Library import 16 (#2433)

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1 files changed, 1177 insertions, 0 deletions

diff --git a/contrib/tools/python3/Lib/multiprocessing/connection.py b/contrib/tools/python3/Lib/multiprocessing/connection.py
new file mode 100644
index 0000000000..dbbf106f68
--- /dev/null
+++ b/contrib/tools/python3/Lib/multiprocessing/connection.py
@@ -0,0 +1,1177 @@
+#
+# A higher level module for using sockets (or Windows named pipes)
+#
+# multiprocessing/connection.py
+#
+# Copyright (c) 2006-2008, R Oudkerk
+# Licensed to PSF under a Contributor Agreement.
+#
+
+__all__ = [ 'Client', 'Listener', 'Pipe', 'wait' ]
+
+import errno
+import io
+import os
+import sys
+import socket
+import struct
+import time
+import tempfile
+import itertools
+
+import _multiprocessing
+
+from . import util
+
+from . import AuthenticationError, BufferTooShort
+from .context import reduction
+_ForkingPickler = reduction.ForkingPickler
+
+try:
+    import _winapi
+    from _winapi import WAIT_OBJECT_0, WAIT_ABANDONED_0, WAIT_TIMEOUT, INFINITE
+except ImportError:
+    if sys.platform == 'win32':
+        raise
+    _winapi = None
+
+#
+#
+#
+
+BUFSIZE = 8192
+# A very generous timeout when it comes to local connections...
+CONNECTION_TIMEOUT = 20.
+
+_mmap_counter = itertools.count()
+
+default_family = 'AF_INET'
+families = ['AF_INET']
+
+if hasattr(socket, 'AF_UNIX'):
+    default_family = 'AF_UNIX'
+    families += ['AF_UNIX']
+
+if sys.platform == 'win32':
+    default_family = 'AF_PIPE'
+    families += ['AF_PIPE']
+
+
+def _init_timeout(timeout=CONNECTION_TIMEOUT):
+    return time.monotonic() + timeout
+
+def _check_timeout(t):
+    return time.monotonic() > t
+
+#
+#
+#
+
+def arbitrary_address(family):
+    '''
+    Return an arbitrary free address for the given family
+    '''
+    if family == 'AF_INET':
+        return ('localhost', 0)
+    elif family == 'AF_UNIX':
+        return tempfile.mktemp(prefix='listener-', dir=util.get_temp_dir())
+    elif family == 'AF_PIPE':
+        return tempfile.mktemp(prefix=r'\\.\pipe\pyc-%d-%d-' %
+                               (os.getpid(), next(_mmap_counter)), dir="")
+    else:
+        raise ValueError('unrecognized family')
+
+def _validate_family(family):
+    '''
+    Checks if the family is valid for the current environment.
+    '''
+    if sys.platform != 'win32' and family == 'AF_PIPE':
+        raise ValueError('Family %s is not recognized.' % family)
+
+    if sys.platform == 'win32' and family == 'AF_UNIX':
+        # double check
+        if not hasattr(socket, family):
+            raise ValueError('Family %s is not recognized.' % family)
+
+def address_type(address):
+    '''
+    Return the types of the address
+
+    This can be 'AF_INET', 'AF_UNIX', or 'AF_PIPE'
+    '''
+    if type(address) == tuple:
+        return 'AF_INET'
+    elif type(address) is str and address.startswith('\\\\'):
+        return 'AF_PIPE'
+    elif type(address) is str or util.is_abstract_socket_namespace(address):
+        return 'AF_UNIX'
+    else:
+        raise ValueError('address type of %r unrecognized' % address)
+
+#
+# Connection classes
+#
+
+class _ConnectionBase:
+    _handle = None
+
+    def __init__(self, handle, readable=True, writable=True):
+        handle = handle.__index__()
+        if handle < 0:
+            raise ValueError("invalid handle")
+        if not readable and not writable:
+            raise ValueError(
+                "at least one of `readable` and `writable` must be True")
+        self._handle = handle
+        self._readable = readable
+        self._writable = writable
+
+    # XXX should we use util.Finalize instead of a __del__?
+
+    def __del__(self):
+        if self._handle is not None:
+            self._close()
+
+    def _check_closed(self):
+        if self._handle is None:
+            raise OSError("handle is closed")
+
+    def _check_readable(self):
+        if not self._readable:
+            raise OSError("connection is write-only")
+
+    def _check_writable(self):
+        if not self._writable:
+            raise OSError("connection is read-only")
+
+    def _bad_message_length(self):
+        if self._writable:
+            self._readable = False
+        else:
+            self.close()
+        raise OSError("bad message length")
+
+    @property
+    def closed(self):
+        """True if the connection is closed"""
+        return self._handle is None
+
+    @property
+    def readable(self):
+        """True if the connection is readable"""
+        return self._readable
+
+    @property
+    def writable(self):
+        """True if the connection is writable"""
+        return self._writable
+
+    def fileno(self):
+        """File descriptor or handle of the connection"""
+        self._check_closed()
+        return self._handle
+
+    def close(self):
+        """Close the connection"""
+        if self._handle is not None:
+            try:
+                self._close()
+            finally:
+                self._handle = None
+
+    def send_bytes(self, buf, offset=0, size=None):
+        """Send the bytes data from a bytes-like object"""
+        self._check_closed()
+        self._check_writable()
+        m = memoryview(buf)
+        if m.itemsize > 1:
+            m = m.cast('B')
+        n = m.nbytes
+        if offset < 0:
+            raise ValueError("offset is negative")
+        if n < offset:
+            raise ValueError("buffer length < offset")
+        if size is None:
+            size = n - offset
+        elif size < 0:
+            raise ValueError("size is negative")
+        elif offset + size > n:
+            raise ValueError("buffer length < offset + size")
+        self._send_bytes(m[offset:offset + size])
+
+    def send(self, obj):
+        """Send a (picklable) object"""
+        self._check_closed()
+        self._check_writable()
+        self._send_bytes(_ForkingPickler.dumps(obj))
+
+    def recv_bytes(self, maxlength=None):
+        """
+        Receive bytes data as a bytes object.
