Repository: pika/pika

Issue:
HeartbeatChecker is confused about heartbeat timeouts
cc @lukebakken, the fix should probably be back-ported to the 0.12 release candidate.

`HeartbeatChecker` constructor presently accepts an interval value and an `idle_count` which defaults to 2. `Connection` class instantiates `HeartbeatChecker` with `interval=hearbeat_timeout` and default `idle_count`.

So, if the connection is configured with a heartbeat timeout of 600 (10 minutes), it will pass 600 as the `interval` arg to `HeartbeatChecker`. So, `HearbeatChecker` will emit heartbeats to the broker only once every 600 seconds. And it will detect heartbeat timeout after 1200 seconds.

So, in the event that receipt of the heartbeat by the broker is slightly delayed (and in absence of any other AMQP frames from the client), the broker can erroneously conclude that connection with the client is lost and prematurely close the connection.

This is clearly not what was intended. `HeartbeatChecker` should be detecting a heartbeat timeout after 600 seconds of inactivity. And it should be sending a heartbeat to the broker more often than just once within the heartbeat timeout window.

I see two problems here:

1. Given `HeartbeatChecker`'s present interface, `Connection` should be instantiating it as`HeartbeatChecker(self, interval=float(self.params.heartbeat) / 2, idle_count=2) or something like that (how often does RabbitMQ broker send heartbeats within one heartbeat timeout interval?)
2. `HeartbeatChecker` is not abstracting the internals of heartbeat processing sufficiently. It's constructor should accept the heartbeat timeout value directly (no interval/idle_count business) and encapsulate the frequency of heartbeats internally without bleeding that detail to the `Connection`.


Discussion:
vitaly-krugl: @lukebakken, let's work out one of these parallel pull requests first, then create the second one after that. 
michaelklishin: This [rabbitmq-users thread](https://groups.google.com/d/msg/rabbitmq-users/Fmfeqe5ocTY/0fxMMVsSAgAJ) is worth mentioning.

Patch:
diff --git a/examples/consume.py b/examples/consume.py
index 7344149..26e4620 100644
--- a/examples/consume.py
+++ b/examples/consume.py
@@ -1,3 +1,4 @@
+"""Basic message consumer example"""
 import functools
 import logging
 import pika
@@ -8,26 +9,36 @@ LOGGER = logging.getLogger(__name__)
 
 logging.basicConfig(level=logging.DEBUG, format=LOG_FORMAT)
 
-def on_message(channel, method_frame, header_frame, body, userdata=None):
-    LOGGER.info('Userdata: {} Message body: {}'.format(userdata, body))
-    channel.basic_ack(delivery_tag=method_frame.delivery_tag)
-
-credentials = pika.PlainCredentials('guest', 'guest')
-parameters =  pika.ConnectionParameters('localhost', credentials=credentials)
-connection = pika.BlockingConnection(parameters)
-
-channel = connection.channel()
-channel.exchange_declare(exchange="test_exchange", exchange_type="direct", passive=False, durable=True, auto_delete=False)
-channel.queue_declare(queue="standard", auto_delete=True)
-channel.queue_bind(queue="standard", exchange="test_exchange", routing_key="standard_key")
-channel.basic_qos(prefetch_count=1)
-
-on_message_callback = functools.partial(on_message, userdata='on_message_userdata')
-channel.basic_consume(on_message_callback, 'standard')
-
-try:
-    channel.start_consuming()
-except KeyboardInterrupt:
-    channel.stop_consuming()
-
-connection.close()
+def on_message(chan, method_frame, _header_frame, body, userdata=None):
+    """Called when a message is received. Log message and ack it."""
+    LOGGER.info('Userdata: %s Message body: %s', userdata, body)
+    chan.basic_ack(delivery_tag=method_frame.delivery_tag)
+
+def main():
+    """Main method."""
+    credentials = pika.PlainCredentials('guest', 'guest')
+    parameters = pika.ConnectionParameters('localhost', credentials=credentials)
+    connection = pika.BlockingConnection(parameters)
+
+    channel = connection.channel()
+    channel.exchange_declare(exchange="test_exchange",
+                             exchange_type="direct",
+                             passive=False,
+                             durable=True,
+                             auto_delete=False)
+    channel.queue_declare(queue="standard", auto_delete=True)
+    channel.queue_bind(queue="standard", exchange="test_exchange", routing_key="standard_key")
+    channel.basic_qos(prefetch_count=1)
+
+    on_message_callback = functools.partial(on_message, userdata='on_message_userdata')
+    channel.basic_consume(on_message_callback, 'standard')
+
+    try:
+        channel.start_consuming()
+    except KeyboardInterrupt:
+        channel.stop_consuming()
+
+    connection.close()
+
+if __name__ == '__main__':
+    main()
diff --git a/pika/connection.py b/pika/connection.py
index 0c4e2a7..bed9bdb 100644
--- a/pika/connection.py
+++ b/pika/connection.py
@@ -1301,7 +1301,7 @@ class Connection(object):
         self._backpressure_multiplier = value
 
