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# Source code for socket

    # Wrapper module for _socket, providing some additional facilities
    # implemented in Python.

    """\
    This module provides socket operations and some related functions.
    On Unix, it supports IP (Internet Protocol) and Unix domain sockets.
    On other systems, it only supports IP. Functions specific for a
    socket are available as methods of the socket object.

    Functions:

    socket() -- create a new socket object
    socketpair() -- create a pair of new socket objects [*]
    fromfd() -- create a socket object from an open file descriptor [*]
    send_fds() -- Send file descriptor to the socket.
    recv_fds() -- Receive file descriptors from the socket.
    fromshare() -- create a socket object from data received from socket.share() [*]
    gethostname() -- return the current hostname
    gethostbyname() -- map a hostname to its IP number
    gethostbyaddr() -- map an IP number or hostname to DNS info
    getservbyname() -- map a service name and a protocol name to a port number
    getprotobyname() -- map a protocol name (e.g. 'tcp') to a number
    ntohs(), ntohl() -- convert 16, 32 bit int from network to host byte order
    htons(), htonl() -- convert 16, 32 bit int from host to network byte order
    inet_aton() -- convert IP addr string (123.45.67.89) to 32-bit packed format
    inet_ntoa() -- convert 32-bit packed format IP to string (123.45.67.89)
    socket.getdefaulttimeout() -- get the default timeout value
    socket.setdefaulttimeout() -- set the default timeout value
    create_connection() -- connects to an address, with an optional timeout and
                           optional source address.
    create_server() -- create a TCP socket and bind it to a specified address.

     [*] not available on all platforms!

    Special objects:

    SocketType -- type object for socket objects
    error -- exception raised for I/O errors
    has_ipv6 -- boolean value indicating if IPv6 is supported

    IntEnum constants:

    AF_INET, AF_UNIX -- socket domains (first argument to socket() call)
    SOCK_STREAM, SOCK_DGRAM, SOCK_RAW -- socket types (second argument)

    Integer constants:

    Many other constants may be defined; these may be used in calls to
    the setsockopt() and getsockopt() methods.
    """

    import _socket
    from _socket import *

    import os, sys, io, selectors
    from enum import IntEnum, IntFlag

    try:
        import errno
    except ImportError:
        errno = None
    EBADF = getattr(errno, 'EBADF', 9)
    EAGAIN = getattr(errno, 'EAGAIN', 11)
    EWOULDBLOCK = getattr(errno, 'EWOULDBLOCK', 11)

    __all__ = ["fromfd", "getfqdn", "create_connection", "create_server",
               "has_dualstack_ipv6", "AddressFamily", "SocketKind"]
    __all__.extend(os._get_exports_list(_socket))

    # Set up the socket.AF_* socket.SOCK_* constants as members of IntEnums for
    # nicer string representations.
    # Note that _socket only knows about the integer values. The public interface
    # in this module understands the enums and translates them back from integers
    # where needed (e.g. .family property of a socket object).

    IntEnum._convert_(
            'AddressFamily',
            __name__,
            lambda C: C.isupper() and C.startswith('AF_'))

    IntEnum._convert_(
            'SocketKind',
            __name__,
            lambda C: C.isupper() and C.startswith('SOCK_'))

    IntFlag._convert_(
            'MsgFlag',
            __name__,
            lambda C: C.isupper() and C.startswith('MSG_'))

    IntFlag._convert_(
            'AddressInfo',
            __name__,
            lambda C: C.isupper() and C.startswith('AI_'))

    _LOCALHOST    = '127.0.0.1'
    _LOCALHOST_V6 = '::1'

    def _intenum_converter(value, enum_klass):
        """Convert a numeric family value to an IntEnum member.

