssl_wrap_socket(socket, ssl_options, server_hostname=None, **kwargs):
      """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 hasattr(ssl, 'SSLContext') and isinstance(context, ssl.SSLContext):
          if server_hostname is not None and getattr(ssl, 'HAS_SNI'):
              # Python doesn't have server-side SNI support so we can't
              # really unittest this, but it can be manually tested with
              # python3.2 -m tornado.httpclient https://sni.velox.ch
              return context.wrap_socket(socket, server_hostname=server_hostname,
                                         **kwargs)
          else:
              return context.wrap_socket(socket, **kwargs)
      else:
          return ssl.wrap_socket(socket, **dict(context, **kwargs))
  