1 files changed, 253 insertions, 0 deletions
diff --git a/image/cache/cache.go b/image/cache/cache.go
new file mode 100644
index 0000000..e074beb
--- /dev/null
+++ b/image/cache/cache.go
@@ -0,0 +1,253 @@
+package cache
+
+import (
+	"encoding/json"
+	"fmt"
+	"reflect"
+	"strings"
+
+	containertypes "github.com/docker/docker/api/types/container"
+	"github.com/docker/docker/dockerversion"
+	"github.com/docker/docker/image"
+	"github.com/docker/docker/layer"
+	"github.com/pkg/errors"
+)
+
+// NewLocal returns a local image cache, based on parent chain
+func NewLocal(store image.Store) *LocalImageCache {
+	return &LocalImageCache{
+		store: store,
+	}
+}
+
+// LocalImageCache is cache based on parent chain.
+type LocalImageCache struct {
+	store image.Store
+}
+
+// GetCache returns the image id found in the cache
+func (lic *LocalImageCache) GetCache(imgID string, config *containertypes.Config) (string, error) {
+	return getImageIDAndError(getLocalCachedImage(lic.store, image.ID(imgID), config))
+}
+
+// New returns an image cache, based on history objects
+func New(store image.Store) *ImageCache {
+	return &ImageCache{
+		store:           store,
+		localImageCache: NewLocal(store),
+	}
+}
+
+// ImageCache is cache based on history objects. Requires initial set of images.
+type ImageCache struct {
+	sources         []*image.Image
+	store           image.Store
+	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) (string, error) {
+	imgID, err := ic.localImageCache.GetCache(parentID, cfg)
+	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])
+	if layer := getLayerForHistoryIndex(target, lenHistory); layer != "" {
+		rootFS.Append(layer)
+	}
+
+	config, err := json.Marshal(&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,
+	})
+	if err != nil {
+		return "", errors.Wrap(err, "failed to marshal image config")
+	}
+
+	imgID, err := ic.store.Create(config)
+	if err != nil {
+		return "", errors.Wrap(err, "failed to create cache image")
+	}
+
+	if parent != nil {
+		if err := ic.store.SetParent(imgID, parent.ID()); err != nil {
+			return "", errors.Wrapf(err, "failed to set parent for %v to %v", target.ID(), parent.ID())
+		}
+	}
+	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 image.Store, imgID image.ID, config *containertypes.Config) (*image.Image, error) {
+	// Loop on the children of the given image and check the config
+	getMatch := func(siblings []image.ID) (*image.Image, error) {
+		var match *image.Image
+		for _, id := range siblings {
+			img, err := imageStore.Get(id)
+			if err != nil {
+				return nil, fmt.Errorf("unable to find image %q", id)
+			}
+
+			if compare(&img.ContainerConfig, config) {
+				// check for the most up to date match
+				if match == nil || match.Created.Before(img.Created) {
+					match = img
+				}
+			}
+		}
+		return match, nil
+	}
+
+	// In this case, this is `FROM scratch`, which isn't an actual image.
+	if imgID == "" {
+		images := imageStore.Map()
+		var siblings []image.ID
+		for id, img := range images {
+			if img.Parent == imgID {
+				siblings = append(siblings, id)
+			}
+		}
+		return getMatch(siblings)
+	}
+
+	// find match from child images
+	siblings := imageStore.Children(imgID)
+	return getMatch(siblings)
+}