python/machine.py: Add _qmp access shim

Like many other Optional[] types, it's not always a given that this
object will be set. Wrap it in a type-shim that raises a meaningful
error and will always return a concrete type.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 20201006235817.3280413-8-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

1 files changed, 13 insertions, 11 deletions

diff --git a/python/qemu/machine.py b/python/qemu/machine.py
index d788e8a..3e9cf09 100644
--- a/python/qemu/machine.py
+++ b/python/qemu/machine.py
@@ -135,7 +135,7 @@ class QEMUMachine:
         self._events = []
         self._iolog = None
         self._qmp_set = True   # Enable QMP monitor by default.
-        self._qmp = None
+        self._qmp_connection: Optional[qmp.QEMUMonitorProtocol] = None
         self._qemu_full_args = None
         self._temp_dir = None
         self._launched = False
@@ -302,14 +302,14 @@ class QEMUMachine:
             if self._remove_monitor_sockfile:
                 assert isinstance(self._monitor_address, str)
                 self._remove_files.append(self._monitor_address)
-            self._qmp = qmp.QEMUMonitorProtocol(
+            self._qmp_connection = qmp.QEMUMonitorProtocol(
                 self._monitor_address,
                 server=True,
                 nickname=self._name
             )
 
     def _post_launch(self):
-        if self._qmp:
+        if self._qmp_connection:
             self._qmp.accept()
 
     def _post_shutdown(self):
@@ -320,9 +320,9 @@ class QEMUMachine:
         # Comprehensive reset for the failed launch case:
         self._early_cleanup()
 
-        if self._qmp:
+        if self._qmp_connection:
             self._qmp.close()
-            self._qmp = None
+            self._qmp_connection = None
 
         self._load_io_log()
 
@@ -434,7 +434,7 @@ class QEMUMachine:
         """
         self._early_cleanup()
 
-        if self._qmp is not None:
+        if self._qmp_connection:
             if not has_quit:
                 # Might raise ConnectionReset
                 self._qmp.cmd('quit')
@@ -515,11 +515,13 @@ class QEMUMachine:
                         line. Default is True.
         @note: call this function before launch().
         """
-        if enabled:
-            self._qmp_set = True
-        else:
-            self._qmp_set = False
-            self._qmp = None
+        self._qmp_set = enabled
+
+    @property
+    def _qmp(self) -> qmp.QEMUMonitorProtocol:
+        if self._qmp_connection is None:
+            raise QEMUMachineError("Attempt to access QMP with no connection")
+        return self._qmp_connection
 
     @classmethod
     def _qmp_args(cls, _conv_keys: bool = True, **args: Any) -> Dict[str, Any]: