The Message class is here primarily to serve as a solid type to use for
mypy static typing for unambiguous annotation and documentation.
We can also stuff JSON serialization and deserialization into this class
itself so it can be re-used even outside this infrastructure.
Signed-off-by: John Snow <jsnow@redhat.com>
---
python/qemu/aqmp/__init__.py | 4 +-
python/qemu/aqmp/message.py | 207 +++++++++++++++++++++++++++++++++++
2 files changed, 210 insertions(+), 1 deletion(-)
create mode 100644 python/qemu/aqmp/message.py
diff --git a/python/qemu/aqmp/__init__.py b/python/qemu/aqmp/__init__.py
index 5c44fabeea..c1ec68a023 100644
--- a/python/qemu/aqmp/__init__.py
+++ b/python/qemu/aqmp/__init__.py
@@ -22,12 +22,14 @@
# the COPYING file in the top-level directory.
from .error import AQMPError, MultiException
+from .message import Message
from .protocol import ConnectError, Runstate
# The order of these fields impact the Sphinx documentation order.
__all__ = (
- # Classes
+ # Classes, most to least important
+ 'Message',
'Runstate',
# Exceptions, most generic to most explicit
diff --git a/python/qemu/aqmp/message.py b/python/qemu/aqmp/message.py
new file mode 100644
index 0000000000..3a4b283032
--- /dev/null
+++ b/python/qemu/aqmp/message.py
@@ -0,0 +1,207 @@
+"""
+QMP Message Format
+
+This module provides the `Message` class, which represents a single QMP
+message sent to or from the server.
+"""
+
+import json
+from json import JSONDecodeError
+from typing import (
+ Dict,
+ Iterator,
+ Mapping,
+ MutableMapping,
+ Optional,
+ Union,
+)
+
+from .error import ProtocolError
+
+
+class Message(MutableMapping[str, object]):
+ """
+ Represents a single QMP protocol message.
+
+ QMP uses JSON objects as its basic communicative unit; so this
+ Python object is a :py:obj:`~collections.abc.MutableMapping`. It may
+ be instantiated from either another mapping (like a `dict`), or from
+ raw `bytes` that still need to be deserialized.
+
+ Once instantiated, it may be treated like any other MutableMapping::
+
+ >>> msg = Message(b'{"hello": "world"}')
+ >>> assert msg['hello'] == 'world'
+ >>> msg['id'] = 'foobar'
+ >>> print(msg)
+ {
+ "hello": "world",
+ "id": "foobar"
+ }
+
+ It can be converted to `bytes`::
+
+ >>> msg = Message({"hello": "world"})
+ >>> print(bytes(msg))
+ b'{"hello":"world","id":"foobar"}'
+
+ Or back into a garden-variety `dict`::
+
+ >>> dict(msg)
+ {'hello': 'world'}
+
+
+ :param value: Initial value, if any.
+ :param eager:
+ When `True`, attempt to serialize or deserialize the initial value
+ immediately, so that conversion exceptions are raised during
+ the call to ``__init__()``.
+ """
+ # pylint: disable=too-many-ancestors
+
+ def __init__(self,
+ value: Union[bytes, Mapping[str, object]] = b'', *,
+ eager: bool = True):
+ self._data: Optional[bytes] = None
+ self._obj: Optional[Dict[str, object]] = None
+
+ if isinstance(value, bytes):
+ self._data = value
+ if eager:
+ self._obj = self._deserialize(self._data)
+ else:
+ self._obj = dict(value)
+ if eager:
+ self._data = self._serialize(self._obj)
+
+ # Methods necessary to implement the MutableMapping interface, see:
+ # https://docs.python.org/3/library/collections.abc.html#collections.abc.MutableMapping
+
+ # We get pop, popitem, clear, update, setdefault, __contains__,
+ # keys, items, values, get, __eq__ and __ne__ for free.
+
+ def __getitem__(self, key: str) -> object:
+ return self._object[key]
+
+ def __setitem__(self, key: str, value: object) -> None:
+ self._object[key] = value
+ self._data = None
+
+ def __delitem__(self, key: str) -> None:
+ del self._object[key]
+ self._data = None
+
+ def __iter__(self) -> Iterator[str]:
+ return iter(self._object)
+
+ def __len__(self) -> int:
+ return len(self._object)
+
+ # Dunder methods not related to MutableMapping:
+
+ def __repr__(self) -> str:
+ return f"Message({self._object!r})"
+
+ def __str__(self) -> str:
+ """Pretty-printed representation of this QMP message."""
+ return json.dumps(self._object, indent=2)
+
+ def __bytes__(self) -> bytes:
+ """bytes representing this QMP message."""
+ if self._data is None:
+ self._data = self._serialize(self._obj or {})
+ return self._data
+
+ #
Is this something intentional?
Err, oops, kind of. I sometimes use little comment blocks to delineate sections of methods. Above, I have a "MutableMapping" section, and then a "Dunder method" section, and this marks the end of the dunder method section, but I neglected to give it its own title. I suppose I could name it "Conversion Methods" or similar.
Thanks,
--js