     #
-    # Connections state properties
+    # Connection state properties
     #
 
     @property
diff --git a/pika/heartbeat.py b/pika/heartbeat.py
index 8d3d20a..7d4d7dd 100644
--- a/pika/heartbeat.py
+++ b/pika/heartbeat.py
@@ -7,38 +7,67 @@ LOGGER = logging.getLogger(__name__)
 
 
 class HeartbeatChecker(object):
-    """Checks to make sure that our heartbeat is received at the expected
-    intervals.
+    """Sends heartbeats to the broker. The provided timeout is used to
+    determine if the connection is stale - no received heartbeats or
+    other activity will close the connection. See the parameter list for more
+    details.
 
     """
-    DEFAULT_INTERVAL = 60
-    MAX_IDLE_COUNT = 2
     _CONNECTION_FORCED = 320
-    _STALE_CONNECTION = "Too Many Missed Heartbeats, No reply in %i seconds"
+    _STALE_CONNECTION = "No activity or too many missed meartbeats in the last %i seconds"
 
-    def __init__(self, connection, interval=DEFAULT_INTERVAL, idle_count=MAX_IDLE_COUNT):
-        """Create a heartbeat on connection sending a heartbeat frame every
-        interval seconds.
+    def __init__(self, connection, timeout):
+        """Create an object that will check for activity on the provided
+        connection as well as receive heartbeat frames from the broker. The
+        timeout parameter defines a window within which this activity must
+        happen. If not, the connection is considered dead and closed.
+
+        The value passed for timeout is also used to calculate an interval
+        at which a heartbeat frame is sent to the broker. The interval is
+        equal to the timeout value divided by two.
 
         :param pika.connection.Connection: Connection object
-        :param int interval: Heartbeat check interval. Note: heartbeats will
-                             be sent at interval / 2 frequency.
-        :param int idle_count: The number of heartbeat intervals without data
-                               received that will close the current connection.
+        :param int timeout: Connection idle timeout. If no activity occurs on the
+                            connection nor heartbeat frames received during the
+                            timeout window the connection will be closed. The
+                            interval used to send heartbeats is calculated from
+                            this value by dividing it by two.
 
         """
+        if timeout < 1:
+            raise ValueError('timeout must >= 0, but got %r' % (timeout,))
+
         self._connection = connection
 
-        # Note: see the following document:
+        # Note: see the following documents:
         # https://www.rabbitmq.com/heartbeats.html#heartbeats-timeout
-        self._interval = float(interval / 2)
-
-        # Note: even though we're sending heartbeats in half the specified
-        # interval, the broker will be sending them to us at the specified
-        # interval. This means we'll be checking for an idle connection
-        # twice as many times as the broker will send heartbeats to us,
-        # so we need to double the max idle count here
-        self._max_idle_count = idle_count * 2
+        # https://github.com/pika/pika/pull/1072
+        # https://groups.google.com/d/topic/rabbitmq-users/Fmfeqe5ocTY/discussion
+        # There is a certain amount of confusion around how client developers
+        # interpret the spec. The spec talks about 2 missed heartbeats as a
+        # *timeout*, plus that any activity on the connection counts for a
+        # heartbeat. This is to avoid edge cases and not to depend on network
+        # latency.
+        self._timeout = timeout
+
+        self._send_interval = float(timeout) / 2
+
+        # Note: Pika will calculate the heartbeat / connectivity check interval
+        # by adding 5 seconds to the negotiated timeout to leave a bit of room
+        # for broker heartbeats that may be right at the edge of the timeout
+        # window. This is different behavior from the RabbitMQ Java client and
+        # the spec that suggests a check interval equivalent to two times the
+        # heartbeat timeout value. But, one advantage of adding a small amount
+        # is that bad connections will be detected faster.
+        # https://github.com/pika/pika/pull/1072#issuecomment-397850795
+        # https://github.com/rabbitmq/rabbitmq-java-client/blob/b55bd20a1a236fc2d1ea9369b579770fa0237615/src/main/java/com/rabbitmq/client/impl/AMQConnection.java#L773-L780
+        # https://github.com/ruby-amqp/bunny/blob/3259f3af2e659a49c38c2470aa565c8fb825213c/lib/bunny/session.rb#L1187-L1192
+        self._check_interval = timeout + 5
+
+        LOGGER.debug('timeout: %f send_interval: %f check_interval: %f',
+                     self._timeout,
+                     self._send_interval,
+                     self._check_interval)
 