+        """
+        self._check_closed()
+        self._check_readable()
+        if maxlength is not None and maxlength < 0:
+            raise ValueError("negative maxlength")
+        buf = self._recv_bytes(maxlength)
+        if buf is None:
+            self._bad_message_length()
+        return buf.getvalue()
+
+    def recv_bytes_into(self, buf, offset=0):
+        """
+        Receive bytes data into a writeable bytes-like object.
+        Return the number of bytes read.
+        """
+        self._check_closed()
+        self._check_readable()
+        with memoryview(buf) as m:
+            # Get bytesize of arbitrary buffer
+            itemsize = m.itemsize
+            bytesize = itemsize * len(m)
+            if offset < 0:
+                raise ValueError("negative offset")
+            elif offset > bytesize:
+                raise ValueError("offset too large")
+            result = self._recv_bytes()
+            size = result.tell()
+            if bytesize < offset + size:
+                raise BufferTooShort(result.getvalue())
+            # Message can fit in dest
+            result.seek(0)
+            result.readinto(m[offset // itemsize :
+                              (offset + size) // itemsize])
+            return size
+
+    def recv(self):
+        """Receive a (picklable) object"""
+        self._check_closed()
+        self._check_readable()
+        buf = self._recv_bytes()
+        return _ForkingPickler.loads(buf.getbuffer())
+
+    def poll(self, timeout=0.0):
+        """Whether there is any input available to be read"""
+        self._check_closed()
+        self._check_readable()
+        return self._poll(timeout)
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, exc_tb):
+        self.close()
+
+
+if _winapi:
+
+    class PipeConnection(_ConnectionBase):
+        """
+        Connection class based on a Windows named pipe.
+        Overlapped I/O is used, so the handles must have been created
+        with FILE_FLAG_OVERLAPPED.
+        """
+        _got_empty_message = False
+        _send_ov = None
+
+        def _close(self, _CloseHandle=_winapi.CloseHandle):
+            ov = self._send_ov
+            if ov is not None:
+                # Interrupt WaitForMultipleObjects() in _send_bytes()
+                ov.cancel()
+            _CloseHandle(self._handle)
+
+        def _send_bytes(self, buf):
+            if self._send_ov is not None:
+                # A connection should only be used by a single thread
+                raise ValueError("concurrent send_bytes() calls "
+                                 "are not supported")
+            ov, err = _winapi.WriteFile(self._handle, buf, overlapped=True)
+            self._send_ov = ov
+            try:
+                if err == _winapi.ERROR_IO_PENDING:
+                    waitres = _winapi.WaitForMultipleObjects(
+                        [ov.event], False, INFINITE)
+                    assert waitres == WAIT_OBJECT_0
+            except:
+                ov.cancel()
+                raise
+            finally:
+                self._send_ov = None
+                nwritten, err = ov.GetOverlappedResult(True)
+            if err == _winapi.ERROR_OPERATION_ABORTED:
+                # close() was called by another thread while
+                # WaitForMultipleObjects() was waiting for the overlapped
+                # operation.
+                raise OSError(errno.EPIPE, "handle is closed")
+            assert err == 0
+            assert nwritten == len(buf)
+
+        def _recv_bytes(self, maxsize=None):
+            if self._got_empty_message:
+                self._got_empty_message = False
+                return io.BytesIO()
+            else:
+                bsize = 128 if maxsize is None else min(maxsize, 128)
+                try:
+                    ov, err = _winapi.ReadFile(self._handle, bsize,
+                                                overlapped=True)
+                    try:
+                        if err == _winapi.ERROR_IO_PENDING:
+                            waitres = _winapi.WaitForMultipleObjects(
+                                [ov.event], False, INFINITE)
+                            assert waitres == WAIT_OBJECT_0
+                    except:
+                        ov.cancel()
+                        raise
+                    finally:
+                        nread, err = ov.GetOverlappedResult(True)
+                        if err == 0:
+                            f = io.BytesIO()
+                            f.write(ov.getbuffer())
+                            return f
+                        elif err == _winapi.ERROR_MORE_DATA:
+                            return self._get_more_data(ov, maxsize)
+                except OSError as e:
+                    if e.winerror == _winapi.ERROR_BROKEN_PIPE:
+                        raise EOFError
+                    else:
+                        raise
+            raise RuntimeError("shouldn't get here; expected KeyboardInterrupt")
+
+        def _poll(self, timeout):
+            if (self._got_empty_message or
+                        _winapi.PeekNamedPipe(self._handle)[0] != 0):
+                return True
+            return bool(wait([self], timeout))
+
+        def _get_more_data(self, ov, maxsize):
+            buf = ov.getbuffer()
+            f = io.BytesIO()
+            f.write(buf)
+            left = _winapi.PeekNamedPipe(self._handle)[1]
+            assert left > 0
+            if maxsize is not None and len(buf) + left > maxsize:
+                self._bad_message_length()
+            ov, err = _winapi.ReadFile(self._handle, left, overlapped=True)
+            rbytes, err = ov.GetOverlappedResult(True)
+            assert err == 0
+            assert rbytes == left
+            f.write(ov.getbuffer())
+            return f
+
+
+class Connection(_ConnectionBase):
+    """
+    Connection class based on an arbitrary file descriptor (Unix only), or
+    a socket handle (Windows).
