image/cache/cache.go
package cache // import "github.com/docker/docker/image/cache"
import (
"context"
"fmt"
"reflect"
"strings"
"github.com/containerd/log"
containertypes "github.com/docker/docker/api/types/container"
"github.com/docker/docker/builder"
"github.com/docker/docker/dockerversion"
"github.com/docker/docker/image"
"github.com/docker/docker/layer"
ocispec "github.com/opencontainers/image-spec/specs-go/v1"
"github.com/pkg/errors"
)
type ImageCacheStore interface {
Get(image.ID) (*image.Image, error)
GetByRef(ctx context.Context, refOrId string) (*image.Image, error)
SetParent(target, parent image.ID) error
GetParent(target image.ID) (image.ID, error)
Create(parent *image.Image, image image.Image, extraLayer layer.DiffID) (image.ID, error)
IsBuiltLocally(id image.ID) (bool, error)
Children(id image.ID) []image.ID
}
func New(ctx context.Context, store ImageCacheStore, cacheFrom []string) (builder.ImageCache, error) {
local := &LocalImageCache{store: store}
if len(cacheFrom) == 0 {
return local, nil
}
cache := &ImageCache{
store: store,
localImageCache: local,
}
for _, ref := range cacheFrom {
img, err := store.GetByRef(ctx, ref)
if err != nil {
if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
return nil, err
}
log.G(ctx).Warnf("Could not look up %s for cache resolution, skipping: %+v", ref, err)
continue
}
cache.Populate(img)
}
return cache, nil
}
// LocalImageCache is cache based on parent chain.
type LocalImageCache struct {
store ImageCacheStore
}
// GetCache returns the image id found in the cache
func (lic *LocalImageCache) GetCache(imgID string, config *containertypes.Config, platform ocispec.Platform) (string, error) {
return getImageIDAndError(getLocalCachedImage(lic.store, image.ID(imgID), config, platform))
}
// ImageCache is cache based on history objects. Requires initial set of images.
type ImageCache struct {
sources []*image.Image
store ImageCacheStore
localImageCache *LocalImageCache
}
// Populate adds an image to the cache (to be queried later)
func (ic *ImageCache) Populate(image *image.Image) {
ic.sources = append(ic.sources, image)
}
// GetCache returns the image id found in the cache
func (ic *ImageCache) GetCache(parentID string, cfg *containertypes.Config, platform ocispec.Platform) (string, error) {
imgID, err := ic.localImageCache.GetCache(parentID, cfg, platform)
if err != nil {
return "", err
}
if imgID != "" {
for _, s := range ic.sources {
if ic.isParent(s.ID(), image.ID(imgID)) {
return imgID, nil
}
}
}
var parent *image.Image
lenHistory := 0
if parentID != "" {
parent, err = ic.store.Get(image.ID(parentID))
if err != nil {
return "", errors.Wrapf(err, "unable to find image %v", parentID)
}
lenHistory = len(parent.History)
}
for _, target := range ic.sources {
if !isValidParent(target, parent) || !isValidConfig(cfg, target.History[lenHistory]) {
continue
}
if len(target.History)-1 == lenHistory { // last
if parent != nil {
if err := ic.store.SetParent(target.ID(), parent.ID()); err != nil {
return "", errors.Wrapf(err, "failed to set parent for %v to %v", target.ID(), parent.ID())
}
}
return target.ID().String(), nil
}
imgID, err := ic.restoreCachedImage(parent, target, cfg)
if err != nil {
return "", errors.Wrapf(err, "failed to restore cached image from %q to %v", parentID, target.ID())
}
ic.sources = []*image.Image{target} // avoid jumping to different target, tuned for safety atm
return imgID.String(), nil
}
return "", nil
}
func (ic *ImageCache) restoreCachedImage(parent, target *image.Image, cfg *containertypes.Config) (image.ID, error) {
var history []image.History
rootFS := image.NewRootFS()
lenHistory := 0
if parent != nil {
history = parent.History
rootFS = parent.RootFS
lenHistory = len(parent.History)
}
history = append(history, target.History[lenHistory])
layer := getLayerForHistoryIndex(target, lenHistory)
if layer != "" {
rootFS.Append(layer)
}
restoredImg := image.Image{
V1Image: image.V1Image{
DockerVersion: dockerversion.Version,
Config: cfg,
Architecture: target.Architecture,
OS: target.OS,
Author: target.Author,
Created: history[len(history)-1].Created,
},
RootFS: rootFS,
History: history,
OSFeatures: target.OSFeatures,
OSVersion: target.OSVersion,
}
imgID, err := ic.store.Create(parent, restoredImg, layer)
if err != nil {
return "", errors.Wrap(err, "failed to create cache image")
}
return imgID, nil
}
func (ic *ImageCache) isParent(imgID, parentID image.ID) bool {
nextParent, err := ic.store.GetParent(imgID)
if err != nil {
return false
}
if nextParent == parentID {
return true
}
return ic.isParent(nextParent, parentID)
}
func getLayerForHistoryIndex(image *image.Image, index int) layer.DiffID {
layerIndex := 0
for i, h := range image.History {
if i == index {
if h.EmptyLayer {
return ""
}
break
}
if !h.EmptyLayer {
layerIndex++
}
}
return image.RootFS.DiffIDs[layerIndex] // validate?
}
func isValidConfig(cfg *containertypes.Config, h image.History) bool {
// todo: make this format better than join that loses data
return strings.Join(cfg.Cmd, " ") == h.CreatedBy
}
func isValidParent(img, parent *image.Image) bool {
if len(img.History) == 0 {
return false
}
if parent == nil || len(parent.History) == 0 && len(parent.RootFS.DiffIDs) == 0 {
return true
}
if len(parent.History) >= len(img.History) {
return false
}
if len(parent.RootFS.DiffIDs) > len(img.RootFS.DiffIDs) {
return false
}
for i, h := range parent.History {
if !reflect.DeepEqual(h, img.History[i]) {
return false
}
}
for i, d := range parent.RootFS.DiffIDs {
if d != img.RootFS.DiffIDs[i] {
return false
}
}
return true
}
func getImageIDAndError(img *image.Image, err error) (string, error) {
if img == nil || err != nil {
return "", err
}
return img.ID().String(), nil
}
// getLocalCachedImage returns the most recent created image that is a child
// of the image with imgID, that had the same config when it was
// created. nil is returned if a child cannot be found. An error is
// returned if the parent image cannot be found.
func getLocalCachedImage(imageStore ImageCacheStore, parentID image.ID, config *containertypes.Config, platform ocispec.Platform) (*image.Image, error) {
if config == nil {
return nil, nil
}
var match *image.Image
for _, id := range imageStore.Children(parentID) {
img, err := imageStore.Get(id)
if err != nil {
return nil, fmt.Errorf("unable to find image %q", id)
}
builtLocally, err := imageStore.IsBuiltLocally(id)
if err != nil {
log.G(context.TODO()).WithFields(log.Fields{
"error": err,
"id": id,
}).Warn("failed to check if image was built locally")
continue
}
if !builtLocally {
continue
}
imgPlatform := img.Platform()
// Discard old linux/amd64 images with empty platform.
if imgPlatform.OS == "" && imgPlatform.Architecture == "" {
continue
}
if !comparePlatform(platform, imgPlatform) {
continue
}
if compare(&img.ContainerConfig, config) {
// check for the most up to date match
if img.Created != nil && (match == nil || match.Created.Before(*img.Created)) {
match = img
}
}
}
return match, nil
}