Enable CLI to Pull Config

[shizhMSFT]

Add a new option named --manifest-config to oras pull so that oras can pull the config file as well even if the config is not named. Like oras push, file name with media type should be passed to the --manifest-config option. The media type is optional and its default value is application/vnd.unknown.config.v1+json. The resulted config will be written to the specified file name.

Examples:

$ oras pull --manifest-config config.json localhost:5000/hello:latest
Downloaded a948904f2f0f hi.txt
Downloaded 57f840b6073c config.json
Pulled localhost:5000/hello:latest
Digest: sha256:a5d8f401e10aa320bd7ecabbfbabb89b0e59e599c9fdc6587edbffaf232fa4f3

$ oras pull --manifest-config config.json:application/vnd.unknown.config.v1+json localhost:5000/hello:latest
Downloaded a948904f2f0f hi.txt
Downloaded 57f840b6073c config.json
Pulled localhost:5000/hello:latest
Digest: sha256:a5d8f401e10aa320bd7ecabbfbabb89b0e59e599c9fdc6587edbffaf232fa4f3

[deitch]

What does passing the media-type do, though? What is the difference in behaviour between passing it or not?

[shizhMSFT]

oras needs to know the media type of the config file. If the config media type does not match, oras drop the config. That also achieves sort of optional config.

Of course, we can pull any configs but it requires the oras command line module to fetch the manifest from the complex storage and parse the manifest.

[SteveLasker]

Sorry I couldn't review yesterday.

Why should we have to specify the --manifest-config for oras pull? This means a consumer would have to know the fully qualified reference demo42.azurecr.io/hello-artifact:v1 and the config: --manifest-config config.json:application/vnd.acme.rocket.config

Repro steps

1. Run CNCF distribution locally

 docker run -it --rm -p 5000:5000 registry

1. Create a config, and document

echo "hello config" > config.json
echo "hello artifact" > artifact.txt

1. Push the artifact, and the config

oras push localhost:5000/hello-artifact:v1 \
  --manifest-config config.json:application/vnd.acme.rocket.config \
  ./artifact.txt

1. Create a download directory

mkdir download
cd download

1. Pull the artifact

oras pull localhost:5000/hello-artifact:v1 \
  --manifest-config config.json

Results

Only the artifact.txt file is returned. The config is missing:

ls
artifact.txt

Workaround

Specify the config mediaType

oras pull localhost:5000/hello-artifact:v1 \
  --manifest-config config.json:application/vnd.acme.rocket.config

Expectation

The config is pulled, as the user shouldn't have to know the fully qualified URL and the config mediaType. The config mediaType is internal details