bpo-32410: Implement loop.sock_sendfile() (#4976)

Doc/library/asyncio-eventloop.rst

@@ -701,6 +701,36 @@ Low-level socket operations
 
       :meth:`AbstractEventLoop.create_server` and :func:`start_server`.
 
+.. coroutinemethod:: AbstractEventLoop.sock_sendfile(sock, file, \
+                                                     offset=0, count=None, \
+                                                     *, fallback=True)
+
+   Send a file using high-performance :mod:`os.sendfile` if possible
+   and return the total number of bytes which were sent.
+
+   Asynchronous version of :meth:`socket.socket.sendfile`.
+
+   *sock* must be non-blocking :class:`~socket.socket` of
+   :const:`socket.SOCK_STREAM` type.
+
+   *file* must be a regular file object opened in binary mode.
+
+   *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 :meth:`file.tell()
+   <io.IOBase.tell>` can be used to figure out the number of bytes
+   which were sent.
+
+   *fallback* set to ``True`` makes asyncio to manually read and send
+   the file when the platform does not support the sendfile syscall
+   (e.g. Windows or SSL socket on Unix).
+
+   Raise :exc:`RuntimeError` if the system does not support
+   *sendfile* syscall and *fallback* is ``False``.
+
+   .. versionadded:: 3.7
+
 
 Resolve host name
 -----------------

Lib/asyncio/base_events.py

@@ -154,6 +154,10 @@ def _run_until_complete_cb(fut):
     futures._get_loop(fut).stop()
 
 
+class _SendfileNotAvailable(RuntimeError):
+    pass
+
+
 class Server(events.AbstractServer):
 
     def __init__(self, loop, sockets):
@@ -647,6 +651,72 @@ class BaseEventLoop(events.AbstractEventLoop):
         return await self.run_in_executor(
             None, socket.getnameinfo, sockaddr, flags)
 
+    async def sock_sendfile(self, sock, file, offset=0, count=None,
+                            *, fallback=True):
+        if self._debug and sock.gettimeout() != 0:
+            raise ValueError("the socket must be non-blocking")
+        self._check_sendfile_params(sock, file, offset, count)
+        try:
+            return await self._sock_sendfile_native(sock, file,
+                                                    offset, count)
+        except _SendfileNotAvailable as exc:
+            if fallback:
+                return await self._sock_sendfile_fallback(sock, file,
+                                                          offset, count)
+            else:
+                raise RuntimeError(exc.args[0]) from None
+
+    async def _sock_sendfile_native(self, sock, file, offset, count):
+        # NB: sendfile syscall is not supported for SSL sockets and
+        # non-mmap files even if sendfile is supported by OS
+        raise _SendfileNotAvailable(
+            f"syscall sendfile is not available for socket {sock!r} "
+            "and file {file!r} combination")
+
+    async def _sock_sendfile_fallback(self, sock, file, offset, count):
+        if offset:
+            file.seek(offset)
+        blocksize = min(count, 16384) if count else 16384
+        buf = bytearray(blocksize)
+        total_sent = 0
+        try:
+            while True:
+                if count:
+                    blocksize = min(count - total_sent, blocksize)
+                    if blocksize <= 0:
+                        break
+                view = memoryview(buf)[:blocksize]
+                read = file.readinto(view)
+                if not read:
+                    break  # EOF
+                await self.sock_sendall(sock, view)
+                total_sent += read
+            return total_sent
+        finally:
+            if total_sent > 0 and hasattr(file, 'seek'):
+                file.seek(offset + total_sent)
+
+    def _check_sendfile_params(self, sock, file, offset, count):
+        if 'b' not in getattr(file, 'mode', 'b'):
+            raise ValueError("file should be opened in binary mode")
+        if not sock.type == socket.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))
+        if not isinstance(offset, int):
+            raise TypeError(
+                "offset must be a non-negative integer (got {!r})".format(
+                    offset))
+        if offset < 0:
+            raise ValueError(
+                "offset must be a non-negative integer (got {!r})".format(
+                    offset))
+
     async def create_connection(
             self, protocol_factory, host=None, port=None,
             *, ssl=None, family=0,

