add ydb deps

1 files changed, 1242 insertions, 0 deletions

diff --git a/contrib/tools/python3/src/Lib/asyncio/selector_events.py b/contrib/tools/python3/src/Lib/asyncio/selector_events.py
new file mode 100644
index 0000000000..96e61f7c3a
--- /dev/null
+++ b/contrib/tools/python3/src/Lib/asyncio/selector_events.py
@@ -0,0 +1,1242 @@
+"""Event loop using a selector and related classes.
+
+A selector is a "notify-when-ready" multiplexer.  For a subclass which
+also includes support for signal handling, see the unix_events sub-module.
+"""
+
+__all__ = 'BaseSelectorEventLoop',
+
+import collections
+import errno
+import functools
+import selectors
+import socket
+import warnings
+import weakref
+try:
+    import ssl
+except ImportError:  # pragma: no cover
+    ssl = None
+
+from . import base_events
+from . import constants
+from . import events
+from . import futures
+from . import protocols
+from . import sslproto
+from . import transports
+from . import trsock
+from .log import logger
+
+
+def _test_selector_event(selector, fd, event):
+    # Test if the selector is monitoring 'event' events
+    # for the file descriptor 'fd'.
+    try:
+        key = selector.get_key(fd)
+    except KeyError:
+        return False
+    else:
+        return bool(key.events & event)
+
+
+class BaseSelectorEventLoop(base_events.BaseEventLoop):
+    """Selector event loop.
+
+    See events.EventLoop for API specification.
+    """
+
+    def __init__(self, selector=None):
+        super().__init__()
+
+        if selector is None:
+            selector = selectors.DefaultSelector()
+        logger.debug('Using selector: %s', selector.__class__.__name__)
+        self._selector = selector
+        self._make_self_pipe()
+        self._transports = weakref.WeakValueDictionary()
+
+    def _make_socket_transport(self, sock, protocol, waiter=None, *,
+                               extra=None, server=None):
+        return _SelectorSocketTransport(self, sock, protocol, waiter,
+                                        extra, server)
+
+    def _make_ssl_transport(
+            self, rawsock, protocol, sslcontext, waiter=None,
+            *, server_side=False, server_hostname=None,
+            extra=None, server=None,
+            ssl_handshake_timeout=constants.SSL_HANDSHAKE_TIMEOUT,
+            ssl_shutdown_timeout=constants.SSL_SHUTDOWN_TIMEOUT,
+    ):
+        ssl_protocol = sslproto.SSLProtocol(
+            self, protocol, sslcontext, waiter,
+            server_side, server_hostname,
+            ssl_handshake_timeout=ssl_handshake_timeout,
+            ssl_shutdown_timeout=ssl_shutdown_timeout
+        )
+        _SelectorSocketTransport(self, rawsock, ssl_protocol,
+                                 extra=extra, server=server)
+        return ssl_protocol._app_transport
+
+    def _make_datagram_transport(self, sock, protocol,
+                                 address=None, waiter=None, extra=None):
+        return _SelectorDatagramTransport(self, sock, protocol,
+                                          address, waiter, extra)
+
+    def close(self):
+        if self.is_running():
+            raise RuntimeError("Cannot close a running event loop")
+        if self.is_closed():
+            return
+        self._close_self_pipe()
+        super().close()
+        if self._selector is not None:
+            self._selector.close()
+            self._selector = None
+
+    def _close_self_pipe(self):
+        self._remove_reader(self._ssock.fileno())
+        self._ssock.close()
+        self._ssock = None
+        self._csock.close()
+        self._csock = None
+        self._internal_fds -= 1
+
+    def _make_self_pipe(self):
+        # A self-socket, really. :-)
+        self._ssock, self._csock = socket.socketpair()
+        self._ssock.setblocking(False)
+        self._csock.setblocking(False)
+        self._internal_fds += 1
+        self._add_reader(self._ssock.fileno(), self._read_from_self)
+
+    def _process_self_data(self, data):
+        pass
+
+    def _read_from_self(self):
+        while True:
+            try:
+                data = self._ssock.recv(4096)
+                if not data:
+                    break
+                self._process_self_data(data)
+            except InterruptedError:
+                continue
+            except BlockingIOError:
+                break
+
+    def _write_to_self(self):
+        # This may be called from a different thread, possibly after
+        # _close_self_pipe() has been called or even while it is
+        # running.  Guard for self._csock being None or closed.  When
+        # a socket is closed, send() raises OSError (with errno set to
+        # EBADF, but let's not rely on the exact error code).