+    """
+
+    if _winapi:
+        def _close(self, _close=_multiprocessing.closesocket):
+            _close(self._handle)
+        _write = _multiprocessing.send
+        _read = _multiprocessing.recv
+    else:
+        def _close(self, _close=os.close):
+            _close(self._handle)
+        _write = os.write
+        _read = os.read
+
+    def _send(self, buf, write=_write):
+        remaining = len(buf)
+        while True:
+            n = write(self._handle, buf)
+            remaining -= n
+            if remaining == 0:
+                break
+            buf = buf[n:]
+
+    def _recv(self, size, read=_read):
+        buf = io.BytesIO()
+        handle = self._handle
+        remaining = size
+        while remaining > 0:
+            chunk = read(handle, remaining)
+            n = len(chunk)
+            if n == 0:
+                if remaining == size:
+                    raise EOFError
+                else:
+                    raise OSError("got end of file during message")
+            buf.write(chunk)
+            remaining -= n
+        return buf
+
+    def _send_bytes(self, buf):
+        n = len(buf)
+        if n > 0x7fffffff:
+            pre_header = struct.pack("!i", -1)
+            header = struct.pack("!Q", n)
+            self._send(pre_header)
+            self._send(header)
+            self._send(buf)
+        else:
+            # For wire compatibility with 3.7 and lower
+            header = struct.pack("!i", n)
+            if n > 16384:
+                # The payload is large so Nagle's algorithm won't be triggered
+                # and we'd better avoid the cost of concatenation.
+                self._send(header)
+                self._send(buf)
+            else:
+                # Issue #20540: concatenate before sending, to avoid delays due
+                # to Nagle's algorithm on a TCP socket.
+                # Also note we want to avoid sending a 0-length buffer separately,
+                # to avoid "broken pipe" errors if the other end closed the pipe.
+                self._send(header + buf)
+
+    def _recv_bytes(self, maxsize=None):
+        buf = self._recv(4)
+        size, = struct.unpack("!i", buf.getvalue())
+        if size == -1:
+            buf = self._recv(8)
+            size, = struct.unpack("!Q", buf.getvalue())
+        if maxsize is not None and size > maxsize:
+            return None
+        return self._recv(size)
+
+    def _poll(self, timeout):
+        r = wait([self], timeout)
+        return bool(r)
+
+
+#
+# Public functions
+#
+
+class Listener(object):
+    '''
+    Returns a listener object.
+
+    This is a wrapper for a bound socket which is 'listening' for
+    connections, or for a Windows named pipe.
+    '''
+    def __init__(self, address=None, family=None, backlog=1, authkey=None):
+        family = family or (address and address_type(address)) \
+                 or default_family
+        address = address or arbitrary_address(family)
+
+        _validate_family(family)
+        if family == 'AF_PIPE':
+            self._listener = PipeListener(address, backlog)
+        else:
+            self._listener = SocketListener(address, family, backlog)
+
+        if authkey is not None and not isinstance(authkey, bytes):
+            raise TypeError('authkey should be a byte string')
+
+        self._authkey = authkey
+
+    def accept(self):
+        '''
+        Accept a connection on the bound socket or named pipe of `self`.
+
+        Returns a `Connection` object.
+        '''
+        if self._listener is None:
+            raise OSError('listener is closed')
+        c = self._listener.accept()
+        if self._authkey:
+            deliver_challenge(c, self._authkey)
+            answer_challenge(c, self._authkey)
+        return c
+
+    def close(self):
+        '''
+        Close the bound socket or named pipe of `self`.