Lib/asyncio/events.py

@@ -464,6 +464,10 @@ class AbstractEventLoop:
     async def sock_accept(self, sock):
         raise NotImplementedError
 
+    async def sock_sendfile(self, sock, file, offset=0, count=None,
+                            *, fallback=None):
+        raise NotImplementedError
+
     # Signal handling.
 
     def add_signal_handler(self, sig, callback, *args):

Lib/asyncio/unix_events.py

@@ -1,6 +1,7 @@
 """Selector event loop for Unix with signal handling."""
 
 import errno
+import io
 import os
 import selectors
 import signal
@@ -308,6 +309,98 @@ class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
                             ssl_handshake_timeout=ssl_handshake_timeout)
         return server
 
+    async def _sock_sendfile_native(self, sock, file, offset, count):
+        try:
+            os.sendfile
+        except AttributeError as exc:
+            raise base_events._SendfileNotAvailable(
+                "os.sendfile() is not available")
+        try:
+            fileno = file.fileno()
+        except (AttributeError, io.UnsupportedOperation) as err:
+            raise base_events._SendfileNotAvailable("not a regular file")
+        try:
+            fsize = os.fstat(fileno).st_size
+        except OSError as err:
+            raise base_events._SendfileNotAvailable("not a regular file")
+        blocksize = count if count else fsize
+        if not blocksize:
+            return 0  # empty file
+
+        fut = self.create_future()
+        self._sock_sendfile_native_impl(fut, None, sock, fileno,
+                                        offset, count, blocksize, 0)
+        return await fut
+
+    def _sock_sendfile_native_impl(self, fut, registered_fd, sock, fileno,
+                                   offset, count, blocksize, total_sent):
+        fd = sock.fileno()
+        if registered_fd is not None:
+            # Remove the callback early.  It should be rare that the
+            # selector says the fd is ready but the call still returns
+            # EAGAIN, and I am willing to take a hit in that case in
+            # order to simplify the common case.
+            self.remove_writer(registered_fd)
+        if fut.cancelled():
+            self._sock_sendfile_update_filepos(fileno, offset, total_sent)
+            return
+        if count:
+            blocksize = count - total_sent
+            if blocksize <= 0:
+                self._sock_sendfile_update_filepos(fileno, offset, total_sent)
+                fut.set_result(total_sent)
+                return
+
+        try:
+            sent = os.sendfile(fd, fileno, offset, blocksize)
+        except (BlockingIOError, InterruptedError):
+            if registered_fd is None:
+                self._sock_add_cancellation_callback(fut, sock)
+            self.add_writer(fd, self._sock_sendfile_native_impl, fut,
+                            fd, sock, fileno,
+                            offset, count, blocksize, total_sent)
+        except OSError as exc:
+            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().
+                err = base_events._SendfileNotAvailable(
+                    "os.sendfile call failed")
+                self._sock_sendfile_update_filepos(fileno, offset, total_sent)
+                fut.set_exception(err)
+            else:
+                self._sock_sendfile_update_filepos(fileno, offset, total_sent)
+                fut.set_exception(exc)
+        except Exception as exc:
+            self._sock_sendfile_update_filepos(fileno, offset, total_sent)
+            fut.set_exception(exc)
+        else:
+            if sent == 0:
+                # EOF
+                self._sock_sendfile_update_filepos(fileno, offset, total_sent)
+                fut.set_result(total_sent)
+            else:
+                offset += sent
+                total_sent += sent
+                if registered_fd is None:
+                    self._sock_add_cancellation_callback(fut, sock)
+                self.add_writer(fd, self._sock_sendfile_native_impl, fut,
+                                fd, sock, fileno,
+                                offset, count, blocksize, total_sent)
+
+    def _sock_sendfile_update_filepos(self, fileno, offset, total_sent):
+        if total_sent > 0:
+            os.lseek(fileno, offset, os.SEEK_SET)
+
+    def _sock_add_cancellation_callback(self, fut, sock):
+        def cb(fut):
+            if fut.cancelled():
+                fd = sock.fileno()
+                if fd != -1:
+                    self.remove_writer(fd)
+        fut.add_done_callback(cb)
+
 
 class _UnixReadPipeTransport(transports.ReadTransport):
 

