distribution/manifest/schema1/config_builder.go

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package schema1
import (
"crypto/sha512"
"encoding/json"
"errors"
"fmt"
"time"
"github.com/docker/distribution"
"github.com/docker/distribution/context"
"github.com/docker/distribution/digest"
"github.com/docker/distribution/manifest"
"github.com/docker/distribution/reference"
"github.com/docker/libtrust"
)
type diffID digest.Digest
// gzippedEmptyTar is a gzip-compressed version of an empty tar file
// (1024 NULL bytes)
var gzippedEmptyTar = []byte{
31, 139, 8, 0, 0, 9, 110, 136, 0, 255, 98, 24, 5, 163, 96, 20, 140, 88,
0, 8, 0, 0, 255, 255, 46, 175, 181, 239, 0, 4, 0, 0,
}
// digestSHA256GzippedEmptyTar is the canonical sha256 digest of
// gzippedEmptyTar
const digestSHA256GzippedEmptyTar = digest.Digest("sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4")
// configManifestBuilder is a type for constructing manifests from an image
// configuration and generic descriptors.
type configManifestBuilder struct {
// bs is a BlobService used to create empty layer tars in the
// blob store if necessary.
bs distribution.BlobService
// pk is the libtrust private key used to sign the final manifest.
pk libtrust.PrivateKey
// configJSON is configuration supplied when the ManifestBuilder was
// created.
configJSON []byte
// ref contains the name and optional tag provided to NewConfigManifestBuilder.
ref reference.Named
// descriptors is the set of descriptors referencing the layers.
descriptors []distribution.Descriptor
// emptyTarDigest is set to a valid digest if an empty tar has been
// put in the blob store; otherwise it is empty.
emptyTarDigest digest.Digest
}
// NewConfigManifestBuilder is used to build new manifests for the current
// schema version from an image configuration and a set of descriptors.
// It takes a BlobService so that it can add an empty tar to the blob store
// if the resulting manifest needs empty layers.
func NewConfigManifestBuilder(bs distribution.BlobService, pk libtrust.PrivateKey, ref reference.Named, configJSON []byte) distribution.ManifestBuilder {
return &configManifestBuilder{
bs: bs,
pk: pk,
configJSON: configJSON,
ref: ref,
}
}
// Build produces a final manifest from the given references
func (mb *configManifestBuilder) Build(ctx context.Context) (m distribution.Manifest, err error) {
type imageRootFS struct {
Type string `json:"type"`
DiffIDs []diffID `json:"diff_ids,omitempty"`
BaseLayer string `json:"base_layer,omitempty"`
}
type imageHistory struct {
Created time.Time `json:"created"`
Author string `json:"author,omitempty"`
CreatedBy string `json:"created_by,omitempty"`
Comment string `json:"comment,omitempty"`
EmptyLayer bool `json:"empty_layer,omitempty"`
}
type imageConfig struct {
RootFS *imageRootFS `json:"rootfs,omitempty"`
History []imageHistory `json:"history,omitempty"`
Architecture string `json:"architecture,omitempty"`
}
var img imageConfig
if err := json.Unmarshal(mb.configJSON, &img); err != nil {
return nil, err
}
if len(img.History) == 0 {
return nil, errors.New("empty history when trying to create schema1 manifest")
}
if len(img.RootFS.DiffIDs) != len(mb.descriptors) {
return nil, fmt.Errorf("number of descriptors and number of layers in rootfs must match: len(%v) != len(%v)", img.RootFS.DiffIDs, mb.descriptors)
}
// Generate IDs for each layer
// For non-top-level layers, create fake V1Compatibility strings that
// fit the format and don't collide with anything else, but don't
// result in runnable images on their own.