        If it's not a known member, return the numeric value itself.
        """
        try:
            return enum_klass(value)
        except ValueError:
            return value

    # WSA error codes
    if sys.platform.lower().startswith("win"):
        errorTab = {}
        errorTab[6] = "Specified event object handle is invalid."
        errorTab[8] = "Insufficient memory available."
        errorTab[87] = "One or more parameters are invalid."
        errorTab[995] = "Overlapped operation aborted."
        errorTab[996] = "Overlapped I/O event object not in signaled state."
        errorTab[997] = "Overlapped operation will complete later."
        errorTab[10004] = "The operation was interrupted."
        errorTab[10009] = "A bad file handle was passed."
        errorTab[10013] = "Permission denied."
        errorTab[10014] = "A fault occurred on the network??"  # WSAEFAULT
        errorTab[10022] = "An invalid operation was attempted."
        errorTab[10024] = "Too many open files."
        errorTab[10035] = "The socket operation would block."
        errorTab[10036] = "A blocking operation is already in progress."
        errorTab[10037] = "Operation already in progress."
        errorTab[10038] = "Socket operation on nonsocket."
        errorTab[10039] = "Destination address required."
        errorTab[10040] = "Message too long."
        errorTab[10041] = "Protocol wrong type for socket."
        errorTab[10042] = "Bad protocol option."
        errorTab[10043] = "Protocol not supported."
        errorTab[10044] = "Socket type not supported."
        errorTab[10045] = "Operation not supported."
        errorTab[10046] = "Protocol family not supported."
        errorTab[10047] = "Address family not supported by protocol family."
        errorTab[10048] = "The network address is in use."
        errorTab[10049] = "Cannot assign requested address."
        errorTab[10050] = "Network is down."
        errorTab[10051] = "Network is unreachable."
        errorTab[10052] = "Network dropped connection on reset."
        errorTab[10053] = "Software caused connection abort."
        errorTab[10054] = "The connection has been reset."
        errorTab[10055] = "No buffer space available."
        errorTab[10056] = "Socket is already connected."
        errorTab[10057] = "Socket is not connected."
        errorTab[10058] = "The network has been shut down."
        errorTab[10059] = "Too many references."
        errorTab[10060] = "The operation timed out."
        errorTab[10061] = "Connection refused."
        errorTab[10062] = "Cannot translate name."
        errorTab[10063] = "The name is too long."
        errorTab[10064] = "The host is down."
        errorTab[10065] = "The host is unreachable."
        errorTab[10066] = "Directory not empty."
        errorTab[10067] = "Too many processes."
        errorTab[10068] = "User quota exceeded."
        errorTab[10069] = "Disk quota exceeded."
        errorTab[10070] = "Stale file handle reference."
        errorTab[10071] = "Item is remote."
        errorTab[10091] = "Network subsystem is unavailable."
        errorTab[10092] = "Winsock.dll version out of range."
        errorTab[10093] = "Successful WSAStartup not yet performed."
        errorTab[10101] = "Graceful shutdown in progress."
        errorTab[10102] = "No more results from WSALookupServiceNext."
        errorTab[10103] = "Call has been canceled."
        errorTab[10104] = "Procedure call table is invalid."
        errorTab[10105] = "Service provider is invalid."
        errorTab[10106] = "Service provider failed to initialize."
        errorTab[10107] = "System call failure."
        errorTab[10108] = "Service not found."
        errorTab[10109] = "Class type not found."
        errorTab[10110] = "No more results from WSALookupServiceNext."
        errorTab[10111] = "Call was canceled."
        errorTab[10112] = "Database query was refused."
        errorTab[11001] = "Host not found."
        errorTab[11002] = "Nonauthoritative host not found."
        errorTab[11003] = "This is a nonrecoverable error."
        errorTab[11004] = "Valid name, no data record requested type."
        errorTab[11005] = "QoS receivers."
        errorTab[11006] = "QoS senders."
        errorTab[11007] = "No QoS senders."
        errorTab[11008] = "QoS no receivers."
        errorTab[11009] = "QoS request confirmed."
        errorTab[11010] = "QoS admission error."
        errorTab[11011] = "QoS policy failure."
        errorTab[11012] = "QoS bad style."
        errorTab[11013] = "QoS bad object."
        errorTab[11014] = "QoS traffic control error."
        errorTab[11015] = "QoS generic error."
        errorTab[11016] = "QoS service type error."
        errorTab[11017] = "QoS flowspec error."
        errorTab[11018] = "Invalid QoS provider buffer."
        errorTab[11019] = "Invalid QoS filter style."
        errorTab[11020] = "Invalid QoS filter style."
        errorTab[11021] = "Incorrect QoS filter count."
        errorTab[11022] = "Invalid QoS object length."
        errorTab[11023] = "Incorrect QoS flow count."
        errorTab[11024] = "Unrecognized QoS object."
        errorTab[11025] = "Invalid QoS policy object."
        errorTab[11026] = "Invalid QoS flow descriptor."
        errorTab[11027] = "Invalid QoS provider-specific flowspec."
        errorTab[11028] = "Invalid QoS provider-specific filterspec."
        errorTab[11029] = "Invalid QoS shape discard mode object."
        errorTab[11030] = "Invalid QoS shaping rate object."
        errorTab[11031] = "Reserved policy QoS element type."
        __all__.append("errorTab")

