fix(src): Close connections to API clients when shutting down

This effectively re-implements asyncio.Server::close_clients which
is only available in python3.13.

In python3.12 asyncio.Server::wait_closed will hang unless these
sockets are closed: python/cpython#104344

Co-authored-by: Steffen Christgau <[email protected]>

src/wsdd.py

@@ -1125,10 +1125,12 @@ def do_POST(self) -> None:
 class ApiServer:
 
     address_monitor: 'NetworkAddressMonitor'
+    clients: List[asyncio.StreamWriter]
 
     def __init__(self, aio_loop: asyncio.AbstractEventLoop, listen_address: bytes,
                  address_monitor: 'NetworkAddressMonitor') -> None:
         self.server = None
+        self.clients = []
         self.address_monitor = address_monitor
 
         # defer server creation
@@ -1148,6 +1150,7 @@ async def create_server(self, aio_loop: asyncio.AbstractEventLoop, listen_addres
                 self.on_connect, path=listen_address))
 
     async def on_connect(self, read_stream: asyncio.StreamReader, write_stream: asyncio.StreamWriter) -> None:
+        self.clients.append(write_stream)
         while True:
             try:
                 line = await read_stream.readline()
@@ -1156,12 +1159,14 @@ async def on_connect(self, read_stream: asyncio.StreamReader, write_stream: asyn
                     if not write_stream.is_closing():
                         await write_stream.drain()
                 else:
+                    self.clients.remove(write_stream)
                     write_stream.close()
                     return
             except UnicodeDecodeError as e:
                 logger.debug('invalid input utf8', e)
             except Exception as e:
                 logger.warning('exception in API client', e)
+                self.clients.remove(write_stream)
                 write_stream.close()
                 return
 
@@ -1221,6 +1226,8 @@ async def cleanup(self) -> None:
         await self.create_task
         if self.server:
             self.server.close()
+            for client in self.clients:
+                client.close()
             await self.server.wait_closed()