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Diffstat (limited to 'python/qemu/aqmp/protocol.py')
| -rw-r--r-- | python/qemu/aqmp/protocol.py | 902 |
1 files changed, 902 insertions, 0 deletions
diff --git a/python/qemu/aqmp/protocol.py b/python/qemu/aqmp/protocol.py new file mode 100644 index 0000000000..32e78749c1 --- /dev/null +++ b/python/qemu/aqmp/protocol.py @@ -0,0 +1,902 @@ +""" +Generic Asynchronous Message-based Protocol Support + +This module provides a generic framework for sending and receiving +messages over an asyncio stream. `AsyncProtocol` is an abstract class +that implements the core mechanisms of a simple send/receive protocol, +and is designed to be extended. + +In this package, it is used as the implementation for the `QMPClient` +class. +""" + +import asyncio +from asyncio import StreamReader, StreamWriter +from enum import Enum +from functools import wraps +import logging +from ssl import SSLContext +from typing import ( + Any, + Awaitable, + Callable, + Generic, + List, + Optional, + Tuple, + TypeVar, + Union, + cast, +) + +from .error import AQMPError +from .util import ( + bottom_half, + create_task, + exception_summary, + flush, + is_closing, + pretty_traceback, + upper_half, + wait_closed, +) + + +T = TypeVar('T') +_TaskFN = Callable[[], Awaitable[None]] # aka ``async def func() -> None`` +_FutureT = TypeVar('_FutureT', bound=Optional['asyncio.Future[Any]']) + + +class Runstate(Enum): + """Protocol session runstate.""" + + #: Fully quiesced and disconnected. + IDLE = 0 + #: In the process of connecting or establishing a session. + CONNECTING = 1 + #: Fully connected and active session. + RUNNING = 2 + #: In the process of disconnecting. + #: Runstate may be returned to `IDLE` by calling `disconnect()`. + DISCONNECTING = 3 + + +class ConnectError(AQMPError): + """ + Raised when the initial connection process has failed. + + This Exception always wraps a "root cause" exception that can be + interrogated for additional information. + + :param error_message: Human-readable string describing the error. + :param exc: The root-cause exception. + """ + def __init__(self, error_message: str, exc: Exception): + super().__init__(error_message) + #: Human-readable error string + self.error_message: str = error_message + #: Wrapped root cause exception + self.exc: Exception = exc + + def __str__(self) -> str: + return f"{self.error_message}: {self.exc!s}" + + +class StateError(AQMPError): + """ + An API command (connect, execute, etc) was issued at an inappropriate time. + + This error is raised when a command like + :py:meth:`~AsyncProtocol.connect()` is issued at an inappropriate + time. + + :param error_message: Human-readable string describing the state violation. + :param state: The actual `Runstate` seen at the time of the violation. + :param required: The `Runstate` required to process this command. + """ + def __init__(self, error_message: str, + state: Runstate, required: Runstate): + super().__init__(error_message) + self.error_message = error_message + self.state = state + self.required = required + + +F = TypeVar('F', bound=Callable[..., Any]) # pylint: disable=invalid-name + + +# Don't Panic. +def require(required_state: Runstate) -> Callable[[F], F]: + """ + Decorator: protect a method so it can only be run in a certain `Runstate`. + + :param required_state: The `Runstate` required to invoke this method. + :raise StateError: When the required `Runstate` is not met. + """ + def _decorator(func: F) -> F: + # _decorator is the decorator that is built by calling the + # require() decorator factory; e.g.: + # + # @require(Runstate.IDLE) def foo(): ... + # will replace 'foo' with the result of '_decorator(foo)'. + + @wraps(func) + def _wrapper(proto: 'AsyncProtocol[Any]', + *args: Any, **kwargs: Any) -> Any: + # _wrapper is the function that gets executed prior to the + # decorated method. + + name = type(proto).