+        csock = self._csock
+        if csock is None:
+            return
+
+        try:
+            csock.send(b'\0')
+        except OSError:
+            if self._debug:
+                logger.debug("Fail to write a null byte into the "
+                             "self-pipe socket",
+                             exc_info=True)
+
+    def _start_serving(self, protocol_factory, sock,
+                       sslcontext=None, server=None, backlog=100,
+                       ssl_handshake_timeout=constants.SSL_HANDSHAKE_TIMEOUT,
+                       ssl_shutdown_timeout=constants.SSL_SHUTDOWN_TIMEOUT):
+        self._add_reader(sock.fileno(), self._accept_connection,
+                         protocol_factory, sock, sslcontext, server, backlog,
+                         ssl_handshake_timeout, ssl_shutdown_timeout)
+
+    def _accept_connection(
+            self, protocol_factory, sock,
+            sslcontext=None, server=None, backlog=100,
+            ssl_handshake_timeout=constants.SSL_HANDSHAKE_TIMEOUT,
+            ssl_shutdown_timeout=constants.SSL_SHUTDOWN_TIMEOUT):
+        # This method is only called once for each event loop tick where the
+        # listening socket has triggered an EVENT_READ. There may be multiple
+        # connections waiting for an .accept() so it is called in a loop.
+        # See https://bugs.python.org/issue27906 for more details.
+        for _ in range(backlog):
+            try:
+                conn, addr = sock.accept()
+                if self._debug:
+                    logger.debug("%r got a new connection from %r: %r",
+                                 server, addr, conn)
+                conn.setblocking(False)
+            except (BlockingIOError, InterruptedError, ConnectionAbortedError):
+                # Early exit because the socket accept buffer is empty.
+                return None
+            except OSError as exc:
+                # There's nowhere to send the error, so just log it.
+                if exc.errno in (errno.EMFILE, errno.ENFILE,
+                                 errno.ENOBUFS, errno.ENOMEM):
+                    # Some platforms (e.g. Linux keep reporting the FD as
+                    # ready, so we remove the read handler temporarily.
+                    # We'll try again in a while.
+                    self.call_exception_handler({
+                        'message': 'socket.accept() out of system resource',
+                        'exception': exc,
+                        'socket': trsock.TransportSocket(sock),
+                    })
+                    self._remove_reader(sock.fileno())
+                    self.call_later(constants.ACCEPT_RETRY_DELAY,
+                                    self._start_serving,
+                                    protocol_factory, sock, sslcontext, server,
+                                    backlog, ssl_handshake_timeout,
+                                    ssl_shutdown_timeout)
+                else:
+                    raise  # The event loop will catch, log and ignore it.
+            else:
+                extra = {'peername': addr}
+                accept = self._accept_connection2(
+                    protocol_factory, conn, extra, sslcontext, server,
+                    ssl_handshake_timeout, ssl_shutdown_timeout)
+                self.create_task(accept)
+
+    async def _accept_connection2(
+            self, protocol_factory, conn, extra,
+            sslcontext=None, server=None,
+            ssl_handshake_timeout=constants.SSL_HANDSHAKE_TIMEOUT,
+            ssl_shutdown_timeout=constants.SSL_SHUTDOWN_TIMEOUT):
+        protocol = None
+        transport = None
+        try:
+            protocol = protocol_factory()
+            waiter = self.create_future()
+            if sslcontext:
+                transport = self._make_ssl_transport(
+                    conn, protocol, sslcontext, waiter=waiter,
+                    server_side=True, extra=extra, server=server,
+                    ssl_handshake_timeout=ssl_handshake_timeout,
+                    ssl_shutdown_timeout=ssl_shutdown_timeout)
+            else:
+                transport = self._make_socket_transport(
+                    conn, protocol, waiter=waiter, extra=extra,
+                    server=server)
+
+            try:
+                await waiter
+            except BaseException:
+                transport.close()
+                raise
+                # It's now up to the protocol to handle the connection.
+
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            if self._debug:
+                context = {
+                    'message':
+                        'Error on transport creation for incoming connection',
+                    'exception': exc,
+                }
+                if protocol is not None:
+                    context['protocol'] = protocol
+                if transport is not None:
+                    context['transport'] = transport
+                self.call_exception_handler(context)
+
+    def _ensure_fd_no_transport(self, fd):
+        fileno = fd
+        if not isinstance(fileno, int):
+            try:
+                fileno = int(fileno.fileno())
+            except (AttributeError, TypeError, ValueError):
+                # This code matches selectors._fileobj_to_fd function.
