Changelog

Changes
=======

py-amqp is fork of amqplib used by Kombu containing additional features and improvements.
The previous amqplib changelog is here:
http://code.google.com/p/py-amqplib/source/browse/CHANGES

.. _version-2.3.2:

2.3.2
=====
:release-date: 2018-05-29 15:30 P.M UTC+3
:release-by: Omer Katz

- Fix a regression that occurs when running amqp on OSX.

  TCP_USER_TIMEOUT is not available when running on OSX.
  We now remove it from the set of known TCP options.

  Fix contributed by **Ofer Horowitz**

.. _version-2.3.1:

2.3.1
=====
:release-date: 2018-05-28 16:30 P.M UTC+3
:release-by: Omer Katz

- Fix a regression that occurs when running amqp under Python 2.7.

  #182 mistakingly replaced a type check with unicode to string_t which is str
  in Python 2.7. text_t should have been used instead.
  This is now fixed and the tests have been adjusted to ensure this never regresses
  again.

  Fix contributed by **Omer Katz**

.. _version-2.3.0:

2.3.0
=====
:release-date: 2018-05-27 16:30 P.M UTC+3
:release-by: Omer Katz

- Cleanup TCP configurations across platforms and unified defaults.

  Fix contributed by **Dan Chowdhury**

- Fix for TypeError when setting socket options.

  Fix contributed by **Matthias Erll**

- Ensure that all call sites for decoding bytes to str allow surrogates,
  as the encoding mechanism now supports.

  Fix contributed by **Stephen Hatch**

- Don't send AAAA DNS request when domain resolved to IPv4 address.

  Fix contributed by **Ihar Hrachyshka & Omer Katz**

- Support for EXTERNAL authentication and specific login_method.

  Fix contributed by **Matthias Erll**

- If the old python-gssapi library is installed the gssapi module will be available.
  We now ensure that we only use the new gssapi library.

  Fix contributed by **Jacopo Notarstefano**

Code Cleanups & Test Coverage:

- :github_user:`eric-eric-eric`
- **Omer Katz**
- **Jon Dufresne**
- **Matthias Urlichs**

.. _version-2.2.2:

2.2.2
=====
:release-date: 2017-09-14 09:00 A.M UTC+2
:release-by: Omer Katz

- Sending empty messages no longer hangs. Instead an empty message is sent correctly.(addresses #151)

  Fix contributed by **Christian Blades**

- Fixed compatibility issues in UTF-8 encoding behavior between Py2/Py3 (#164)

  Fix contributed by **Tyler James Harden**

.. _version-2.2.1:

2.2.1
=====
:release-date: 2017-07-14 09:00 A.M UTC+2
:release-by: Omer Katz

- Fix implicit conversion from bytes to string on the connection object. (Issue #155)

  This issue has caused Celery to crash on connection to RabbitMQ.

  Fix contributed by **Omer Katz**

.. _version-2.2.0:

2.2.0
=====
:release-date: 2017-07-12 10:00 A.M UTC+2
:release-by: Ask Solem

- Fix random delays in task execution.

  This is a bug that caused performance issues due to polling timeouts that occur when receiving incomplete AMQP frames. (Issues #3978 #3737 #3814)

  Fix contributed by **Robert Kopaczewski**

- Calling ``conn.collect()`` multiple times will no longer raise an ``AttributeError`` when no channels exist.

  Fix contributed by **Gord Chung**

- Fix compatibility code for Python 2.7.6.

  Fix contributed by **Jonathan Schuff**

- When running in Windows, py-amqp will no longer use the unsupported TCP option TCP_MAXSEG.

  Fix contributed by **Tony Breeds**

- Added support for setting the SNI hostname header.

  The SSL protocol version is now set to SSLv23

  Contributed by **Dhananjay Sathe**

- Authentication mechanisms were refactored to be more modular. GSSAPI authentication is now supported.

  Contributed by **Alexander Dutton**

- Do not reconnect on collect.

  Fix contributed by **Gord Chung**

.. _version-2.1.4:

2.1.4
=====
:release-date: 2016-12-14 03:40 P.M PST
:release-by: Ask Solem

- Removes byte string comparison warnings when running under ``python -b``.

    Fix contributed by **Jon Dufresne**.

- Linux version parsing broke when the version included a '+' character
  (Issue #119).

- Now sets default TCP settings for platforms that support them (e.g. Linux).

