[PATCH RFC 19/32] python//qmp.py: add QMPProtocolError

[John Snow]

In the case that we receive a reply but are unable to understand it, use
this exception name to indicate that case.

Signed-off-by: John Snow <address@hidden>
---
 python/qemu/lib/qmp.py | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/python/qemu/lib/qmp.py b/python/qemu/lib/qmp.py
index e460234f2e..5fb16f4b42 100644
--- a/python/qemu/lib/qmp.py
+++ b/python/qemu/lib/qmp.py
@@ -62,6 +62,12 @@ class QMPTimeoutError(QMPError):
     """
 
 
+class QMPProtocolError(QMPError):
+    """
+    QMP protocol error; unexpected response
+    """
+
+
 class QMPResponseError(QMPError):
     """
     Represents erroneous QMP monitor reply
@@ -265,6 +271,10 @@ def command(self, cmd, **kwds):
         ret = self.cmd(cmd, kwds)
         if 'error' in ret:
             raise QMPResponseError(ret)
+        if 'return' not in ret:
+            raise QMPProtocolError(
+                "'return' key not found in QMP response '{}'".format(str(ret))
+            )
         return cast(QMPReturnValue, ret['return'])
 
     def pull_event(self, wait=False):
-- 
2.21.1