+                raise ValueError(f"Invalid file object: {fd!r}") from None
+        try:
+            transport = self._transports[fileno]
+        except KeyError:
+            pass
+        else:
+            if not transport.is_closing():
+                raise RuntimeError(
+                    f'File descriptor {fd!r} is used by transport '
+                    f'{transport!r}')
+
+    def _add_reader(self, fd, callback, *args):
+        self._check_closed()
+        handle = events.Handle(callback, args, self, None)
+        try:
+            key = self._selector.get_key(fd)
+        except KeyError:
+            self._selector.register(fd, selectors.EVENT_READ,
+                                    (handle, None))
+        else:
+            mask, (reader, writer) = key.events, key.data
+            self._selector.modify(fd, mask | selectors.EVENT_READ,
+                                  (handle, writer))
+            if reader is not None:
+                reader.cancel()
+        return handle
+
+    def _remove_reader(self, fd):
+        if self.is_closed():
+            return False
+        try:
+            key = self._selector.get_key(fd)
+        except KeyError:
+            return False
+        else:
+            mask, (reader, writer) = key.events, key.data
+            mask &= ~selectors.EVENT_READ
+            if not mask:
+                self._selector.unregister(fd)
+            else:
+                self._selector.modify(fd, mask, (None, writer))
+
+            if reader is not None:
+                reader.cancel()
+                return True
+            else:
+                return False
+
+    def _add_writer(self, fd, callback, *args):
+        self._check_closed()
+        handle = events.Handle(callback, args, self, None)
+        try:
+            key = self._selector.get_key(fd)
+        except KeyError:
+            self._selector.register(fd, selectors.EVENT_WRITE,
+                                    (None, handle))
+        else:
+            mask, (reader, writer) = key.events, key.data
+            self._selector.modify(fd, mask | selectors.EVENT_WRITE,
+                                  (reader, handle))
+            if writer is not None:
+                writer.cancel()
+        return handle
+
+    def _remove_writer(self, fd):
+        """Remove a writer callback."""
+        if self.is_closed():
+            return False
+        try:
+            key = self._selector.get_key(fd)
+        except KeyError:
+            return False
+        else:
+            mask, (reader, writer) = key.events, key.data
+            # Remove both writer and connector.
+            mask &= ~selectors.EVENT_WRITE
+            if not mask:
+                self._selector.unregister(fd)
+            else:
+                self._selector.modify(fd, mask, (reader, None))
+
+            if writer is not None:
+                writer.cancel()
+                return True
+            else:
+                return False
+
+    def add_reader(self, fd, callback, *args):
+        """Add a reader callback."""
+        self._ensure_fd_no_transport(fd)
+        self._add_reader(fd, callback, *args)
+
+    def remove_reader(self, fd):
+        """Remove a reader callback."""
+        self._ensure_fd_no_transport(fd)
+        return self._remove_reader(fd)
+
+    def add_writer(self, fd, callback, *args):
+        """Add a writer callback.."""
+        self._ensure_fd_no_transport(fd)
+        self._add_writer(fd, callback, *args)
+
+    def remove_writer(self, fd):
+        """Remove a writer callback."""
+        self._ensure_fd_no_transport(fd)
+        return self._remove_writer(fd)
+
+    async def sock_recv(self, sock, n):
+        """Receive data from the socket.
+
+        The return value is a bytes object representing the data received.
+        The maximum amount of data to be received at once is specified by
+        nbytes.
+        """
+        base_events._check_ssl_socket(sock)
+        if self._debug and sock.gettimeout() != 0:
+            raise ValueError("the socket must be non-blocking")
+        try:
+            return sock.recv(n)
+        except (BlockingIOError, InterruptedError):
+            pass
+        fut = self.create_future()
+        fd = sock.fileno()
+        self._ensure_fd_no_transport(fd)
+        handle = self._add_reader(fd, self._sock_recv, fut, sock, n)
+        fut.add_done_callback(
+            functools.partial(self._sock_read_done, fd, handle=handle))
+        return await fut
+
+    def _sock_read_done(self, fd, fut, handle=None):
+        if handle is None or not handle.cancelled():
+            self.remove_reader(fd)
+
+    def _sock_recv(self, fut, sock, n):
+        # _sock_recv() can add itself as an I/O callback if the operation can't
+        # be done immediately. Don't use it directly, call sock_recv().
+        if fut.done():
+            return
+        try:
+            data = sock.recv(n)
+        except (BlockingIOError, InterruptedError):
+            return  # try again next time
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            fut.set_exception(exc)
+        else:
+            fut.set_result(data)
+
+    async def sock_recv_into(self, sock, buf):
+        """Receive data from the socket.
+
+        The received data is written into *buf* (a writable buffer).
+        The return value is the number of bytes written.
+        """
+        base_events._check_ssl_socket(sock)
+        if self._debug and sock.gettimeout() != 0:
+            raise ValueError("the socket must be non-blocking")
+        try:
+            return sock.recv_into(buf)
+        except (BlockingIOError, InterruptedError):
+            pass
+        fut = self.create_future()
+        fd = sock.fileno()
+        self._ensure_fd_no_transport(fd)
+        handle = self._add_reader(fd, self._sock_recv_into, fut, sock, buf)
+        fut.add_done_callback(
+            functools.partial(self._sock_read_done, fd, handle=handle))
+        return await fut
+
+    def _sock_recv_into(self, fut, sock, buf):
+        # _sock_recv_into() can add itself as an I/O callback if the operation
+        # can't be done immediately. Don't use it directly, call
+        # sock_recv_into().
+        if fut.done():
+            return
+        try:
+            nbytes = sock.recv_into(buf)
+        except (BlockingIOError, InterruptedError):
+            return  # try again next time
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            fut.set_exception(exc)
+        else:
+            fut.set_result(nbytes)
+
+    async def sock_recvfrom(self, sock, bufsize):
+        """Receive a datagram from a datagram socket.
