[AIRFLOW-4363] Fix JSON encoding error

[retornam]

From the docker-py code comments for APIClient pull,
the decode parameter should be set to True, when the
stream parameter is also set to True. This will allow
decoding JSON data returned from the docker registry
server into dicts

Signed-off-by: Raymond Etornam [email protected]

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Issue link: AIRFLOW-4363

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[brokenjacobs]

This breaks the pull functionality because the very next function in the loop tries to do a string decode on this dictionary.
Leading to:

    output = json.loads(l.decode('utf-8').strip())
AttributeError: 'dict' object has no attribute 'decode'```

Basically this entire PR breaks image pulls as written. 

[dimberman]

Darn. @brokenjacobs do you have a suggestion for a fix for this?

[brokenjacobs]

Testing a fix right now.

[retornam]

#8287

[brokenjacobs]

remove the entire json.loads() line... change the loop:
for output in self.cli.pull(self.image, stream=True, decode=True):
That fixes it.

[hagope]

After upgrading from 1.10.9 to 1.10.10, you may see the following error:

[2020-04-20 23:14:44,087] {{docker_operator.py:267}} INFO - Pulling docker image XXXX:latest
[2020-04-20 23:14:44,140] {{taskinstance.py:1145}} ERROR - 'dict' object has no attribute 'decode'
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/airflow/models/taskinstance.py", line 983, in _run_raw_task
    result = task_copy.execute(context=context)
  File "/usr/local/lib/python3.7/site-packages/airflow/operators/docker_operator.py", line 269, in execute
    output = json.loads(l.decode('utf-8').strip())
AttributeError: 'dict' object has no attribute 'decode'

You can patch this in your Dockerfile by adding the following (per @brokenjacobs above):

RUN sed -i '268s/l/output/' /usr/local/lib/python3.7/site-packages/airflow/operators/docker_operator.py
RUN sed -i '269s/output/#output/' /usr/local/lib/python3.7/site-packages/airflow/operators/docker_operator.py