         # Initialize counters
         self._bytes_received = 0
@@ -47,21 +76,10 @@ class HeartbeatChecker(object):
         self._heartbeat_frames_sent = 0
         self._idle_byte_intervals = 0
 
-        # The handle for the last timer
-        self._timer = None
-
-        # Setup the timer to fire in _interval seconds
-        self._setup_timer()
-
-    @property
-    def active(self):
-        """Return True if the connection's heartbeat attribute is set to this
-        instance.
-
-        :rtype True
-
-        """
-        return self._connection.heartbeat is self
+        self._send_timer = None
+        self._check_timer = None
+        self._start_send_timer()
+        self._start_check_timer()
 
     @property
     def bytes_received_on_connection(self):
@@ -78,74 +96,78 @@ class HeartbeatChecker(object):
         to trip the max idle threshold.
 
         """
-        return self._idle_byte_intervals >= self._max_idle_count
+        return self._idle_byte_intervals > 0
 
     def received(self):
         """Called when a heartbeat is received"""
         LOGGER.debug('Received heartbeat frame')
         self._heartbeat_frames_received += 1
 
-    def send_and_check(self):
-        """Invoked by a timer to send a heartbeat when we need to, check to see
+    def _send_heartbeat(self):
+        """Invoked by a timer to send a heartbeat when we need to.
+
+        """
+        LOGGER.debug('Sending heartbeat frame')
+        self._send_heartbeat_frame()
+        self._start_send_timer()
+
+    def _check_heartbeat(self):
+        """Invoked by a timer to check for broker heartbeats. Checks to see
         if we've missed any heartbeats and disconnect our connection if it's
         been idle too long.
 
         """
+        if self._has_received_data:
+            self._idle_byte_intervals = 0
+        else:
+            # Connection has not received any data, increment the counter
+            self._idle_byte_intervals += 1
+
         LOGGER.debug('Received %i heartbeat frames, sent %i, '
-                     'idle intervals %i, max idle count %i',
+                     'idle intervals %i',
                      self._heartbeat_frames_received,
                      self._heartbeat_frames_sent,
-                     self._idle_byte_intervals,
-                     self._max_idle_count)
+                     self._idle_byte_intervals)
 
         if self.connection_is_idle:
-            return self._close_connection()
-
-        # Connection has not received any data, increment the counter
-        if not self._has_received_data:
-            self._idle_byte_intervals += 1
-        else:
-            self._idle_byte_intervals = 0
+            self._close_connection()
+            return
 
-        # Update the counters of bytes sent/received and the frames received
-        self._update_counters()
-
-        # Send a heartbeat frame
-        self._send_heartbeat_frame()
-
-        # Update the timer to fire again
-        self._start_timer()
+        self._start_check_timer()
 
     def stop(self):
         """Stop the heartbeat checker"""
-        if self._timer:
-            LOGGER.debug('Removing timeout for next heartbeat interval')
-            self._connection.remove_timeout(self._timer)
-            self._timer = None
+        if self._send_timer:
+            LOGGER.debug('Removing timer for next heartbeat send interval')
+            self._connection.remove_timeout(self._send_timer)  # pylint: disable=W0212
+            self._send_timer = None
+        if self._check_timer:
+            LOGGER.debug('Removing timer for next heartbeat check interval')
+            self._connection.remove_timeout(self._check_timer)  # pylint: disable=W0212
+            self._check_timer = None
 
     def _close_connection(self):
         """Close the connection with the AMQP Connection-Forced value."""
         LOGGER.info('Connection is idle, %i stale byte intervals',
                     self._idle_byte_intervals)
-        duration = self._max_idle_count * self._interval
-        text = HeartbeatChecker._STALE_CONNECTION % duration
+        text = HeartbeatChecker._STALE_CONNECTION % self._timeout
 