__name__ + + if proto.runstate != required_state: + if proto.runstate == Runstate.CONNECTING: + emsg = f"{name} is currently connecting." + elif proto.runstate == Runstate.DISCONNECTING: + emsg = (f"{name} is disconnecting." + " Call disconnect() to return to IDLE state.") + elif proto.runstate == Runstate.RUNNING: + emsg = f"{name} is already connected and running." + elif proto.runstate == Runstate.IDLE: + emsg = f"{name} is disconnected and idle." + else: + assert False + raise StateError(emsg, proto.runstate, required_state) + # No StateError, so call the wrapped method. + return func(proto, *args, **kwargs) + + # Return the decorated method; + # Transforming Func to Decorated[Func]. + return cast(F, _wrapper) + + # Return the decorator instance from the decorator factory. Phew! + return _decorator + + +class AsyncProtocol(Generic[T]): + """ + AsyncProtocol implements a generic async message-based protocol. + + This protocol assumes the basic unit of information transfer between + client and server is a "message", the details of which are left up + to the implementation. It assumes the sending and receiving of these + messages is full-duplex and not necessarily correlated; i.e. it + supports asynchronous inbound messages. + + It is designed to be extended by a specific protocol which provides + the implementations for how to read and send messages. These must be + defined in `_do_recv()` and `_do_send()`, respectively. + + Other callbacks have a default implementation, but are intended to be + either extended or overridden: + + - `_establish_session`: + The base implementation starts the reader/writer tasks. + A protocol implementation can override this call, inserting + actions to be taken prior to starting the reader/writer tasks + before the super() call; actions needing to occur afterwards + can be written after the super() call. + - `_on_message`: + Actions to be performed when a message is received. + - `_cb_outbound`: + Logging/Filtering hook for all outbound messages. + - `_cb_inbound`: + Logging/Filtering hook for all inbound messages. + This hook runs *before* `_on_message()`. + + :param name: + Name used for logging messages, if any. By default, messages + will log to 'qemu.aqmp.protocol', but each individual connection + can be given its own logger by giving it a name; messages will + then log to 'qemu.aqmp.protocol.${name}'. + """ + # pylint: disable=too-many-instance-attributes + + #: Logger object for debugging messages from this connection. + logger = logging.getLogger(__name__) + + # Maximum allowable size of read buffer + _limit = (64 * 1024) + + # ------------------------- + # Section: Public interface + # ------------------------- + + def __init__(self, name: Optional[str] = None) -> None: + #: The nickname for this connection, if any. + self.name: Optional[str] = name + if self.name is not None: + self.logger = self.logger.getChild(self.name) + + # stream I/O + self._reader: Optional[StreamReader] = None + self._writer: Optional[StreamWriter] = None + + # Outbound Message queue + self._outgoing: asyncio.Queue[T] + + # Special, long-running tasks: + self._reader_task: Optional[asyncio.Future[None]] = None + self._writer_task: Optional[asyncio.Future[None]] = None + + # Aggregate of the above two tasks, used for Exception management. + self._bh_tasks: Optional[asyncio.Future[Tuple[None, None]]] = None + + #: Disconnect task. The disconnect implementation runs in a task + #: so that asynchronous disconnects (initiated by the + #: reader/writer) are allowed to wait for the reader/writers to + #: exit. + self._dc_task: Optional[asyncio.Future[None]] = None + + self._runstate = Runstate.IDLE + self._runstate_changed: Optional[asyncio.Event] = None + + def __repr__(self) -> str: + cls_name = type(self).__name__ + tokens = [] + if self.name is not None: + tokens.append(f"name={self.name!r}") + tokens.append(f"runstate={self.runstate.name}") + return f"<{cls_name} {' '.join(tokens)}>" + + @property # @upper_half + def runstate(self) -> Runstate: + """The current `Runstate` of the connection.""" + return self._runstate + + @upper_half + async def runstate_changed(self) -> Runstate: + """ + Wait for the `runstate` to change, then return that runstate. + """ + await self._runstate_event.wait() + return self.runstate + + @upper_half + @require(Runstate.IDLE) + async def accept(self, address: Union[str, Tuple[str, int]], + ssl: Optional[SSLContext] = None) -> None: + """ + Accept a connection and begin processing message queues. + + If this call fails, `runstate` is guaranteed to be set back to `IDLE`. + + :param address: + Address to listen to; UNIX socket path or TCP address/port. + :param ssl: SSL context to use, if any. + + :raise StateError: When the `Runstate` is not `IDLE`. + :raise ConnectError: If a connection could not be accepted. + """ + await self._new_session(address, ssl, accept=True) + + @upper_half + @require(Runstate.IDLE) + async def connect(self, address: Union[str, Tuple[str, int]], + ssl: Optional[SSLContext] = None) -> None: + """ + Connect to the server and begin processing message queues. + + If this call fails, `runstate` is guaranteed to be set back to `IDLE`. + + :param