Use _write_async_message for sensor updates

Clients that don't keep up with sensor updates will now be disconnected,
instead of causing the server to use an ever-increasing amount of RAM.

This required some unintuitive changes to keep mypy happy, due to
python/mypy#17723.

src/aiokatcp/connection.py

@@ -35,7 +35,7 @@
 from typing import Any, Callable, Iterable, Optional, TypeVar
 
 import decorator
-from typing_extensions import Protocol
+from typing_extensions import Protocol, Self
 
 from . import core
 
@@ -44,7 +44,6 @@
 _BLANK_RE = re.compile(rb"^[ \t]*[\r\n]?$")
 # typing.Protocol requires a contravariant typevar
 _C_contra = TypeVar("_C_contra", bound="Connection", contravariant=True)
-_C = TypeVar("_C", bound="Connection")
 
 
 class ConvertCRProtocol(asyncio.StreamReaderProtocol):
@@ -127,8 +126,8 @@ async def handle_message(self, conn: _C_contra, msg: core.Message) -> None:
 
 class Connection:
     def __init__(
-        self: _C,
-        owner: _ConnectionOwner[_C],
+        self,
+        owner: _ConnectionOwner[Self],
         reader: asyncio.StreamReader,
         writer: asyncio.StreamWriter,
         is_server: bool,
@@ -193,7 +192,8 @@ async def drain(self) -> None:
                         self.logger.warning("Connection closed while draining: %s", error)
                         self._close_writer()
 
-    async def _run(self: _C) -> None:
+    # The self: Self is needed due to https://github.com/python/mypy/issues/17723
+    async def _run(self: Self) -> None:
         while True:
             # If the output buffer gets too full, pause processing requests
             await self.drain()

src/aiokatcp/server.py

@@ -1,4 +1,4 @@
-# Copyright 2017, 2019, 2022 National Research Foundation (SARAO)
+# Copyright 2017, 2019, 2022, 2024 National Research Foundation (SARAO)
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are met:
@@ -64,6 +64,8 @@
 class ClientConnection(connection.Connection):
     """Server's view of the connection from a single client."""
 
+    owner: "DeviceServer"
+
     def __init__(
         self,
         owner: "DeviceServer",
@@ -99,7 +101,7 @@ def sensor_update(self, s: sensor.Sensor, reading: sensor.Reading) -> None:
         msg = core.Message.inform(
             "sensor-status", reading.timestamp, 1, s.name, reading.status, reading.value
         )
-        self.write_message(msg)
+        self.owner._write_async_message(self, msg)
 
 
 class RequestContext: