Fix ConnectionResetError not being raised when the transport is closed (

#7180)

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`ConnectionResetError` will always be raised when `StreamWriter.write`
is called after `connection_lost` has been called on the `BaseProtocol`

<!-- Please give a short brief about these changes. -->

Restores pre 3.8.3 behavior

fixes #7172

- [x] I think the code is well written
- [x] Unit tests for the changes exist
- [x] Documentation reflects the changes
- [x] If you provide code modification, please add yourself to
`CONTRIBUTORS.txt`
  * The format is &lt;Name&gt; &lt;Surname&gt;.
  * Please keep alphabetical order, the file is sorted by names.
- [x] Add a new news fragment into the `CHANGES` folder
  * name it `<issue_id>.<type>` for example (588.bugfix)
* if you don't have an `issue_id` change it to the pr id after creating
the pr
  * ensure type is one of the following:
    * `.feature`: Signifying a new feature.
    * `.bugfix`: Signifying a bug fix.
    * `.doc`: Signifying a documentation improvement.
    * `.removal`: Signifying a deprecation or removal of public API.
* `.misc`: A ticket has been closed, but it is not of interest to users.
* Make sure to use full sentences with correct case and punctuation, for
example: "Fix issue with non-ascii contents in doctest text files."

---------

Co-authored-by: Sviatoslav Sydorenko <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Sam Bull <[email protected]>
(cherry picked from commit 974323f)

CHANGES/7180.bugfix

@@ -0,0 +1 @@
+``ConnectionResetError`` will always be raised when ``StreamWriter.write`` is called after ``connection_lost`` has been called on the ``BaseProtocol``

CONTRIBUTORS.txt

@@ -150,6 +150,7 @@ Ilya Gruzinov
 Ingmar Steen
 Ivan Lakovic
 Ivan Larin
+J. Nick Koston
 Jacob Champion
 Jaesung Lee
 Jake Davis

aiohttp/base_protocol.py

@@ -18,11 +18,15 @@ def __init__(self, loop: asyncio.AbstractEventLoop) -> None:
         self._loop: asyncio.AbstractEventLoop = loop
         self._paused = False
         self._drain_waiter: Optional[asyncio.Future[None]] = None
-        self._connection_lost = False
         self._reading_paused = False
 
         self.transport: Optional[asyncio.Transport] = None
 
+    @property
+    def connected(self) -> bool:
+        """Return True if the connection is open."""
+        return self.transport is not None
+
     def pause_writing(self) -> None:
         assert not self._paused
         self._paused = True
@@ -59,7 +63,6 @@ def connection_made(self, transport: asyncio.BaseTransport) -> None:
         self.transport = tr
 
     def connection_lost(self, exc: Optional[BaseException]) -> None:
-        self._connection_lost = True
         # Wake up the writer if currently paused.
         self.transport = None
         if not self._paused:
@@ -76,7 +79,7 @@ def connection_lost(self, exc: Optional[BaseException]) -> None:
             waiter.set_exception(exc)
 
     async def _drain_helper(self) -> None:
-        if self._connection_lost:
+        if not self.connected:
             raise ConnectionResetError("Connection lost")
         if not self._paused:
             return

aiohttp/http_writer.py

@@ -35,7 +35,6 @@ def __init__(
         on_headers_sent: _T_OnHeadersSent = None,
     ) -> None:
         self._protocol = protocol
-        self._transport = protocol.transport
 
         self.loop = loop
         self.length = None
@@ -52,7 +51,7 @@ def __init__(
 
     @property
     def transport(self) -> Optional[asyncio.Transport]:
-        return self._transport
+        return self._protocol.transport
 
     @property
     def protocol(self) -> BaseProtocol:
@@ -71,10 +70,10 @@ def _write(self, chunk: bytes) -> None:
         size = len(chunk)
         self.buffer_size += size
         self.output_size += size
-
-        if self._transport is None or self._transport.is_closing():
+        transport = self.transport
+        if not self._protocol.connected or transport is None or transport.is_closing():
             raise ConnectionResetError("Cannot write to closing transport")
-        self._transport.write(chunk)
+        transport.write(chunk)
 
     async def write(
         self, chunk: bytes, *, drain: bool = True, LIMIT: int = 0x10000
@@ -159,7 +158,6 @@ async def write_eof(self, chunk: bytes = b"") -> None:
         await self.drain()
 
         self._eof = True
-        self._transport = None
 
     async def drain(self) -> None:
         """Flush the write buffer.

tests/test_base_protocol.py

@@ -45,22 +45,22 @@ async def test_connection_lost_not_paused() -> None:
     pr = BaseProtocol(loop=loop)
     tr = mock.Mock()
     pr.connection_made(tr)
-    assert not pr._connection_lost
+    assert pr.connected
     pr.connection_lost(None)
     assert pr.transport is None
-    assert pr._connection_lost
+    assert not pr.connected
 
 
 async def test_connection_lost_paused_without_waiter() -> None:
     loop = asyncio.get_event_loop()
     pr = BaseProtocol(loop=loop)
     tr = mock.Mock()
     pr.connection_made(tr)
-    assert not pr._connection_lost
+    assert pr.connected
     pr.pause_writing()
     pr.connection_lost(None)
     assert pr.transport is None
-    assert pr._connection_lost
+    assert not pr.connected
 
 
 async def test_drain_lost() -> None:

tests/test_client_proto.py

@@ -134,3 +134,17 @@ async def test_eof_received(loop) -> None:
     assert proto._read_timeout_handle is not None
     proto.eof_received()
     assert proto._read_timeout_handle is None
+
+
+async def test_connection_lost_sets_transport_to_none(loop: Any, mocker: Any) -> None:
+    """Ensure that the transport is set to None when the connection is lost.
+
+    This ensures the writer knows that the connection is closed.
+    """
+    proto = ResponseHandler(loop=loop)
+    proto.connection_made(mocker.Mock())
+    assert proto.transport is not None
+
+    proto.connection_lost(OSError())
+
+    assert proto.transport is None

tests/test_http_writer.py

@@ -236,6 +236,23 @@ async def test_write_to_closing_transport(protocol, transport, loop) -> None:
         await msg.write(b"After closing")
 
 
+async def test_write_to_closed_transport(
+    protocol: Any, transport: Any, loop: Any
+) -> None:
+    """Test that writing to a closed transport raises ConnectionResetError.
+
+    The StreamWriter checks to see if protocol.transport is None before
+    writing to the transport. If it is None, it raises ConnectionResetError.
+    """
+    msg = http.StreamWriter(protocol, loop)
+
+    await msg.write(b"Before transport close")
+    protocol.transport = None
+
+    with pytest.raises(ConnectionResetError, match="Cannot write to closing transport"):
+        await msg.write(b"After transport closed")
+
+
 async def test_drain(protocol, transport, loop) -> None:
     msg = http.StreamWriter(protocol, loop)
     await msg.drain()