+
+        The return value is a tuple of (bytes, address) representing the
+        datagram received and the address it came from.
+        The maximum amount of data to be received at once is specified by
+        nbytes.
+        """
+        base_events._check_ssl_socket(sock)
+        if self._debug and sock.gettimeout() != 0:
+            raise ValueError("the socket must be non-blocking")
+        try:
+            return sock.recvfrom(bufsize)
+        except (BlockingIOError, InterruptedError):
+            pass
+        fut = self.create_future()
+        fd = sock.fileno()
+        self._ensure_fd_no_transport(fd)
+        handle = self._add_reader(fd, self._sock_recvfrom, fut, sock, bufsize)
+        fut.add_done_callback(
+            functools.partial(self._sock_read_done, fd, handle=handle))
+        return await fut
+
+    def _sock_recvfrom(self, fut, sock, bufsize):
+        # _sock_recvfrom() can add itself as an I/O callback if the operation
+        # can't be done immediately. Don't use it directly, call
+        # sock_recvfrom().
+        if fut.done():
+            return
+        try:
+            result = sock.recvfrom(bufsize)
+        except (BlockingIOError, InterruptedError):
+            return  # try again next time
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            fut.set_exception(exc)
+        else:
+            fut.set_result(result)
+
+    async def sock_recvfrom_into(self, sock, buf, nbytes=0):
+        """Receive data from the socket.
+
+        The received data is written into *buf* (a writable buffer).
+        The return value is a tuple of (number of bytes written, address).
+        """
+        base_events._check_ssl_socket(sock)
+        if self._debug and sock.gettimeout() != 0:
+            raise ValueError("the socket must be non-blocking")
+        if not nbytes:
+            nbytes = len(buf)
+
+        try:
+            return sock.recvfrom_into(buf, nbytes)
+        except (BlockingIOError, InterruptedError):
+            pass
+        fut = self.create_future()
+        fd = sock.fileno()
+        self._ensure_fd_no_transport(fd)
+        handle = self._add_reader(fd, self._sock_recvfrom_into, fut, sock, buf,
+                                  nbytes)
+        fut.add_done_callback(
+            functools.partial(self._sock_read_done, fd, handle=handle))
+        return await fut
+
+    def _sock_recvfrom_into(self, fut, sock, buf, bufsize):
+        # _sock_recv_into() can add itself as an I/O callback if the operation
+        # can't be done immediately. Don't use it directly, call
+        # sock_recv_into().
+        if fut.done():
+            return
+        try:
+            result = sock.recvfrom_into(buf, bufsize)
+        except (BlockingIOError, InterruptedError):
+            return  # try again next time
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            fut.set_exception(exc)
+        else:
+            fut.set_result(result)
+
+    async def sock_sendall(self, sock, data):
+        """Send data to the socket.
+
+        The socket must be connected to a remote socket. This method continues
+        to send data from data until either all data has been sent or an
+        error occurs. None is returned on success. On error, an exception is
+        raised, and there is no way to determine how much data, if any, was
+        successfully processed by the receiving end of the connection.
+        """
+        base_events._check_ssl_socket(sock)
+        if self._debug and sock.gettimeout() != 0:
+            raise ValueError("the socket must be non-blocking")
+        try:
+            n = sock.send(data)
+        except (BlockingIOError, InterruptedError):
+            n = 0
+
+        if n == len(data):
+            # all data sent
+            return
+
+        fut = self.create_future()
+        fd = sock.fileno()
+        self._ensure_fd_no_transport(fd)
+        # use a trick with a list in closure to store a mutable state
+        handle = self._add_writer(fd, self._sock_sendall, fut, sock,
+                                  memoryview(data), [n])
+        fut.add_done_callback(
+            functools.partial(self._sock_write_done, fd, handle=handle))
+        return await fut
+
+    def _sock_sendall(self, fut, sock, view, pos):
+        if fut.done():
+            # Future cancellation can be scheduled on previous loop iteration
+            return
+        start = pos[0]
+        try:
+            n = sock.send(view[start:])
+        except (BlockingIOError, InterruptedError):
+            return
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            fut.set_exception(exc)
+            return
+
+        start += n
+
+        if start == len(view):
+            fut.set_result(None)
+        else:
+            pos[0] = start
+
+    async def sock_sendto(self, sock, data, address):
+        """Send data to the socket.
+
+        The socket must be connected to a remote socket. This method continues
+        to send data from data until either all data has been sent or an
+        error occurs. None is returned on success. On error, an exception is
+        raised, and there is no way to determine how much data, if any, was
+        successfully processed by the receiving end of the connection.