+        '''
+        listener = self._listener
+        if listener is not None:
+            self._listener = None
+            listener.close()
+
+    @property
+    def address(self):
+        return self._listener._address
+
+    @property
+    def last_accepted(self):
+        return self._listener._last_accepted
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, exc_tb):
+        self.close()
+
+
+def Client(address, family=None, authkey=None):
+    '''
+    Returns a connection to the address of a `Listener`
+    '''
+    family = family or address_type(address)
+    _validate_family(family)
+    if family == 'AF_PIPE':
+        c = PipeClient(address)
+    else:
+        c = SocketClient(address)
+
+    if authkey is not None and not isinstance(authkey, bytes):
+        raise TypeError('authkey should be a byte string')
+
+    if authkey is not None:
+        answer_challenge(c, authkey)
+        deliver_challenge(c, authkey)
+
+    return c
+
+
+if sys.platform != 'win32':
+
+    def Pipe(duplex=True):
+        '''
+        Returns pair of connection objects at either end of a pipe
+        '''
+        if duplex:
+            s1, s2 = socket.socketpair()
+            s1.setblocking(True)
+            s2.setblocking(True)
+            c1 = Connection(s1.detach())
+            c2 = Connection(s2.detach())
+        else:
+            fd1, fd2 = os.pipe()
+            c1 = Connection(fd1, writable=False)
+            c2 = Connection(fd2, readable=False)
+
+        return c1, c2
+
+else:
+
+    def Pipe(duplex=True):
+        '''
+        Returns pair of connection objects at either end of a pipe
+        '''
+        address = arbitrary_address('AF_PIPE')
+        if duplex:
+            openmode = _winapi.PIPE_ACCESS_DUPLEX
+            access = _winapi.GENERIC_READ | _winapi.GENERIC_WRITE
+            obsize, ibsize = BUFSIZE, BUFSIZE
+        else:
+            openmode = _winapi.PIPE_ACCESS_INBOUND
+            access = _winapi.GENERIC_WRITE
+            obsize, ibsize = 0, BUFSIZE
+
+        h1 = _winapi.CreateNamedPipe(
+            address, openmode | _winapi.FILE_FLAG_OVERLAPPED |
+            _winapi.FILE_FLAG_FIRST_PIPE_INSTANCE,
+            _winapi.PIPE_TYPE_MESSAGE | _winapi.PIPE_READMODE_MESSAGE |
+            _winapi.PIPE_WAIT,
+            1, obsize, ibsize, _winapi.NMPWAIT_WAIT_FOREVER,
+            # default security descriptor: the handle cannot be inherited
+            _winapi.NULL
+            )
+        h2 = _winapi.CreateFile(
+            address, access, 0, _winapi.NULL, _winapi.OPEN_EXISTING,
+            _winapi.FILE_FLAG_OVERLAPPED, _winapi.NULL
+            )
+        _winapi.SetNamedPipeHandleState(
+            h2, _winapi.PIPE_READMODE_MESSAGE, None, None
+            )
+
+        overlapped = _winapi.ConnectNamedPipe(h1, overlapped=True)
+        _, err = overlapped.GetOverlappedResult(True)
+        assert err == 0
+
+        c1 = PipeConnection(h1, writable=duplex)
+        c2 = PipeConnection(h2, readable=duplex)
+
+        return c1, c2
+
+#
+# Definitions for connections based on sockets
+#
+
+class SocketListener(object):
+    '''
+    Representation of a socket which is bound to an address and listening
+    '''
+    def __init__(self, address, family, backlog=1):
+        self._socket = socket.socket(getattr(socket, family))
+        try:
+            # SO_REUSEADDR has different semantics on Windows (issue #2550).
+            if os.name == 'posix':
+                self._socket.setsockopt(socket.SOL_SOCKET,
+                                        socket.SO_REUSEADDR, 1)
+            self._socket.setblocking(True)
+            self._socket.bind(address)
+            self._socket.listen(backlog)
+            self._address = self._socket.getsockname()
+        except OSError:
+            self._socket.close()
+            raise
+        self._family = family
+        self._last_accepted = None
+
+        if family == 'AF_UNIX' and not util.is_abstract_socket_namespace(address):
+            # Linux abstract socket namespaces do not need to be explicitly unlinked
+            self._unlink = util.Finalize(
+                self, os.unlink, args=(address,), exitpriority=0
+                )
+        else:
+            self._unlink = None
+
+    def accept(self):
+        s, self._last_accepted = self._socket.accept()
+        s.setblocking(True)
+        return Connection(s.detach())
+
+    def close(self):
+        try:
+            self._socket.close()
+        finally:
+            unlink = self._unlink
+            if unlink is not None:
+                self._unlink = None
+                unlink()
+
+
+def SocketClient(address):
+    '''
+    Return a connection object connected to the socket given by `address`
+    '''
+    family = address_type(address)
+    with socket.socket( getattr(socket, family) ) as s:
+        s.setblocking(True)
+        s.connect(address)
+        return Connection(s.detach())
+
+#
+# Definitions for connections based on named pipes
+#
+
+if sys.platform == 'win32':
+
+    class PipeListener(object):
+        '''
+        Representation of a named pipe
+        '''
+        def __init__(self, address, backlog=None):
+            self._address = address
+            self._handle_queue = [self._new_handle(first=True)]
+
+            self._last_accepted = None
+            util.sub_debug('listener created with address=%r', self._address)
+            self.close = util.Finalize(
+                self, PipeListener._finalize_pipe_listener,
+                args=(self._handle_queue, self._address), exitpriority=0
+                )
+
+        def _new_handle(self, first=False):
+            flags = _winapi.PIPE_ACCESS_DUPLEX | _winapi.FILE_FLAG_OVERLAPPED
+            if first:
+                flags |= _winapi.FILE_FLAG_FIRST_PIPE_INSTANCE
+            return _winapi.CreateNamedPipe(
+                self._address, flags,
+                _winapi.PIPE_TYPE_MESSAGE | _winapi.PIPE_READMODE_MESSAGE |
+                _winapi.PIPE_WAIT,
+                _winapi.PIPE_UNLIMITED_INSTANCES, BUFSIZE, BUFSIZE,
+                _winapi.NMPWAIT_WAIT_FOREVER, _winapi.NULL
+                )
+
+        def accept(self):
+            self._handle_queue.append(self._new_handle())
+            handle = self._handle_queue.pop(0)
+            try:
+                ov = _winapi.ConnectNamedPipe(handle, overlapped=True)
+            except OSError as e:
+                if e.winerror != _winapi.ERROR_NO_DATA:
+                    raise
+                # ERROR_NO_DATA can occur if a client has already connected,
+                # written data and then disconnected -- see Issue 14725.
