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stargzify.go
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stargzify.go
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// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// The stargzify command converts a remote container image into an equivalent
// image with its layers transformed into stargz files instead of gzipped tar
// files. The image is still a valid container image, but its layers contain
// multiple gzip streams instead of one and have a Table of Contents at the end.
package main
import (
"crypto/sha256"
"encoding/hex"
"flag"
"fmt"
"hash"
"io"
"io/ioutil"
"log"
"net/http"
"os"
"strings"
"github.com/google/go-containerregistry/pkg/authn"
"github.com/google/go-containerregistry/pkg/logs"
"github.com/google/go-containerregistry/pkg/name"
v1 "github.com/google/go-containerregistry/pkg/v1"
"github.com/google/go-containerregistry/pkg/v1/empty"
"github.com/google/go-containerregistry/pkg/v1/mutate"
"github.com/google/go-containerregistry/pkg/v1/remote"
"github.com/google/go-containerregistry/pkg/v1/stream"
"github.com/google/go-containerregistry/pkg/v1/types"
"github.com/mc256/crfs/stargz"
)
var (
upgrade = flag.Bool("upgrade", false, "upgrade the image in-place by overwriting the tag")
flatten = flag.Bool("flatten", false, "flatten the image's layers into a single layer")
insecure = flag.Bool("insecure", false, "allow HTTP connections to the registry which has the prefix \"http://\"")
usage = `usage: %[1]s [-upgrade] [-flatten] input [output]
Converting images:
# converts "ubuntu" from dockerhub and uploads to your GCR project
%[1]s ubuntu gcr.io/<your-project>/ubuntu:stargz
# converts and overwrites :latest
%[1]s -upgrade gcr.io/<your-project>/ubuntu:latest
# converts and flattens "ubuntu"
%[1]s -flatten ubuntu gcr.io/<your-project>/ubuntu:flattened
# converts "ubuntu" from dockerhub and uploads to your registry using HTTP
%[1]s -insecure ubuntu http://registry:5000/<path>/ubuntu:stargz
Converting files:
%[1]s file:/tmp/input.tar.gz file:output.stargz
# writes to /tmp/input.stargz
%[1]s file:/tmp/input.tar.gz
`
)
func main() {
flag.Parse()
if len(flag.Args()) < 1 {
printUsage()
}
// Set up logs package to get useful messages i.e. progress.
logs.Warn.SetOutput(os.Stderr)
logs.Progress.SetOutput(os.Stderr)
if strings.HasPrefix(flag.Args()[0], "file:") {
// We'll use "file:" prefix as a signal to convert single files.
convertFile()
} else {
convertImage()
}
}
func printUsage() {
log.Fatalf(usage, os.Args[0])
}
func convertFile() {
var in, out string
if len(flag.Args()) > 0 {
in = strings.TrimPrefix(flag.Args()[0], "file:")
}
if len(flag.Args()) > 1 {
out = strings.TrimPrefix(flag.Args()[1], "file:")
}
var f, fo *os.File // file in, file out
var err error
switch in {
case "":
printUsage()
case "-":
f = os.Stdin
default:
f, err = os.Open(in)
if err != nil {
log.Fatal(err)
}
}
defer f.Close()
if out == "" {
if in == "-" {
out = "-"
} else {
base := strings.TrimSuffix(in, ".gz")
base = strings.TrimSuffix(base, ".tgz")
base = strings.TrimSuffix(base, ".tar")
out = base + ".stargz"
}
}
if out == "-" {
fo = os.Stdout
} else {
fo, err = os.Create(out)
if err != nil {
log.Fatal(err)
}
}
w := stargz.NewWriter(fo)
if err := w.AppendTar(f); err != nil {
log.Fatal(err)
}
if err := w.Close(); err != nil {
log.Fatal(err)
}
if err := fo.Close(); err != nil {
log.Fatal(err)
}
}
func parseFlags(args []string) (string, string) {
if len(args) < 1 {
printUsage()
}
var src, dst string
src = args[0]
if len(args) < 2 {
if *upgrade {
dst = src
} else {
printUsage()
}
} else if len(args) == 2 {
if *upgrade {
log.Println("expected one argument with -upgrade")
printUsage()
} else {
dst = args[1]
}
} else {
log.Println("too many arguments")
printUsage()
}
return src, dst
}
func convertImage() {
src, dst := parseFlags(flag.Args())
srcRef, err := parseReference(src)
if err != nil {
log.Fatal(err)
}
// Pull source image.