+        """
+        base_events._check_ssl_socket(sock)
+        if self._debug and sock.gettimeout() != 0:
+            raise ValueError("the socket must be non-blocking")
+        try:
+            return sock.sendto(data, address)
+        except (BlockingIOError, InterruptedError):
+            pass
+
+        fut = self.create_future()
+        fd = sock.fileno()
+        self._ensure_fd_no_transport(fd)
+        # use a trick with a list in closure to store a mutable state
+        handle = self._add_writer(fd, self._sock_sendto, fut, sock, data,
+                                  address)
+        fut.add_done_callback(
+            functools.partial(self._sock_write_done, fd, handle=handle))
+        return await fut
+
+    def _sock_sendto(self, fut, sock, data, address):
+        if fut.done():
+            # Future cancellation can be scheduled on previous loop iteration
+            return
+        try:
+            n = sock.sendto(data, 0, address)
+        except (BlockingIOError, InterruptedError):
+            return
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            fut.set_exception(exc)
+        else:
+            fut.set_result(n)
+
+    async def sock_connect(self, sock, address):
+        """Connect to a remote socket at address.
+
+        This method is a coroutine.
+        """
+        base_events._check_ssl_socket(sock)
+        if self._debug and sock.gettimeout() != 0:
+            raise ValueError("the socket must be non-blocking")
+
+        if sock.family == socket.AF_INET or (
+                base_events._HAS_IPv6 and sock.family == socket.AF_INET6):
+            resolved = await self._ensure_resolved(
+                address, family=sock.family, type=sock.type, proto=sock.proto,
+                loop=self,
+            )
+            _, _, _, _, address = resolved[0]
+
+        fut = self.create_future()
+        self._sock_connect(fut, sock, address)
+        try:
+            return await fut
+        finally:
+            # Needed to break cycles when an exception occurs.
+            fut = None
+
+    def _sock_connect(self, fut, sock, address):
+        fd = sock.fileno()
+        try:
+            sock.connect(address)
+        except (BlockingIOError, InterruptedError):
+            # Issue #23618: When the C function connect() fails with EINTR, the
+            # connection runs in background. We have to wait until the socket
+            # becomes writable to be notified when the connection succeed or
+            # fails.
+            self._ensure_fd_no_transport(fd)
+            handle = self._add_writer(
+                fd, self._sock_connect_cb, fut, sock, address)
+            fut.add_done_callback(
+                functools.partial(self._sock_write_done, fd, handle=handle))
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            fut.set_exception(exc)
+        else:
+            fut.set_result(None)
+        finally:
+            fut = None
+
+    def _sock_write_done(self, fd, fut, handle=None):
+        if handle is None or not handle.cancelled():
+            self.remove_writer(fd)
+
+    def _sock_connect_cb(self, fut, sock, address):
+        if fut.done():
+            return
+
+        try:
+            err = sock.getsockopt(socket.SOL_SOCKET, socket.SO_ERROR)
+            if err != 0:
+                # Jump to any except clause below.
+                raise OSError(err, f'Connect call failed {address}')
+        except (BlockingIOError, InterruptedError):
+            # socket is still registered, the callback will be retried later
+            pass
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            fut.set_exception(exc)
+        else:
+            fut.set_result(None)
+        finally:
+            fut = None
+
+    async def sock_accept(self, sock):
+        """Accept a connection.
+
+        The socket must be bound to an address and listening for connections.
+        The return value is a pair (conn, address) where conn is a new socket
+        object usable to send and receive data on the connection, and address
+        is the address bound to the socket on the other end of the connection.
+        """
+        base_events._check_ssl_socket(sock)
+        if self._debug and sock.gettimeout() != 0:
+            raise ValueError("the socket must be non-blocking")
+        fut = self.create_future()
+        self._sock_accept(fut, sock)
+        return await fut
+
+    def _sock_accept(self, fut, sock):
+        fd = sock.fileno()
+        try:
+            conn, address = sock.accept()
+            conn.setblocking(False)
+        except (BlockingIOError, InterruptedError):
+            self._ensure_fd_no_transport(fd)
+            handle = self._add_reader(fd, self._sock_accept, fut, sock)
+            fut.add_done_callback(
+                functools.partial(self._sock_read_done, fd, handle=handle))
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            fut.set_exception(exc)
+        else:
+            fut.set_result((conn, address))
+
+    async def _sendfile_native(self, transp, file, offset, count):
+        del self._transports[transp._sock_fd]
+        resume_reading = transp.is_reading()
+        transp.pause_reading()
+        await transp._make_empty_waiter()
+        try:
+            return await self.sock_sendfile(transp._sock, file, offset, count,
+                                            fallback=False)
+        finally:
+            transp._reset_empty_waiter()
+            if resume_reading:
+                transp.resume_reading()
+            self._transports[transp._sock_fd] = transp
+
+    def _process_events(self, event_list):
+        for key, mask in event_list:
+            fileobj, (reader, writer) = key.fileobj, key.data
+            if mask & selectors.EVENT_READ and reader is not None:
+                if reader._cancelled:
+                    self._remove_reader(fileobj)
+                else:
+                    self._add_callback(reader)
+            if mask & selectors.EVENT_WRITE and writer is not None:
+                if writer._cancelled:
+                    self._remove_writer(fileobj)
+                else:
+                    self._add_callback(writer)
+
+    def _stop_serving(self, sock):
+        self._remove_reader(sock.fileno())
+        sock.close()
+
+
+class _SelectorTransport(transports._FlowControlMixin,
+                         transports.Transport):
+
+    max_size = 256 * 1024  # Buffer size passed to recv().
