Add custom subcommand for podman (or podman-remote) CLI

[benoitf]

Feature request description

There are existing set of commands for podman.

I would like to be able to add my own sub-command

for example I could add my own podman foo command

Suggest potential solution

It could be implemented like for common CLI. Example git cli

if I have in my path executables starting by podman- (in the case of git it's git-) then it adds the command

example with git:

if I add a new file

/usr/local/bin/git-foo

with content

echo "executing the custom foo"

I can then invoke git foo command

I expect to have the same way using podman, that all the podman-**** commands could be invoked using podman ****

Have you considered any alternatives?

could be some fancy plug-ins systems but using something very simple and commonly used looks easier.

Additional context

Add any other context or screenshots about the feature request here.

[vrothberg]

The last time we've discussed a plug-in system (Podman f2f), there was consensus on not doing one. Counter arguments I recall:

• Unclear requirements. A simple system does not meet complex requirements such as hooking into existing commands.
• Docker already has a plugin system that is being deprecated.
• Plugins can conflict with future Podman commands.
• Simple plugins only executing other binaries don't require Podman to call them.

I personally think that this should be use-case driven. A certain use case (e.g., Compose) may very well get an exception that doesn't require a generic solution.

[slemeur]

cc @vyasgun

[github-actions[bot]]

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[cdrage]

@vrothberg @vyasgun @rhatdan

I believe last meeting we discussed the possibility of having a "hidden" command of podman compose which would essentially redirect to docker-compose binary.

We could do this as a plugin system where podman will check the same directory (similar to where podman-mac-helper is) and execute the binary if it's found.

[cdrage]

Comment on slack with regards to the discussion which I thought may help:

For #13425 the part about implementing it in Go seems interesting.
So about Compose, I looked up how nerdctl implements it and it's very similar to how kompose does it to Kubernetes, so it lead to me to a rabbit hole of information.

It's interesting that if we did want to integrate it natively and in Go rather than relying on the python implementation or the binary, we can do it like so:

Load up everything similar to nerdctl and kompose : https://github.com/containerd/nerdctl/blob/f21bca52d09cccf5c16f9a881049a3f44e3165c9/pkg/composer/composer.go#L84

But what nerdctl which is what I found interesting is they convert the compose spec to containerd files: https://github.com/containerd/nerdctl/blob/f21bca52d09cccf5c16f9a881049a3f44e3165c9/pkg/composer/serviceparser/serviceparser.go#L465

There is a larggggeeeee list of stuff they ignore / will implement in the future (see: https://github.com/containerd/nerdctl/blob/f21bca52d09cccf5c16f9a881049a3f44e3165c9/pkg/composer/serviceparser/serviceparser.go#L55), but for each service in the compose spec, they convert it to the CLI equivalent for containerd.

The same can be done with podman, but instead of the CLI equivalent, it converts it to the libpod.Container
Just some research / thought was interesting for implementation. it may be worth it to actually code it with Go