GitLab: https://gitlab.com/jsnow/qemu/-/commits/python-async-qmp-aqmp CI: https://gitlab.com/jsnow/qemu/-/pipelines/347375602 Docs: https://people.redhat.com/~jsnow/sphinx/html/qemu.aqmp.html
Hi! This patch series adds an Asynchronous QMP package to the Python library. It offers a few improvements over the previous library: - out-of-band support - true asynchronous event support - avoids undocumented interfaces abusing non-blocking sockets - unit tests! - documentation! This library serves as the basis for a new qmp-shell program that will offer improved reconnection support, true asynchronous display of events, VM and job status update notifiers, and so on. My intent is to eventually publish this library directly to PyPI as a standalone package. I would like to phase out our usage of the old QMP library over time; eventually replacing it entirely with this one. (Since v2 of this series, I have authored a compatibility shim not included in this series that can be used to run all of iotests on this new library successfully with very minimal churn.) This series looks big by line count, but it's *mostly* docstrings. Seriously! This package has *no* external dependencies whatsoever. Notes & Design ============== Here are some notes on the design of how the library works, to serve as a primer for review; however I also **highly recommend** browsing the generated Sphinx documentation for this series. Here's that link again: https://people.redhat.com/~jsnow/sphinx/html/qemu.aqmp.html The core machinery is split between the AsyncProtocol and QMPClient classes. AsyncProtocol provides the generic machinery, while QMPClient provides the QMP-specific details. The design uses two independent coroutines that act as the "bottom half", a writer task and a reader task. These tasks run for the duration of the connection and independently send and receive messages, respectively. A third task, disconnect, is scheduled asynchronously whenever an unrecoverable error occurs and facilitates coalescing of the other two tasks. This diagram for how execute() operates may be helpful for understanding how AsyncProtocol is laid out. The arrows indicate the direction of a QMP message; the long horizontal dash indicates the separation between the upper and lower halves of the event loop. The queue mechanisms between both dashes serve as the intermediaries between the upper and lower halves. +---------+ | caller | +---------+ ^ | | v +---------+ +---------------> |execute()| -----------+ | +---------+ | | | [-----------------------------------------------------------] | | | v +----+------+ +----------------+ +------+-------+ | ExecQueue | | EventListeners | |Outbound Queue| +----+------+ +----+-----------+ +------+-------+ ^ ^ | | | | [-----------------------------------------------------------] | | | | | v +--+----------------+---+ +-----------+-----------+ | Reader Task/Coroutine | | Writer Task/Coroutine | +-----------+-----------+ +-----------+-----------+ ^ | | v +-----+------+ +-----+------+ |StreamReader| |StreamWriter| +------------+ +------------+ The caller will invoke execute(), which in turn will deposit a message in the outbound send queue. This will wake up the writer task, which well send the message over the wire. The execute() method will then yield to wait for a reply delivered to an execution queue created solely for that execute statement. When a message arrives, the Reader task will unblock and route the message either to the EventListener subsystem, or place it in the appropriate pending execution queue. Once a message is placed in the pending execution queue, execute() will unblock and the execution will conclude, returning the result of the RPC call to the caller. Patch Layout ============ Patches 1-4 add tiny pre-requisites, utilities, etc. Patches 5-12 add a generic async message-based protocol class, AsyncProtocol. They are split fairly small and should be reasonably self-contained. Patches 13-15 check in more QMP-centric components. Patches 16-21 add qmp_client.py, with a new 'QMPClient()' class. They're split into reasonably tiny pieces here. Patches 22-23 add a few finishing touches, they are small patches. Patches 24-25 adds unit tests. They're a little messy still, but they've been quite helpful to me so far. Coverage of protocol.py is at about ~86%. Future Work =========== These items are in progress: - A synchronous QMP wrapper that allows this library to be easily used from non-async code; this will also allow me to prove it works well by demoing its replacement throughout iotests. This work is feature-complete, but needs polish. All of iotests is now passing with Async QMP and this Sync wrapper. This will be its own follow-up series. - A QMP server class; to facilitate writing of unit tests. An early version is done, but possibly not feature complete. More polish and tests are warranted. This will be its own follow-up series. - More unit tests for qmp_client.py, qmp_server.py and other modules. Changelog ========= V3: - (02, 05) Typo fixes (Eric Blake) - (04) Rewrote the "wait_closed" compatibility function for Python 3.6; the older version raised unwanted exceptions in error pathways. (Niteesh) - (04, 05, 06, 08) Rewrote _bh_disconnect fairly substantially again; the problem is that exceptions can surface during both flushing of the stream and when waiting for the stream to close. These errors can be new, primary causes of failure or secondary