text: import contextlib
  import errno
  import os.path
  import socket
  import sys
  import tempfile
  import unittest
  
  from .. import support
  from . import warnings_helper
  
  HOST = "localhost"
  HOSTv4 = "127.0.0.1"
  HOSTv6 = "::1"
  
  # WASI SDK 15.0 does not provide gethostname, stub raises OSError ENOTSUP.
  has_gethostname = not support.is_wasi
  
  
  def find_unused_port(family=socket.AF_INET, socktype=socket.SOCK_STREAM):
      """Returns an unused port that should be suitable for binding.  This is
      achieved by creating a temporary socket with the same family and type as
      the 'sock' parameter (default is AF_INET, SOCK_STREAM), and binding it to
      the specified host address (defaults to 0.0.0.0) with the port set to 0,
      eliciting an unused ephemeral port from the OS.  The temporary socket is
      then closed and deleted, and the ephemeral port is returned.
  
      Either this method or bind_port() should be used for any tests where a
      server socket needs to be bound to a particular port for the duration of
      the test.  Which one to use depends on whether the calling code is creating
      a python socket, or if an unused port needs to be provided in a constructor
      or passed to an external program (i.e. the -accept argument to openssl's
      s_server mode).  Always prefer bind_port() over find_unused_port() where
      possible.  Hard coded ports should *NEVER* be used.  As soon as a server
      socket is bound to a hard coded port, the ability to run multiple instances
      of the test simultaneously on the same host is compromised, which makes the
      test a ticking time bomb in a buildbot environment. On Unix buildbots, this
      may simply manifest as a failed test, which can be recovered from without
      intervention in most cases, but on Windows, the entire python process can
      completely and utterly wedge, requiring someone to log in to the buildbot
      and manually kill the affected process.
  
      (This is easy to reproduce on Windows, unfortunately, and can be traced to
      the SO_REUSEADDR socket option having different semantics on Windows versus
      Unix/Linux.  On Unix, you can't have two AF_INET SOCK_STREAM sockets bind,
      listen and then accept connections on identical host/ports.  An EADDRINUSE
      OSError will be raised at some point (depending on the platform and
      the order bind and listen were called on each socket).
  
      However, on Windows, if SO_REUSEADDR is set on the sockets, no EADDRINUSE
      will ever be raised when attempting to bind two identical host/ports. When
      accept() is called on each socket, the second caller's process will steal
      the port from the first caller, leaving them both in an awkwardly wedged
      state where they'll no longer respond to any signals or graceful kills, and
      must be forcibly killed via OpenProcess()/TerminateProcess().
  
      The solution on Windows is to use the SO_EXCLUSIVEADDRUSE socket option
      instead of SO_REUSEADDR, which effectively affords the same semantics as
      SO_REUSEADDR on Unix.  Given the propensity of Unix developers in the Open
      Source world compared to Windows ones, this is a common mistake.  A quick
      look over OpenSSL's 0.9.8g source shows that they use SO_REUSEADDR when
      openssl.exe is called with the 's_server' option, for example. See
      http://bugs.python.org/issue2550 for more info.  The following site also
      has a very thorough description about the implications of both REUSEADDR
      and EXCLUSIVEADDRUSE on Windows:
      http://msdn2.microsoft.com/en-us/library/ms740621(VS.85).aspx)
  
      XXX: although this approach is a vast improvement on previous attempts to
      elicit unused ports, it rests heavily on the assumption that the ephemeral
      port returned to us by the OS won't immediately be dished back out to some
      other process when we close and delete our temporary socket but before our
      calling code has a chance to bind the returned port.  We can deal with this
      issue if/when we come across it.
      """
  
      with socket.socket(family, socktype) as tempsock:
          port = bind_port(tempsock)
      del tempsock
      return port
  
  def bind_port(sock, host=HOST):
      """Bind the socket to a free port and return the port number.  Relies on
      ephemeral ports in order to ensure we are using an unbound port.  This is
      important as many tests may be running simultaneously, especially in a
      buildbot environment.  This method raises an exception if the sock.family
      is AF_INET and sock.type is SOCK_STREAM, *and* the socket has SO_REUSEADDR
      or SO_REUSEPORT set on it.  Tests should *never* set these socket options
      for TCP/IP sockets.  The only case for setting these options is testing
      multicasting via multiple UDP sockets.
  
      Additionally, if the SO_EXCLUSIVEADDRUSE socket option is available (i.e.
      on Windows), it will be set on the socket.  This will prevent anyone else
      from bind()'ing to our host/port for the duration of the test.
      """
  
      if sock.family == socket.AF_INET and sock.type == socket.SOCK_STREAM:
          if hasattr(socket, 'SO_REUSEADDR'):
              if sock.getsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR) == 1:
                  raise support.TestFailed("tests should never set the "
                                           "SO_REUSEADDR socket option on "
                                           "TCP/IP sockets!")
          if hasattr(socket, 'SO_REUSEPORT'):
              try:
                  if sock.getsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT) == 1:
                      raise support.TestFailed("tests should never set the "
                                               "SO_REUSEPORT socket option on "
                                               "TCP/IP sockets!")
              except OSError:
                  # Python's socket module was compiled using modern headers
                  # thus defining SO_REUSEPORT but this process is running
                  # under an older kernel that does not support SO_REUSEPORT.
                  pass
          if hasattr(socket, 'SO_EXCLUSIVEADDRUSE'):
              sock.setsockopt(socket.SOL_SOCKET, socket.SO_EXCLUSIVEADDRUSE, 1)
  
      sock.bind((host, 0))
      port = sock.getsockname()[1]
      return port
  
  def bind_unix_socket(sock, addr):
      """Bind a unix socket, raising SkipTest if PermissionError is raised."""
      assert sock.family == socket.AF_UNIX
      try:
          sock.bind(addr)
      except PermissionError:
          sock.close()
          raise unittest.SkipTest('cannot bind AF_UNIX sockets')
  
  def _is_ipv6_enabled():
      """Check whether IPv6 is enabled on this host."""
      if socket.has_ipv6:
          sock = None
          try:
              sock = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
              sock.bind((HOSTv6, 0))
              return True
          except OSError:
              pass
          finally:
              if sock:
                  sock.close()
      return False
  
