Fix returning last log line in docker operator

[davidcaron]

Iterable values in cli.attach(..., stream=True) are not necessarily single lines.
Lines can be merged together or split because of buffering.
When this split happens just before the last newline character, the returned value of execute is an empty byte string.

Also, fix the return type annotation (the return type is not changed, only the annotation).

I used these files to recreate the issue:

Dockerfile

FROM python:3.8-slim-buster
WORKDIR /code
ADD main.py .
CMD [ "python", "main.py" ]

main.py

from random import randint

for _ in range(randint(1, 100)):
    print(f"output")

print("last_line")

script.py

from docker import APIClient


cli = APIClient()


def run_image():
    container = cli.create_container(
        command="python main.py",
        host_config=cli.create_host_config(auto_remove=False),
        image="docker-bug",
        tty=True,
    )

    lines = cli.attach(container=container["Id"], stdout=True, stderr=True, stream=True)

    cli.start(container["Id"])

    line = list(lines)[-1]

    cli.wait(container["Id"])

    print("--- LAST LINES ---")
    print(repr(line))
    print(repr(cli.logs(container=container["Id"], tail=1).strip()))

    cli.remove_container(container["Id"])


if __name__ == "__main__":
    for i in range(1000):
        run_image()

When running:

$ docker build -t docker-bug .
$ python script.py

The output will look something like:

--- LAST LINES ---
b'output\r\noutput\r\noutput\r\noutput\r\noutput\r\noutput\r\noutput\r\nlast_line\r\n'
b'last_line'
--- LAST LINES ---
b'output\r\noutput\r\noutput\r\noutput\r\noutput\r\noutput\r\noutput\r\noutput\r\noutput\r\nlast_line\r\n'
b'last_line'
--- LAST LINES ---
b'output\r\noutput\r\nlast_line\r\n'
b'last_line'

[boring-cyborg]

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[davidcaron]

Related, but different issue: #13536 (converts return type to str, but this PR keeps bytes)

I believe execute should return a decoded str... but I kept the current return type, so there should be no breaking change in this PR.

[dstandish]

why not strip here also?

[davidcaron]

I agree it should probably be stripped, but my intention was to keep the current behavior when do_xcom_push and xcom_all are all true.

[dstandish]

should we perhaps decode utf-8 (assuming that's what comes out of logs, so that we return a string type? sincere question... 🤔

[dstandish]

coincidence someone is doing exactly that: https://github.com/apache/airflow/pull/13536/files

[davidcaron]

Yes, and I think this would make more sense, but again I wanted to avoid a breaking change...

I would actually be happy with this other PR being merged, as it now includes the fix in my PR.

[davidcaron]

@dstandish Thanks for your review.

If #13536 gets merged, this one can be closed.

I would personally consider this PR a bug fix, and #13536 a breaking change.

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed in 5 days if no further activity occurs. Thank you for your contributions.