address: + Address to connect to; UNIX socket path or TCP address/port. + :param ssl: SSL context to use, if any. + + :raise StateError: When the `Runstate` is not `IDLE`. + :raise ConnectError: If a connection cannot be made to the server. + """ + await self._new_session(address, ssl) + + @upper_half + async def disconnect(self) -> None: + """ + Disconnect and wait for all tasks to fully stop. + + If there was an exception that caused the reader/writers to + terminate prematurely, it will be raised here. + + :raise Exception: When the reader or writer terminate unexpectedly. + """ + self.logger.debug("disconnect() called.") + self._schedule_disconnect() + await self._wait_disconnect() + + # -------------------------- + # Section: Session machinery + # -------------------------- + + @property + def _runstate_event(self) -> asyncio.Event: + # asyncio.Event() objects should not be created prior to entrance into + # an event loop, so we can ensure we create it in the correct context. + # Create it on-demand *only* at the behest of an 'async def' method. + if not self._runstate_changed: + self._runstate_changed = asyncio.Event() + return self._runstate_changed + + @upper_half + @bottom_half + def _set_state(self, state: Runstate) -> None: + """ + Change the `Runstate` of the protocol connection. + + Signals the `runstate_changed` event. + """ + if state == self._runstate: + return + + self.logger.debug("Transitioning from '%s' to '%s'.", + str(self._runstate), str(state)) + self._runstate = state + self._runstate_event.set() + self._runstate_event.clear() + + @upper_half + async def _new_session(self, + address: Union[str, Tuple[str, int]], + ssl: Optional[SSLContext] = None, + accept: bool = False) -> None: + """ + Establish a new connection and initialize the session. + + Connect or accept a new connection, then begin the protocol + session machinery. If this call fails, `runstate` is guaranteed + to be set back to `IDLE`. + + :param address: + Address to connect to/listen on; + UNIX socket path or TCP address/port. + :param ssl: SSL context to use, if any. + :param accept: Accept a connection instead of connecting when `True`. + + :raise ConnectError: + When a connection or session cannot be established. + + This exception will wrap a more concrete one. In most cases, + the wrapped exception will be `OSError` or `EOFError`. If a + protocol-level failure occurs while establishing a new + session, the wrapped error may also be an `AQMPError`. + """ + assert self.runstate == Runstate.IDLE + + try: + phase = "connection" + await self._establish_connection(address, ssl, accept) + + phase = "session" + await self._establish_session() + + except BaseException as err: + emsg = f"Failed to establish {phase}" + self.logger.error("%s: %s", emsg, exception_summary(err)) + self.logger.debug("%s:\n%s\n", emsg, pretty_traceback()) + try: + # Reset from CONNECTING back to IDLE. + await self.disconnect() + except: + emsg = "Unexpected bottom half exception" + self.logger.critical("%s:\n%s\n", emsg, pretty_traceback()) + raise + + # NB: CancelledError is not a BaseException before Python 3.8 + if isinstance(err, asyncio.CancelledError): + raise + + if isinstance(err, Exception): + raise ConnectError(emsg, err) from err + + # Raise BaseExceptions un-wrapped, they're more important. + raise + + assert self.runstate == Runstate.RUNNING + + @upper_half + async def _establish_connection( + self, + address: Union[str, Tuple[str, int]], + ssl: Optional[SSLContext] = None, + accept: bool = False + ) -> None: + """ + Establish a new connection. + + :param address: + Address to connect to/listen on; + UNIX socket path or TCP address/port. + :param ssl: SSL context to use, if any. + :param accept: Accept a connection instead of connecting when `True`. + """ + assert self.runstate == Runstate.IDLE + self._set_state(Runstate.CONNECTING) + + # Allow runstate watchers to witness 'CONNECTING' state; some + # failures in the streaming layer are synchronous and will not + # otherwise yield. + await asyncio.sleep(0) + + if accept: + await self._do_accept(address, ssl) + else: + await self._do_connect(address, ssl) + + @upper_half + async def _do_accept(self, address: Union[str, Tuple[str, int]], + ssl: Optional[SSLContext] = None) -> None: + """ + Acting as the transport server, accept a single connection. + + :param address: + Address to listen on; UNIX socket path or TCP address/port. + :param ssl: SSL context to use, if any. + + :raise OSError: For stream-related errors. + """ + self.logger.debug("Awaiting