Add support for coroutine functions as listener callbacks

The `Connection.add_listener()`, `Connection.add_log_listener()` and
`Connection.add_termination_listener()` now allow coroutine functions as
callbacks.

Fixes: #567.

Author: elprans

asyncpg/connection.py

@@ -11,10 +11,12 @@
 import collections.abc
 import functools
 import itertools
+import inspect
 import os
 import sys
 import time
 import traceback
+import typing
 import warnings
 import weakref
 
@@ -133,27 +135,32 @@ async def add_listener(self, channel, callback):
         :param str channel: Channel to listen on.
 
         :param callable callback:
-            A callable receiving the following arguments:
+            A callable or a coroutine function receiving the following
+            arguments:
             **connection**: a Connection the callback is registered with;
             **pid**: PID of the Postgres server that sent the notification;
             **channel**: name of the channel the notification was sent to;
             **payload**: the payload.
+
+        .. versionchanged:: 0.24.0
+            The ``callback`` argument may be a coroutine function.
         """
         self._check_open()
         if channel not in self._listeners:
             await self.fetch('LISTEN {}'.format(utils._quote_ident(channel)))
             self._listeners[channel] = set()
-        self._listeners[channel].add(callback)
+        self._listeners[channel].add(_Callback.from_callable(callback))
 
     async def remove_listener(self, channel, callback):
         """Remove a listening callback on the specified channel."""
         if self.is_closed():
             return
         if channel not in self._listeners:
             return
-        if callback not in self._listeners[channel]:
+        cb = _Callback.from_callable(callback)
+        if cb not in self._listeners[channel]:
             return
-        self._listeners[channel].remove(callback)
+        self._listeners[channel].remove(cb)
         if not self._listeners[channel]:
             del self._listeners[channel]
             await self.fetch('UNLISTEN {}'.format(utils._quote_ident(channel)))
@@ -166,44 +173,51 @@ def add_log_listener(self, callback):
         DEBUG, INFO, or LOG.
 
         :param callable callback:
-            A callable receiving the following arguments:
+            A callable or a coroutine function receiving the following
+            arguments:
             **connection**: a Connection the callback is registered with;
             **message**: the `exceptions.PostgresLogMessage` message.
 
         .. versionadded:: 0.12.0
+
+        .. versionchanged:: 0.24.0
+            The ``callback`` argument may be a coroutine function.
         """
         if self.is_closed():
             raise exceptions.InterfaceError('connection is closed')
-        self._log_listeners.add(callback)
+        self._log_listeners.add(_Callback.from_callable(callback))
 
     def remove_log_listener(self, callback):
         """Remove a listening callback for log messages.
 
         .. versionadded:: 0.12.0
         """
-        self._log_listeners.discard(callback)
+        self._log_listeners.discard(_Callback.from_callable(callback))
 
     def add_termination_listener(self, callback):
         """Add a listener that will be called when the connection is closed.
 
         :param callable callback:
-            A callable receiving one argument:
+            A callable or a coroutine function receiving one argument:
             **connection**: a Connection the callback is registered with.
 
         .. versionadded:: 0.21.0
+
+        .. versionchanged:: 0.24.0
+            The ``callback`` argument may be a coroutine function.
         """
-        self._termination_listeners.add(callback)
+        self._termination_listeners.add(_Callback.from_callable(callback))
 
     def remove_termination_listener(self, callback):
         """Remove a listening callback for connection termination.
 
         :param callable callback:
-            The callable that was passed to
+            The callable or coroutine function that was passed to
             :meth:`Connection.add_termination_listener`.
 
         .. versionadded:: 0.21.0
         """
-        self._termination_listeners.discard(callback)
+        self._termination_listeners.discard(_Callback.from_callable(callback))
 
     def get_server_pid(self):
         """Return the PID of the Postgres server the connection is bound to."""
@@ -1430,8 +1444,11 @@ def _process_log_message(self, fields, last_query):
 
         con_ref = self._unwrap()
         for cb in self._log_listeners:
-            self._loop.call_soon(
-                self._call_log_listener, cb, con_ref, message)
+            if cb.is_async:
+                self._loop.create_task(cb.cb(con_ref, message))
+            else:
+                self._loop.call_soon(
+                    self._call_log_listener, cb.cb, con_ref, message)
 
     def _call_log_listener(self, cb, con_ref, message):
         try:
@@ -1449,16 +1466,19 @@ def _call_termination_listeners(self):
 
         con_ref = self._unwrap()
         for cb in self._termination_listeners:
-            try:
-                cb(con_ref)
-            except Exception as ex:
-                self._loop.call_exception_handler({
-                    'message': (
-                        'Unhandled exception in asyncpg connection '
-                        'termination listener callback {!r}'.format(cb)
-                    ),
-                    'exception': ex
-                })
+            if cb.is_async:
+                self._loop.create_task(cb.cb(con_ref))
+            else:
+                try:
+                    cb.cb(con_ref)
+                except Exception as ex:
+                    self._loop.call_exception_handler({
+                        'message': (
+                            'Unhandled exception in asyncpg connection '
+                            'termination listener callback {!r}'.format(cb)
+                        ),
+                        'exception': ex
+                    })
 
         self._termination_listeners.clear()
 
