Make sure TCP connections end gracefully

TCP connections establish sessions, and expect graceful shut downs (FIN
packet). Make sure on connection close, this packet gets sent.

mcproto/connection.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import asyncio
+import errno
 import socket
 from abc import ABC, abstractmethod
 from typing import Generic, Optional, TypeVar
@@ -160,6 +161,14 @@ def write(self, data: bytes) -> None:
 
     def _close(self) -> None:
         """Close the underlying connection."""
+        # Gracefully end the connection first (shutdown), informing the other side
+        # we're disconnecting, and waiting for them to disconnect cleanly (TCP FIN)
+        try:
+            self.socket.shutdown(socket.SHUT_RDWR)
+        except OSError as exc:
+            if exc.errno != errno.ENOTCONN:
+                raise
+
         self.socket.close()
 
 
@@ -218,6 +227,7 @@ async def write(self, data: bytes) -> None:
 
     async def _close(self) -> None:
         """Close the underlying connection."""
+        # Close automatically performs a graceful TCP connection shutdown too
         self.writer.close()
 
     @property

tests/mcproto/test_connection.py

@@ -36,6 +36,9 @@ def recv(self, length: int) -> bytearray:
     def close(self) -> None:
         self._closed = True
 
+    def shutdown(self, __how: int, /) -> None:
+        pass
+
 
 class MockStreamWriter(CustomMockMixin, MagicMock):
     spec_set = asyncio.StreamWriter