srcImg, err := remote.Image(srcRef, remote.WithAuthFromKeychain(authn.DefaultKeychain))
if err != nil {
log.Fatal(err)
}
// Grab original config, clear the layer info from the config file. We want to
// preserve the relevant config.
srcCfg, err := srcImg.ConfigFile()
if err != nil {
log.Fatal(err)
}
srcCfg.RootFS.DiffIDs = []v1.Hash{}
srcCfg.History = []v1.History{}
// Use an empty image with the rest of src's config file as a base.
img, err := mutate.ConfigFile(empty.Image, srcCfg)
if err != nil {
log.Fatal(err)
}
layers, err := convertLayers(srcImg)
if err != nil {
log.Fatal(err)
}
for _, layer := range layers {
img, err = mutate.Append(img, mutate.Addendum{
Layer: layer,
History: v1.History{
// Leave our mark.
CreatedBy: fmt.Sprintf("stargzify %s %s", src, dst),
},
})
if err != nil {
log.Fatal(err)
}
}
// Push the stargzified image to dst.
dstRef, err := parseReference(dst)
if err != nil {
log.Fatal(err)
}
dstAuth, err := authn.DefaultKeychain.Resolve(dstRef.Context().Registry)
if err != nil {
log.Fatal(err)
}
if err := remote.Write(dstRef, img, remote.WithAuth(dstAuth), remote.WithTransport(http.DefaultTransport)); err != nil {
log.Fatal(err)
}
}
func convertLayers(img v1.Image) ([]v1.Layer, error) {
if *flatten {
r := mutate.Extract(img)
return []v1.Layer{newLayer(r)}, nil
}
layers, err := img.Layers()
if err != nil {
return nil, err
}
converted := []v1.Layer{}
for _, layer := range layers {
r, err := layer.Uncompressed()
if err != nil {
return nil, err
}
converted = append(converted, newLayer(r))
}
return converted, nil
}
type layer struct {
rc io.ReadCloser
d *digester
diff *v1.Hash
digest *v1.Hash
}
// parseReference is like go-containerregistry/pkg/name.ParseReference but additionally
// supports the reference starting with "http://" to mean insecure.
func parseReference(ref string) (name.Reference, error) {
var opts []name.Option
if strings.HasPrefix(ref, "http://") {
if !*insecure {
return nil, fmt.Errorf("-insecure flag required when connecting using HTTP to %q", ref)
}
ref = strings.TrimPrefix(ref, "http://")
opts = append(opts, name.Insecure)
}
return name.ParseReference(ref, opts...)
}
// newLayer converts the given io.ReadCloser to a stargz layer.
func newLayer(rc io.ReadCloser) v1.Layer {
return &layer{
rc: rc,
d: &digester{
h: sha256.New(),
},
}
}
func (l *layer) Digest() (v1.Hash, error) {
if l.digest == nil {
return v1.Hash{}, stream.ErrNotComputed
}
return *l.digest, nil
}
func (l *layer) Size() (int64, error) {
if l.digest == nil {
return -1, stream.ErrNotComputed
}
return l.d.n, nil
}
func (l *layer) DiffID() (v1.Hash, error) {
if l.diff == nil {
return v1.Hash{}, stream.ErrNotComputed
}
return *l.diff, nil
}
func (l *layer) MediaType() (types.MediaType, error) {
// TODO: We might want to set our own media type to indicate stargz layers,
// but that has the potential to break registry compatibility.
return types.DockerLayer, nil
}
func (l *layer) Compressed() (io.ReadCloser, error) {
pr, pw := io.Pipe()
// Convert input blob to stargz while computing diffid, digest, and size.
go func() {
w := stargz.NewWriter(io.MultiWriter(pw, l.d))
if err := w.AppendTar(l.rc); err != nil {
pw.CloseWithError(err)
return
}
if err := w.Close(); err != nil {
pw.CloseWithError(err)
return
}
diffid, err := v1.NewHash(w.DiffID())
if err != nil {
pw.CloseWithError(err)
return
}
l.diff = &diffid
l.digest = &v1.Hash{
Algorithm: "sha256",
Hex: hex.EncodeToString(l.d.h.Sum(nil)),
}
pw.Close()
}()
return ioutil.NopCloser(pr), nil
}
func (l *layer) Uncompressed() (io.ReadCloser, error) {
return l.rc, nil
}
// digester tracks the sha256 and length of what is written to it.
type digester struct {
h hash.Hash
n int64
}
func (d *digester) Write(b []byte) (int, error) {
n, err := d.h.Write(b)
d.n += int64(n)
return n, err
}