connection on %s ...", address) + connected = asyncio.Event() + server: Optional[asyncio.AbstractServer] = None + + async def _client_connected_cb(reader: asyncio.StreamReader, + writer: asyncio.StreamWriter) -> None: + """Used to accept a single incoming connection, see below.""" + nonlocal server + nonlocal connected + + # A connection has been accepted; stop listening for new ones. + assert server is not None + server.close() + await server.wait_closed() + server = None + + # Register this client as being connected + self._reader, self._writer = (reader, writer) + + # Signal back: We've accepted a client! + connected.set() + + if isinstance(address, tuple): + coro = asyncio.start_server( + _client_connected_cb, + host=address[0], + port=address[1], + ssl=ssl, + backlog=1, + limit=self._limit, + ) + else: + coro = asyncio.start_unix_server( + _client_connected_cb, + path=address, + ssl=ssl, + backlog=1, + limit=self._limit, + ) + + server = await coro # Starts listening + await connected.wait() # Waits for the callback to fire (and finish) + assert server is None + + self.logger.debug("Connection accepted.") + + @upper_half + async def _do_connect(self, address: Union[str, Tuple[str, int]], + ssl: Optional[SSLContext] = None) -> None: + """ + Acting as the transport client, initiate a connection to a server. + + :param address: + Address to connect to; UNIX socket path or TCP address/port. + :param ssl: SSL context to use, if any. + + :raise OSError: For stream-related errors. + """ + self.logger.debug("Connecting to %s ...", address) + + if isinstance(address, tuple): + connect = asyncio.open_connection( + address[0], + address[1], + ssl=ssl, + limit=self._limit, + ) + else: + connect = asyncio.open_unix_connection( + path=address, + ssl=ssl, + limit=self._limit, + ) + self._reader, self._writer = await connect + + self.logger.debug("Connected.") + + @upper_half + async def _establish_session(self) -> None: + """ + Establish a new session. + + Starts the readers/writer tasks; subclasses may perform their + own negotiations here. The Runstate will be RUNNING upon + successful conclusion. + """ + assert self.runstate == Runstate.CONNECTING + + self._outgoing = asyncio.Queue() + + reader_coro = self._bh_loop_forever(self._bh_recv_message, 'Reader') + writer_coro = self._bh_loop_forever(self._bh_send_message, 'Writer') + + self._reader_task = create_task(reader_coro) + self._writer_task = create_task(writer_coro) + + self._bh_tasks = asyncio.gather( + self._reader_task, + self._writer_task, + ) + + self._set_state(Runstate.RUNNING) + await asyncio.sleep(0) # Allow runstate_event to process + + @upper_half + @bottom_half + def _schedule_disconnect(self) -> None: + """ + Initiate a disconnect; idempotent. + + This method is used both in the upper-half as a direct + consequence of `disconnect()`, and in the bottom-half in the + case of unhandled exceptions in the reader/writer tasks. + + It can be invoked no matter what the `runstate` is. + """ + if not self._dc_task: + self._set_state(Runstate.DISCONNECTING) + self.logger.debug("Scheduling disconnect.") + self._dc_task = create_task(self._bh_disconnect()) + + @upper_half + async def _wait_disconnect(self) -> None: + """ + Waits for a previously scheduled disconnect to finish. + + This method will gather any bottom half exceptions and re-raise + the one that occurred first; presuming it to be the root cause + of any subsequent Exceptions. It is intended to be used in the + upper half of the call chain. + + :raise Exception: + Arbitrary exception re-raised on behalf of the reader/writer. + """ + assert self.runstate == Runstate.DISCONNECTING + assert self._dc_task + + aws: List[Awaitable[object]] = [self._dc_task] + if self._bh_tasks: + aws.insert(0, self._bh_tasks) + all_defined_tasks = asyncio.gather(*aws) + + # Ensure disconnect is done; Exception (if any) is not raised here: + await asyncio.wait((self._dc_task,)) + + try: + await all_defined_tasks # Raise Exceptions from the bottom half. + finally: + self._cleanup() + self._set_state(Runstate.IDLE) + + @upper_half + def _cleanup(self) -> None: + """ + Fully reset this object to a clean state and return to `IDLE`. + """ + def _paranoid_task_erase(task: _FutureT) -> Optional[_FutureT]: + # Help to erase a task, ENSURING it is fully quiesced first. + assert (task is None) or task.done() + return None if (task and task.done()) else task + + assert self.runstate == Runstate.DISCONNECTING + self._dc_task = _paranoid_task_erase(self._dc_task) + self._reader_task = _paranoid_task_erase(self._reader_task) + self._writer_task = _paranoid_task_erase(self._writer_task) + self._bh_tasks = _paranoid_task_erase(self._bh_tasks) + + self._reader = None + self._writer = None + + # NB: _runstate_changed cannot be cleared because we still need it to + # send the final runstate changed event ...! + + # ---------------------------- + # Section: Bottom Half methods + # ---------------------------- + + @bottom_half + async def _bh_disconnect(self) -> None: + """ + Disconnect and cancel all outstanding tasks. + + It is designed to be called from its task context, + :py:obj:`~AsyncProtocol._dc_task`. By running in its own task, + it is free to wait on any pending actions that may still need to + occur in either the reader or writer tasks. + """ + assert self.runstate == Runstate.DISCONNECTING + + def _done(task: Optional['asyncio.Future[Any]']) -> bool: + return task is not None and task.done() + + # NB: We can't rely on _bh_tasks being done() here, it may not + # yet have had a chance to run and gather itself. + tasks = tuple(filter(None, (self._writer_task, self._reader_task))) + error_pathway = _done(self._reader_task) or _done(self._writer_task) + + try: + # Try to flush the writer, if possible: + if not error_pathway: + await self._bh_flush_writer() + except BaseException as err: + error_pathway = True + emsg = "Failed to flush the writer" + self.logger.error("%s: %s", emsg, exception_summary(err)) + self.logger.debug("%s:\n%s\n", emsg, pretty_traceback()) + raise + finally: + # Cancel any still-running tasks: + if self._writer_task is not None and not self._writer_task.done(): + self.logger.debug("Cancelling writer task.") + self._writer_task.cancel() + if self._reader_task is not None and not self._reader_task.done(): + self.logger.debug("Cancelling reader task.") + self._reader_task.cancel() + + # Close out the tasks entirely (Won't raise): + if tasks: + self.logger.debug("Waiting for tasks to complete ...") + await asyncio.wait(tasks) + + # Lastly, close the stream itself. (May raise): + await self._bh_close_stream(error_pathway) + self.logger.debug("Disconnected.") + + @bottom_half + async def _bh_flush_writer(self) -> None: + if not self._writer_task: + return + + self.logger.debug("Draining the outbound queue ...") + await self._outgoing.join() + if self._writer is not None: + self.logger.debug("Flushing the StreamWriter ...") + await flush(self._writer) + + @bottom_half + async def _bh_close_stream(self, error_pathway: bool = False) -> None: + # NB: Closing the writer also implcitly closes the reader. + if not self._writer: + return + + if not is_closing(self._writer): + self.logger.debug("Closing StreamWriter.") + self._writer.close() + + self.logger.debug("Waiting for StreamWriter to close ...") + try: + await wait_closed(self._writer) + except Exception: # pylint: disable=broad-except + # It's hard to tell if the Stream is already closed or + # not. Even if one of the tasks has failed, it may have + # failed for a higher-layered protocol reason. The + # stream could still be open and perfectly fine. + # I don't know how to discern its health here. + + if error_pathway: + # We already know that *something* went wrong. Let's + # just trust that the Exception we already have is the + # better one to present to the user, even if we don't + # genuinely *know* the relationship between the two. + self.logger.debug( + "Discarding Exception from wait_closed:\n%s\n", + pretty_traceback(), + ) + else: + # Oops, this is a brand-new error! + raise + finally: + self.logger.debug("StreamWriter closed.") + + @bottom_half + async def _bh_loop_forever(self, async_fn: _TaskFN, name: str) -> None: + """ + Run one of the bottom-half methods in a loop forever. + + If the bottom half ever raises any exception, schedule a + disconnect that will terminate the entire loop. + + :param async_fn: The bottom-half method to run in a loop. + :param name: The name of this task, used for logging. + """ + try: + while True: + await async_fn() + except asyncio.CancelledError: + # We have been cancelled by _bh_disconnect, exit gracefully. + self.logger.debug("Task.%s: cancelled.", name) + return + except BaseException as err: + self.logger.error("Task.%s: %s", + name, exception_summary(err)) + self.logger.debug("Task.%s: failure:\n%s\n", + name, pretty_traceback()) + self._schedule_disconnect() + raise + finally: + self.logger.debug("Task.