feat: add support for DockerfileInline

[tushar5526]

Fixes #4108

As nerdctl currently uses "nerdctl build" to build the service images, write the inline file to a temporary file and use "-f" to specify the temporary dockerfile.

TODO: Add tests if the approach looks fine.

[tushar5526]

I was a bit confused about where to place this logic: writing the inline file to a temporary path and then modifying the build command to build using that file.

It seems like Build object on Service is something that is meant to be reusable, so I placed the logic of temporary file generation at the time of parsing the service and generating the Build config.

[tushar5526]

@apostasie, can I get a cursory review of the approach?

[apostasie]

Hey @tushar5526
Looks fine to me.

You do need to make sure that dockerfile and dockerfileinline cannot be specified together though:
https://docs.docker.com/reference/compose-file/build/

[tushar5526]

It looks like composecli package "github.com/compose-spec/compose-go/v2/cli" is already doing that job for me.

[AkihiroSuda]

Please squash and sign off the commits.
(make sure that the Signed-off-by: NAME <EMAIL> line with your real name is included in the commit message)

[tushar5526]

Done, thanks!

[AkihiroSuda]

CI is failing
https://github.com/containerd/nerdctl/actions/runs/15929816575/job/44936014200?pr=4305

FAIL - has whitespace errors. See git show --check 5651e76d85e12092b65f3e35b8994d2244e35698.

[tushar5526]

I think its good to go now.

[AkihiroSuda]

The tmp file has to be removed on completion of the build?

[tushar5526]

Hmm, at the moment, it does not clear it up. We are creating this file at the "service parser" phase, the actual build command just gets back the modified BuildArgs. I will take a look and see if I can clear up the tmp file.

[tushar5526]

It seems like I can store the dockerfile_inline value in the Build struct, and then during the build phase, I can create the temporary file, use it for the build, and then clear it up.

type Build struct {
	Force     bool     // force build even if already present
	BuildArgs []string // {"-t", "example.com/foo", "--target", "foo", "/path/to/ctx"}
	// something like follows
	DockerfileInline string
       // TODO: call BuildKit API directly without executing `nerdctl build`
}

Do you have any objections to putting it there?

[AkihiroSuda]

No objection

[tushar5526]

Done.

[AkihiroSuda]

Thanks