+            else:
+                try:
+                    res = _winapi.WaitForMultipleObjects(
+                        [ov.event], False, INFINITE)
+                except:
+                    ov.cancel()
+                    _winapi.CloseHandle(handle)
+                    raise
+                finally:
+                    _, err = ov.GetOverlappedResult(True)
+                    assert err == 0
+            return PipeConnection(handle)
+
+        @staticmethod
+        def _finalize_pipe_listener(queue, address):
+            util.sub_debug('closing listener with address=%r', address)
+            for handle in queue:
+                _winapi.CloseHandle(handle)
+
+    def PipeClient(address):
+        '''
+        Return a connection object connected to the pipe given by `address`
+        '''
+        t = _init_timeout()
+        while 1:
+            try:
+                _winapi.WaitNamedPipe(address, 1000)
+                h = _winapi.CreateFile(
+                    address, _winapi.GENERIC_READ | _winapi.GENERIC_WRITE,
+                    0, _winapi.NULL, _winapi.OPEN_EXISTING,
+                    _winapi.FILE_FLAG_OVERLAPPED, _winapi.NULL
+                    )
+            except OSError as e:
+                if e.winerror not in (_winapi.ERROR_SEM_TIMEOUT,
+                                      _winapi.ERROR_PIPE_BUSY) or _check_timeout(t):
+                    raise
+            else:
+                break
+        else:
+            raise
+
+        _winapi.SetNamedPipeHandleState(
+            h, _winapi.PIPE_READMODE_MESSAGE, None, None
+            )
+        return PipeConnection(h)
+
+#
+# Authentication stuff
+#
+
+MESSAGE_LENGTH = 40  # MUST be > 20
+
+_CHALLENGE = b'#CHALLENGE#'
+_WELCOME = b'#WELCOME#'
+_FAILURE = b'#FAILURE#'
+
+# multiprocessing.connection Authentication Handshake Protocol Description
+# (as documented for reference after reading the existing code)
+# =============================================================================
+#
+# On Windows: native pipes with "overlapped IO" are used to send the bytes,
+# instead of the length prefix SIZE scheme described below. (ie: the OS deals
+# with message sizes for us)
+#
+# Protocol error behaviors:
+#
+# On POSIX, any failure to receive the length prefix into SIZE, for SIZE greater
+# than the requested maxsize to receive, or receiving fewer than SIZE bytes
+# results in the connection being closed and auth to fail.
+#
+# On Windows, receiving too few bytes is never a low level _recv_bytes read
+# error, receiving too many will trigger an error only if receive maxsize
+# value was larger than 128 OR the if the data arrived in smaller pieces.
+#
+#      Serving side                           Client side
+#     ------------------------------  ---------------------------------------
+# 0.                                  Open a connection on the pipe.
+# 1.  Accept connection.
+# 2.  Random 20+ bytes -> MESSAGE
+#     Modern servers always send
+#     more than 20 bytes and include
+#     a {digest} prefix on it with
+#     their preferred HMAC digest.
+#     Legacy ones send ==20 bytes.
+# 3.  send 4 byte length (net order)
+#     prefix followed by:
+#       b'#CHALLENGE#' + MESSAGE
+# 4.                                  Receive 4 bytes, parse as network byte
+#                                     order integer. If it is -1, receive an
+#                                     additional 8 bytes, parse that as network
+#                                     byte order. The result is the length of
+#                                     the data that follows -> SIZE.
+# 5.                                  Receive min(SIZE, 256) bytes -> M1
+# 6.                                  Assert that M1 starts with:
+#                                       b'#CHALLENGE#'
+# 7.                                  Strip that prefix from M1 into -> M2
+# 7.1.                                Parse M2: if it is exactly 20 bytes in
+#                                     length this indicates a legacy server
+#                                     supporting only HMAC-MD5. Otherwise the
+# 7.2.                                preferred digest is looked up from an
+#                                     expected "{digest}" prefix on M2. No prefix
+#                                     or unsupported digest? <- AuthenticationError
+# 7.3.                                Put divined algorithm name in -> D_NAME
+# 8.                                  Compute HMAC-D_NAME of AUTHKEY, M2 -> C_DIGEST
+# 9.                                  Send 4 byte length prefix (net order)
+#                                     followed by C_DIGEST bytes.
