run

README.md

run

Outputs the equivalent argv of what you would get with a docker run command.

This considers the given image's CMD, ENTRYPOINT, and docker run's --entrypoint flag.

$ run hello-world@sha256:96ebeec770e1af26469c98913277e1c3b40933202ca398cefc16177c3f26cc75
["cmd","/C","type C:\\hello.txt"]

$ run --entrypoint /crane hello-world@sha256:96ebeec770e1af26469c98913277e1c3b40933202ca398cefc16177c3f26cc75
["/crane"]

$ run hello-world@sha256:96ebeec770e1af26469c98913277e1c3b40933202ca398cefc16177c3f26cc75 crane
["crane"]

$ run gcr.io/go-containerregistry/crane version
["/ko-app/crane","version"]

$ run --entrypoint '["crane", "ls"]' gcr.io/go-containerregistry/crane ubuntu
["crane","ls","ubuntu"]

main.go

package main

import (
      "encoding/json"
      "errors"
      "fmt"
      "log"

      "github.com/google/go-containerregistry/pkg/crane"
      flag "github.com/spf13/pflag"
)

var entrypoint string

func init() {
      flag.StringVar(&entrypoint, "entrypoint", "", "Overwrite the default ENTRYPOINT of the image")
      flag.Parse()
}

func main() {
      if err := run(); err != nil {
        log.Fatal(err)
      }
}

func run() error {
      args := flag.Args()

      if len(args) < 1 {
        return errors.New("no args")
      }
      img, err := crane.Pull(args[0])
      if err != nil {
        return err
      }

      cf, err := img.ConfigFile()
      if err != nil {
        return err
      }

      exec := []string{}
      if entrypoint != "" {
        b := []byte(entrypoint)
        p := make([]string, 0, 1)
        if err := json.Unmarshal(b, &p); err == nil {
            cf.Config.Entrypoint = p
        } else {
            cf.Config.Entrypoint = []string{entrypoint}
        }
        cf.Config.Cmd = nil
      }

      exec = append(exec, cf.Config.Entrypoint...)
      if len(args) > 1 {
        exec = append(exec, args[1:]...)
      } else if len(cf.Config.Cmd) > 0 {
        exec = append(exec, cf.Config.Cmd...)
      }

      b, err := json.Marshal(exec)
      if err != nil {
        return err
      }

      fmt.Println(string(b))

      return nil
}

...it comes down to whether you treat a container as a process or an environment in which to run processes.

Nice! I think you condensed everything into the ideal one-line summary. I'm going to use that! 😁