zaqar transport is broken with python3

[Michele Baldessari]

In https://github.com/openstack/zaqar/blob/master/zaqar/transport/websocket/protocol.py we do the following:
...
try:
    import mimetools
    Message = mimetools.Message
except ImportError:
    from email.mime import message
    Message = message.MIMEMessage
...

        if self._state == 'HEADERS' and b'\r\n\r\n' in self._data:
            headers, self._data = self._data.split(b'\r\n\r\n', 1)
            headers = Message(io.BytesIO(headers))

The above does not work with python3 because it will throw an exception:
2019-02-27 14:22:19.359 1 ERROR asyncio
2019-02-27 14:22:21.002 1 ERROR asyncio [-] Exception in callback _SelectorSocketTransport._read_ready()
handle: <Handle _SelectorSocketTransport._read_ready()>: TypeError: Argument is not an instance of Message
2019-02-27 14:22:21.002 1 ERROR asyncio Traceback (most recent call last):
2019-02-27 14:22:21.002 1 ERROR asyncio File "/usr/lib64/python3.6/asyncio/events.py", line 145, in _run
2019-02-27 14:22:21.002 1 ERROR asyncio self._callback(*self._args)
2019-02-27 14:22:21.002 1 ERROR asyncio File "/usr/lib64/python3.6/asyncio/selector_events.py", line 721, in _read_ready
2019-02-27 14:22:21.002 1 ERROR asyncio self._protocol.data_received(data)
2019-02-27 14:22:21.002 1 ERROR asyncio File "/usr/lib/python3.6/site-packages/zaqar/transport/websocket/protocol.py", line 255, in data_received
2019-02-27 14:22:21.002 1 ERROR asyncio headers = Message(io.BytesIO(headers))
2019-02-27 14:22:21.002 1 ERROR asyncio File "/usr/lib64/python3.6/email/mime/message.py", line 29, in __init__
2019-02-27 14:22:21.002 1 ERROR asyncio raise TypeError('Argument is not an instance of Message')
2019-02-27 14:22:21.002 1 ERROR asyncio TypeError: Argument is not an instance of Message

The problem is that the message class in mimetools is not really compatible with the class in email.mime. Here is a small reproducer to show the issue:
╭─michele@holtby ~ 11:00:40
╰─$ more bugmime.py
import io
try:
    import mimetools
    Message = mimetools.Message
except ImportError:
    from email.mime import message
    Message = message.MIMEMessage

s = io.BytesIO(b'Host: 192.168.24.1:46643\r\nUser-Agent: python-requests/2.20.0\r\nAccept-Encoding: gzip, deflate\r\nAccept: */*\r\nConnection: keep-al
ive\r\nContent-Type: application/json\r\nContent-Length: 5349')
a = Message(s)
print(str(a))
╭─michele@holtby ~ 11:00:42
╰─$ python2 bugmime.py
Host: 192.168.24.1:46643
User-Agent: python-requests/2.20.0
Accept-Encoding: gzip, deflate
Accept: */*
Connection: keep-alive
Content-Type: application/json
Content-Length: 5349
╭─michele@holtby ~ 11:00:47
╰─$ python3 bugmime.py
Traceback (most recent call last):
  File "bugmime.py", line 10, in <module>
    a = Message(s)
  File "/usr/lib64/python3.7/email/mime/message.py", line 29, in __init__
    raise TypeError('Argument is not an instance of Message')
TypeError: Argument is not an instance of Message

[Michele Baldessari (michele)]

https://review.openstack.org/#/c/639983/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/639983
Committed: https://git.openstack.org/cgit/openstack/zaqar/commit/?id=ff19fdeb5452f19d8420cfb041aa846bdf58c84e
Submitter: Zuul
Branch: master

commit ff19fdeb5452f19d8420cfb041aa846bdf58c84e
Author: Damien Ciabrini <email address hidden>
Date: Thu Feb 28 11:43:29 2019 +0100

    Python 3: Fix parsing of received notification

    The parsing of incoming notifications is performed with a helper
    which normally resolves to a mimetools class.

    For Python3, package mimetools doesn't exist anymore, and the helper
    resolves to a class with incompatible signature.

    In order to mimick the original helper behaviour and return a message
    object as expected, use a different facility from package email.

    Change-Id: I92f10755f1a98239df3b3a1494207299a3681a84
    Closes-Bug: #1818046
    Co-Authored-By: Michele Baldessari <email address hidden>
    Co-Authored-By: Alex Schultz <email address hidden>

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/zaqar 8.0.0.0rc1 release candidate.