    class _GiveupOnSendfile(Exception): pass

    class socket(_socket.socket):

        """A subclass of _socket.socket adding the makefile() method."""

        __slots__ = ["__weakref__", "_io_refs", "_closed"]

        def __init__(self, family=-1, type=-1, proto=-1, fileno=None):
            # For user code address family and type values are IntEnum members, but
            # for the underlying _socket.socket they're just integers. The
            # constructor of _socket.socket converts the given argument to an
            # integer automatically.
            if fileno is None:
                if family == -1:
                    family = AF_INET
                if type == -1:
                    type = SOCK_STREAM
                if proto == -1:
                    proto = 0
            _socket.socket.__init__(self, family, type, proto, fileno)
            self._io_refs = 0
            self._closed = False

        def __enter__(self):
            return self

        def __exit__(self, *args):
            if not self._closed:
                self.close()

        def __repr__(self):
            """Wrap __repr__() to reveal the real class name and socket
            address(es).
            """
            closed = getattr(self, '_closed', False)
            s = "<%s.%s%s fd=%i, family=%s, type=%s, proto=%i" \
                % (self.__class__.__module__,
                   self.__class__.__qualname__,
                   " [closed]" if closed else "",
                   self.fileno(),
                   self.family,
                   self.type,
                   self.proto)
            if not closed:
                # getsockname and getpeername may not be available on WASI.
                try:
                    laddr = self.getsockname()
                    if laddr:
                        s += ", laddr=%s" % str(laddr)
                except (error, AttributeError):
                    pass
                try:
                    raddr = self.getpeername()
                    if raddr:
                        s += ", raddr=%s" % str(raddr)
                except (error, AttributeError):
                    pass
            s += '>'
            return s

        def __getstate__(self):
            raise TypeError(f"cannot pickle {self.__class__.__name__!r} object")

        def dup(self):
            """dup() -> socket object

            Duplicate the socket. Return a new socket object connected to the same
            system resource. The new socket is non-inheritable.
            """
            fd = dup(self.fileno())
            sock = self.__class__(self.family, self.type, self.proto, fileno=fd)
            sock.settimeout(self.gettimeout())
            return sock

        def accept(self):
            """accept() -> (socket object, address info)

            Wait for an incoming connection.  Return a new socket
            representing the connection, and the address of the client.
            For IP sockets, the address info is a pair (hostaddr, port).
            """
            fd, addr = self._accept()
            sock = socket(self.family, self.type, self.proto, fileno=fd)
            # Issue #7995: if no default timeout is set and the listening
            # socket had a (non-zero) timeout, force the new socket in blocking
            # mode to override platform-specific socket flags inheritance.
            if getdefaulttimeout() is None and self.gettimeout():
                sock.setblocking(True)
            return sock, addr

        def makefile(self, mode="r", buffering=None, *,
                     encoding=None, errors=None, newline=None):
            """makefile(...) -> an I/O stream connected to the socket

            The arguments are as for io.open() after the filename, except the only
            supported mode values are 'r' (default), 'w' and 'b'.
            """
            # XXX refactor to share code?
            if not set(mode) <= {"r", "w", "b"}:
                raise ValueError("invalid mode %r (only r, w, b allowed)" % (mode,))
            writing = "w" in mode
            reading = "r" in mode or not writing
            assert reading or writing
            binary = "b" in mode
            rawmode = ""
            if reading:
                rawmode += "r"
            if writing:
                rawmode += "w"
            raw = SocketIO(self, rawmode)
            self._io_refs += 1
            if buffering is None:
                buffering = -1
            if buffering < 0:
                buffering = io.DEFAULT_BUFFER_SIZE
            if buffering == 0:
                if not binary:
                    raise ValueError("unbuffered streams must be binary")
                return raw
            if reading and writing:
                buffer = io.BufferedRWPair(raw, raw, buffering)
            elif reading:
                buffer = io.BufferedReader(raw, buffering)
            else:
                assert writing
                buffer = io.BufferedWriter(raw, buffering)
            if binary:
                return buffer
            encoding = io.text_encoding(encoding)
            text = io.TextIOWrapper(buffer, encoding, errors, newline)
            text.mode = mode
            return text

