bpo-30064: Fix asyncio loop.sock_* race condition issue (#20369)

Lib/asyncio/selector_events.py

@@ -266,6 +266,7 @@ def _add_reader(self, fd, callback, *args):
                                   (handle, writer))
             if reader is not None:
                 reader.cancel()
+        return handle
 
     def _remove_reader(self, fd):
         if self.is_closed():
@@ -302,6 +303,7 @@ def _add_writer(self, fd, callback, *args):
                                   (reader, handle))
             if writer is not None:
                 writer.cancel()
+        return handle
 
     def _remove_writer(self, fd):
         """Remove a writer callback."""
@@ -329,7 +331,7 @@ def _remove_writer(self, fd):
     def add_reader(self, fd, callback, *args):
         """Add a reader callback."""
         self._ensure_fd_no_transport(fd)
-        return self._add_reader(fd, callback, *args)
+        self._add_reader(fd, callback, *args)
 
     def remove_reader(self, fd):
         """Remove a reader callback."""
@@ -339,7 +341,7 @@ def remove_reader(self, fd):
     def add_writer(self, fd, callback, *args):
         """Add a writer callback.."""
         self._ensure_fd_no_transport(fd)
-        return self._add_writer(fd, callback, *args)
+        self._add_writer(fd, callback, *args)
 
     def remove_writer(self, fd):
         """Remove a writer callback."""
@@ -362,12 +364,14 @@ async def sock_recv(self, sock, n):
             pass
         fut = self.create_future()
         fd = sock.fileno()
-        self.add_reader(fd, self._sock_recv, fut, sock, n)
+        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))
+            functools.partial(self._sock_read_done, fd, handle=handle))
         return await fut
 
-    def _sock_read_done(self, fd, 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):
@@ -401,9 +405,10 @@ async def sock_recv_into(self, sock, buf):
             pass
         fut = self.create_future()
         fd = sock.fileno()
-        self.add_reader(fd, self._sock_recv_into, fut, sock, buf)
+        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))
+            functools.partial(self._sock_read_done, fd, handle=handle))
         return await fut
 
     def _sock_recv_into(self, fut, sock, buf):
@@ -446,11 +451,12 @@ async def sock_sendall(self, sock, data):
 
         fut = self.create_future()
         fd = sock.fileno()
-        fut.add_done_callback(
-            functools.partial(self._sock_write_done, fd))
+        self._ensure_fd_no_transport(fd)
         # use a trick with a list in closure to store a mutable state
-        self.add_writer(fd, self._sock_sendall, fut, sock,
+        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):
@@ -502,9 +508,11 @@ def _sock_connect(self, fut, sock, address):
             # 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))
-            self.add_writer(fd, self._sock_connect_cb, fut, sock, address)
+                functools.partial(self._sock_write_done, fd, handle=handle))
         except (SystemExit, KeyboardInterrupt):
             raise
         except BaseException as exc:
@@ -512,7 +520,8 @@ def _sock_connect(self, fut, sock, address):
         else:
             fut.set_result(None)
 
-    def _sock_write_done(self, fd, fut):
+    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):

Lib/test/test_asyncio/test_sock_lowlevel.py

@@ -1,4 +1,5 @@
 import socket
+import time
 import asyncio
 import sys
 from asyncio import proactor_events
@@ -122,6 +123,136 @@ def test_sock_client_ops(self):
             sock = socket.socket()
             self._basetest_sock_recv_into(httpd, sock)
 
