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Tue, 13 Apr 2021 11:56:10 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-312-f9L2cPjUPwS_iyt-XlwkqA-1; Tue, 13 Apr 2021 11:56:03 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7393B79EC5 for ; Tue, 13 Apr 2021 15:56:02 +0000 (UTC) Received: from scv.redhat.com (ovpn-117-61.rdu2.redhat.com [10.10.117.61]) by smtp.corp.redhat.com (Postfix) with ESMTP id B4EB06A034; Tue, 13 Apr 2021 15:56:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618329365; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XufJ2CLgjzIAubGvoiYCX7qy1kGVUEO3CHR9Ppm6GRY=; b=gk0JavkqhuQHwSWAFl/tOfIL0oZtdRiSa+ZPheVghXnh4PTKzMrjj2akjWVH/5/8uIkjC2 CppRyw3YPzED41hCTrGrFi9GD17tXGo41uvNTr2CiqfKRaaRQPIjcK1YIrvbBpSNOXHjN0 pNcQoMb8QSk7VgchKyNib1FSdJzCbhc= X-MC-Unique: f9L2cPjUPwS_iyt-XlwkqA-1 From: John Snow To: qemu-devel@nongnu.org Subject: [PATCH RFC 4/7] message: add QMP Message type Date: Tue, 13 Apr 2021 11:55:50 -0400 Message-Id: <20210413155553.2660523-5-jsnow@redhat.com> In-Reply-To: <20210413155553.2660523-1-jsnow@redhat.com> References: <20210413155553.2660523-1-jsnow@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jsnow@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.133.124; envelope-from=jsnow@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: crosa@redhat.com, John Snow , ehabkost@redhat.com, stefanha@redhat.com, armbru@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" This is an abstraction that represents a single message either sent to or received from the server. It is used to subclass the AsyncProtocol(Generic[T]) type. It was written such that it can be populated by either raw data or by a dict, with the other form being generated on-demand, as-needed. It behaves almost exactly like a dict, but has some extra methods and a special constructor. (It should quack fairly convincingly.) Signed-off-by: John Snow --- message.py | 196 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 196 insertions(+) create mode 100644 message.py diff --git a/message.py b/message.py new file mode 100644 index 0000000..5c7e828 --- /dev/null +++ b/message.py @@ -0,0 +1,196 @@ +""" +QMP Message format and errors. + +This module provides the `Message` class, which represents a single QMP +message sent to or from the server. Several error-classes that depend on +knowing the format of this message are also included here. +""" + +import json +from json import JSONDecodeError +from typing import ( + Dict, + ItemsView, + Iterable, + KeysView, + Optional, + Union, + ValuesView, +) + +from error import ( + DeserializationError, + ProtocolError, + UnexpectedTypeError, +) + + +class Message: + """ + Represents a single QMP protocol message. + + QMP uses JSON objects as its basic communicative unit; so this + object behaves like a MutableMapping. It may be instantiated from + either another mapping (like a dict), or from raw bytes that still + need to be deserialized. + + :param value: Initial value, if any. + :param eager: When true, attempt to serialize (or deserialize) the + initial value immediately, such that conversion exceptio= ns + are raised during the call to the initialization method. + """ + # TODO: make Message properly a MutableMapping so it can be typed as s= uch? + def __init__(self, + value: Union[bytes, Dict[str, object]] =3D b'', *, + eager: bool =3D True): + self._data: Optional[bytes] =3D None + self._obj: Optional[Dict[str, object]] =3D None + + if isinstance(value, bytes): + self._data =3D value + if eager: + self._obj =3D self._deserialize(self._data) + else: + self._obj =3D value + if eager: + self._data =3D self._serialize(self._obj) + + @classmethod + def _serialize(cls, value: object) -> bytes: + """ + Serialize a JSON object as bytes. + + :raises: ValueError, TypeError from the json library. + """ + return json.dumps(value, separators=3D(',', ':')).encode('utf-8') + + @classmethod + def _deserialize(cls, data: bytes) -> Dict[str, object]: + """ + Deserialize JSON bytes into a native python dict. + + :raises: DeserializationError if JSON deserialization + fails for any reason. + :raises: UnexpectedTypeError if data does not represent + a JSON object. + """ + try: + obj =3D json.loads(data) + except JSONDecodeError as err: + emsg =3D "Failed to deserialize QMP message." + raise DeserializationError(emsg, data) from err + if not isinstance(obj, dict): + raise UnexpectedTypeError( + "Incoming QMP message is not a JSON object.", + data + ) + return obj + + @property + def data(self) -> bytes: + """ + bytes representing this QMP message. + + Generated on-demand if required. + """ + if self._data is None: + self._data =3D self._serialize(self._obj or {}) + return self._data + + @property + def _object(self) -> Dict[str, object]: + """ + dict representing this QMP message. + + Generated on-demand if required; Private because it returns an + object that could be used to validate the internal state of the + Message object. + """ + if self._obj is None: + self._obj =3D self._deserialize(self._data or b'') + return self._obj + + def __str__(self) -> str: + """Pretty-printed representation of this QMP message.""" + return json.dumps(self._object, indent=3D2) + + def __bytes__(self) -> bytes: + return self.data + + def __contains__(self, item: str) -> bool: # Container, Collection + return item in self._object + + def __iter__(self) -> Iterable[str]: # Iterable, Collection, Mapping + return iter(self._object) + + def __len__(self) -> int: # Sized, Collection, Mapping + return len(self._object) + + def __getitem__(self, key: str) -> object: # Mapping + return self._object[key] + + def __setitem__(self, key: str, value: object) -> None: # MutableMapp= ing + self._object[key] =3D value + self._data =3D None + + def __delitem__(self, key: str) -> None: # MutableMapping + del self._object[key] + self._data =3D None + + def keys(self) -> KeysView[str]: + """Return a KeysView object containing all field names.""" + return self._object.keys() + + def items(self) -> ItemsView[str, object]: + """Return an ItemsView object containing all key:value pairs.""" + return self._object.items() + + def values(self) -> ValuesView[object]: + """Return a ValuesView object containing all field values.""" + return self._object.values() + + def get(self, key: str, + default: Optional[object] =3D None) -> Optional[object]: + """Get the value for a single key.""" + return self._object.get(key, default) + + +class MsgProtocolError(ProtocolError): + """Abstract error class for protocol errors that have a JSON object.""" + def __init__(self, error_message: str, msg: Message): + super().__init__(error_message) + self.msg =3D msg + + def __str__(self) -> str: + return "\n".join([ + super().__str__(), + f" Message was: {str(self.msg)}\n", + ]) + + +class ObjectTypeError(MsgProtocolError): + """ + Incoming message was a JSON object, but has an unexpected data shape. + + e.g.: A malformed greeting may cause this error. + """ + + +# FIXME: Remove this? Current draft simply trashes these replies. + +# class OrphanedError(MsgProtocolError): +# """ +# Received message, but had no queue to deliver it to. +# +# e.g.: A reply arrives from the server, but the ID does not match any +# pending execution requests we are aware of. +# """ + + +class ServerParseError(MsgProtocolError): + """ + Server sent a `ParsingError` message. + + e.g. A reply arrives from the server, but it is missing the "ID" + field, which indicates a parsing error on behalf of the server. + """ --=20 2.30.2