+
+    _buffer_factory = bytearray  # Constructs initial value for self._buffer.
+
+    # Attribute used in the destructor: it must be set even if the constructor
+    # is not called (see _SelectorSslTransport which may start by raising an
+    # exception)
+    _sock = None
+
+    def __init__(self, loop, sock, protocol, extra=None, server=None):
+        super().__init__(extra, loop)
+        self._extra['socket'] = trsock.TransportSocket(sock)
+        try:
+            self._extra['sockname'] = sock.getsockname()
+        except OSError:
+            self._extra['sockname'] = None
+        if 'peername' not in self._extra:
+            try:
+                self._extra['peername'] = sock.getpeername()
+            except socket.error:
+                self._extra['peername'] = None
+        self._sock = sock
+        self._sock_fd = sock.fileno()
+
+        self._protocol_connected = False
+        self.set_protocol(protocol)
+
+        self._server = server
+        self._buffer = self._buffer_factory()
+        self._conn_lost = 0  # Set when call to connection_lost scheduled.
+        self._closing = False  # Set when close() called.
+        self._paused = False  # Set when pause_reading() called
+
+        if self._server is not None:
+            self._server._attach()
+        loop._transports[self._sock_fd] = self
+
+    def __repr__(self):
+        info = [self.__class__.__name__]
+        if self._sock is None:
+            info.append('closed')
+        elif self._closing:
+            info.append('closing')
+        info.append(f'fd={self._sock_fd}')
+        # test if the transport was closed
+        if self._loop is not None and not self._loop.is_closed():
+            polling = _test_selector_event(self._loop._selector,
+                                           self._sock_fd, selectors.EVENT_READ)
+            if polling:
+                info.append('read=polling')
+            else:
+                info.append('read=idle')
+
+            polling = _test_selector_event(self._loop._selector,
+                                           self._sock_fd,
+                                           selectors.EVENT_WRITE)
+            if polling:
+                state = 'polling'
+            else:
+                state = 'idle'
+
+            bufsize = self.get_write_buffer_size()
+            info.append(f'write=<{state}, bufsize={bufsize}>')
+        return '<{}>'.format(' '.join(info))
+
+    def abort(self):
+        self._force_close(None)
+
+    def set_protocol(self, protocol):
+        self._protocol = protocol
+        self._protocol_connected = True
+
+    def get_protocol(self):
+        return self._protocol
+
+    def is_closing(self):
+        return self._closing
+
+    def is_reading(self):
+        return not self.is_closing() and not self._paused
+
+    def pause_reading(self):
+        if not self.is_reading():
+            return
+        self._paused = True
+        self._loop._remove_reader(self._sock_fd)
+        if self._loop.get_debug():
+            logger.debug("%r pauses reading", self)
+
+    def resume_reading(self):
+        if self._closing or not self._paused:
+            return
+        self._paused = False
+        self._add_reader(self._sock_fd, self._read_ready)
+        if self._loop.get_debug():
+            logger.debug("%r resumes reading", self)
+
+    def close(self):
+        if self._closing:
+            return
+        self._closing = True
+        self._loop._remove_reader(self._sock_fd)
+        if not self._buffer:
+            self._conn_lost += 1
+            self._loop._remove_writer(self._sock_fd)
+            self._loop.call_soon(self._call_connection_lost, None)
+
+    def __del__(self, _warn=warnings.warn):
+        if self._sock is not None:
+            _warn(f"unclosed transport {self!r}", ResourceWarning, source=self)
+            self._sock.close()
+
+    def _fatal_error(self, exc, message='Fatal error on transport'):
+        # Should be called from exception handler only.
+        if isinstance(exc, OSError):
+            if self._loop.get_debug():
+                logger.debug("%r: %s", self, message, exc_info=True)
+        else:
+            self._loop.call_exception_handler({
+                'message': message,
+                'exception': exc,
+                'transport': self,
+                'protocol': self._protocol,
+            })
+        self._force_close(exc)
+
+    def _force_close(self, exc):
+        if self._conn_lost:
+            return
+        if self._buffer:
+            self._buffer.clear()
+            self._loop._remove_writer(self._sock_fd)
+        if not self._closing:
+            self._closing = True
+            self._loop._remove_reader(self._sock_fd)
+        self._conn_lost += 1
+        self._loop.call_soon(self._call_connection_lost, exc)
+
+    def _call_connection_lost(self, exc):
+        try:
+            if self._protocol_connected:
+                self._protocol.connection_lost(exc)
+        finally:
+            self._sock.close()
+            self._sock = None
+            self._protocol = None
+            self._loop = None
+            server = self._server
+            if server is not None:
+                server._detach()
+                self._server = None
+
+    def get_write_buffer_size(self):
+        return len(self._buffer)
+
+    def _add_reader(self, fd, callback, *args):
+        if not self.is_reading():
+            return
+        self._loop._add_reader(fd, callback, *args)
+
+
+class _SelectorSocketTransport(_SelectorTransport):
+
+    _start_tls_compatible = True
+    _sendfile_compatible = constants._SendfileMode.TRY_NATIVE
+
+    def __init__(self, loop, sock, protocol, waiter=None,
+                 extra=None, server=None):
+
+        self._read_ready_cb = None
+        super().__init__(loop, sock, protocol, extra, server)
+        self._eof = False
+        self._empty_waiter = None
+
+        # Disable the Nagle algorithm -- small writes will be
+        # sent without waiting for the TCP ACK.  This generally
+        # decreases the latency (in some cases significantly.)
