telnet server: prompt app not cancelled when client close connection

 If client closes the telnet connection (either due to user typing "Ctrl-] then 'quit'" or due to network shutdown) in middle of the prompt application, the application will hang forever and resources maintained in TelnetServer.connections and TelnetServer._application_tasks are not released.

Author: wuf

prompt_toolkit/contrib/telnet/server.py

@@ -87,6 +87,7 @@ def __init__(self, connection: socket.socket, encoding: str) -> None:
  self._connection = connection
  self._errors = "strict"
  self._buffer: List[bytes] = []
+ self._closed = False
 
  def write(self, data: str) -> None:
  data = data.replace("\n", "\r\n")
@@ -98,12 +99,16 @@ def isatty(self) -> bool:
 
  def flush(self) -> None:
  try:
- self._connection.send(b"".join(self._buffer))
+ if not self._closed:
+ self._connection.send(b"".join(self._buffer))
  except OSError as e:
  logger.warning("Couldn't send data over socket: %s" % e)
 
  self._buffer = []
 
+ def close(self) -> None:
+ self._closed = True
+
  @property
  def encoding(self) -> str:
  return self._encoding
@@ -137,6 +142,7 @@ def __init__(
  self._closed = False
  self._ready = asyncio.Event()
  self.vt100_output = None
+ self._task = None
 
  # Create "Output" object.
  self.size = Size(rows=40, columns=79)
@@ -186,6 +192,9 @@ def handle_incoming_data() -> None:
  # Connection closed by client.
  logger.info("Connection closed by client. %r %r" % self.addr)
  self.close()
+ # to abort the prompt app
+ if self._task:
+ self._task.cancel()
 
  # Add reader.
  loop = get_event_loop()
@@ -196,7 +205,9 @@ def handle_incoming_data() -> None:
  await self._ready.wait()
  with create_app_session(input=self.vt100_input, output=self.vt100_output):
  self.context = contextvars.copy_context()
- await self.interact(self)
+ self._task = get_event_loop().create_task(self.interact(self))
+ await self._task
+ self._task = None
  except Exception as e:
  print("Got %s" % type(e).__name__, e)
  import traceback
@@ -222,6 +233,7 @@ def close(self) -> None:
  self.vt100_input.close()
  get_event_loop().remove_reader(self.conn)
  self.conn.close()
+ self.stdout.close()
 
  def send(self, formatted_text: AnyFormattedText) -> None:
  """