        if hasattr(os, 'sendfile'):

            def _sendfile_use_sendfile(self, file, offset=0, count=None):
                self._check_sendfile_params(file, offset, count)
                sockno = self.fileno()
                try:
                    fileno = file.fileno()
                except (AttributeError, io.UnsupportedOperation) as err:
                    raise _GiveupOnSendfile(err)  # not a regular file
                try:
                    fsize = os.fstat(fileno).st_size
                except OSError as err:
                    raise _GiveupOnSendfile(err)  # not a regular file
                if not fsize:
                    return 0  # empty file
                # Truncate to 1GiB to avoid OverflowError, see bpo-38319.
                blocksize = min(count or fsize, 2 ** 30)
                timeout = self.gettimeout()
                if timeout == 0:
                    raise ValueError("non-blocking sockets are not supported")
                # poll/select have the advantage of not requiring any
                # extra file descriptor, contrarily to epoll/kqueue
                # (also, they require a single syscall).
                if hasattr(selectors, 'PollSelector'):
                    selector = selectors.PollSelector()
                else:
                    selector = selectors.SelectSelector()
                selector.register(sockno, selectors.EVENT_WRITE)

                total_sent = 0
                # localize variable access to minimize overhead
                selector_select = selector.select
                os_sendfile = os.sendfile
                try:
                    while True:
                        if timeout and not selector_select(timeout):
                            raise TimeoutError('timed out')
                        if count:
                            blocksize = min(count - total_sent, blocksize)
                            if blocksize <= 0:
                                break
                        try:
                            sent = os_sendfile(sockno, fileno, offset, blocksize)
                        except BlockingIOError:
                            if not timeout:
                                # Block until the socket is ready to send some
                                # data; avoids hogging CPU resources.
                                selector_select()
                            continue
                        except OSError as err:
                            if total_sent == 0:
                                # We can get here for different reasons, the main
                                # one being 'file' is not a regular mmap(2)-like
                                # file, in which case we'll fall back on using
                                # plain send().
                                raise _GiveupOnSendfile(err)
                            raise err from None
                        else:
                            if sent == 0:
                                break  # EOF
                            offset += sent
                            total_sent += sent
                    return total_sent
                finally:
                    if total_sent > 0 and hasattr(file, 'seek'):
                        file.seek(offset)
        else:
            def _sendfile_use_sendfile(self, file, offset=0, count=None):
                raise _GiveupOnSendfile(
                    "os.sendfile() not available on this platform")

        def _sendfile_use_send(self, file, offset=0, count=None):
            self._check_sendfile_params(file, offset, count)
            if self.gettimeout() == 0:
                raise ValueError("non-blocking sockets are not supported")
            if offset:
                file.seek(offset)
            blocksize = min(count, 8192) if count else 8192
            total_sent = 0
            # localize variable access to minimize overhead
            file_read = file.read
            sock_send = self.send
            try:
                while True:
                    if count:
                        blocksize = min(count - total_sent, blocksize)
                        if blocksize <= 0:
                            break
                    data = memoryview(file_read(blocksize))
                    if not data:
                        break  # EOF
                    while True:
                        try:
                            sent = sock_send(data)
                        except BlockingIOError:
                            continue
                        else:
                            total_sent += sent
                            if sent < len(data):
                                data = data[sent:]
                            else:
                                break
                return total_sent
            finally:
                if total_sent > 0 and hasattr(file, 'seek'):
                    file.seek(offset + total_sent)

        def _check_sendfile_params(self, file, offset, count):
            if 'b' not in getattr(file, 'mode', 'b'):
                raise ValueError("file should be opened in binary mode")
            if not self.type & SOCK_STREAM:
                raise ValueError("only SOCK_STREAM type sockets are supported")
            if count is not None:
                if not isinstance(count, int):
                    raise TypeError(
                        "count must be a positive integer (got {!r})".format(count))
                if count <= 0:
                    raise ValueError(
                        "count must be a positive integer (got {!r})".format(count))

        def sendfile(self, file, offset=0, count=None):
            """sendfile(file[, offset[, count]]) -> sent