    +----------------------+---------------+
    |   Constant           |   Value       |
    +======================+===============+
    | ``TCP_KEEPIDLE``     | ``60``        |
    +----------------------+---------------+
    | ``TCP_KEEPINTVL``    | ``10``        |
    +----------------------+---------------+
    | ``TCP_KEEPCNT``      | ``9``         |
    +----------------------+---------------+
    | ``TCP_USER_TIMEOUT`` | ``1000`` (1s) |
    +----------------------+---------------+

    This will help detecting the socket being closed earlier, which is very
    important in failover and load balancing scenarios.

.. _version-2.1.3:

2.1.3
=====
:release-date: 2016-12-07 06:00 P.M PST
:release-by: Ask Solem

- Fixes compatibility with Python 2.7.5 and below (Issue #107).

.. _version-2.1.2:

2.1.2
=====
:release-date: 2016-12-07 02:00 P.M PST

- Linux: Now sets the :data:`~socket.TCP_USER_TIMEOUT` flag if available
  for better failed connection detection.

    Contributed by **Jelte Fennema**.

    The timeout is set to the ``connect_timeout`` value by default,
    but can also be specified by using the ``socket_settings`` argument
    to :class:`~amqp.Connection`:

    .. code-block:: python

        from amqp import Connection
        from amqp.platform import TCP_USER_TIMEOUT

        conn = Connection(socket_settings={
            TCP_USER_TIMEOUT: int(60 * 1000),  # six minutes in ms.
        })

    When using :pypi:`Kombu` this can be specified as part of the
    ``transport_options``:

    .. code-block:: python

        from amqp.platform import TCP_USER_TIMEOUT
        from kombu import Connection

        conn = Connection(transport_options={
            'socket_settings': {
                TCP_USER_TIMEOUT: int(60 * 1000),  # six minutes in ms.
            },
        })

    Or when using :pypi:`Celery` it can be specified using the
    ``broker_transport_options`` setting:

    .. code-block:: python

        from amqp.platform import TCP_USER_TIMEOUT
        from celery import Celery

        app = Celery()
        app.conf.update(
            broker_transport_options={
                TCP_USER_TIMEOUT: int(60 * 1000),  # six minutes in ms.
            }
        )

- Python compatibility: Fixed compatibility when using the python ``-b`` flag.

    Fix contributed by Jon Dufresne.

.. _version-2.1.1:

2.1.1
=====
:release-date: 2016-10-13 06:36 P.M PDT
:release-by: Ask Solem

.. _version-2.1.0:

- **Requirements**

    - Now depends on :ref:`Vine 1.1.3 <vine:version-1.1.3>`.

- Frame writer: Account for overhead when calculating frame size.

    The client would crash if the message was within a certain size.

-  Fixed struct unicode problems (#108)

    * Standardize pack invocations on bytestrings.

    * Leave some literals as strings to enable interpolation.

    * Fix flake8 fail.

    Fix contributed by **Brendan Smithyman**.


2.1.0
=====
:release-date: 2016-09-07 04:23 P.M PDT
:release-by: Ask Solem

- **Requirements**

    - Now depends on :ref:`Vine 1.1.2 <vine:version-1.1.2>`.

- Now licensed under the BSD license!

    Thanks to Barry Pederson for approving the license change,
    which unifies the license used across all projects in the Celery
    organization.

- Datetimes in method frame arguments are now handled properly.

- Fixed compatibility with Python <= 2.7.6

- Frame_writer is no longer a generator, which should solve
  a rare "generator already executing" error (Issue #103).

.. _version-2.0.3:

2.0.3
=====
:release-date: 2016-07-11 08:00 P.M PDT
:release-by: Ask Solem

- SSLTransport: Fixed crash "no attribute sslopts" when ``ssl=True``
  (Issue #100).

- Fixed incompatible argument spec for ``Connection.Close`` (Issue #45).

    This caused the RabbitMQ server to raise an exception (INTERNAL ERROR).

- Transport: No longer implements `__del__` to make sure gc can collect
  connections.

    It's the responsibility of the caller to close connections, this was
    simply a relic from the amqplib library.

.. _version-2.0.2:

2.0.2
=====
:release-date: 2016-06-10 5:40 P.M PDT
:release-by: Ask Solem

- Python 3: Installation requirements ended up being a generator
  and crashed setup.py.

