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author | John Snow <jsnow@redhat.com> | 2021-09-15 12:29:48 -0400 |
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committer | John Snow <jsnow@redhat.com> | 2021-09-27 12:10:29 -0400 |
commit | e0fea0b3ac85aefacbecf732d18f6d7ba438fa69 (patch) | |
tree | 59491810225ef56a608f4fe00ea83e64766f5d93 /python | |
parent | 577737be55a3e9e5d592ad31d4b7c71ebccf3dc8 (diff) | |
download | qemu-e0fea0b3ac85aefacbecf732d18f6d7ba438fa69.zip qemu-e0fea0b3ac85aefacbecf732d18f6d7ba438fa69.tar.gz qemu-e0fea0b3ac85aefacbecf732d18f6d7ba438fa69.tar.bz2 |
python/aqmp: add execute() interfaces
Add execute() and execute_msg().
_execute() is split into _issue() and _reply() halves so that
hypothetical subclasses of QMP that want to support different execution
paradigms can do so.
I anticipate a synchronous interface may have need of separating the
send/reply phases. However, I do not wish to expose that interface here
and want to actively discourage it, so they remain private interfaces.
Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 20210915162955.333025-21-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>
Diffstat (limited to 'python')
-rw-r--r-- | python/qemu/aqmp/__init__.py | 4 | ||||
-rw-r--r-- | python/qemu/aqmp/qmp_client.py | 202 |
2 files changed, 198 insertions, 8 deletions
diff --git a/python/qemu/aqmp/__init__.py b/python/qemu/aqmp/__init__.py index d975c75..4b7df53 100644 --- a/python/qemu/aqmp/__init__.py +++ b/python/qemu/aqmp/__init__.py @@ -25,7 +25,7 @@ from .error import AQMPError from .events import EventListener from .message import Message from .protocol import ConnectError, Runstate, StateError -from .qmp_client import QMPClient +from .qmp_client import ExecInterruptedError, ExecuteError, QMPClient # The order of these fields impact the Sphinx documentation order. @@ -40,4 +40,6 @@ __all__ = ( 'AQMPError', 'StateError', 'ConnectError', + 'ExecuteError', + 'ExecInterruptedError', ) diff --git a/python/qemu/aqmp/qmp_client.py b/python/qemu/aqmp/qmp_client.py index fa0cc7c..879348f 100644 --- a/python/qemu/aqmp/qmp_client.py +++ b/python/qemu/aqmp/qmp_client.py @@ -7,8 +7,7 @@ used to either connect to a listening server, or used to listen and accept an incoming connection from that server. """ -# The import workarounds here are fixed in the next commit. -import asyncio # pylint: disable=unused-import # noqa +import asyncio import logging from typing import ( Dict, @@ -22,8 +21,8 @@ from typing import ( from .error import AQMPError, ProtocolError from .events import Events from .message import Message -from .models import Greeting -from .protocol import AsyncProtocol +from .models import ErrorResponse, Greeting +from .protocol import AsyncProtocol, Runstate, require from .util import ( bottom_half, exception_summary, @@ -65,11 +64,32 @@ class NegotiationError(_WrappedProtocolError): """ +class ExecuteError(AQMPError): + """ + Exception raised by `QMPClient.execute()` on RPC failure. + + :param error_response: The RPC error response object. + :param sent: The sent RPC message that caused the failure. + :param received: The raw RPC error reply received. + """ + def __init__(self, error_response: ErrorResponse, + sent: Message, received: Message): + super().__init__(error_response.error.desc) + #: The sent `Message` that caused the failure + self.sent: Message = sent + #: The received `Message` that indicated failure + self.received: Message = received + #: The parsed error response + self.error: ErrorResponse = error_response + #: The QMP error class + self.error_class: str = error_response.error.class_ + + class ExecInterruptedError(AQMPError): """ - Exception raised when an RPC is interrupted. + Exception raised by `execute()` (et al) when an RPC is interrupted. - This error is raised when an execute() statement could not be + This error is raised when an `execute()` statement could not be completed. This can occur because the connection itself was terminated before a reply was received. @@ -112,6 +132,27 @@ class ServerParseError(_MsgProtocolError): """ +class BadReplyError(_MsgProtocolError): + """ + An execution reply was successfully routed, but not understood. + + If a QMP message is received with an 'id' field to allow it to be + routed, but is otherwise malformed, this exception will be raised. + + A reply message is malformed if it is missing either the 'return' or + 'error' keys, or if the 'error' value has missing keys or members of + the wrong type. + + :param error_message: Human-readable string describing the error. + :param msg: The malformed reply that was received. + :param sent: The message that was sent that prompted the error. + """ + def __init__(self, error_message: str, msg: Message, sent: Message): + super().