            Send a file until EOF is reached by using high-performance
            os.sendfile() and return the total number of bytes which
            were sent.
            *file* must be a regular file object opened in binary mode.
            If os.sendfile() is not available (e.g. Windows) or file is
            not a regular file socket.send() will be used instead.
            *offset* tells from where to start reading the file.
            If specified, *count* is the total number of bytes to transmit
            as opposed to sending the file until EOF is reached.
            File position is updated on return or also in case of error in
            which case file.tell() can be used to figure out the number of
            bytes which were sent.
            The socket must be of SOCK_STREAM type.
            Non-blocking sockets are not supported.
            """
            try:
                return self._sendfile_use_sendfile(file, offset, count)
            except _GiveupOnSendfile:
                return self._sendfile_use_send(file, offset, count)

        def _decref_socketios(self):
            if self._io_refs > 0:
                self._io_refs -= 1
            if self._closed:
                self.close()

        def _real_close(self, _ss=_socket.socket):
            # This function should not reference any globals. See issue #808164.
            _ss.close(self)

        def close(self):
            # This function should not reference any globals. See issue #808164.
            self._closed = True
            if self._io_refs <= 0:
                self._real_close()

        def detach(self):
            """detach() -> file descriptor

            Close the socket object without closing the underlying file descriptor.
            The object cannot be used after this call, but the file descriptor
            can be reused for other purposes.  The file descriptor is returned.
            """
            self._closed = True
            return super().detach()

        @property
        def family(self):
            """Read-only access to the address family for this socket.
            """
            return _intenum_converter(super().family, AddressFamily)

        @property
        def type(self):
            """Read-only access to the socket type.
            """
            return _intenum_converter(super().type, SocketKind)

        if os.name == 'nt':
            def get_inheritable(self):
                return os.get_handle_inheritable(self.fileno())
            def set_inheritable(self, inheritable):
                os.set_handle_inheritable(self.fileno(), inheritable)
        else:
            def get_inheritable(self):
                return os.get_inheritable(self.fileno())
            def set_inheritable(self, inheritable):
                os.set_inheritable(self.fileno(), inheritable)
        get_inheritable.__doc__ = "Get the inheritable flag of the socket"
        set_inheritable.__doc__ = "Set the inheritable flag of the socket"

    def fromfd(fd, family, type, proto=0):
        """ fromfd(fd, family, type[, proto]) -> socket object

        Create a socket object from a duplicate of the given file
        descriptor.  The remaining arguments are the same as for socket().
        """
        nfd = dup(fd)
        return socket(family, type, proto, nfd)

    if hasattr(_socket.socket, "sendmsg"):
        import array

        def send_fds(sock, buffers, fds, flags=0, address=None):
            """ send_fds(sock, buffers, fds[, flags[, address]]) -> integer

            Send the list of file descriptors fds over an AF_UNIX socket.
            """
            return sock.sendmsg(buffers, [(_socket.SOL_SOCKET,
                _socket.SCM_RIGHTS, array.array("i", fds))])
        __all__.append("send_fds")

    if hasattr(_socket.socket, "recvmsg"):
        import array

        def recv_fds(sock, bufsize, maxfds, flags=0):
            """ recv_fds(sock, bufsize, maxfds[, flags]) -> (data, list of file
            descriptors, msg_flags, address)

            Receive up to maxfds file descriptors returning the message
            data and a list containing the descriptors.
            """
            # Array of ints
            fds = array.array("i")
            msg, ancdata, flags, addr = sock.recvmsg(bufsize,
                _socket.CMSG_LEN(maxfds * fds.itemsize))
            for cmsg_level, cmsg_type, cmsg_data in ancdata:
                if (cmsg_level == _socket.SOL_SOCKET and cmsg_type == _socket.SCM_RIGHTS):
                    fds.frombytes(cmsg_data[:
                            len(cmsg_data) - (len(cmsg_data) % fds.itemsize)])

            return msg, list(fds), flags, addr
        __all__.append("recv_fds")

    if hasattr(_socket.socket, "share"):
        def fromshare(info):
            """ fromshare(info) -> socket object

