python/aqmp: add _raw() execution interface

This is added in anticipation of wanting it for a synchronous wrapper
for the iotest interface. Normally, execute() and execute_msg() both
raise QMP errors in the form of Python exceptions.

Many iotests expect the entire reply as-is. To reduce churn there, add a
private execution interface that will ease transition churn. However, I
do not wish to encourage its use, so it will remain a private interface.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 20210915162955.333025-22-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

python/qemu/aqmp/qmp_client.py

@@ -484,6 +484,57 @@ class QMPClient(AsyncProtocol[Message], Events):
         exec_id = await self._issue(msg)
         return await self._reply(exec_id)
 
+    @upper_half
+    @require(Runstate.RUNNING)
+    async def _raw(
+            self,
+            msg: Union[Message, Mapping[str, object], bytes],
+            assign_id: bool = True,
+    ) -> Message:
+        """
+        Issue a raw `Message` to the QMP server and await a reply.
+
+        :param msg:
+            A Message to send to the server. It may be a `Message`, any
+            Mapping (including Dict), or raw bytes.
+        :param assign_id:
+            Assign an arbitrary execution ID to this message. If
+            `False`, the existing id must either be absent (and no other
+            such pending execution may omit an ID) or a string. If it is
+            a string, it must not start with '__aqmp#' and no other such
+            pending execution may currently be using that ID.
+
+        :return: Execution reply from the server.
+
+        :raise ExecInterruptedError:
+            When the reply could not be retrieved because the connection
+            was lost, or some other problem.
+        :raise TypeError:
+            When assign_id is `False`, an ID is given, and it is not a string.
+        :raise ValueError:
+            When assign_id is `False`, but the ID is not usable;
+            Either because it starts with '__aqmp#' or it is already in-use.
+        """
+        # 1. convert generic Mapping or bytes to a QMP Message
+        # 2. copy Message objects so that we assign an ID only to the copy.
+        msg = Message(msg)
+
+        exec_id = msg.get('id')
+        if not assign_id and 'id' in msg:
+            if not isinstance(exec_id, str):
+                raise TypeError(f"ID ('{exec_id}') must be a string.")
+            if exec_id.startswith('__aqmp#'):
+                raise ValueError(
+                    f"ID ('{exec_id}') must not start with '__aqmp#'."
+                )
+
+        if not assign_id and exec_id in self._pending:
+            raise ValueError(
+                f"ID '{exec_id}' is in-use and cannot be used."
+            )
+
+        return await self._execute(msg, assign_id=assign_id)
+
     @upper_half
     @require(Runstate.RUNNING)
     async def execute_msg(self, msg: Message) -> object: