[PATCH v2 08/24] python/aqmp: add logging to AsyncProtocol

[John Snow <jsnow@redhat.com>]

Give the connection and the reader/writer tasks nicknames, and add
logging statements throughout.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 python/qemu/aqmp/protocol.py | 71 ++++++++++++++++++++++++++++++++----
 1 file changed, 64 insertions(+), 7 deletions(-)

diff --git a/python/qemu/aqmp/protocol.py b/python/qemu/aqmp/protocol.py
index 247b60c31a6..f9295546cda 100644
--- a/python/qemu/aqmp/protocol.py
+++ b/python/qemu/aqmp/protocol.py
@@ -14,6 +14,7 @@
 from asyncio import StreamReader, StreamWriter
 from enum import Enum
 from functools import wraps
+import logging
 from ssl import SSLContext
 from typing import (
     Any,
@@ -31,8 +32,10 @@
 from .util import (
     bottom_half,
     create_task,
+    exception_summary,
     flush,
     is_closing,
+    pretty_traceback,
     upper_half,
     wait_closed,
 )
@@ -173,14 +176,28 @@ class AsyncProtocol(Generic[T]):
          can be written after the super() call.
      - `_on_message`:
          Actions to be performed when a message is received.
+
+    :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__)
+
     # -------------------------
     # Section: Public interface
     # -------------------------
 
-    def __init__(self) -> None:
+    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
@@ -207,6 +224,14 @@ def __init__(self) -> 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."""
@@ -275,6 +300,8 @@ def _set_state(self, state: Runstate) -> None:
         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()
@@ -314,8 +341,15 @@ async def _new_session(self,
 
         except BaseException as err:
             emsg = f"Failed to establish {phase}"
-            # Reset from CONNECTING back to IDLE.
-            await self.disconnect()
+            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):
@@ -365,12 +399,16 @@ async def _do_connect(self, address: Union[str, Tuple[str, int]],
 
         :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)
         else:
             connect = asyncio.open_unix_connection(path=address, ssl=ssl)
         self._reader, self._writer = await connect
 
+        self.logger.debug("Connected.")
+
     @upper_half
     async def _establish_session(self) -> None:
         """
@@ -384,8 +422,8 @@ async def _establish_session(self) -> None:
 
         self._outgoing = asyncio.Queue()
 
-        reader_coro = self._bh_loop_forever(self._bh_recv_message)
-        writer_coro = self._bh_loop_forever(self._bh_send_message)
+        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)
@@ -412,6 +450,7 @@ def _schedule_disconnect(self) -> None:
         """
         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
@@ -497,8 +536,10 @@ def _exception(
         # This implicitly closes the reader, too.
         if self._writer:
             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 as err:  # pylint: disable=broad-except
@@ -509,6 +550,10 @@ def _exception(
                         self._reader_task, self._writer_task))):
                     raise
 
+            self.logger.debug("StreamWriter closed.")
+
+        self.logger.debug("Disconnected.")
+
     @bottom_half
     async def _bh_stop_writer(self, force: bool = False) -> None:
         if not self._writer_task or self._writer_task.done():
@@ -516,10 +561,13 @@ async def _bh_stop_writer(self, force: bool = False) -> None:
 
         # If we're not in a hurry, drain the outbound queue.
         if not force:
+            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)
 
+        self.logger.debug("Cancelling writer task ...")
         self._writer_task.cancel()
         # Waits for the writer to finish but does NOT raise its exception.
         await asyncio.wait((self._writer_task,))
@@ -529,12 +577,13 @@ async def _bh_stop_reader(self) -> None:
         if not self._reader_task or self._reader_task.done():
             return
 
+        self.logger.debug("Cancelling reader task ...")
         self._reader_task.cancel()
         # Waits for the reader to finish but does NOT raise its exception.
         await asyncio.wait((self._reader_task,))
 
     @bottom_half
-    async def _bh_loop_forever(self, async_fn: _TaskFN) -> None:
+    async def _bh_loop_forever(self, async_fn: _TaskFN, name: str) -> None:
         """
         Run one of the bottom-half methods in a loop forever.
 
@@ -542,16 +591,24 @@ async def _bh_loop_forever(self, async_fn: _TaskFN) -> None:
         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:
+        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:
-- 
2.31.1