Lib/test/test_asyncio/test_base_events.py

@@ -1787,5 +1787,163 @@ class RunningLoopTests(unittest.TestCase):
             outer_loop.close()
 
 
+class BaseLoopSendfileTests(test_utils.TestCase):
+
+    DATA = b"12345abcde" * 16 * 1024  # 160 KiB
+
+    class MyProto(asyncio.Protocol):
+
+        def __init__(self, loop):
+            self.started = False
+            self.closed = False
+            self.data = bytearray()
+            self.fut = loop.create_future()
+
+        def connection_made(self, transport):
+            self.started = True
+
+        def data_received(self, data):
+            self.data.extend(data)
+
+        def connection_lost(self, exc):
+            self.closed = True
+            self.fut.set_result(None)
+
+        async def wait_closed(self):
+            await self.fut
+
+    @classmethod
+    def setUpClass(cls):
+        with open(support.TESTFN, 'wb') as fp:
+            fp.write(cls.DATA)
+        super().setUpClass()
+
+    @classmethod
+    def tearDownClass(cls):
+        support.unlink(support.TESTFN)
+        super().tearDownClass()
+
+    def setUp(self):
+        from asyncio.selector_events import BaseSelectorEventLoop
+        # BaseSelectorEventLoop() has no native implementation
+        self.loop = BaseSelectorEventLoop()
+        self.set_event_loop(self.loop)
+        self.file = open(support.TESTFN, 'rb')
+        self.addCleanup(self.file.close)
+        super().setUp()
+
+    def make_socket(self, blocking=False):
+        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        sock.setblocking(blocking)
+        self.addCleanup(sock.close)
+        return sock
+
+    def run_loop(self, coro):
+        return self.loop.run_until_complete(coro)
+
+    def prepare(self):
+        sock = self.make_socket()
+        proto = self.MyProto(self.loop)
+        port = support.find_unused_port()
+        server = self.run_loop(self.loop.create_server(
+            lambda: proto, support.HOST, port))
+        self.run_loop(self.loop.sock_connect(sock, (support.HOST, port)))
+
+        def cleanup():
+            server.close()
+            self.run_loop(server.wait_closed())
+
+        self.addCleanup(cleanup)
+
+        return sock, proto
+
+    def test__sock_sendfile_native_failure(self):
+        sock, proto = self.prepare()
+
+        with self.assertRaisesRegex(base_events._SendfileNotAvailable,
+                                    "sendfile is not available"):
+            self.run_loop(self.loop._sock_sendfile_native(sock, self.file,
+                                                          0, None))
+
+        self.assertEqual(proto.data, b'')
+        self.assertEqual(self.file.tell(), 0)
+
+    def test_sock_sendfile_no_fallback(self):
+        sock, proto = self.prepare()
+
+        with self.assertRaisesRegex(RuntimeError,
+                                    "sendfile is not available"):
+            self.run_loop(self.loop.sock_sendfile(sock, self.file,
+                                                  fallback=False))
+
+        self.assertEqual(self.file.tell(), 0)
+        self.assertEqual(proto.data, b'')
+
+    def test_sock_sendfile_fallback(self):
+        sock, proto = self.prepare()
+
+        ret = self.run_loop(self.loop.sock_sendfile(sock, self.file))
+        sock.close()
+        self.run_loop(proto.wait_closed())
+
+        self.assertEqual(ret, len(self.DATA))
+        self.assertEqual(self.file.tell(), len(self.DATA))
+        self.assertEqual(proto.data, self.DATA)
+
+    def test_sock_sendfile_fallback_offset_and_count(self):
+        sock, proto = self.prepare()
+
+        ret = self.run_loop(self.loop.sock_sendfile(sock, self.file,
+                                                    1000, 2000))
+        sock.close()
+        self.run_loop(proto.wait_closed())
+
+        self.assertEqual(ret, 2000)
+        self.assertEqual(self.file.tell(), 3000)
+        self.assertEqual(proto.data, self.DATA[1000:3000])
+
+    def test_blocking_socket(self):
+        self.loop.set_debug(True)
+        sock = self.make_socket(blocking=True)
+        with self.assertRaisesRegex(ValueError, "must be non-blocking"):
+            self.run_loop(self.loop.sock_sendfile(sock, self.file))
+
+    def test_nonbinary_file(self):
+        sock = self.make_socket()
+        with open(support.TESTFN, 'r') as f:
+            with self.assertRaisesRegex(ValueError, "binary mode"):
+                self.run_loop(self.loop.sock_sendfile(sock, f))
+
+    def test_nonstream_socket(self):
+        sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+        self.addCleanup(sock.close)
+        with self.assertRaisesRegex(ValueError, "only SOCK_STREAM type"):
+            self.run_loop(self.loop.sock_sendfile(sock, self.file))
+
+    def test_notint_count(self):
+        sock = self.make_socket()
+        with self.assertRaisesRegex(TypeError,
+                                    "count must be a positive integer"):
+            self.run_loop(self.loop.sock_sendfile(sock, self.file, 0, 'count'))
+
+    def test_negative_count(self):
+        sock = self.make_socket()
+        with self.assertRaisesRegex(ValueError,
+                                    "count must be a positive integer"):
+            self.run_loop(self.loop.sock_sendfile(sock, self.file, 0, -1))
+
+    def test_notint_offset(self):
+        sock = self.make_socket()
+        with self.assertRaisesRegex(TypeError,
+                                    "offset must be a non-negative integer"):
+            self.run_loop(self.loop.sock_sendfile(sock, self.file, 'offset'))
+
+    def test_negative_offset(self):
+        sock = self.make_socket()
+        with self.assertRaisesRegex(ValueError,
+                                    "offset must be a non-negative integer"):
+            self.run_loop(self.loop.sock_sendfile(sock, self.file, -1))
+
+
 if __name__ == '__main__':
     unittest.main()