failures. Distinguishing between them is tricky. The new disconnection method takes much greater pains to ensure that even if Exceptions occur, disconnect *will* complete. This adds robustness to cases exposed by iotests where one or more endpoints might segfault or abort and cleanup can be challenged. - (11) Fixed logging hook names (Niteesh) - (24, 25) Bumped avocado dependency to v90; It added support for async test functions which made my prior workaround non-suitable. The choices were to mandate <90 and keep the workarounds or mandate >=90 and drop the workarounds. I went with the latter. V2: Renamed classes/methods: - Renamed qmp_protocol.py to qmp_client.py - Renamed 'QMP' class to 'QMPClient' - Renamed _begin_new_session() to _establish_session() - Split _establish_connection() out from _new_session(). - Removed _results() method Bugfixes: - Suppress duplicate Exceptions when attempting to drain the StreamWriter - Delay initialization of asyncio.Queue and asyncio.Event variables to _new_session or later -- they must not be created outside of the loop, even if they are not async functions. - Rework runstate_changed events to guarantee visibility of events to waiters - Improve connect()/accept() cleanup to work with asyncio.CancelledError, asyncio.TimeoutError - No-argument form of Message() now succeeds properly. - flush utility will correctly yield when data is below the "high water mark", giving the stream a chance to actually flush. - Increase read buffer size to accommodate query-qmp-schema (Thanks Niteesh) Ugly bits from V1 removed: - Remove tertiary filtering from EventListener (for now), accompanying documentation removed from events.py - Use asyncio.wait() instead of custom wait_task_done() - MultiException is removed in favor of just raising the first Exception that occurs in the bottom half; other Exceptions if any are logged instead. Improvements: - QMPClient now allows ID-less execution statements via the _raw() interface. - Add tests that grant ~86% coverage of protocol.py to the avocado test suite. - Removed 'force' parameter from _bh_disconnect; the disconnection routine determines for itself if we are in the error pathway or not instead now. This removes any chance of duplicate calls to _schedule_disconnect accidentally dropping the 'force' setting. Debugging/Testing changes: - Add debug: bool parameter to asyncio_run utility wrapper - Improve error messages for '@require' decorator - Add debugging message for state change events - Avoid flushing the StreamWriter if we don't have one (This circumstance only arises in testing, but it's helpful.) - Improved __repr__ method for AsyncProtocol, and removed __str__ method. enforcing eval(__repr__(x)) == x does not make sense for AsyncProtocol. - Misc logging message changes - Add a suite of fancy Task debugging utilities. - Most tracebacks now log at the DEBUG level instead of CRITICAL/ERROR/WARNING; In those error cases, a one-line summary is logged instead. Misc. aesthetic changes: - Misc docstring fixes, whitespace, etc. - Reordered the definition of some methods to try and keep similar methods near each other (Moved _cleanup near _bh_disconnect in QMPClient.) John Snow (25): python/aqmp: add asynchronous QMP (AQMP) subpackage python/aqmp: add error classes python/pylint: Add exception for TypeVar names ('T') python/aqmp: add asyncio compatibility wrappers python/aqmp: add generic async message-based protocol support python/aqmp: add runstate state machine to AsyncProtocol python/aqmp: Add logging utility helpers python/aqmp: add logging to AsyncProtocol python/aqmp: add AsyncProtocol.accept() method python/aqmp: add configurable read buffer limit python/aqmp: add _cb_inbound and _cb_outbound logging hooks python/aqmp: add AsyncProtocol._readline() method python/aqmp: add QMP Message format python/aqmp: add well-known QMP object models python/aqmp: add QMP event support python/pylint: disable too-many-function-args python/aqmp: add QMP protocol support python/pylint: disable no-member check python/aqmp: Add message routing to QMP protocol python/aqmp: add execute() interfaces python/aqmp: add _raw() execution interface python/aqmp: add asyncio_run compatibility wrapper python/aqmp: add scary message python: bump avocado to v90.0 python/aqmp: add AsyncProtocol unit tests python/Pipfile.lock | 8 +- python/qemu/aqmp/__init__.py | 59 +++ python/qemu/aqmp/error.py | 50 ++ python/qemu/aqmp/events.py | 706 ++++++++++++++++++++++++++ python/qemu/aqmp/message.py | 209 ++++++++ python/qemu/aqmp/models.py | 133 +++++ python/qemu/aqmp/protocol.py | 902 +++++++++++++++++++++++++++++++++ python/qemu/aqmp/py.typed | 0 python/qemu/aqmp/qmp_client.py | 621 +++++++++++++++++++++++ python/qemu/aqmp/util.py | 217 ++++++++ python/setup.cfg | 7 +- python/tests/null_proto.py | 70 +++ python/tests/protocol.py | 535 +++++++++++++++++++ 13 files changed, 3511 insertions(+), 6 deletions(-) create mode 100644 python/qemu/aqmp/__init__.py create mode 100644 python/qemu/aqmp/error.py create mode 100644 python/qemu/aqmp/events.py create mode 100644 python/qemu/aqmp/message.py create mode 100644 python/qemu/aqmp/models.py create mode 100644 python/qemu/aqmp/protocol.py create mode 100644 python/qemu/aqmp/py.typed create mode 100644 python/qemu/aqmp/qmp_client.py create mode 100644 python/qemu/aqmp/util.py create mode 100644 python/tests/null_proto.py create mode 100644 python/tests/protocol.py -- 2.31.1
