digester.go

// Copyright 2015 The Bazel Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//////////////////////////////////////////////////////////////////////
//This binary implements the ability to load a docker image, calculate its image manifest sha256 hash and output a digest file.
package main

import (
	"flag"
	"io/ioutil"
	"log"
	"os"

	"github.com/bazelbuild/rules_docker/container/go/pkg/compat"
	"github.com/bazelbuild/rules_docker/container/go/pkg/oci"
	"github.com/bazelbuild/rules_docker/container/go/pkg/utils"
)

var (
	dst          = flag.String("dst", "", "The destination location of the digest file to write to.")
	imgTarball   = flag.String("tarball", "", "Path to the image tarball as generated by docker save. Required if --config was not specified.")
	imgConfig    = flag.String("config", "", "Path to the image config JSON file. Required if --tarball was not specified.")
	baseManifest = flag.String("manifest", "", "Path to the manifest of the base image. This should be the very first image in the chain of images and is only really required for Windows images with a base image that has foreign layers.")
	format       = flag.String("format", "", "The format of the uploaded image (Docker or OCI).")
	layers       utils.ArrayStringFlags
)

func main() {
	flag.Var(&layers, "layer", "One or more layers with the following comma separated values (Compressed layer tarball, Uncompressed layer tarball, digest file, diff ID file). e.g., --layer layer.tar.gz,layer.tar,<file with digest>,<file with diffID>.")
	flag.Parse()

	if *dst == "" {
		log.Fatalln("Required option -dst was not specified.")
	}
	if *imgConfig == "" {
		log.Fatalln("Option --config is required.")
	}
	imgParts, err := compat.ImagePartsFromArgs(*imgConfig, *baseManifest, *imgTarball, layers)
	if err != nil {
		log.Fatalf("Unable to determine parts of the image from the specified arguments: %v", err)
	}
	img, err := compat.ReadImage(imgParts)
	if err != nil {
		log.Fatalf("Error reading image: %v", err)
	}
	if *format == "OCI" {
		img, err = oci.AsOCIImage(img)
		if err != nil {
			log.Fatalf("Failed to convert image to OCI format: %v", err)
		}
	}

	d, err := img.Digest()
	if err != nil {
		log.Fatalf("Unable to get digest of image: %v", err)
	}
	if err := ioutil.WriteFile(*dst, []byte(d.String()), os.ModePerm); err != nil {
		log.Fatalf("Error outputting digest file to %s: %v", *dst, err)
	}
}