Added '.run()' method to TelnetServer.

This is a better than having a separate .start() and .stop() when it comes to
cancellation.

Author: jonathanslenders

examples/telnet/hello-world.py

@@ -32,10 +32,7 @@ async def interact(connection):
 
 async def main():
     server = TelnetServer(interact=interact, port=2323)
-    server.start()
-
-    # Run forever.
-    await Future()
+    await server.run()
 
 
 if __name__ == "__main__":

examples/telnet/toolbar.py

@@ -37,10 +37,7 @@ def get_toolbar():
 
 async def main():
     server = TelnetServer(interact=interact, port=2323)
-    server.start()
-
-    # Run forever.
-    await Future()
+    await server.run()
 
 
 if __name__ == "__main__":

src/prompt_toolkit/contrib/telnet/server.py

@@ -283,10 +283,11 @@ def __init__(
         self.encoding = encoding
         self.style = style
         self.enable_cpr = enable_cpr
+
+        self._run_task: asyncio.Task[None] | None = None
         self._application_tasks: list[asyncio.Task[None]] = []
 
         self.connections: set[TelnetConnection] = set()
-        self._listen_socket: socket.socket | None = None
 
     @classmethod
     def _create_socket(cls, host: str, port: int) -> socket.socket:
@@ -298,44 +299,74 @@ def _create_socket(cls, host: str, port: int) -> socket.socket:
         s.listen(4)
         return s
 
-    def start(self) -> None:
+    async def run(self, ready_cb: Callable[[], None] | None = None) -> None:
         """
-        Start the telnet server.
-        Don't forget to call `loop.run_forever()` after doing this.
+        Run the telnet server, until this gets cancelled.
+
+        :param ready_cb: Callback that will be called at the point that we're
+            actually listening.
         """
-        self._listen_socket = self._create_socket(self.host, self.port)
+        socket = self._create_socket(self.host, self.port)
         logger.info(
             "Listening for telnet connections on %s port %r", self.host, self.port
         )
 
-        get_running_loop().add_reader(self._listen_socket, self._accept)
+        get_running_loop().add_reader(socket, lambda: self._accept(socket))
+
+        if ready_cb:
+            ready_cb()
+
+        try:
+            # Run forever, until cancelled.
+            await asyncio.Future()
+        finally:
+            get_running_loop().remove_reader(socket)
+            socket.close()
+
+            # Wait for all applications to finish.
+            for t in self._application_tasks:
+                t.cancel()
+
+            # (This is similar to
+            # `Application.cancel_and_wait_for_background_tasks`. We wait for the
+            # background tasks to complete, but don't propagate exceptions, because
+            # we can't use `ExceptionGroup` yet.)
+            if len(self._application_tasks) > 0:
+                await asyncio.wait(
+                    self._application_tasks,
+                    timeout=None,
+                    return_when=asyncio.ALL_COMPLETED,
+                )
+
+    def start(self) -> None:
+        """
+        Start the telnet server (stop by calling and awaiting `stop()`).
+
+        Note: When possible, it's better to call `.run()` instead.
+        """
+        if self._run_task is not None:
+            # Already running.
+            return
+
+        self._run_task = get_running_loop().create_task(self.run())
 
     async def stop(self) -> None:
-        if self._listen_socket:
-            get_running_loop().remove_reader(self._listen_socket)
-            self._listen_socket.close()
-
-        # Wait for all applications to finish.
-        for t in self._application_tasks:
-            t.cancel()
-
-        # (This is similar to
-        # `Application.cancel_and_wait_for_background_tasks`. We wait for the
-        # background tasks to complete, but don't propagate exceptions, because
-        # we can't use `ExceptionGroup` yet.)
-        if len(self._application_tasks) > 0:
-            await asyncio.wait(
-                self._application_tasks, timeout=None, return_when=asyncio.ALL_COMPLETED
-            )
+        """
+        Stop a telnet server that was started using `.start()` and wait for the
+        cancellation to complete.
+        """
+        if self._run_task is not None:
+            self._run_task.cancel()
+            try:
+                await self._run_task
+            except asyncio.CancelledError:
+                pass
 
-    def _accept(self) -> None:
+    def _accept(self, listen_socket: socket.socket) -> None:
         """
         Accept new incoming connection.
         """
-        if self._listen_socket is None:
-            return  # Should not happen. `_accept` is called after `start`.
-
-        conn, addr = self._listen_socket.accept()
+        conn, addr = listen_socket.accept()
         logger.info("New connection %r %r", *addr)
 
         # Run application for this connection.