         # NOTE: this won't achieve the perceived effect of sending
         # Connection.Close to broker, because the frame will only get buffered
         # in memory before the next statement terminates the connection.
         self._connection.close(HeartbeatChecker._CONNECTION_FORCED, text)
 
-        self._connection._on_terminate(HeartbeatChecker._CONNECTION_FORCED,
+        self._connection._on_terminate(HeartbeatChecker._CONNECTION_FORCED,  # pylint: disable=W0212
                                        text)
 
     @property
     def _has_received_data(self):
-        """Returns True if the connection has received data on the connection.
+        """Returns True if the connection has received data.
 
         :rtype: bool
 
         """
-        return not self._bytes_received == self.bytes_received_on_connection
+        return self._bytes_received != self.bytes_received_on_connection
 
     @staticmethod
     def _new_heartbeat_frame():
@@ -161,25 +183,27 @@ class HeartbeatChecker(object):
 
         """
         LOGGER.debug('Sending heartbeat frame')
-        self._connection._send_frame(self._new_heartbeat_frame())
+        self._connection._send_frame(  # pylint: disable=W0212
+            self._new_heartbeat_frame())
         self._heartbeat_frames_sent += 1
 
-    def _setup_timer(self):
-        """Use the connection objects delayed_call function which is
-        implemented by the Adapter for calling the check_heartbeats function
-        every interval seconds.
-
-        """
-        self._timer = self._connection.add_timeout(self._interval,
-                                                   self.send_and_check)
-
-    def _start_timer(self):
-        """If the connection still has this object set for heartbeats, add a
-        new timer.
+    def _start_send_timer(self):
+        """Start a new heartbeat send timer."""
+        self._send_timer = self._connection.add_timeout(  # pylint: disable=W0212
+            self._send_interval,
+            self._send_heartbeat)
+
+    def _start_check_timer(self):
+        """Start a new heartbeat check timer."""
+        # Note: update counters now to get current values
+        # at the start of the timeout window. Values will be
+        # checked against the connection's byte count at the
+        # end of the window
+        self._update_counters()
 
-        """
-        if self.active:
-            self._setup_timer()
+        self._check_timer = self._connection.add_timeout(  # pylint: disable=W0212
+            self._check_interval,
+            self._check_heartbeat)
 
     def _update_counters(self):
         """Update the internal counters for bytes sent and received and the


Test patch:
diff --git a/tests/unit/heartbeat_tests.py b/tests/unit/heartbeat_tests.py
index f0431c2..71fa552 100644
--- a/tests/unit/heartbeat_tests.py
+++ b/tests/unit/heartbeat_tests.py
@@ -8,11 +8,11 @@ import mock
 
 from pika import connection, frame, heartbeat
 
-
 class HeartbeatTests(unittest.TestCase):
 
     INTERVAL = 60
-    HALF_INTERVAL = INTERVAL / 2
+    SEND_INTERVAL = float(INTERVAL) / 2
+    CHECK_INTERVAL = INTERVAL + 5
 
     def setUp(self):
         self.mock_conn = mock.Mock(spec=connection.Connection)
@@ -25,23 +25,26 @@ class HeartbeatTests(unittest.TestCase):
         del self.obj
         del self.mock_conn
 
-    def test_default_initialization_interval(self):
-        self.assertEqual(self.obj._interval, self.HALF_INTERVAL)
-
-    def test_default_initialization_max_idle_count(self):
-        self.assertEqual(self.obj._max_idle_count, self.obj.MAX_IDLE_COUNT * 2)
-
     def test_constructor_assignment_connection(self):
         self.assertIs(self.obj._connection, self.mock_conn)
 