@@ -1468,8 +1488,11 @@ def _process_notification(self, pid, channel, payload):
 
         con_ref = self._unwrap()
         for cb in self._listeners[channel]:
-            self._loop.call_soon(
-                self._call_listener, cb, con_ref, pid, channel, payload)
+            if cb.is_async:
+                self._loop.create_task(cb.cb(con_ref, pid, channel, payload))
+            else:
+                self._loop.call_soon(
+                    self._call_listener, cb.cb, con_ref, pid, channel, payload)
 
     def _call_listener(self, cb, con_ref, pid, channel, payload):
         try:
@@ -2154,6 +2177,26 @@ def _maybe_cleanup(self):
             self._on_remove(old_entry._statement)
 
 
+class _Callback(typing.NamedTuple):
+
+    cb: typing.Callable[..., None]
+    is_async: bool
+
+    @classmethod
+    def from_callable(cls, cb: typing.Callable[..., None]) -> '_Callback':
+        if inspect.iscoroutinefunction(cb):
+            is_async = True
+        elif callable(cb):
+            is_async = False
+        else:
+            raise exceptions.InterfaceError(
+                'expected a callable or an `async def` function,'
+                'got {!r}'.format(cb)
+            )
+
+        return cls(cb, is_async)
+
+
 class _Atomic:
     __slots__ = ('_acquired',)
 

tests/test_listeners.py

@@ -23,15 +23,20 @@ async def test_listen_01(self):
 
                 q1 = asyncio.Queue()
                 q2 = asyncio.Queue()
+                q3 = asyncio.Queue()
 
                 def listener1(*args):
                     q1.put_nowait(args)
 
                 def listener2(*args):
                     q2.put_nowait(args)
 
+                async def async_listener3(*args):
+                    q3.put_nowait(args)
+
                 await con.add_listener('test', listener1)
                 await con.add_listener('test', listener2)
+                await con.add_listener('test', async_listener3)
 
                 await con.execute("NOTIFY test, 'aaaa'")
 
@@ -41,8 +46,12 @@ def listener2(*args):
                 self.assertEqual(
                     await q2.get(),
                     (con, con.get_server_pid(), 'test', 'aaaa'))
+                self.assertEqual(
+                    await q3.get(),
+                    (con, con.get_server_pid(), 'test', 'aaaa'))
 
                 await con.remove_listener('test', listener2)
+                await con.remove_listener('test', async_listener3)
 
                 await con.execute("NOTIFY test, 'aaaa'")
 
@@ -117,13 +126,20 @@ class TestLogListeners(tb.ConnectedTestCase):
     })
     async def test_log_listener_01(self):
         q1 = asyncio.Queue()
+        q2 = asyncio.Queue()
 
         def notice_callb(con, message):
             # Message fields depend on PG version, hide some values.
             dct = message.as_dict()
             del dct['server_source_line']
             q1.put_nowait((con, type(message), dct))
 
+        async def async_notice_callb(con, message):
+            # Message fields depend on PG version, hide some values.
+            dct = message.as_dict()
+            del dct['server_source_line']
+            q2.put_nowait((con, type(message), dct))
+
         async def raise_notice():
             await self.con.execute(
                 """DO $$
@@ -140,6 +156,7 @@ async def raise_warning():
 
         con = self.con
         con.add_log_listener(notice_callb)
+        con.add_log_listener(async_notice_callb)
 
         expected_msg = {
             'context': 'PL/pgSQL function inline_code_block line 2 at RAISE',
@@ -182,7 +199,21 @@ async def raise_warning():
             msg,
             (con, exceptions.PostgresWarning, expected_msg_warn))
 
+        msg = await q2.get()
+        msg[2].pop('server_source_filename', None)
+        self.assertEqual(
+            msg,
+            (con, exceptions.PostgresLogMessage, expected_msg_notice))
+
+        msg = await q2.get()
+        msg[2].pop('server_source_filename', None)
+        self.assertEqual(
+            msg,
+            (con, exceptions.PostgresWarning, expected_msg_warn))
+
         con.remove_log_listener(notice_callb)
+        con.remove_log_listener(async_notice_callb)
+
         await raise_notice()
         self.assertTrue(q1.empty())
 
@@ -291,19 +322,26 @@ class TestConnectionTerminationListener(tb.ProxiedClusterTestCase):
     async def test_connection_termination_callback_called_on_remote(self):
 
         called = False
+        async_called = False
 
         def close_cb(con):
             nonlocal called
             called = True
 
+        async def async_close_cb(con):
+            nonlocal async_called
+            async_called = True
+
         con = await self.connect()
         con.add_termination_listener(close_cb)
+        con.add_termination_listener(async_close_cb)
         self.proxy.close_all_connections()
         try:
             await con.fetchval('SELECT 1')
         except Exception:
             pass
         self.assertTrue(called)
+        self.assertTrue(async_called)
 
     async def test_connection_termination_callback_called_on_local(self):