%s: exiting.", name) + + @bottom_half + async def _bh_send_message(self) -> None: + """ + Wait for an outgoing message, then send it. + + Designed to be run in `_bh_loop_forever()`. + """ + msg = await self._outgoing.get() + try: + await self._send(msg) + finally: + self._outgoing.task_done() + + @bottom_half + async def _bh_recv_message(self) -> None: + """ + Wait for an incoming message and call `_on_message` to route it. + + Designed to be run in `_bh_loop_forever()`. + """ + msg = await self._recv() + await self._on_message(msg) + + # -------------------- + # Section: Message I/O + # -------------------- + + @upper_half + @bottom_half + def _cb_outbound(self, msg: T) -> T: + """ + Callback: outbound message hook. + + This is intended for subclasses to be able to add arbitrary + hooks to filter or manipulate outgoing messages. The base + implementation does nothing but log the message without any + manipulation of the message. + + :param msg: raw outbound message + :return: final outbound message + """ + self.logger.debug("--> %s", str(msg)) + return msg + + @upper_half + @bottom_half + def _cb_inbound(self, msg: T) -> T: + """ + Callback: inbound message hook. + + This is intended for subclasses to be able to add arbitrary + hooks to filter or manipulate incoming messages. The base + implementation does nothing but log the message without any + manipulation of the message. + + This method does not "handle" incoming messages; it is a filter. + The actual "endpoint" for incoming messages is `_on_message()`. + + :param msg: raw inbound message + :return: processed inbound message + """ + self.logger.debug("<-- %s", str(msg)) + return msg + + @upper_half + @bottom_half + async def _readline(self) -> bytes: + """ + Wait for a newline from the incoming reader. + + This method is provided as a convenience for upper-layer + protocols, as many are line-based. + + This method *may* return a sequence of bytes without a trailing + newline if EOF occurs, but *some* bytes were received. In this + case, the next call will raise `EOFError`. It is assumed that + the layer 5 protocol will decide if there is anything meaningful + to be done with a partial message. + + :raise OSError: For stream-related errors. + :raise EOFError: + If the reader stream is at EOF and there are no bytes to return. + :return: bytes, including the newline. + """ + assert self._reader is not None + msg_bytes = await self._reader.readline() + + if not msg_bytes: + if self._reader.at_eof(): + raise EOFError + + return msg_bytes + + @upper_half + @bottom_half + async def _do_recv(self) -> T: + """ + Abstract: Read from the stream and return a message. + + Very low-level; intended to only be called by `_recv()`. + """ + raise NotImplementedError + + @upper_half + @bottom_half + async def _recv(self) -> T: + """ + Read an arbitrary protocol message. + + .. warning:: + This method is intended primarily for `_bh_recv_message()` + to use in an asynchronous task loop. Using it outside of + this loop will "steal" messages from the normal routing + mechanism. It is safe to use prior to `_establish_session()`, + but should not be used otherwise. + + This method uses `_do_recv()` to retrieve the raw message, and + then transforms it using `_cb_inbound()`. + + :return: A single (filtered, processed) protocol message. + """ + message = await self._do_recv() + return self._cb_inbound(message) + + @upper_half + @bottom_half + def _do_send(self, msg: T) -> None: + """ + Abstract: Write a message to the stream. + + Very low-level; intended to only be called by `_send()`. + """ + raise NotImplementedError + + @upper_half + @bottom_half + async def _send(self, msg: T) -> None: + """ + Send an arbitrary protocol message. + + This method will transform any outgoing messages according to + `_cb_outbound()`. + + .. warning:: + Like `_recv()`, this method is intended to be called by + the writer task loop that processes outgoing + messages. Calling it directly may circumvent logic + implemented by the caller meant to correlate outgoing and + incoming messages. + + :raise OSError: For problems with the underlying stream. + """ + msg = self._cb_outbound(msg) + self._do_send(msg) + + @bottom_half + async def _on_message(self, msg: T) -> None: + """ + Called to handle the receipt of a new message. + + .. caution:: + This is executed from within the reader loop, so be advised + that waiting on either the reader or writer task will lead + to deadlock. Additionally, any unhandled exceptions will + directly cause the loop to halt, so logic may be best-kept + to a minimum if at all possible. + + :param msg: The incoming message, already logged/filtered. + """ + # Nothing to do in the abstract case. |