demo: delve-entrypoint-mutating

main.go

package main

import (
	"archive/tar"
	"bytes"
	"fmt"
	"github.com/google/go-containerregistry/pkg/crane"
	"github.com/google/go-containerregistry/pkg/name"
	v1 "github.com/google/go-containerregistry/pkg/v1"
	"github.com/google/go-containerregistry/pkg/v1/mutate"
	"github.com/google/go-containerregistry/pkg/v1/tarball"
	"io"
	"log"
	"os"
)

func main() {
	log.Printf("pulling the image...")

	img, err := crane.Pull("registry.trendyol.com/platform/base/poc/simple-golang-app:latest")
	if err != nil {
		panic(err)
	}

	log.Printf("creating layer...")

	l, err := createLayer("./dlv")
	if err != nil {
		panic(err)
	}

	log.Printf("appending layer...")

	i, err := mutate.AppendLayers(img, l)
	if err != nil {
		panic(err)
	}

	log.Printf("tagging layer...")

	tag, err := name.NewTag("furkanturkal/delve:foo")
	if err != nil {
		panic(err)
	}

	log.Printf("image %s pushed to the registry succesfully\n", tag.String())

	cfg, err := i.ConfigFile()
	if err != nil {
		log.Fatalf("getting config: %v", err)
	}
	cfg = cfg.DeepCopy()

	fmt.Printf("%+v", cfg.Config.Entrypoint)

	cfg.Config.Entrypoint = []string{"./dlv", "--listen=:40000", "--headless=true", "--api-version=2", "exec", cfg.Config.Entrypoint[0]}

	li, err := mutate.Config(i, cfg.Config)
	if err != nil {
		log.Fatalf("mutating config: %v", err)
	}

	fmt.Printf("update entrypoint to: %+v", cfg.Config.Entrypoint)

	log.Printf("pushing layer...")

	//if s, err := daemon.Write(tag, newImg); err != nil {
	//	panic(err)
	//} else {
	//	fmt.Println(s)

	if err := crane.Push(li, tag.String()); err != nil {
		panic(err)
	}

	log.Printf("DONE")
}

func createLayer(fpath string) (v1.Layer, error) {
	var b bytes.Buffer
	tw := tar.NewWriter(&b)

	file, err := os.Open(fpath)
	if err != nil {
		return nil, err
	}
	defer file.Close()

	stat, err := file.Stat()
	if err != nil {
		return nil, err
	}

	header := &tar.Header{
		Name:    "/src/" + fpath,
		Size:    stat.Size(),
		Mode:    int64(stat.Mode()),
		ModTime: stat.ModTime(),
	}

	header.Typeflag = tar.TypeReg

	err = tw.WriteHeader(header)
	if err != nil {
		return nil, err
	}

	_, err = io.Copy(tw, file)
	if err != nil {
		return nil, err
	}

	if err := tw.Close(); err != nil {
		return nil, fmt.Errorf("failed to finish tar: %w", err)
	}

	return tarball.LayerFromReader(&b)
}