+    async def _basetest_sock_recv_racing(self, httpd, sock):
+        sock.setblocking(False)
+        await self.loop.sock_connect(sock, httpd.address)
+
+        task = asyncio.create_task(self.loop.sock_recv(sock, 1024))
+        await asyncio.sleep(0)
+        task.cancel()
+
+        asyncio.create_task(
+            self.loop.sock_sendall(sock, b'GET / HTTP/1.0\r\n\r\n'))
+        data = await self.loop.sock_recv(sock, 1024)
+        # consume data
+        await self.loop.sock_recv(sock, 1024)
+
+        self.assertTrue(data.startswith(b'HTTP/1.0 200 OK'))
+
+    async def _basetest_sock_recv_into_racing(self, httpd, sock):
+        sock.setblocking(False)
+        await self.loop.sock_connect(sock, httpd.address)
+
+        data = bytearray(1024)
+        with memoryview(data) as buf:
+            task = asyncio.create_task(
+                self.loop.sock_recv_into(sock, buf[:1024]))
+            await asyncio.sleep(0)
+            task.cancel()
+
+            task = asyncio.create_task(
+                self.loop.sock_sendall(sock, b'GET / HTTP/1.0\r\n\r\n'))
+            nbytes = await self.loop.sock_recv_into(sock, buf[:1024])
+            # consume data
+            await self.loop.sock_recv_into(sock, buf[nbytes:])
+            self.assertTrue(data.startswith(b'HTTP/1.0 200 OK'))
+
+        await task
+
+    async def _basetest_sock_send_racing(self, listener, sock):
+        listener.bind(('127.0.0.1', 0))
+        listener.listen(1)
+
+        # make connection
+        sock.setblocking(False)
+        task = asyncio.create_task(
+            self.loop.sock_connect(sock, listener.getsockname()))
+        await asyncio.sleep(0)
+        server = listener.accept()[0]
+        server.setblocking(False)
+
+        with server:
+            await task
+
+            # fill the buffer
+            with self.assertRaises(BlockingIOError):
+                while True:
+                    sock.send(b' ' * 5)
+
+            # cancel a blocked sock_sendall
+            task = asyncio.create_task(
+                self.loop.sock_sendall(sock, b'hello'))
+            await asyncio.sleep(0)
+            task.cancel()
+
+            # clear the buffer
+            async def recv_until():
+                data = b''
+                while not data:
+                    data = await self.loop.sock_recv(server, 1024)
+                    data = data.strip()
+                return data
+            task = asyncio.create_task(recv_until())
+
+            # immediately register another sock_sendall
+            await self.loop.sock_sendall(sock, b'world')
+            data = await task
+            # ProactorEventLoop could deliver hello
+            self.assertTrue(data.endswith(b'world'))
+
+    async def _basetest_sock_connect_racing(self, listener, sock):
+        listener.bind(('127.0.0.1', 0))
+        addr = listener.getsockname()
+        sock.setblocking(False)
+
+        task = asyncio.create_task(self.loop.sock_connect(sock, addr))
+        await asyncio.sleep(0)
+        task.cancel()
+
+        listener.listen(1)
+        i = 0
+        while True:
+            try:
+                await self.loop.sock_connect(sock, addr)
+                break
+            except ConnectionRefusedError:  # on Linux we need another retry
+                await self.loop.sock_connect(sock, addr)
+                break
+            except OSError as e:  # on Windows we need more retries
+                # A connect request was made on an already connected socket
+                if getattr(e, 'winerror', 0) == 10056:
+                    break
+
+                # https://stackoverflow.com/a/54437602/3316267
+                if getattr(e, 'winerror', 0) != 10022:
+                    raise
+                i += 1
+                if i >= 128:
+                    raise  # too many retries
+                # avoid touching event loop to maintain race condition
+                time.sleep(0.01)
+
+    def test_sock_client_racing(self):
+        with test_utils.run_test_server() as httpd:
+            sock = socket.socket()
+            with sock:
+                self.loop.run_until_complete(asyncio.wait_for(
+                    self._basetest_sock_recv_racing(httpd, sock), 10))
+            sock = socket.socket()
+            with sock:
+                self.loop.run_until_complete(asyncio.wait_for(
+                    self._basetest_sock_recv_into_racing(httpd, sock), 10))
+        listener = socket.socket()
+        sock = socket.socket()
+        with listener, sock:
+            self.loop.run_until_complete(asyncio.wait_for(
+                self._basetest_sock_send_racing(listener, sock), 10))
+        listener = socket.socket()
+        sock = socket.socket()
+        with listener, sock:
+            self.loop.run_until_complete(asyncio.wait_for(
+                self._basetest_sock_connect_racing(listener, sock), 10))
+
     async def _basetest_huge_content(self, address):
         sock = socket.socket()
         sock.setblocking(False)

Misc/NEWS.d/next/Library/2020-05-25-11-52-23.bpo-30064.6CICsH.rst

@@ -0,0 +1 @@
+Fix asyncio ``loop.sock_*`` race condition issue