    Fix contributed by ChangBo Guo(gcb).

- Python <= 2.7.7: struct.pack arguments cannot be unicode

    Fix contributed by Alan Justino and Xin Li.

- Python 3.4: Fixed use of `bytes % int`.

    Fix contributed by Alan Justino.

- Connection/Transport: Fixed handling of default port.

    Fix contributed by Quentin Pradet.

.. _version-2.0.1:

2.0.1
=====
:release-date: 2016-05-31 6:20 P.M PDT
:release-by: Ask Solem

- Adds backward compatibility layer for the 1.4 API.

    Using the connection without calling ``.connect()`` first will now work,
    but a warning is emitted and the behavior is deprecated and will be
    removed in version 2.2.

- Fixes kombu 3.0/celery 3.1 compatibility (Issue #88).

    Fix contributed by Bas ten Berge.

- Fixed compatibility with Python 2.7.3 (Issue #85)

    Fix contributed by Bas ten Berge.

- Fixed bug where calling drain_events() with a timeout of 0 would actually
  block until a frame is received.

- Documentation moved to http://amqp.readthedocs.io (Issue #89).

    See https://blog.readthedocs.com/securing-subdomains/ for the reasoning
    behind this change.

    Fix contributed by Adam Chainz.

.. _version-2.0.0:

2.0.0
=====
:release-date: 2016-05-26 1:44 P.M PDT
:release-by: Ask Solem

- No longer supports Python 2.6

- You must now call Connection.connect() to establish the connection.

    The Connection constructor no longer has side effects, so you have
    to explicitly call connect first.

- Library rewritten to anticipate async changes.

- Connection now exposes underlying socket options.

    This change allows to set arbitrary TCP socket options during the creation of
    the transport.

    Those values can be set passing a dictionray where the key is the name of
    the parameter we want to set.
    The names of the keys are the ones reported above.

    Contributed by Andrea Rosa, Dallas Marlow and Rongze Zhu.

- Additional logging for heartbeats.

    Contributed by Davanum Srinivas, and Dmitry Mescheryakov.

- SSL: Fixes issue with remote connection hanging

    Fix contributed by Adrien Guinet.

- SSL: ``ssl`` dict argument now supports the ``check_hostname`` key
    (Issue #63).

    Contributed by Vic Kumar.

- Contributions by:

    Adrien Guinet
    Andrea Rosa
    Artyom Koval
    Corey Farwell
    Craig Jellick
    Dallas Marlow
    Davanum Srinivas
    Federico Ficarelli
    Jared Lewis
    Rémy Greinhofer
    Rongze Zhu
    Yury Selivanov
    Vic Kumar
    Vladimir Bolshakov
    :github_user:`lezeroq`

.. _version-1.4.9:

1.4.9
=====
:release-date: 2016-01-08 5:50 P.M PST
:release-by: Ask Solem

- Fixes compatibility with Linux/macOS instances where the ``ctypes`` module
  does not exist.

    Fix contributed by Jared Lewis.

.. _version-1.4.8:

1.4.8
=====
:release-date: 2015-12-07 12:25 A.M
:release-by: Ask Solem

- ``abstract_channel.wait`` now accepts a float `timeout` parameter expressed
    in seconds

    Contributed by Goir.

.. _version-1.4.7:

1.4.7
=====
:release-date: 2015-10-02 05:30 P.M PDT
:release-by: Ask Solem

- Fixed libSystem error on macOS 10.11 (El Capitan)

    Fix contributed by Eric Wang.

- ``channel.basic_publish`` now raises :exc:`amqp.exceptions.NotConfirmed` on
    ``basic.nack``.

- AMQP timestamps received are now converted from GMT instead of local time
    (Issue #67).

- Wheel package installation now supported by both Python 2 and Python3.

    Fix contributed by Rémy Greinhofer.

.. _version-1.4.6:

1.4.6
=====
:release-date: 2014-08-11 06:00 P.M UTC
:release-by: Ask Solem

- Now keeps buffer when socket times out.

    Fix contributed by Artyom Koval.

- Adds ``Connection.Transport`` attribute that can be used to specify
  a different transport implementation.

    Contributed by Yury Selivanov.

.. _version-1.4.5:

1.4.5
=====
:release-date: 2014-04-15 09:00 P.M UTC
:release-by: Ask Solem

- Can now deserialize more AMQP types.