-    def test_constructor_assignment_heartbeat_interval(self):
-        self.assertEqual(self.obj._interval, self.HALF_INTERVAL)
+    def test_constructor_assignment_intervals(self):
+        self.assertEqual(self.obj._send_interval, self.SEND_INTERVAL)
+        self.assertEqual(self.obj._check_interval, self.CHECK_INTERVAL)
 
     def test_constructor_initial_bytes_received(self):
-        self.assertEqual(self.obj._bytes_received, 0)
+        # Note: _bytes_received is initialized by calls
+        # to _start_check_timer which calls _update_counters
+        # which reads the initial values from the connection
+        self.assertEqual(self.obj._bytes_received,
+                         self.mock_conn.bytes_received)
 
     def test_constructor_initial_bytes_sent(self):
-        self.assertEqual(self.obj._bytes_received, 0)
+        # Note: _bytes_received is initialized by calls
+        # to _start_check_timer which calls _update_counters
+        # which reads the initial values from the connection
+        self.assertEqual(self.obj._bytes_sent,
+                         self.mock_conn.bytes_sent)
 
     def test_constructor_initial_heartbeat_frames_received(self):
         self.assertEqual(self.obj._heartbeat_frames_received, 0)
@@ -52,18 +55,15 @@ class HeartbeatTests(unittest.TestCase):
     def test_constructor_initial_idle_byte_intervals(self):
         self.assertEqual(self.obj._idle_byte_intervals, 0)
 
-    @mock.patch('pika.heartbeat.HeartbeatChecker._setup_timer')
-    def test_constructor_called_setup_timer(self, timer):
-        heartbeat.HeartbeatChecker(self.mock_conn)
+    @mock.patch('pika.heartbeat.HeartbeatChecker._start_send_timer')
+    def test_constructor_called_start_send_timer(self, timer):
+        heartbeat.HeartbeatChecker(self.mock_conn, self.INTERVAL)
         timer.assert_called_once_with()
 
-    def test_active_true(self):
-        self.mock_conn.heartbeat = self.obj
-        self.assertTrue(self.obj.active)
-
-    def test_active_false(self):
-        self.mock_conn.heartbeat = mock.Mock()
-        self.assertFalse(self.obj.active)
+    @mock.patch('pika.heartbeat.HeartbeatChecker._start_check_timer')
+    def test_constructor_called_start_check_timer(self, timer):
+        heartbeat.HeartbeatChecker(self.mock_conn, self.INTERVAL)
+        timer.assert_called_once_with()
 
     def test_bytes_received_on_connection(self):
         self.mock_conn.bytes_received = 128
@@ -81,54 +81,63 @@ class HeartbeatTests(unittest.TestCase):
         self.assertTrue(self.obj._heartbeat_frames_received, 1)
 
     @mock.patch('pika.heartbeat.HeartbeatChecker._close_connection')
-    def test_send_and_check_not_closed(self, close_connection):
-        obj = heartbeat.HeartbeatChecker(self.mock_conn)
-        obj.send_and_check()
+    def test_send_heartbeat_not_closed(self, close_connection):
+        obj = heartbeat.HeartbeatChecker(self.mock_conn, self.INTERVAL)
+        obj._send_heartbeat()
         close_connection.assert_not_called()
 
     @mock.patch('pika.heartbeat.HeartbeatChecker._close_connection')
-    def test_send_and_check_missed_bytes(self, close_connection):
-        obj = heartbeat.HeartbeatChecker(self.mock_conn)
+    def test_check_heartbeat_not_closed(self, close_connection):
+        obj = heartbeat.HeartbeatChecker(self.mock_conn, self.INTERVAL)
+        self.mock_conn.bytes_received = 128
+        obj._check_heartbeat()
+        close_connection.assert_not_called()
+
+    @mock.patch('pika.heartbeat.HeartbeatChecker._close_connection')
+    def test_check_heartbeat_missed_bytes(self, close_connection):
+        obj = heartbeat.HeartbeatChecker(self.mock_conn, self.INTERVAL)
         obj._idle_byte_intervals = self.INTERVAL
-        obj.send_and_check()
+        obj._check_heartbeat()
         close_connection.assert_called_once_with()
 
-    def test_send_and_check_increment_no_bytes(self):
+    def test_check_heartbeat_increment_no_bytes(self):
         self.mock_conn.bytes_received = 100
         self.obj._bytes_received = 100
-        self.obj.send_and_check()
+        self.obj._check_heartbeat()
         self.assertEqual(self.obj._idle_byte_intervals, 1)
 