Lib/test/test_asyncio/test_events.py

@@ -2555,6 +2555,8 @@ class AbstractEventLoopTests(unittest.TestCase):
                 await loop.sock_connect(f, f)
             with self.assertRaises(NotImplementedError):
                 await loop.sock_accept(f)
+            with self.assertRaises(NotImplementedError):
+                await loop.sock_sendfile(f, mock.Mock())
             with self.assertRaises(NotImplementedError):
                 await loop.connect_read_pipe(f, mock.sentinel.pipe)
             with self.assertRaises(NotImplementedError):

Lib/test/test_asyncio/test_unix_events.py

@@ -1,6 +1,7 @@
 """Tests for unix_events.py."""
 
 import collections
+import contextlib
 import errno
 import io
 import os
@@ -21,6 +22,7 @@ if sys.platform == 'win32':
 
 import asyncio
 from asyncio import log
+from asyncio import base_events
 from asyncio import unix_events
 from test.test_asyncio import utils as test_utils
 
@@ -417,6 +419,255 @@ class SelectorEventLoopUnixSocketTests(test_utils.TestCase):
             self.loop.run_until_complete(coro)
 
 
+@unittest.skipUnless(hasattr(os, 'sendfile'),
+                     'sendfile is not supported')
+class SelectorEventLoopUnixSockSendfileTests(test_utils.TestCase):
+    DATA = b"12345abcde" * 16 * 1024  # 160 KiB
+
+    class MyProto(asyncio.Protocol):
+
+        def __init__(self, loop):
+            self.started = False
+            self.closed = False
+            self.data = bytearray()
+            self.fut = loop.create_future()
+            self.transport = None
+
+        def connection_made(self, transport):
+            self.started = True
+            self.transport = transport
+
+        def data_received(self, data):
+            self.data.extend(data)
+
+        def connection_lost(self, exc):
+            self.closed = True
+            self.fut.set_result(None)
+
+        async def wait_closed(self):
+            await self.fut
+
+    @classmethod
+    def setUpClass(cls):
+        with open(support.TESTFN, 'wb') as fp:
+            fp.write(cls.DATA)
+        super().setUpClass()
+
+    @classmethod
+    def tearDownClass(cls):
+        support.unlink(support.TESTFN)
+        super().tearDownClass()
+
+    def setUp(self):
+        self.loop = asyncio.new_event_loop()
+        self.set_event_loop(self.loop)
+        self.file = open(support.TESTFN, 'rb')
+        self.addCleanup(self.file.close)
+        super().setUp()
+
+    def make_socket(self, blocking=False):
+        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        sock.setblocking(blocking)
+        self.addCleanup(sock.close)
+        return sock
+
+    def run_loop(self, coro):
+        return self.loop.run_until_complete(coro)
+
+    def prepare(self):
+        sock = self.make_socket()
+        proto = self.MyProto(self.loop)
+        port = support.find_unused_port()
+        server = self.run_loop(self.loop.create_server(
+            lambda: proto, support.HOST, port))
+        self.run_loop(self.loop.sock_connect(sock, (support.HOST, port)))
+
+        def cleanup():
+            proto.transport.close()
+            self.run_loop(proto.wait_closed())
+
+            server.close()
+            self.run_loop(server.wait_closed())
+
+        self.addCleanup(cleanup)
+
+        return sock, proto
+
+    def test_success(self):
+        sock, proto = self.prepare()
+        ret = self.run_loop(self.loop.sock_sendfile(sock, self.file))
+        sock.close()
+        self.run_loop(proto.wait_closed())
+
+        self.assertEqual(ret, len(self.DATA))
+        self.assertEqual(proto.data, self.DATA)
+        self.assertEqual(self.file.tell(), len(self.DATA))
+