            Create a socket object from the bytes object returned by
            socket.share(pid).
            """
            return socket(0, 0, 0, info)
        __all__.append("fromshare")

    if hasattr(_socket, "socketpair"):

        def socketpair(family=None, type=SOCK_STREAM, proto=0):
            """socketpair([family[, type[, proto]]]) -> (socket object, socket object)

            Create a pair of socket objects from the sockets returned by the platform
            socketpair() function.
            The arguments are the same as for socket() except the default family is
            AF_UNIX if defined on the platform; otherwise, the default is AF_INET.
            """
            if family is None:
                try:
                    family = AF_UNIX
                except NameError:
                    family = AF_INET
            a, b = _socket.socketpair(family, type, proto)
            a = socket(family, type, proto, a.detach())
            b = socket(family, type, proto, b.detach())
            return a, b

    else:

        # Origin: https://gist.github.com/4325783, by Geert Jansen.  Public domain.
        def socketpair(family=AF_INET, type=SOCK_STREAM, proto=0):
            if family == AF_INET:
                host = _LOCALHOST
            elif family == AF_INET6:
                host = _LOCALHOST_V6
            else:
                raise ValueError("Only AF_INET and AF_INET6 socket address families "
                                 "are supported")
            if type != SOCK_STREAM:
                raise ValueError("Only SOCK_STREAM socket type is supported")
            if proto != 0:
                raise ValueError("Only protocol zero is supported")

            # We create a connected TCP socket. Note the trick with
            # setblocking(False) that prevents us from having to create a thread.
            lsock = socket(family, type, proto)
            try:
                lsock.bind((host, 0))
                lsock.listen()
                # On IPv6, ignore flow_info and scope_id
                addr, port = lsock.getsockname()[:2]
                csock = socket(family, type, proto)
                try:
                    csock.setblocking(False)
                    try:
                        csock.connect((addr, port))
                    except (BlockingIOError, InterruptedError):
                        pass
                    csock.setblocking(True)
                    ssock, _ = lsock.accept()
                except:
                    csock.close()
                    raise
            finally:
                lsock.close()
            return (ssock, csock)
        __all__.append("socketpair")

    socketpair.__doc__ = """socketpair([family[, type[, proto]]]) -> (socket object, socket object)
    Create a pair of socket objects from the sockets returned by the platform
    socketpair() function.
    The arguments are the same as for socket() except the default family is AF_UNIX
    if defined on the platform; otherwise, the default is AF_INET.
    """

    _blocking_errnos = { EAGAIN, EWOULDBLOCK }

    class SocketIO(io.RawIOBase):

        """Raw I/O implementation for stream sockets.

        This class supports the makefile() method on sockets.  It provides
        the raw I/O interface on top of a socket object.
        """

        # One might wonder why not let FileIO do the job instead.  There are two
        # main reasons why FileIO is not adapted:
        # - it wouldn't work under Windows (where you can't used read() and
        #   write() on a socket handle)
        # - it wouldn't work with socket timeouts (FileIO would ignore the
        #   timeout and consider the socket non-blocking)

        # XXX More docs

        def __init__(self, sock, mode):
            if mode not in ("r", "w", "rw", "rb", "wb", "rwb"):
                raise ValueError("invalid mode: %r" % mode)
            io.RawIOBase.__init__(self)
            self._sock = sock
            if "b" not in mode:
                mode += "b"
            self._mode = mode
            self._reading = "r" in mode
            self._writing = "w" in mode
            self._timeout_occurred = False

        def readinto(self, b):
            """Read up to len(b) bytes into the writable buffer *b* and return
            the number of bytes read.  If the socket is non-blocking and no bytes
            are available, None is returned.