    Now handles types ``short string``, ``short short int``,
    ``short short unsigned int``, ``short int``,  ``short unsigned int``,
    ``long unsigned int``,  ``long long int``, ``long long unsigned int``
    and ``float`` which for some reason was missing, even in the original
    amqplib module.

- SSL: Workaround for Python SSL bug.

    A bug in the python socket library causes ``ssl.read/write()``
    on a closed socket to raise :exc:`AttributeError` instead of
    :exc:`IOError`.

    Fix contributed by Craig Jellick.

- ``Transport.__del_`` now handles errors occurring at late interpreter
  shutdown (Issue #36).

.. _version-1.4.4:

1.4.4
=====
:release-date: 2014-03-03 04:00 P.M UTC
:release-by: Ask Solem

- SSL transport accidentally disconnected after read timeout.

    Fix contributed by Craig Jellick.

.. _version-1.4.3:

1.4.3
=====
:release-date: 2014-02-09 03:00 P.M UTC
:release-by: Ask Solem

- Fixed bug where more data was requested from the socket
  than was actually needed.

    Contributed by Ionel Cristian Mărieș.

.. _version-1.4.2:

1.4.2
=====
:release-date: 2014-01-23 05:00 P.M UTC

- Heartbeat negotiation would use heartbeat value from server even
  if heartbeat disabled (Issue #31).

.. _version-1.4.1:

1.4.1
=====
:release-date: 2014-01-14 09:30 P.M UTC
:release-by: Ask Solem

- Fixed error occurring when heartbeats disabled.

.. _version-1.4.0:

1.4.0
=====
:release-date: 2014-01-13 03:00 P.M UTC
:release-by: Ask Solem

- Heartbeat implementation improved (Issue #6).

    The new heartbeat behavior is the same approach as taken by the
    RabbitMQ java library.

    This also means that clients should preferably call the ``heartbeat_tick``
    method more frequently (like every second) instead of using the old
    ``rate`` argument (which is now ignored).

    - Heartbeat interval is negotiated with the server.
    - Some delay is allowed if the heartbeat is late.
    - Monotonic time is used to keep track of the heartbeat
      instead of relying on the caller to call the checking function
      at the right time.

    Contributed by Dustin J. Mitchell.

- NoneType is now supported in tables and arrays.

    Contributed by Dominik Fässler.

- SSLTransport: Now handles ``ENOENT``.

    Fix contributed by Adrien Guinet.

.. _version-1.3.3:

1.3.3
=====
:release-date: 2013-11-11 03:30 P.M UTC
:release-by: Ask Solem

- SSLTransport: Now keeps read buffer if an exception is raised
  (Issue #26).

    Fix contributed by Tommie Gannert.

.. _version-1.3.2:

1.3.2
=====
:release-date: 2013-10-29 02:00 P.M UTC
:release-by: Ask Solem

- Message.channel is now a channel object (not the channel id).

- Bug in previous version caused the socket to be flagged as disconnected
  at EAGAIN/EINTR.

.. _version-1.3.1:

1.3.1
=====
:release-date: 2013-10-24 04:00 P.M UTC
:release-by: Ask Solem

- Now implements Connection.connected (Issue #22).

- Fixed bug where ``str(AMQPError)`` did not return string.

.. _version-1.3.0:

1.3.0
=====
:release-date: 2013-09-04 02:39 P.M UTC
:release-by: Ask Solem

- Now sets ``Message.channel`` on delivery (Issue #12)

    amqplib used to make the channel object available
    as ``Message.delivery_info['channel']``, but this was removed
    in py-amqp.  librabbitmq sets ``Message.channel``,
    which is a more reasonable solution in our opinion as that
    keeps the delivery info intact.

- New option to wait for publish confirmations (Issue #3)

    There is now a new Connection ``confirm_publish`` that will
    force any ``basic_publish`` call to wait for confirmation.

    Enabling publisher confirms like this degrades performance
    considerably, but can be suitable for some applications
    and now it's possible by configuration.

- ``queue_declare`` now returns named tuple of type
  :class:`~amqp.protocol.basic_declare_ok_t`.

    Supporting fields: ``queue``, ``message_count``, and
    ``consumer_count``.

- Contents of ``Channel.returned_messages`` is now named tuples.

    Supporting fields: ``reply_code``, ``reply_text``, ``exchange``,
    ``routing_key``, and ``message``.