+# 10. Receive 4 or 4+8 byte length
+#     prefix (#4 dance) -> SIZE.
+# 11. Receive min(SIZE, 256) -> C_D.
+# 11.1. Parse C_D: legacy servers
+#     accept it as is, "md5" -> D_NAME
+# 11.2. modern servers check the length
+#     of C_D, IF it is 16 bytes?
+# 11.2.1. "md5" -> D_NAME
+#         and skip to step 12.
+# 11.3. longer? expect and parse a "{digest}"
+#     prefix into -> D_NAME.
+#     Strip the prefix and store remaining
+#     bytes in -> C_D.
+# 11.4. Don't like D_NAME? <- AuthenticationError
+# 12. Compute HMAC-D_NAME of AUTHKEY,
+#     MESSAGE into -> M_DIGEST.
+# 13. Compare M_DIGEST == C_D:
+# 14a: Match? Send length prefix &
+#       b'#WELCOME#'
+#    <- RETURN
+# 14b: Mismatch? Send len prefix &
+#       b'#FAILURE#'
+#    <- CLOSE & AuthenticationError
+# 15.                                 Receive 4 or 4+8 byte length prefix (net
+#                                     order) again as in #4 into -> SIZE.
+# 16.                                 Receive min(SIZE, 256) bytes -> M3.
+# 17.                                 Compare M3 == b'#WELCOME#':
+# 17a.                                Match? <- RETURN
+# 17b.                                Mismatch? <- CLOSE & AuthenticationError
+#
+# If this RETURNed, the connection remains open: it has been authenticated.
+#
+# Length prefixes are used consistently. Even on the legacy protocol, this
+# was good fortune and allowed us to evolve the protocol by using the length
+# of the opening challenge or length of the returned digest as a signal as
+# to which protocol the other end supports.
+
+_ALLOWED_DIGESTS = frozenset(
+        {b'md5', b'sha256', b'sha384', b'sha3_256', b'sha3_384'})
+_MAX_DIGEST_LEN = max(len(_) for _ in _ALLOWED_DIGESTS)
+
+# Old hmac-md5 only server versions from Python <=3.11 sent a message of this
+# length. It happens to not match the length of any supported digest so we can
+# use a message of this length to indicate that we should work in backwards
+# compatible md5-only mode without a {digest_name} prefix on our response.
+_MD5ONLY_MESSAGE_LENGTH = 20
+_MD5_DIGEST_LEN = 16
+_LEGACY_LENGTHS = (_MD5ONLY_MESSAGE_LENGTH, _MD5_DIGEST_LEN)
+
+
+def _get_digest_name_and_payload(message: bytes) -> (str, bytes):
+    """Returns a digest name and the payload for a response hash.
+
+    If a legacy protocol is detected based on the message length
+    or contents the digest name returned will be empty to indicate
+    legacy mode where MD5 and no digest prefix should be sent.
+    """
+    # modern message format: b"{digest}payload" longer than 20 bytes
+    # legacy message format: 16 or 20 byte b"payload"
+    if len(message) in _LEGACY_LENGTHS:
+        # Either this was a legacy server challenge, or we're processing
+        # a reply from a legacy client that sent an unprefixed 16-byte
+        # HMAC-MD5 response. All messages using the modern protocol will
+        # be longer than either of these lengths.
+        return '', message
+    if (message.startswith(b'{') and
+        (curly := message.find(b'}', 1, _MAX_DIGEST_LEN+2)) > 0):
+        digest = message[1:curly]
+        if digest in _ALLOWED_DIGESTS:
+            payload = message[curly+1:]
+            return digest.decode('ascii'), payload
+    raise AuthenticationError(
+            'unsupported message length, missing digest prefix, '
+            f'or unsupported digest: {message=}')
+
+
+def _create_response(authkey, message):
+    """Create a MAC based on authkey and message
+
+    The MAC algorithm defaults to HMAC-MD5, unless MD5 is not available or
+    the message has a '{digest_name}' prefix. For legacy HMAC-MD5, the response
+    is the raw MAC, otherwise the response is prefixed with '{digest_name}',
+    e.g. b'{sha256}abcdefg...'
+
+    Note: The MAC protects the entire message including the digest_name prefix.
+    """
+    import hmac
+    digest_name = _get_digest_name_and_payload(message)[0]
+    # The MAC protects the entire message: digest header and payload.
+    if not digest_name:
+        # Legacy server without a {digest} prefix on message.
+        # Generate a legacy non-prefixed HMAC-MD5 reply.
+        try:
+            return hmac.new(authkey, message, 'md5').digest()
+        except ValueError:
+            # HMAC-MD5 is not available (FIPS mode?), fall back to
+            # HMAC-SHA2-256 modern protocol. The legacy server probably
+            # doesn't support it and will reject us anyways. :shrug:
+            digest_name = 'sha256'
+    # Modern protocol, indicate the digest used in the reply.
