Do not pull all available tags with --pull

[meyerj]

rocker --pull <image> without a tag pulls all available tags for that image, and hence can fill the disk quickly.

The reason is that the underlying docker_client.pull(image,tag=None) pulls all available tags if no specific tag is specfied:

If no tag was specified, the method will return a list of Image objects belonging to this repository.

So the removed method rocker.core.pull_image(image_name) would have to decompose the URL given at the command line, and either pass the tag separately, or append :latest to image_name if no other tag was specified.

This patch removes the broken method completely. It is not needed, because the pull flag can simply be forwarded to the docker_client.build() command, at least for docker-py version 2.5.1 provided by Ubuntu Bionic and version 1.8.0 provided by Ubuntu Xenial.

Verified with:

$ docker pull ubuntu:bionic
bionic: Pulling from library/ubuntu
171857c49d0f: Already exists 
419640447d26: Already exists 
61e52f862619: Already exists 
Digest: sha256:646942475da61b4ce9cc5b3fadb42642ea90e5d0de46111458e100ff2c7031e6
Status: Downloaded newer image for ubuntu:bionic
docker.io/library/ubuntu:bionic
$ docker tag ubuntu:bionic ubuntu:latest
$ rocker ubuntu    # expectation: same as ubuntu:latest
[...]
Building docker file with arguments:  {'path': '/tmp/tmppa0oykh2', 'rm': True, 'nocache': False, 'pull': False}
[...]
root@a95d93f22ee6:/# cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=18.04
DISTRIB_CODENAME=bionic
DISTRIB_DESCRIPTION="Ubuntu 18.04.5 LTS"
root@a95d93f22ee6:/# exit
exit

So the version tagged as ubuntu:latest is actually ubuntu:bionic. rocker did not attempt to pull a newer version.

--pull still has the desired effect and the docker daemon pulls the image during the build:

$ rocker --pull ubuntu    # expectation: same as ubuntu:latest
[...]
Building docker file with arguments:  {'path': '/tmp/tmp8zlicrod', 'rm': True, 'nocache': False, 'pull': True}
[...]
root@475275ae66cc:/# cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=20.04
DISTRIB_CODENAME=focal
DISTRIB_DESCRIPTION="Ubuntu 20.04.1 LTS"
root@475275ae66cc:/# exit
exit

Without this patch, the second invocation rocker --pull ubuntu would take very long and pull all available tags.

[codecov]

Codecov Report

Merging #100 into master will decrease coverage by 0.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #100      +/-   ##
==========================================
- Coverage   86.70%   86.52%   -0.18%     
==========================================
  Files           7        7              
  Lines         564      579      +15     
==========================================
+ Hits          489      501      +12     
- Misses         75       78       +3     

Impacted Files	Coverage Δ
src/rocker/cli.py	0.00% <ø> (ø)
src/rocker/core.py	90.14% <ø> (-1.08%)	⬇️
src/rocker/extensions.py	100.00% <0.00%> (ø)

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[tfoote]

Thanks it's always great to reduce the amount of code and make it more efficient.