- Sockets now set to close on exec using the ``FD_CLOEXEC`` flag.

    Currently only supported on platforms supporting this flag,
    which does not include Windows.

    Contributed by Tommie Gannert.

.. _version-1.2.1:

1.2.1
=====
:release-date: 2013-08-16 05:30 P.M UTC
:release-by: Ask Solem

- Adds promise type: :meth:`amqp.utils.promise`

- Merges fixes from 1.0.x

.. _version-1.2.0:

1.2.0
=====
:release-date: 2012-11-12 04:00 P.M UTC
:release-by: Ask Solem

- New exception hierarchy:

    - :class:`~amqp.AMQPError`
        - :class:`~amqp.ConnectionError`
            - :class:`~amqp.RecoverableConnectionError`
                - :class:`~amqp.ConsumerCancelled`
                - :class:`~amqp.ConnectionForced`
                - :class:`~amqp.ResourceError`
            - :class:`~IrrecoverableConnectionError`
                - :class:`~amqp.ChannelNotOpen`
                - :class:`~amqp.FrameError`
                - :class:`~amqp.FrameSyntaxError`
                - :class:`~amqp.InvalidCommand`
                - :class:`~amqp.InvalidPath`
                - :class:`~amqp.NotAllowed`
                - :class:`~amqp.UnexpectedFrame`
                - :class:`~amqp.AMQPNotImplementedError`
                - :class:`~amqp.InternalError`
        - :class:`~amqp.ChannelError`
            - :class:`~RecoverableChannelError`
                - :class:`~amqp.ContentTooLarge`
                - :class:`~amqp.NoConsumers`
                - :class:`~amqp.ResourceLocked`
            - :class:`~IrrecoverableChannelError`
                - :class:`~amqp.AccessRefused`
                - :class:`~amqp.NotFound`
                - :class:`~amqp.PreconditionFailed`


.. _version-1.1.0:

1.1.0
=====
:release-date: 2013-11-08 10:36 P.M UTC
:release-by: Ask Solem

- No longer supports Python 2.5

- Fixed receiving of float table values.

- Now Supports Python 3 and Python 2.6+ in the same source code.

- Python 3 related fixes.

.. _version-1.0.13:

1.0.13
======
:release-date: 2013-07-31 04:00 P.M BST
:release-by: Ask Solem

- Fixed problems with the SSL transport (Issue #15).

    Fix contributed by Adrien Guinet.

- Small optimizations

.. _version-1.0.12:

1.0.12
======
:release-date: 2013-06-25 02:00 P.M BST
:release-by: Ask Solem

- Fixed another Python 3 compatibility problem.

.. _version-1.0.11:

1.0.11
======
:release-date: 2013-04-11 06:00 P.M BST
:release-by: Ask Solem

- Fixed Python 3 incompatibility in ``amqp/transport.py``.

.. _version-1.0.10:

1.0.10
======
:release-date: 2013-03-21 03:30 P.M UTC
:release-by: Ask Solem

- Fixed Python 3 incompatibility in ``amqp/serialization.py``.
  (Issue #11).

.. _version-1.0.9:

1.0.9
=====
:release-date: 2013-03-08 10:40 A.M UTC
:release-by: Ask Solem

- Publisher ack callbacks should now work after typo fix (Issue #9).

- ``channel(explicit_id)`` will now claim that id from the array
  of unused channel ids.

- Fixes Jython compatibility.

.. _version-1.0.8:

1.0.8
=====
:release-date: 2013-02-08 01:00 P.M UTC
:release-by: Ask Solem

- Fixed SyntaxError on Python 2.5

.. _version-1.0.7:

1.0.7
=====
:release-date: 2013-02-08 01:00 P.M UTC
:release-by: Ask Solem

- Workaround for bug on some Python 2.5 installations where (2**32) is 0.

- Can now serialize the ARRAY type.

    Contributed by Adam Wentz.

- Fixed tuple format bug in exception (Issue #4).

.. _version-1.0.6:

1.0.6
=====
:release-date: 2012-11-29 01:14 P.M UTC
:release-by: Ask Solem

- ``Channel.close`` is now ignored if the connection attribute is None.

.. _version-1.0.5:

1.0.5
=====
:release-date: 2012-11-21 04:00 P.M UTC
:release-by: Ask Solem

- ``Channel.basic_cancel`` is now ignored if the channel was already closed.