+    def test_with_offset_and_count(self):
+        sock, proto = self.prepare()
+        ret = self.run_loop(self.loop.sock_sendfile(sock, self.file,
+                                                    1000, 2000))
+        sock.close()
+        self.run_loop(proto.wait_closed())
+
+        self.assertEqual(proto.data, self.DATA[1000:3000])
+        self.assertEqual(self.file.tell(), 3000)
+        self.assertEqual(ret, 2000)
+
+    def test_sendfile_not_available(self):
+        sock, proto = self.prepare()
+        with mock.patch('asyncio.unix_events.os', spec=[]):
+            with self.assertRaisesRegex(base_events._SendfileNotAvailable,
+                                        "os[.]sendfile[(][)] is not available"):
+                self.run_loop(self.loop._sock_sendfile_native(sock, self.file,
+                                                              0, None))
+        self.assertEqual(self.file.tell(), 0)
+
+    def test_sendfile_not_a_file(self):
+        sock, proto = self.prepare()
+        f = object()
+        with self.assertRaisesRegex(base_events._SendfileNotAvailable,
+                                    "not a regular file"):
+            self.run_loop(self.loop._sock_sendfile_native(sock, f,
+                                                          0, None))
+        self.assertEqual(self.file.tell(), 0)
+
+    def test_sendfile_iobuffer(self):
+        sock, proto = self.prepare()
+        f = io.BytesIO()
+        with self.assertRaisesRegex(base_events._SendfileNotAvailable,
+                                    "not a regular file"):
+            self.run_loop(self.loop._sock_sendfile_native(sock, f,
+                                                          0, None))
+        self.assertEqual(self.file.tell(), 0)
+
+    def test_sendfile_not_regular_file(self):
+        sock, proto = self.prepare()
+        f = mock.Mock()
+        f.fileno.return_value = -1
+        with self.assertRaisesRegex(base_events._SendfileNotAvailable,
+                                    "not a regular file"):
+            self.run_loop(self.loop._sock_sendfile_native(sock, f,
+                                                          0, None))
+        self.assertEqual(self.file.tell(), 0)
+
+    def test_sendfile_zero_size(self):
+        sock, proto = self.prepare()
+        fname = support.TESTFN + '.suffix'
+        with open(fname, 'wb') as f:
+            pass  # make zero sized file
+        f = open(fname, 'rb')
+        self.addCleanup(f.close)
+        self.addCleanup(support.unlink, fname)
+        ret = self.run_loop(self.loop._sock_sendfile_native(sock, f,
+                                                            0, None))
+        sock.close()
+        self.run_loop(proto.wait_closed())
+
+        self.assertEqual(ret, 0)
+        self.assertEqual(self.file.tell(), 0)
+
+    def test_mix_sendfile_and_regular_send(self):
+        buf = b'1234567890' * 1024 * 1024  # 10 MB
+        sock, proto = self.prepare()
+        self.run_loop(self.loop.sock_sendall(sock, buf))
+        ret = self.run_loop(self.loop.sock_sendfile(sock, self.file))
+        self.run_loop(self.loop.sock_sendall(sock, buf))
+        sock.close()
+        self.run_loop(proto.wait_closed())
+
+        self.assertEqual(ret, len(self.DATA))
+        expected = buf + self.DATA + buf
+        self.assertEqual(proto.data, expected)
+        self.assertEqual(self.file.tell(), len(self.DATA))
+
+    def test_cancel1(self):
+        sock, proto = self.prepare()
+
+        fut = self.loop.create_future()
+        fileno = self.file.fileno()
+        self.loop._sock_sendfile_native_impl(fut, None, sock, fileno,