  IPV6_ENABLED = _is_ipv6_enabled()
  
  
  _bind_nix_socket_error = None
  def skip_unless_bind_unix_socket(test):
      """Decorator for tests requiring a functional bind() for unix sockets."""
      if not hasattr(socket, 'AF_UNIX'):
          return unittest.skip('No UNIX Sockets')(test)
      global _bind_nix_socket_error
      if _bind_nix_socket_error is None:
          from .os_helper import TESTFN, unlink
          path = TESTFN + "can_bind_unix_socket"
          with socket.socket(socket.AF_UNIX) as sock:
              try:
                  sock.bind(path)
                  _bind_nix_socket_error = False
              except OSError as e:
                  _bind_nix_socket_error = e
              finally:
                  unlink(path)
      if _bind_nix_socket_error:
          msg = 'Requires a functional unix bind(): %s' % _bind_nix_socket_error
          return unittest.skip(msg)(test)
      else:
          return test
  
  
  def get_socket_conn_refused_errs():
      """
      Get the different socket error numbers ('errno') which can be received
      when a connection is refused.
      """
      errors = [errno.ECONNREFUSED]
      if hasattr(errno, 'ENETUNREACH'):
          # On Solaris, ENETUNREACH is returned sometimes instead of ECONNREFUSED
          errors.append(errno.ENETUNREACH)
      if hasattr(errno, 'EADDRNOTAVAIL'):
          # bpo-31910: socket.create_connection() fails randomly
          # with EADDRNOTAVAIL on Travis CI
          errors.append(errno.EADDRNOTAVAIL)
      if hasattr(errno, 'EHOSTUNREACH'):
          # bpo-37583: The destination host cannot be reached
          errors.append(errno.EHOSTUNREACH)
      if not IPV6_ENABLED:
          errors.append(errno.EAFNOSUPPORT)
      return errors
  
  
  _NOT_SET = object()
  
  @contextlib.contextmanager
  def transient_internet(resource_name, *, timeout=_NOT_SET, errnos=()):
      """Return a context manager that raises ResourceDenied when various issues
      with the internet connection manifest themselves as exceptions."""
      nntplib = warnings_helper.import_deprecated("nntplib")
      import urllib.error
      if timeout is _NOT_SET:
          timeout = support.INTERNET_TIMEOUT
  
      default_errnos = [
          ('ECONNREFUSED', 111),
          ('ECONNRESET', 104),
          ('EHOSTUNREACH', 113),
          ('ENETUNREACH', 101),
          ('ETIMEDOUT', 110),
          # socket.create_connection() fails randomly with
          # EADDRNOTAVAIL on Travis CI.
          ('EADDRNOTAVAIL', 99),
      ]
      default_gai_errnos = [
          ('EAI_AGAIN', -3),
          ('EAI_FAIL', -4),
          ('EAI_NONAME', -2),
          ('EAI_NODATA', -5),
          # Encountered when trying to resolve IPv6-only hostnames
          ('WSANO_DATA', 11004),
      ]
  
      denied = support.ResourceDenied("Resource %r is not available" % resource_name)
      captured_errnos = errnos
      gai_errnos = []
      if not captured_errnos:
          captured_errnos = [getattr(errno, name, num)
                             for (name, num) in default_errnos]
          gai_errnos = [getattr(socket, name, num)
                        for (name, num) in default_gai_errnos]
  
      def filter_error(err):
          n = getattr(err, 'errno', None)
          if (isinstance(err, TimeoutError) or
              (isinstance(err, socket.gaierror) and n in gai_errnos) or
              (isinstance(err, urllib.error.HTTPError) and
               500 <= err.code <= 599) or
              (isinstance(err, urllib.error.URLError) and
                   (("ConnectionRefusedError" in err.reason) or
                    ("TimeoutError" in err.reason) or
                    ("EOFError" in err.reason))) or
              n in captured_errnos):
              if not support.verbose:
                  sys.stderr.write(denied.args[0] + "\n")
              raise denied from err
  
      old_timeout = socket.getdefaulttimeout()
      try:
          if timeout is not None:
              socket.setdefaulttimeout(timeout)
          yield
      except nntplib.NNTPTemporaryError as err:
          if support.verbose:
              sys.stderr.write(denied.args[0] + "\n")
          raise denied from err
      except OSError as err:
          # urllib can wrap original socket errors multiple times (!), we must
          # unwrap to get at the original error.
          while True:
              a = err.args
              if len(a) >= 1 and isinstance(a[0], OSError):
                  err = a[0]
              # The error can also be wrapped as args[1]:
              #    except socket.error as msg:
              #        raise OSError('socket error', msg) from msg
              elif len(a) >= 2 and isinstance(a[1], OSError):
                  err = a[1]
              else:
                  break
          filter_error(err)
          raise
      # XXX should we catch generic exceptions and look for their
      # __cause__ or __context__?
      finally:
          socket.setdefaulttimeout(old_timeout)
  
  
  def create_unix_domain_name():
      """
      Create a UNIX domain name: socket.bind() argument of a AF_UNIX socket.
  
      Return a path relative to the current directory to get a short path
      (around 27 ASCII characters).
      """
      return tempfile.mktemp(prefix="test_python_", suffix='.sock',
                             dir=os.path.curdir)
  