- ``Channel.events`` is now a dict of sets::

    >>> channel.events['basic_return'].add(on_basic_return)
    >>> channel.events['basic_return'].discard(on_basic_return)

.. _version-1.0.4:

1.0.4
=====
:release-date: 2012-11-13 04:00 P.M UTC
:release-by: Ask Solem

- Fixes Python 2.5 support

.. _version-1.0.3:

1.0.3
=====
:release-date: 2012-11-12 04:00 P.M UTC
:release-by: Ask Solem

- Now can also handle float in headers/tables when receiving messages.

- Now uses :class:`array.array` to keep track of unused channel ids.

- The :data:`~amqp.exceptions.METHOD_NAME_MAP` has been updated for
  amqp/0.9.1 and Rabbit extensions.

- Removed a bunch of accidentally included images.

.. _version-1.0.2:

1.0.2
=====
:release-date: 2012-11-06 05:00 P.M UTC
:release-by: Ask Solem

- Now supports float values in headers/tables.

.. _version-1.0.1:

1.0.1
=====
:release-date: 2012-11-05 01:00 P.M UTC
:release-by: Ask Solem

- Connection errors no longer includes :exc:`AttributeError`.

- Fixed problem with using the SSL transport in a non-blocking context.

    Fix contributed by Mher Movsisyan.


.. _version-1.0.0:

1.0.0
=====
:release-date: 2012-11-05 01:00 P.M UTC
:release-by: Ask Solem

- Channels are now restored on channel error, so that the connection does not
  have to closed.

.. _version-0.9.4:

Version 0.9.4
=============

- Adds support for ``exchange_bind`` and ``exchange_unbind``.

    Contributed by Rumyana Neykova

- Fixed bugs in funtests and demo scripts.

    Contributed by Rumyana Neykova

.. _version-0.9.3:

Version 0.9.3
=============

- Fixed bug that could cause the consumer to crash when reading
  large message payloads asynchronously.

- Serialization error messages now include the invalid value.

.. _version-0.9.2:

Version 0.9.2
=============

- Consumer cancel notification support was broken (Issue #1)

    Fix contributed by Andrew Grangaard

.. _version-0.9.1:

Version 0.9.1
=============

- Supports draining events from multiple channels (``Connection.drain_events``)
- Support for timeouts
- Support for heartbeats
    - ``Connection.heartbeat_tick(rate=2)`` must called at regular intervals
      (half of the heartbeat value if rate is 2).
    - Or some other scheme by using ``Connection.send_heartbeat``.
- Supports RabbitMQ extensions:
    - Consumer Cancel Notifications
        - by default a cancel results in ``ChannelError`` being raised
        - but not if a ``on_cancel`` callback is passed to ``basic_consume``.
    - Publisher confirms
        - ``Channel.confirm_select()`` enables publisher confirms.
        - ``Channel.events['basic_ack'].append(my_callback)`` adds a callback
          to be called when a message is confirmed. This callback is then
          called with the signature ``(delivery_tag, multiple)``.
- Support for ``basic_return``
- Uses AMQP 0-9-1 instead of 0-8.
    - ``Channel.access_request`` and ``ticket`` arguments to methods
      **removed**.
    - Supports the ``arguments`` argument to ``basic_consume``.
    - ``internal`` argument to ``exchange_declare`` removed.
    - ``auto_delete`` argument to ``exchange_declare`` deprecated
    - ``insist`` argument to ``Connection`` removed.
    - ``Channel.alerts`` has been removed.
    - Support for ``Channel.basic_recover_async``.
    - ``Channel.basic_recover`` deprecated.
- Exceptions renamed to have idiomatic names:
    - ``AMQPException`` -> ``AMQPError``
    - ``AMQPConnectionException`` -> ConnectionError``
    - ``AMQPChannelException`` -> ChannelError``
    - ``Connection.known_hosts`` removed.
    - ``Connection`` no longer supports redirects.
    - ``exchange`` argument to ``queue_bind`` can now be empty
      to use the "default exchange".
- Adds ``Connection.is_alive`` that tries to detect
  whether the connection can still be used.
- Adds ``Connection.connection_errors`` and ``.channel_errors``,
  a list of recoverable errors.
- Exposes the underlying socket as ``Connection.sock``.
- Adds ``Channel.no_ack_consumers`` to keep track of consumer tags
  that set the no_ack flag.
- Slightly better at error recovery