+                                             0, None, len(self.DATA), 0)
+        fut.cancel()
+        with contextlib.suppress(asyncio.CancelledError):
+            self.run_loop(fut)
+        with self.assertRaises(KeyError):
+            self.loop._selector.get_key(sock)
+
+    def test_cancel2(self):
+        sock, proto = self.prepare()
+
+        fut = self.loop.create_future()
+        fileno = self.file.fileno()
+        self.loop._sock_sendfile_native_impl(fut, None, sock, fileno,
+                                             0, None, len(self.DATA), 0)
+        fut.cancel()
+        self.loop._sock_sendfile_native_impl(fut, sock.fileno(), sock, fileno,
+                                             0, None, len(self.DATA), 0)
+        with self.assertRaises(KeyError):
+            self.loop._selector.get_key(sock)
+
+    def test_blocking_error(self):
+        sock, proto = self.prepare()
+
+        fileno = self.file.fileno()
+        fut = mock.Mock()
+        fut.cancelled.return_value = False
+        with mock.patch('os.sendfile', side_effect=BlockingIOError()):
+            self.loop._sock_sendfile_native_impl(fut, None, sock, fileno,
+                                                 0, None, len(self.DATA), 0)
+        key = self.loop._selector.get_key(sock)
+        self.assertIsNotNone(key)
+        fut.add_done_callback.assert_called_once_with(mock.ANY)
+
+    def test_os_error_first_call(self):
+        sock, proto = self.prepare()
+
+        fileno = self.file.fileno()
+        fut = self.loop.create_future()
+        with mock.patch('os.sendfile', side_effect=OSError()):
+            self.loop._sock_sendfile_native_impl(fut, None, sock, fileno,
+                                                 0, None, len(self.DATA), 0)
+        with self.assertRaises(KeyError):
+            self.loop._selector.get_key(sock)
+        exc = fut.exception()
+        self.assertIsInstance(exc, base_events._SendfileNotAvailable)
+        self.assertEqual(0, self.file.tell())
+
+    def test_os_error_next_call(self):
+        sock, proto = self.prepare()
+
+        fileno = self.file.fileno()
+        fut = self.loop.create_future()
+        err = OSError()
+        with mock.patch('os.sendfile', side_effect=err):
+            self.loop._sock_sendfile_native_impl(fut, sock.fileno(),
+                                                 sock, fileno,
+                                                 1000, None, len(self.DATA),
+                                                 1000)
+        with self.assertRaises(KeyError):
+            self.loop._selector.get_key(sock)
+        exc = fut.exception()
+        self.assertIs(exc, err)
+        self.assertEqual(1000, self.file.tell())
+
+    def test_exception(self):
+        sock, proto = self.prepare()
+
+        fileno = self.file.fileno()
+        fut = self.loop.create_future()
+        err = RuntimeError()
+        with mock.patch('os.sendfile', side_effect=err):
+            self.loop._sock_sendfile_native_impl(fut, sock.fileno(),
+                                                 sock, fileno,
+                                                 1000, None, len(self.DATA),
+                                                 1000)
+        with self.assertRaises(KeyError):
+            self.loop._selector.get_key(sock)
+        exc = fut.exception()
+        self.assertIs(exc, err)
+        self.assertEqual(1000, self.file.tell())
+
 
 class UnixReadPipeTransportTests(test_utils.TestCase):
 

Misc/NEWS.d/next/Library/2017-12-22-16-05-01.bpo-32410.8JzhvH.rst

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+Implement ``loop.sock_sendfile`` for asyncio event loop.