+        base_events._set_nodelay(self._sock)
+
+        self._loop.call_soon(self._protocol.connection_made, self)
+        # only start reading when connection_made() has been called
+        self._loop.call_soon(self._add_reader,
+                             self._sock_fd, self._read_ready)
+        if waiter is not None:
+            # only wake up the waiter when connection_made() has been called
+            self._loop.call_soon(futures._set_result_unless_cancelled,
+                                 waiter, None)
+
+    def set_protocol(self, protocol):
+        if isinstance(protocol, protocols.BufferedProtocol):
+            self._read_ready_cb = self._read_ready__get_buffer
+        else:
+            self._read_ready_cb = self._read_ready__data_received
+
+        super().set_protocol(protocol)
+
+    def _read_ready(self):
+        self._read_ready_cb()
+
+    def _read_ready__get_buffer(self):
+        if self._conn_lost:
+            return
+
+        try:
+            buf = self._protocol.get_buffer(-1)
+            if not len(buf):
+                raise RuntimeError('get_buffer() returned an empty buffer')
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            self._fatal_error(
+                exc, 'Fatal error: protocol.get_buffer() call failed.')
+            return
+
+        try:
+            nbytes = self._sock.recv_into(buf)
+        except (BlockingIOError, InterruptedError):
+            return
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            self._fatal_error(exc, 'Fatal read error on socket transport')
+            return
+
+        if not nbytes:
+            self._read_ready__on_eof()
+            return
+
+        try:
+            self._protocol.buffer_updated(nbytes)
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            self._fatal_error(
+                exc, 'Fatal error: protocol.buffer_updated() call failed.')
+
+    def _read_ready__data_received(self):
+        if self._conn_lost:
+            return
+        try:
+            data = self._sock.recv(self.max_size)
+        except (BlockingIOError, InterruptedError):
+            return
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            self._fatal_error(exc, 'Fatal read error on socket transport')
+            return
+
+        if not data:
+            self._read_ready__on_eof()
+            return
+
+        try:
+            self._protocol.data_received(data)
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            self._fatal_error(
+                exc, 'Fatal error: protocol.data_received() call failed.')
+
+    def _read_ready__on_eof(self):
+        if self._loop.get_debug():
+            logger.debug("%r received EOF", self)
+
+        try:
+            keep_open = self._protocol.eof_received()
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            self._fatal_error(
+                exc, 'Fatal error: protocol.eof_received() call failed.')
+            return
+
+        if keep_open:
+            # We're keeping the connection open so the
+            # protocol can write more, but we still can't
+            # receive more, so remove the reader callback.
+            self._loop._remove_reader(self._sock_fd)
+        else:
+            self.close()
+
+    def write(self, data):
+        if not isinstance(data, (bytes, bytearray, memoryview)):
+            raise TypeError(f'data argument must be a bytes-like object, '
+                            f'not {type(data).__name__!r}')
+        if self._eof:
+            raise RuntimeError('Cannot call write() after write_eof()')
+        if self._empty_waiter is not None:
+            raise RuntimeError('unable to write; sendfile is in progress')
+        if not data:
+            return
+
+        if self._conn_lost:
+            if self._conn_lost >= constants.LOG_THRESHOLD_FOR_CONNLOST_WRITES:
+                logger.warning('socket.send() raised exception.')
+            self._conn_lost += 1
+            return
+
+        if not self._buffer:
+            # Optimization: try to send now.
+            try:
+                n = self._sock.send(data)
+            except (BlockingIOError, InterruptedError):
+                pass
+            except (SystemExit, KeyboardInterrupt):
+                raise
+            except BaseException as exc:
+                self._fatal_error(exc, 'Fatal write error on socket transport')
+                return
+            else:
+                data = data[n:]
+                if not data:
+                    return
+            # Not all was written; register write handler.
+            self._loop._add_writer(self._sock_fd, self._write_ready)
+
+        # Add it to the buffer.
+        self._buffer.extend(data)
+        self._maybe_pause_protocol()
+
+    def _write_ready(self):
+        assert self._buffer, 'Data should not be empty'
+
+        if self._conn_lost:
+            return
+        try:
+            n = self._sock.send(self._buffer)
+        except (BlockingIOError, InterruptedError):
+            pass
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            self._loop._remove_writer(self._sock_fd)
+            self._buffer.clear()
+            self._fatal_error(exc, 'Fatal write error on socket transport')
+            if self._empty_waiter is not None:
+                self._empty_waiter.set_exception(exc)
+        else:
+            if n:
+                del self._buffer[:n]
+            self._maybe_resume_protocol()  # May append to buffer.