__init__(error_message, msg) + #: The sent `Message` that caused the failure + self.sent = sent + + class QMPClient(AsyncProtocol[Message], Events): """ Implements a QMP client connection. @@ -174,6 +215,9 @@ class QMPClient(AsyncProtocol[Message], Events): # Cached Greeting, if one was awaited. self._greeting: Optional[Greeting] = None + # Command ID counter + self._execute_id = 0 + # Incoming RPC reply messages. self._pending: Dict[ Union[str, None], @@ -363,12 +407,135 @@ class QMPClient(AsyncProtocol[Message], Events): assert self._writer is not None self._writer.write(bytes(msg)) + @upper_half + def _get_exec_id(self) -> str: + exec_id = f"__aqmp#{self._execute_id:05d}" + self._execute_id += 1 + return exec_id + + @upper_half + async def _issue(self, msg: Message) -> Union[None, str]: + """ + Issue a QMP `Message` and do not wait for a reply. + + :param msg: The QMP `Message` to send to the server. + + :return: The ID of the `Message` sent. + """ + msg_id: Optional[str] = None + if 'id' in msg: + assert isinstance(msg['id'], str) + msg_id = msg['id'] + + self._pending[msg_id] = asyncio.Queue(maxsize=1) + await self._outgoing.put(msg) + + return msg_id + + @upper_half + async def _reply(self, msg_id: Union[str, None]) -> Message: + """ + Await a reply to a previously issued QMP message. + + :param msg_id: The ID of the previously issued message. + + :return: The reply from the server. + :raise ExecInterruptedError: + When the reply could not be retrieved because the connection + was lost, or some other problem. + """ + queue = self._pending[msg_id] + result = await queue.get() + + try: + if isinstance(result, ExecInterruptedError): + raise result + return result + finally: + del self._pending[msg_id] + + @upper_half + async def _execute(self, msg: Message, assign_id: bool = True) -> Message: + """ + Send a QMP `Message` to the server and await a reply. + + This method *assumes* you are sending some kind of an execute + statement that *will* receive a reply. + + An execution ID will be assigned if assign_id is `True`. It can be + disabled, but this requires that an ID is manually assigned + instead. For manually assigned IDs, you must not use the string + '__aqmp#' anywhere in the ID. + + :param msg: The QMP `Message` to execute. + :param assign_id: If True, assign a new execution 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. + """ + if assign_id: + msg['id'] = self._get_exec_id() + elif 'id' in msg: + assert isinstance(msg['id'], str) + assert '__aqmp#' not in msg['id'] + + exec_id = await self._issue(msg) + return await self._reply(exec_id) + + @upper_half + @require(Runstate.RUNNING) + async def execute_msg(self, msg: Message) -> object: + """ + Execute a QMP command and return its value. + + :param msg: The QMP `Message` to execute. + + :return: + The command execution return value from the server. The type of + object returned depends on the command that was issued, + though most in QEMU return a `dict`. + :raise ValueError: + If the QMP `Message` does not have either the 'execute' or + 'exec-oob' fields set. + :raise ExecuteError: When the server returns an error response. + :raise ExecInterruptedError: if the connection was terminated early. + """ + if not ('execute' in msg or 'exec-oob' in msg): + raise ValueError("Requires 'execute' or 'exec-oob' message") + + # Copy the Message so that the ID assigned by _execute() is + # local to this method; allowing the ID to be seen in raised + # Exceptions but without modifying the caller's held copy. + msg = Message(msg) + reply = await self._execute(msg) + + if 'error' in reply: + try: + error_response = ErrorResponse(reply) + except (KeyError, TypeError) as err: + # Error response was malformed. + raise BadReplyError( + "QMP error reply is malformed", reply, msg, + ) from err + + raise ExecuteError(error_response, msg, reply) + + if 'return' not in reply: + raise BadReplyError( + "QMP reply is missing a 'error' or 'return' member", + reply, msg, + ) + + return reply['return'] + @classmethod def make_execute_msg(cls, cmd: str, arguments: Optional[Mapping[str, object]] = None, oob: bool = False) -> Message: """ - Create an executable message to be sent later. + Create an executable message to be sent by `execute_msg` later. :param cmd: QMP command name. :param arguments: Arguments (if any). Must be JSON-serializable. @@ -380,3 +547,24 @@ class QMPClient(AsyncProtocol[Message], Events): if arguments is not None: msg['arguments'] = arguments return msg + + @upper_half + async def execute(self, cmd: str, + arguments: Optional[Mapping[str, object]] = None, + oob: bool = False) -> object: + """ + Execute a QMP command and return its value. + + :param cmd: QMP command name. + :param arguments: Arguments (if any). Must be JSON-serializable. + :param oob: If `True`, execute "out of band". + + :return: + The command execution return value from the server. The type of + object returned depends on the command that was issued, + though most in QEMU return a `dict`. + :raise ExecuteError: When the server returns an error response. + :raise ExecInterruptedError: if the connection was terminated early. + """ + msg = self.make_execute_msg(cmd, arguments, oob=oob) + return await self.execute_msg(msg) |