            If *b* is non-empty, a 0 return value indicates that the connection
            was shutdown at the other end.
            """
            self._checkClosed()
            self._checkReadable()
            if self._timeout_occurred:
                raise OSError("cannot read from timed out object")
            while True:
                try:
                    return self._sock.recv_into(b)
                except timeout:
                    self._timeout_occurred = True
                    raise
                except error as e:
                    if e.errno in _blocking_errnos:
                        return None
                    raise

        def write(self, b):
            """Write the given bytes or bytearray object *b* to the socket
            and return the number of bytes written.  This can be less than
            len(b) if not all data could be written.  If the socket is
            non-blocking and no bytes could be written None is returned.
            """
            self._checkClosed()
            self._checkWritable()
            try:
                return self._sock.send(b)
            except error as e:
                # XXX what about EINTR?
                if e.errno in _blocking_errnos:
                    return None
                raise

        def readable(self):
            """True if the SocketIO is open for reading.
            """
            if self.closed:
                raise ValueError("I/O operation on closed socket.")
            return self._reading

        def writable(self):
            """True if the SocketIO is open for writing.
            """
            if self.closed:
                raise ValueError("I/O operation on closed socket.")
            return self._writing

        def seekable(self):
            """True if the SocketIO is open for seeking.
            """
            if self.closed:
                raise ValueError("I/O operation on closed socket.")
            return super().seekable()

        def fileno(self):
            """Return the file descriptor of the underlying socket.
            """
            self._checkClosed()
            return self._sock.fileno()

        @property
        def name(self):
            if not self.closed:
                return self.fileno()
            else:
                return -1

        @property
        def mode(self):
            return self._mode

        def close(self):
            """Close the SocketIO object.  This doesn't close the underlying
            socket, except if all references to it have disappeared.
            """
            if self.closed:
                return
            io.RawIOBase.close(self)
            self._sock._decref_socketios()
            self._sock = None

    def getfqdn(name=''):
        """Get fully qualified domain name from name.

        An empty argument is interpreted as meaning the local host.

        First the hostname returned by gethostbyaddr() is checked, then
        possibly existing aliases. In case no FQDN is available and `name`
        was given, it is returned unchanged. If `name` was empty, '0.0.0.0' or '::',
        hostname from gethostname() is returned.
        """
        name = name.strip()
        if not name or name in ('0.0.0.0', '::'):
            name = gethostname()
        try:
            hostname, aliases, ipaddrs = gethostbyaddr(name)
        except error:
            pass
        else:
            aliases.insert(0, hostname)
            for name in aliases:
                if '.' in name:
                    break
            else:
                name = hostname
        return name

    _GLOBAL_DEFAULT_TIMEOUT = object()

    def create_connection(address, timeout=_GLOBAL_DEFAULT_TIMEOUT,
                          source_address=None, *, all_errors=False):
        """Connect to *address* and return the socket object.

        Convenience function.  Connect to *address* (a 2-tuple ``(host,
        port)``) and return the socket object.  Passing the optional
        *timeout* parameter will set the timeout on the socket instance
        before attempting to connect.  If no *timeout* is supplied, the
        global default timeout setting returned by :func:`getdefaulttimeout`
        is used.  If *source_address* is set it must be a tuple of (host, port)
        for the socket to bind as a source address before making the connection.
        A host of '' or port 0 tells the OS to use the default. When a connection
        cannot be created, raises the last error if *all_errors* is False,
        and an ExceptionGroup of all errors if *all_errors* is True.
        """

        host, port = address
        exceptions = []
        for res in getaddrinfo(host, port, 0, SOCK_STREAM):
            af, socktype, proto, canonname, sa = res
            sock = None
            try:
                sock = socket(af, socktype, proto)
                if timeout is not _GLOBAL_DEFAULT_TIMEOUT:
                    sock.settimeout(timeout)
                if source_address:
                    sock.bind(source_address)
                sock.connect(sa)
                # Break explicitly a reference cycle
                exceptions.clear()
                return sock

            except error as exc:
                if not all_errors:
                    exceptions.clear()  # raise only the last error
                exceptions.append(exc)
                if sock is not None:
                    sock.close()

        if len(exceptions):
            try:
                if not all_errors:
                    raise exceptions[0]
                raise ExceptionGroup("create_connection failed", exceptions)
            finally:
                # Break explicitly a reference cycle
                exceptions.clear()
        else:
            raise error("getaddrinfo returns an empty list")