+            if not self._buffer:
+                self._loop._remove_writer(self._sock_fd)
+                if self._empty_waiter is not None:
+                    self._empty_waiter.set_result(None)
+                if self._closing:
+                    self._call_connection_lost(None)
+                elif self._eof:
+                    self._sock.shutdown(socket.SHUT_WR)
+
+    def write_eof(self):
+        if self._closing or self._eof:
+            return
+        self._eof = True
+        if not self._buffer:
+            self._sock.shutdown(socket.SHUT_WR)
+
+    def can_write_eof(self):
+        return True
+
+    def _call_connection_lost(self, exc):
+        super()._call_connection_lost(exc)
+        if self._empty_waiter is not None:
+            self._empty_waiter.set_exception(
+                ConnectionError("Connection is closed by peer"))
+
+    def _make_empty_waiter(self):
+        if self._empty_waiter is not None:
+            raise RuntimeError("Empty waiter is already set")
+        self._empty_waiter = self._loop.create_future()
+        if not self._buffer:
+            self._empty_waiter.set_result(None)
+        return self._empty_waiter
+
+    def _reset_empty_waiter(self):
+        self._empty_waiter = None
+
+
+class _SelectorDatagramTransport(_SelectorTransport):
+
+    _buffer_factory = collections.deque
+
+    def __init__(self, loop, sock, protocol, address=None,
+                 waiter=None, extra=None):
+        super().__init__(loop, sock, protocol, extra)
+        self._address = address
+        self._buffer_size = 0
+        self._loop.call_soon(self._protocol.connection_made, self)
+        # only start reading when connection_made() has been called
+        self._loop.call_soon(self._add_reader,
+                             self._sock_fd, self._read_ready)
+        if waiter is not None:
+            # only wake up the waiter when connection_made() has been called
+            self._loop.call_soon(futures._set_result_unless_cancelled,
+                                 waiter, None)
+
+    def get_write_buffer_size(self):
+        return self._buffer_size
+
+    def _read_ready(self):
+        if self._conn_lost:
+            return
+        try:
+            data, addr = self._sock.recvfrom(self.max_size)
+        except (BlockingIOError, InterruptedError):
+            pass
+        except OSError as exc:
+            self._protocol.error_received(exc)
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            self._fatal_error(exc, 'Fatal read error on datagram transport')
+        else:
+            self._protocol.datagram_received(data, addr)
+
+    def sendto(self, data, addr=None):
+        if not isinstance(data, (bytes, bytearray, memoryview)):
+            raise TypeError(f'data argument must be a bytes-like object, '
+                            f'not {type(data).__name__!r}')
+        if not data:
+            return
+
+        if self._address:
+            if addr not in (None, self._address):
+                raise ValueError(
+                    f'Invalid address: must be None or {self._address}')
+            addr = self._address
+
+        if self._conn_lost and self._address:
+            if self._conn_lost >= constants.LOG_THRESHOLD_FOR_CONNLOST_WRITES:
+                logger.warning('socket.send() raised exception.')
+            self._conn_lost += 1
+            return
+
+        if not self._buffer:
+            # Attempt to send it right away first.
+            try:
+                if self._extra['peername']:
+                    self._sock.send(data)
+                else:
+                    self._sock.sendto(data, addr)
+                return
+            except (BlockingIOError, InterruptedError):
+                self._loop._add_writer(self._sock_fd, self._sendto_ready)
+            except OSError as exc:
+                self._protocol.error_received(exc)
+                return
+            except (SystemExit, KeyboardInterrupt):
+                raise
+            except BaseException as exc:
+                self._fatal_error(
+                    exc, 'Fatal write error on datagram transport')
+                return
+
+        # Ensure that what we buffer is immutable.
+        self._buffer.append((bytes(data), addr))
+        self._buffer_size += len(data)
+        self._maybe_pause_protocol()
+
+    def _sendto_ready(self):
+        while self._buffer:
+            data, addr = self._buffer.popleft()
+            self._buffer_size -= len(data)
+            try:
+                if self._extra['peername']:
+                    self._sock.send(data)
+                else:
+                    self._sock.sendto(data, addr)
+            except (BlockingIOError, InterruptedError):
+                self._buffer.appendleft((data, addr))  # Try again later.
+                self._buffer_size += len(data)
+                break
+            except OSError as exc:
+                self._protocol.error_received(exc)
+                return
+            except (SystemExit, KeyboardInterrupt):
+                raise
+            except BaseException as exc:
+                self._fatal_error(
+                    exc, 'Fatal write error on datagram transport')
+                return
+
+        self._maybe_resume_protocol()  # May append to buffer.
+        if not self._buffer:
+            self._loop._remove_writer(self._sock_fd)
+            if self._closing:
+                self._call_connection_lost(None)