+    response = hmac.new(authkey, message, digest_name).digest()
+    return b'{%s}%s' % (digest_name.encode('ascii'), response)
+
+
+def _verify_challenge(authkey, message, response):
+    """Verify MAC challenge
+
+    If our message did not include a digest_name prefix, the client is allowed
+    to select a stronger digest_name from _ALLOWED_DIGESTS.
+
+    In case our message is prefixed, a client cannot downgrade to a weaker
+    algorithm, because the MAC is calculated over the entire message
+    including the '{digest_name}' prefix.
+    """
+    import hmac
+    response_digest, response_mac = _get_digest_name_and_payload(response)
+    response_digest = response_digest or 'md5'
+    try:
+        expected = hmac.new(authkey, message, response_digest).digest()
+    except ValueError:
+        raise AuthenticationError(f'{response_digest=} unsupported')
+    if len(expected) != len(response_mac):
+        raise AuthenticationError(
+                f'expected {response_digest!r} of length {len(expected)} '
+                f'got {len(response_mac)}')
+    if not hmac.compare_digest(expected, response_mac):
+        raise AuthenticationError('digest received was wrong')
+
+
+def deliver_challenge(connection, authkey: bytes, digest_name='sha256'):
+    if not isinstance(authkey, bytes):
+        raise ValueError(
+            "Authkey must be bytes, not {0!s}".format(type(authkey)))
+    assert MESSAGE_LENGTH > _MD5ONLY_MESSAGE_LENGTH, "protocol constraint"
+    message = os.urandom(MESSAGE_LENGTH)
+    message = b'{%s}%s' % (digest_name.encode('ascii'), message)
+    # Even when sending a challenge to a legacy client that does not support
+    # digest prefixes, they'll take the entire thing as a challenge and
+    # respond to it with a raw HMAC-MD5.
+    connection.send_bytes(_CHALLENGE + message)
+    response = connection.recv_bytes(256)        # reject large message
+    try:
+        _verify_challenge(authkey, message, response)
+    except AuthenticationError:
+        connection.send_bytes(_FAILURE)
+        raise
+    else:
+        connection.send_bytes(_WELCOME)
+
+
+def answer_challenge(connection, authkey: bytes):
+    if not isinstance(authkey, bytes):
+        raise ValueError(
+            "Authkey must be bytes, not {0!s}".format(type(authkey)))
+    message = connection.recv_bytes(256)         # reject large message
+    if not message.startswith(_CHALLENGE):
+        raise AuthenticationError(
+                f'Protocol error, expected challenge: {message=}')
+    message = message[len(_CHALLENGE):]
+    if len(message) < _MD5ONLY_MESSAGE_LENGTH:
+        raise AuthenticationError('challenge too short: {len(message)} bytes')
+    digest = _create_response(authkey, message)
+    connection.send_bytes(digest)
+    response = connection.recv_bytes(256)        # reject large message
+    if response != _WELCOME:
+        raise AuthenticationError('digest sent was rejected')
+
+#
+# Support for using xmlrpclib for serialization
+#
+
+class ConnectionWrapper(object):
+    def __init__(self, conn, dumps, loads):
+        self._conn = conn
+        self._dumps = dumps
+        self._loads = loads
+        for attr in ('fileno', 'close', 'poll', 'recv_bytes', 'send_bytes'):
+            obj = getattr(conn, attr)
+            setattr(self, attr, obj)
+    def send(self, obj):
+        s = self._dumps(obj)
+        self._conn.send_bytes(s)
+    def recv(self):
+        s = self._conn.recv_bytes()
+        return self._loads(s)
+
+def _xml_dumps(obj):
+    return xmlrpclib.dumps((obj,), None, None, None, 1).encode('utf-8')
+
+def _xml_loads(s):
+    (obj,), method = xmlrpclib.loads(s.decode('utf-8'))
+    return obj
+
+class XmlListener(Listener):
+    def accept(self):
+        global xmlrpclib
+        import xmlrpc.client as xmlrpclib
+        obj = Listener.accept(self)
+        return ConnectionWrapper(obj, _xml_dumps, _xml_loads)
+
+def XmlClient(*args, **kwds):
+    global xmlrpclib
+    import xmlrpc.client as xmlrpclib
+    return ConnectionWrapper(Client(*args, **kwds), _xml_dumps, _xml_loads)
+
+#
+# Wait
+#
+
+if sys.platform == 'win32':
+
+    def _exhaustive_wait(handles, timeout):
+        # Return ALL handles which are currently signalled.  (Only
+        # returning the first signalled might create starvation issues.)
+        L = list(handles)
+        ready = []
+        while L:
+            res = _winapi.WaitForMultipleObjects(L, False, timeout)
+            if res == WAIT_TIMEOUT:
+                break
+            elif WAIT_OBJECT_0 <= res < WAIT_OBJECT_0 + len(L):
+                res -= WAIT_OBJECT_0
+            elif WAIT_ABANDONED_0 <= res < WAIT_ABANDONED_0 + len(L):
+                res -= WAIT_ABANDONED_0
+            else:
+                raise RuntimeError('Should not get here')
+            ready.append(L[res])
+            L = L[res+1:]
+            timeout = 0
+        return ready
+
+    _ready_errors = {_winapi.ERROR_BROKEN_PIPE, _winapi.ERROR_NETNAME_DELETED}
+
+    def wait(object_list, timeout=None):
+        '''
+        Wait till an object in object_list is ready/readable.
