python/qmp/protocol: add open_with_socket()

Instead of listening for incoming connections with a SocketAddr, add a
new method open_with_socket() that accepts an existing socket.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20230111080101.969151-2-marcandre.lureau@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

python/qemu/qmp/protocol.py

@@ -18,6 +18,7 @@ from asyncio import StreamReader, StreamWriter
 from enum import Enum
 from functools import wraps
 import logging
+import socket
 from ssl import SSLContext
 from typing import (
     Any,
@@ -296,6 +297,19 @@ class AsyncProtocol(Generic[T]):
         await self.accept()
         assert self.runstate == Runstate.RUNNING
 
+    @upper_half
+    @require(Runstate.IDLE)
+    async def open_with_socket(self, sock: socket.socket) -> None:
+        """
+        Start connection with given socket.
+
+        :param sock: A socket.
+
+        :raise StateError: When the `Runstate` is not `IDLE`.
+        """
+        self._reader, self._writer = await asyncio.open_connection(sock=sock)
+        self._set_state(Runstate.CONNECTING)
+
     @upper_half
     @require(Runstate.IDLE)
     async def start_server(self, address: SocketAddrT,
@@ -343,6 +357,7 @@ class AsyncProtocol(Generic[T]):
             protocol-level failure occurs while establishing a new
             session, the wrapped error may also be an `QMPError`.
         """
+        if not self._reader:
             if self._accepted is None:
                 raise QMPError("Cannot call accept() before start_server().")
             await self._session_guard(