-    def test_send_and_check_increment_bytes(self):
+    def test_check_heartbeat_increment_bytes(self):
         self.mock_conn.bytes_received = 100
         self.obj._bytes_received = 128
-        self.obj.send_and_check()
+        self.obj._check_heartbeat()
         self.assertEqual(self.obj._idle_byte_intervals, 0)
 
     @mock.patch('pika.heartbeat.HeartbeatChecker._update_counters')
-    def test_send_and_check_update_counters(self, update_counters):
-        obj = heartbeat.HeartbeatChecker(self.mock_conn)
-        obj.send_and_check()
+    def test_check_heartbeat_update_counters(self, update_counters):
+        heartbeat.HeartbeatChecker(self.mock_conn, self.INTERVAL)
         update_counters.assert_called_once_with()
 
     @mock.patch('pika.heartbeat.HeartbeatChecker._send_heartbeat_frame')
-    def test_send_and_check_send_heartbeat_frame(self, send_heartbeat_frame):
-        obj = heartbeat.HeartbeatChecker(self.mock_conn)
-        obj.send_and_check()
+    def test_send_heartbeat_sends_heartbeat_frame(self, send_heartbeat_frame):
+        obj = heartbeat.HeartbeatChecker(self.mock_conn, self.INTERVAL)
+        obj._send_heartbeat()
         send_heartbeat_frame.assert_called_once_with()
 
-    @mock.patch('pika.heartbeat.HeartbeatChecker._start_timer')
-    def test_send_and_check_start_timer(self, start_timer):
-        obj = heartbeat.HeartbeatChecker(self.mock_conn)
-        obj.send_and_check()
-        start_timer.assert_called_once_with()
+    @mock.patch('pika.heartbeat.HeartbeatChecker._start_send_timer')
+    def test_send_heartbeat_start_timer(self, start_send_timer):
+        heartbeat.HeartbeatChecker(self.mock_conn, self.INTERVAL)
+        start_send_timer.assert_called_once_with()
+
+    @mock.patch('pika.heartbeat.HeartbeatChecker._start_check_timer')
+    def test_check_heartbeat_start_timer(self, start_check_timer):
+        heartbeat.HeartbeatChecker(self.mock_conn, self.INTERVAL)
+        start_check_timer.assert_called_once_with()
 
     def test_connection_close(self):
         self.obj._idle_byte_intervals = 3
         self.obj._idle_heartbeat_intervals = 4
         self.obj._close_connection()
-        reason = self.obj._STALE_CONNECTION % (
-            self.obj._max_idle_count * self.obj._interval)
+        reason = self.obj._STALE_CONNECTION % self.obj._timeout
         self.mock_conn.close.assert_called_once_with(
             self.obj._CONNECTION_FORCED, reason)
         self.mock_conn._on_terminate.assert_called_once_with(
@@ -157,20 +166,17 @@ class HeartbeatTests(unittest.TestCase):
         self.obj._send_heartbeat_frame()
         self.assertEqual(self.obj._heartbeat_frames_sent, 1)
 
-    def test_setup_timer_called(self):
-        self.mock_conn.add_timeout.assert_called_once_with(
-            self.HALF_INTERVAL, self.obj.send_and_check)
-
-    @mock.patch('pika.heartbeat.HeartbeatChecker._setup_timer')
-    def test_start_timer_not_active(self, setup_timer):
-        self.obj._start_timer()
-        setup_timer.assert_not_called()
+    def test_start_send_timer_called(self):
+        want = [mock.call(self.SEND_INTERVAL, self.obj._send_heartbeat),
+                mock.call(self.CHECK_INTERVAL, self.obj._check_heartbeat)]
+        got = self.mock_conn.add_timeout.call_args_list
+        self.assertEqual(got, want)
 
-    @mock.patch('pika.heartbeat.HeartbeatChecker._setup_timer')
-    def test_start_timer_active(self, setup_timer):
+    @mock.patch('pika.heartbeat.HeartbeatChecker._start_send_timer')
+    def test_start_timer_active(self, setup_send_timer):
         self.mock_conn.heartbeat = self.obj
-        self.obj._start_timer()
-        self.assertTrue(setup_timer.called)
+        self.obj._start_send_timer()
+        self.assertTrue(setup_send_timer.called)
 
     def test_update_counters_bytes_received(self):
         self.mock_conn.bytes_received = 256