    def has_dualstack_ipv6():
        """Return True if the platform supports creating a SOCK_STREAM socket
        which can handle both AF_INET and AF_INET6 (IPv4 / IPv6) connections.
        """
        if not has_ipv6 \
                or not hasattr(_socket, 'IPPROTO_IPV6') \
                or not hasattr(_socket, 'IPV6_V6ONLY'):
            return False
        try:
            with socket(AF_INET6, SOCK_STREAM) as sock:
                sock.setsockopt(IPPROTO_IPV6, IPV6_V6ONLY, 0)
                return True
        except error:
            return False

    def create_server(address, *, family=AF_INET, backlog=None, reuse_port=False,
                      dualstack_ipv6=False):
        """Convenience function which creates a SOCK_STREAM type socket
        bound to *address* (a 2-tuple (host, port)) and return the socket
        object.

        *family* should be either AF_INET or AF_INET6.
        *backlog* is the queue size passed to socket.listen().
        *reuse_port* dictates whether to use the SO_REUSEPORT socket option.
        *dualstack_ipv6*: if true and the platform supports it, it will
        create an AF_INET6 socket able to accept both IPv4 or IPv6
        connections. When false it will explicitly disable this option on
        platforms that enable it by default (e.g. Linux).

        >>> with create_server(('', 8000)) as server:
        ...     while True:
        ...         conn, addr = server.accept()
        ...         # handle new connection
        """
        if reuse_port and not hasattr(_socket, "SO_REUSEPORT"):
            raise ValueError("SO_REUSEPORT not supported on this platform")
        if dualstack_ipv6:
            if not has_dualstack_ipv6():
                raise ValueError("dualstack_ipv6 not supported on this platform")
            if family != AF_INET6:
                raise ValueError("dualstack_ipv6 requires AF_INET6 family")
        sock = socket(family, SOCK_STREAM)
        try:
            # Note about Windows. We don't set SO_REUSEADDR because:
            # 1) It's unnecessary: bind() will succeed even in case of a
            # previous closed socket on the same address and still in
            # TIME_WAIT state.
            # 2) If set, another socket is free to bind() on the same
            # address, effectively preventing this one from accepting
            # connections. Also, it may set the process in a state where
            # it'll no longer respond to any signals or graceful kills.
            # See: https://learn.microsoft.com/windows/win32/winsock/using-so-reuseaddr-and-so-exclusiveaddruse
            if os.name not in ('nt', 'cygwin') and \
                    hasattr(_socket, 'SO_REUSEADDR'):
                try:
                    sock.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
                except error:
                    # Fail later on bind(), for platforms which may not
                    # support this option.
                    pass
            if reuse_port:
                sock.setsockopt(SOL_SOCKET, SO_REUSEPORT, 1)
            if has_ipv6 and family == AF_INET6:
                if dualstack_ipv6:
                    sock.setsockopt(IPPROTO_IPV6, IPV6_V6ONLY, 0)
                elif hasattr(_socket, "IPV6_V6ONLY") and \
                        hasattr(_socket, "IPPROTO_IPV6"):
                    sock.setsockopt(IPPROTO_IPV6, IPV6_V6ONLY, 1)
            try:
                sock.bind(address)
            except error as err:
                msg = '%s (while attempting to bind on address %r)' % \
                    (err.strerror, address)
                raise error(err.errno, msg) from None
            if backlog is None:
                sock.listen()
            else:
                sock.listen(backlog)
            return sock
        except error:
            sock.close()
            raise

    def getaddrinfo(host, port, family=0, type=0, proto=0, flags=0):
        """Resolve host and port into list of address info entries.

        Translate the host/port argument into a sequence of 5-tuples that contain
        all the necessary arguments for creating a socket connected to that service.
        host is a domain name, a string representation of an IPv4/v6 address or
        None. port is a string service name such as 'http', a numeric port number or
        None. By passing None as the value of host and port, you can pass NULL to
        the underlying C API.

        The family, type and proto arguments can be optionally specified in order to
        narrow the list of addresses returned. Passing zero as a value for each of
        these arguments selects the full range of results.
        """
        # We override this function since we want to translate the numeric family
        # and socket type values to enum constants.
        addrlist = []
        for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
            af, socktype, proto, canonname, sa = res
            addrlist.append((_intenum_converter(af, AddressFamily),
                             _intenum_converter(socktype, SocketKind),
                             proto, canonname, sa))
        return addrlist