fetch.sh

for i in $(crane ls bitnami/node | grep -E '^[0-9]+'); do crane manifest bitnami/node:$i; done >/tmp/layers.jsonish

layers.go

package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"os"
)

type image struct {
	Layers []layer `json:"layers"`
}

type layer struct {
	Size   int    `json:"size"`
	Digest string `json:"digest"`
}

func mainE() error {
	dec := json.NewDecoder(os.Stdin)

	blobs := map[string]int{}
	imagesTotal := 0
	ociImagesTotal := 0
	stupidTotal := 0

	for {
		var img image
		err := dec.Decode(&img)
		if errors.Is(err, io.EOF) {
			break
		}
		if err != nil {
			return err
		}
		imagesTotal++
		if img.Layers != nil {
			ociImagesTotal++
		}
		for _, l := range img.Layers {
			stupidTotal += l.Size
			blobs[l.Digest] = l.Size
		}
	}

	total := 0
	for _, s := range blobs {
		total += s
	}
	fmt.Printf("Total images: %d\n", imagesTotal)
	fmt.Printf("Total OCI images: %d\n", ociImagesTotal)

	fmt.Printf("Undeduplicated total: %d GB\n", stupidTotal/1024/1024/1024)
	fmt.Printf("Total: %d GB\n", total/1024/1024/1024)
	fmt.Printf("Saving %.2f%%\n", (1-float64(total)/float64(stupidTotal))*100)
	return nil
}

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