Fix "Unable to detect disconnect when using NOTIFY/LISTEN", Closes ai…

…o-libs#249

aiopg/connection.py

@@ -30,7 +30,12 @@
 import psycopg2.extras
 
 from .log import logger
-from .utils import _ContextManager, create_completed_future, get_running_loop
+from .utils import (
+    ClosableQueue,
+    _ContextManager,
+    create_completed_future,
+    get_running_loop,
+)
 
 TIMEOUT = 60.0
 
@@ -762,6 +767,7 @@ def __init__(
         self._writing = False
         self._echo = echo
         self._notifies = asyncio.Queue()  # type: ignore
+        self._notifies_proxy = ClosableQueue(self._notifies)
         self._weakref = weakref.ref(self)
         self._loop.add_reader(
             self._fileno, self._ready, self._weakref  # type: ignore
@@ -806,6 +812,7 @@ def _ready(weak_self: "weakref.ref[Any]") -> None:
                     # chain exception otherwise
                     exc2.__cause__ = exc
                     exc = exc2
+            self.notifies.close(exc)
             if waiter is not None and not waiter.done():
                 waiter.set_exception(exc)
         else:
@@ -1182,9 +1189,9 @@ def __del__(self) -> None:
             self._loop.call_exception_handler(context)
 
     @property
-    def notifies(self) -> asyncio.Queue:  # type: ignore
-        """Return notification queue."""
-        return self._notifies
+    def notifies(self) -> ClosableQueue:
+        """Return notification queue (an asyncio.Queue -like object)."""
+        return self._notifies_proxy
 
     async def _get_oids(self) -> Tuple[Any, Any]:
         cursor = await self.cursor()

aiopg/utils.py

@@ -122,3 +122,46 @@ async def __anext__(self) -> _TObj:
             finally:
                 self._obj = None
             raise
+
+
+class ClosableQueue:
+    """
+    Proxy object for an asyncio.Queue that is "closable"
+
+    When the ClosableQueue is closed, with an exception object as parameter,
+    subsequent or ongoing attempts to read from the queue will result in that
+    exception being result in that exception being raised.
+    """
+
+    def __init__(self, queue: asyncio.Queue):
+        self._queue = queue
+        self._close_exception = asyncio.Future()  # type: asyncio.Future[None]
+
+    def close(self, exception: Exception) -> None:
+        if not self._close_exception.done():
+            self._close_exception.set_exception(exception)
+
+    async def get(self) -> Any:
+        loop = get_running_loop()
+        get = loop.create_task(self._queue.get())
+
+        _, pending = await asyncio.wait(
+            [get, self._close_exception],
+            return_when=asyncio.FIRST_COMPLETED,
+        )
+
+        if get.done():
+            return get.result()
+        get.cancel()
+        self._close_exception.result()
+
+    def empty(self) -> bool:
+        return self._queue.empty()
+
+    def qsize(self) -> int:
+        return self._queue.qsize()
+
+    def get_nowait(self) -> Any:
+        if self._close_exception.done():
+            self._close_exception.result()
+        return self._queue.get_nowait()

docs/core.rst

@@ -289,7 +289,7 @@ Example::
 
    .. attribute:: notifies
 
-      An :class:`asyncio.Queue` instance for received notifications.
+      An instance of an :class:`asyncio.Queue` subclass for received notifications.
 
       .. seealso:: :ref:`aiopg-core-notifications`
 
@@ -983,6 +983,12 @@ Receiving part should establish listening on notification channel by
 `LISTEN`_ call and wait notification events from
 :attr:`Connection.notifies` queue.
 
+.. note::
+
+  calling `await connection.notifies.get()` may raise a psycopg2 exception
+  if the underlying connection gets disconnected while you're waiting for
+  notifications.
+
 There is usage example:
 
 .. literalinclude:: ../examples/notify.py

examples/notify.py

@@ -1,5 +1,7 @@
 import asyncio
 
+import psycopg2
+
 import aiopg
 
 dsn = "dbname=aiopg user=aiopg password=passwd host=127.0.0.1"
@@ -19,8 +21,12 @@ async def listen(conn):
     async with conn.cursor() as cur:
         await cur.execute("LISTEN channel")
         while True:
-            msg = await conn.notifies.get()
-            if msg.payload == "finish":
+            try:
+                msg = await conn.notifies.get()
+            except psycopg2.Error as ex:
+                print("ERROR: ", ex)
+                return
+            if msg.payload == 'finish':
                 return
             else:
                 print("Receive <-", msg.payload)

tests/test_connection.py

@@ -593,3 +593,38 @@ async def test_connection_on_server_restart(connect, pg_server, docker):
             delay *= 2
     else:
         pytest.fail("Cannot connect to the restarted server")
+
+
+async def test_connection_notify_on_server_restart(connect, pg_server, docker,
+                                                   loop):
+    conn = await connect()
+
+    async def read_notifies():
+        while True:
+            await conn.notifies.get()
+
+    reader = loop.create_task(read_notifies())
+    await asyncio.sleep(0.1)
+
+    docker.restart(container=pg_server['Id'])
+
+    try:
+        with pytest.raises(psycopg2.OperationalError):
+            await asyncio.wait_for(reader, 10)
+    finally:
+        conn.close()
+        reader.cancel()
+
+        # Wait for postgres to be up and running again before moving on
+        # so as the restart won't affect other tests
+        delay = 0.001
+        for i in range(100):
+            try:
+                conn = await connect()
+                conn.close()
+                break
+            except psycopg2.Error:
+                time.sleep(delay)
+                delay *= 2
+        else:
+            pytest.fail("Cannot connect to the restarted server")

tests/test_utils.py

@@ -0,0 +1,42 @@
+import asyncio
+
+from aiopg.utils import ClosableQueue
+
+
+async def test_closable_queue_noclose():
+    the_queue = asyncio.Queue()
+    queue = ClosableQueue(the_queue)
+    assert queue.empty()
+    assert queue.qsize() == 0
+
+    await the_queue.put(1)
+    assert not queue.empty()
+    assert queue.qsize() == 1
+    v = await queue.get()
+    assert v == 1
+
+    await the_queue.put(2)
+    v = queue.get_nowait()
+    assert v == 2
+
+
+async def test_closable_queue_close(loop):
+    the_queue = asyncio.Queue()
+    queue = ClosableQueue(the_queue)
+    v1 = None
+
+    async def read():
+        nonlocal v1
+        v1 = await queue.get()
+        await queue.get()
+
+    reader = loop.create_task(read())
+    await the_queue.put(1)
+    await asyncio.sleep(0.1)
+    assert v1 == 1
+
+    queue.close(RuntimeError("connection closed"))
+    try:
+        await reader
+    except RuntimeError as ex:
+        assert ex.args == ("connection closed",)