Return 12 character short_ids

[benfasoli]

Hi all 👋 Thanks for the work here - I've found it really helpful for several projects.

I'd like to discuss changing the behavior of Model.short_id from returning a 10 character string to a 12 character string which aligns more closely with the docker cli. It looks like this has been requested previously by #1491 and #2660.

For example (from the docs), running docker ps without explicitly setting --no-trunc:

$ docker ps

CONTAINER ID        IMAGE                        COMMAND                CREATED              STATUS              PORTS               NAMES
4c01db0b339c        ubuntu:12.04                 bash                   17 seconds ago       Up 16 seconds       3300-3310/tcp       webapp
d7886598dbe2        crosbymichael/redis:latest   /redis-server --dir    33 minutes ago       Up 33 minutes       6379/tcp            redis,webapp/db

It looks like 12 character ids were once the intended behavior - the object reprs in the docker-py documentation from #1186 show 12 digit ids:

>>> client.containers.list()
[<Container '45e6d2de7c54'>, <Container 'db18e4f20eaa'>, ...]

The specific issue I'm having is that the 12 character container ID is used by docker as a container's default hostname. Here's a minimal example of a container trying to connect to itself by hostname:

import docker


client = docker.from_env()


nginx_container = client.containers.run("nginx:latest", detach=True, auto_remove=True)


# Networking with 64 character id as hostname will fail.
exit_code, response = nginx_container.exec_run(f"curl {nginx_container.id}")
assert exit_code == 6
assert b"Could not resolve host:" in response

# Networking with 10 character id as hostname will fail.
exit_code, response = nginx_container.exec_run(f"curl {nginx_container.short_id}")
assert exit_code == 6
assert b"Could not resolve host:" in response

# Networking with 12 character id as hostname will succeed 🚀
exit_code, response = nginx_container.exec_run(f"curl {nginx_container.id[:12]}")
assert exit_code == 0, response
assert b"Welcome to nginx!" in response


nginx_container.stop()

API requests treat the id as a variable width prefix and returns valid responses as long as the prefix doesn't match multiple resources. So I think using 12 characters shouldn't break backwards compatibility for code that currently uses the 10 character short_id.

Here's a first pass at the implementation.

1. Return a 12 character short_id for classes that inherit from docker.models.resource.Model and a 19 character short_id for Image ids prefixed by sha256:.
2. Expand the fake_api ids to 64 characters.
3. Modify ImageTest.test_short_id to expect a 12 character response.
4. Add ContainerTest.test_short_id to expect a 12 character response.

This currently fail flake8's E501 (line > 79 characters) requirement in a few places but I left the formatting as is for now since there are existing docstrings which fail E501 and it made the changes more readable. Happy to tweak to your preference.

Closes #1491
Closes #2660

[ghost]

Up, that doesn't seems like a big deal but it would improve the python API. I was thinking about creating a database storing container stats but I couldn't choose a coherent length for the short ID because of this python/docker cli discrepancy.
It is always possible to use the full length ID, but it is almost never used because it's non user-friendly.

[milas]

Thanks for the improvement and tests! Will get this included in the upcoming 6.0.0 release 🙂