type v1Compatibility struct {
ID string `json:"id"`
Parent string `json:"parent,omitempty"`
Comment string `json:"comment,omitempty"`
Created time.Time `json:"created"`
ContainerConfig struct {
Cmd []string
} `json:"container_config,omitempty"`
Author string `json:"author,omitempty"`
ThrowAway bool `json:"throwaway,omitempty"`
}
fsLayerList := make([]FSLayer, len(img.History))
history := make([]History, len(img.History))
parent := ""
layerCounter := 0
for i, h := range img.History[:len(img.History)-1] {
var blobsum digest.Digest
if h.EmptyLayer {
if blobsum, err = mb.emptyTar(ctx); err != nil {
return nil, err
}
} else {
if len(img.RootFS.DiffIDs) <= layerCounter {
return nil, errors.New("too many non-empty layers in History section")
}
blobsum = mb.descriptors[layerCounter].Digest
layerCounter++
}
v1ID := digest.FromBytes([]byte(blobsum.Hex() + " " + parent)).Hex()
if i == 0 && img.RootFS.BaseLayer != "" {
// windows-only baselayer setup
baseID := sha512.Sum384([]byte(img.RootFS.BaseLayer))
parent = fmt.Sprintf("%x", baseID[:32])
}
v1Compatibility := v1Compatibility{
ID: v1ID,
Parent: parent,
Comment: h.Comment,
Created: h.Created,
Author: h.Author,
}
v1Compatibility.ContainerConfig.Cmd = []string{img.History[i].CreatedBy}
if h.EmptyLayer {
v1Compatibility.ThrowAway = true
}
jsonBytes, err := json.Marshal(&v1Compatibility)
if err != nil {
return nil, err
}
reversedIndex := len(img.History) - i - 1
history[reversedIndex].V1Compatibility = string(jsonBytes)
fsLayerList[reversedIndex] = FSLayer{BlobSum: blobsum}
parent = v1ID
}
latestHistory := img.History[len(img.History)-1]
var blobsum digest.Digest
if latestHistory.EmptyLayer {
if blobsum, err = mb.emptyTar(ctx); err != nil {
return nil, err
}
} else {
if len(img.RootFS.DiffIDs) <= layerCounter {
return nil, errors.New("too many non-empty layers in History section")
}
blobsum = mb.descriptors[layerCounter].Digest
}
fsLayerList[0] = FSLayer{BlobSum: blobsum}
dgst := digest.FromBytes([]byte(blobsum.Hex() + " " + parent + " " + string(mb.configJSON)))
// Top-level v1compatibility string should be a modified version of the
// image config.
transformedConfig, err := MakeV1ConfigFromConfig(mb.configJSON, dgst.Hex(), parent, latestHistory.EmptyLayer)
if err != nil {
return nil, err
}
history[0].V1Compatibility = string(transformedConfig)
tag := ""
if tagged, isTagged := mb.ref.(reference.Tagged); isTagged {
tag = tagged.Tag()
}
mfst := Manifest{
Versioned: manifest.Versioned{
SchemaVersion: 1,
},
Name: mb.ref.Name(),
Tag: tag,
Architecture: img.Architecture,
FSLayers: fsLayerList,
History: history,
}
return Sign(&mfst, mb.pk)
}
// emptyTar pushes a compressed empty tar to the blob store if one doesn't
// already exist, and returns its blobsum.
func (mb *configManifestBuilder) emptyTar(ctx context.Context) (digest.Digest, error) {
if mb.emptyTarDigest != "" {
// Already put an empty tar
return mb.emptyTarDigest, nil
}
descriptor, err := mb.bs.Stat(ctx, digestSHA256GzippedEmptyTar)
switch err {
case nil:
mb.emptyTarDigest = descriptor.Digest
return descriptor.Digest, nil
case distribution.ErrBlobUnknown:
// nop
default:
return "", err
}
// Add gzipped empty tar to the blob store
descriptor, err = mb.bs.Put(ctx, "", gzippedEmptyTar)
if err != nil {
return "", err
}
mb.emptyTarDigest = descriptor.Digest
return descriptor.Digest, nil
}
// AppendReference adds a reference to the current ManifestBuilder
func (mb *configManifestBuilder) AppendReference(d distribution.Describable) error {
descriptor := d.Descriptor()
if err := descriptor.Digest.Validate(); err != nil {
return err
}
mb.descriptors = append(mb.descriptors, descriptor)
return nil
}
// References returns the current references added to this builder
func (mb *configManifestBuilder) References() []distribution.Descriptor {
return mb.descriptors
}
// MakeV1ConfigFromConfig creates an legacy V1 image config from image config JSON
func MakeV1ConfigFromConfig(configJSON []byte, v1ID, parentV1ID string, throwaway bool) ([]byte, error) {
// Top-level v1compatibility string should be a modified version of the
// image config.
var configAsMap map[string]*json.RawMessage
if err := json.Unmarshal(configJSON, &configAsMap); err != nil {
return nil, err
}
// Delete fields that didn't exist in old manifest
delete(configAsMap, "rootfs")
delete(configAsMap, "history")
configAsMap["id"] = rawJSON(v1ID)
if parentV1ID != "" {
configAsMap["parent"] = rawJSON(parentV1ID)
}
if throwaway {
configAsMap["throwaway"] = rawJSON(true)
}
return json.Marshal(configAsMap)
}
func rawJSON(value interface{}) *json.RawMessage {
jsonval, err := json.Marshal(value)
if err != nil {
return nil
}
return (*json.RawMessage)(&jsonval)
}