+
+        Returns list of those objects in object_list which are ready/readable.
+        '''
+        if timeout is None:
+            timeout = INFINITE
+        elif timeout < 0:
+            timeout = 0
+        else:
+            timeout = int(timeout * 1000 + 0.5)
+
+        object_list = list(object_list)
+        waithandle_to_obj = {}
+        ov_list = []
+        ready_objects = set()
+        ready_handles = set()
+
+        try:
+            for o in object_list:
+                try:
+                    fileno = getattr(o, 'fileno')
+                except AttributeError:
+                    waithandle_to_obj[o.__index__()] = o
+                else:
+                    # start an overlapped read of length zero
+                    try:
+                        ov, err = _winapi.ReadFile(fileno(), 0, True)
+                    except OSError as e:
+                        ov, err = None, e.winerror
+                        if err not in _ready_errors:
+                            raise
+                    if err == _winapi.ERROR_IO_PENDING:
+                        ov_list.append(ov)
+                        waithandle_to_obj[ov.event] = o
+                    else:
+                        # If o.fileno() is an overlapped pipe handle and
+                        # err == 0 then there is a zero length message
+                        # in the pipe, but it HAS NOT been consumed...
+                        if ov and sys.getwindowsversion()[:2] >= (6, 2):
+                            # ... except on Windows 8 and later, where
+                            # the message HAS been consumed.
+                            try:
+                                _, err = ov.GetOverlappedResult(False)
+                            except OSError as e:
+                                err = e.winerror
+                            if not err and hasattr(o, '_got_empty_message'):
+                                o._got_empty_message = True
+                        ready_objects.add(o)
+                        timeout = 0
+
+            ready_handles = _exhaustive_wait(waithandle_to_obj.keys(), timeout)
+        finally:
+            # request that overlapped reads stop
+            for ov in ov_list:
+                ov.cancel()
+
+            # wait for all overlapped reads to stop
+            for ov in ov_list:
+                try:
+                    _, err = ov.GetOverlappedResult(True)
+                except OSError as e:
+                    err = e.winerror
+                    if err not in _ready_errors:
+                        raise
+                if err != _winapi.ERROR_OPERATION_ABORTED:
+                    o = waithandle_to_obj[ov.event]
+                    ready_objects.add(o)
+                    if err == 0:
+                        # If o.fileno() is an overlapped pipe handle then
+                        # a zero length message HAS been consumed.
+                        if hasattr(o, '_got_empty_message'):
+                            o._got_empty_message = True
+
+        ready_objects.update(waithandle_to_obj[h] for h in ready_handles)
+        return [o for o in object_list if o in ready_objects]
+
+else:
+
+    import selectors
+
+    # 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'):
+        _WaitSelector = selectors.PollSelector
+    else:
+        _WaitSelector = selectors.SelectSelector
+
+    def wait(object_list, timeout=None):
+        '''
+        Wait till an object in object_list is ready/readable.
+
+        Returns list of those objects in object_list which are ready/readable.
+        '''
+        with _WaitSelector() as selector:
+            for obj in object_list:
+                selector.register(obj, selectors.EVENT_READ)
+
+            if timeout is not None:
+                deadline = time.monotonic() + timeout
+
+            while True:
+                ready = selector.select(timeout)
+                if ready:
+                    return [key.fileobj for (key, events) in ready]
+                else:
+                    if timeout is not None:
+                        timeout = deadline - time.monotonic()
+                        if timeout < 0:
+                            return ready
+
+#
+# Make connection and socket objects shareable if possible
+#
+
+if sys.platform == 'win32':
+    def reduce_connection(conn):
+        handle = conn.fileno()
+        with socket.fromfd(handle, socket.AF_INET, socket.SOCK_STREAM) as s:
+            from . import resource_sharer
+            ds = resource_sharer.DupSocket(s)
+            return rebuild_connection, (ds, conn.readable, conn.writable)
+    def rebuild_connection(ds, readable, writable):
+        sock = ds.detach()
+        return Connection(sock.detach(), readable, writable)
+    reduction.register(Connection, reduce_connection)
+
+    def reduce_pipe_connection(conn):
+        access = ((_winapi.FILE_GENERIC_READ if conn.readable else 0) |
+                  (_winapi.FILE_GENERIC_WRITE if conn.writable else 0))
+        dh = reduction.DupHandle(conn.fileno(), access)
+        return rebuild_pipe_connection, (dh, conn.readable, conn.writable)
+    def rebuild_pipe_connection(dh, readable, writable):
+        handle = dh.detach()
+        return PipeConnection(handle, readable, writable)
+    reduction.register(PipeConnection, reduce_pipe_connection)
+
+else:
+    def reduce_connection(conn):
+        df = reduction.DupFd(conn.fileno())
+        return rebuild_connection, (df, conn.readable, conn.writable)
+    def rebuild_connection(df, readable, writable):
+        fd = df.detach()
+        return Connection(fd, readable, writable)
+    reduction.register(Connection, reduce_connection)