1 files changed, 149 insertions, 0 deletions
diff --git a/get-docker-cache-id.go b/get-docker-cache-id.go
new file mode 100644
index 000000000000..cbaf367cda6a
--- /dev/null
+++ b/get-docker-cache-id.go
@@ -0,0 +1,149 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"strings"
+	"io/ioutil"
+)
+
+const DOCKER_DB_DIR = "/var/lib/docker/image/btrfs"
+const REPO_FILE = DOCKER_DB_DIR + "/repositories.json"
+const CFG_FILE = "/etc/docker-btrfs.json"
+
+func getImageTag() (string, string) {
+	buf, err := ioutil.ReadFile(CFG_FILE)
+	if err != nil {
+		panic(err)
+	}
+	var dat map[string]interface{}
+	err = json.Unmarshal(buf, &dat)
+	if err != nil {
+		panic(err)
+	}
+	return dat["docker_image"].(string), dat["docker_tag"].(string)
+}
+
+func getImageId(image string, tag string) string {
+	buf, err := ioutil.ReadFile(REPO_FILE)
+	if err != nil {
+		panic(err)
+	}
+	var dat map[string]interface{}
+	err = json.Unmarshal(buf, &dat)
+	if err != nil {
+		panic(err)
+	}
+	repositories := dat["Repositories"].(map[string]interface{})
+	imageTags := repositories[image].(map[string]interface{})
+	return imageTags[image+":"+tag].(string)
+}
+
+func getDiffIds(imgId string) []string {
+	imgPath := strings.Replace(imgId, ":", "/", 1)
+	buf, err := ioutil.ReadFile(DOCKER_DB_DIR + "/imagedb/content/" + imgPath)
+	if err != nil {
+		panic(err)
+	}
+	var dat map[string]interface{}
+	err = json.Unmarshal(buf, &dat)
+	if err != nil {
+		panic(err)
+	}
+	rootfs := dat["rootfs"].(map[string]interface{})
+	diffIdsInterface := rootfs["diff_ids"].([]interface{})
+	diffIdsStr := make([]string, len(diffIdsInterface))
+	for i, v := range diffIdsInterface {
+		diffIdsStr[i] = strings.Replace(v.(string), "sha256:", "", 1)
+	}
+	return diffIdsStr
+}
+
+type Node struct {
+	parent string
+	id string
+	diff string
+	cache string
+}
+
+func getNode(id string) Node {
+	var node Node
+
+	node.id = id
+
+	buf, err := ioutil.ReadFile(DOCKER_DB_DIR + "/layerdb/sha256/" + id + "/cache-id")
+	if err != nil {
+		panic(err)
+	}
+	node.cache = strings.Replace(string(buf), "sha256:", "", 1)
+
+	buf, err = ioutil.ReadFile(DOCKER_DB_DIR + "/layerdb/sha256/" + id + "/diff")
+	if err != nil {
+		panic(err)
+	}
+	node.diff = strings.Replace(string(buf), "sha256:", "", 1)
+
+	buf, err = ioutil.ReadFile(DOCKER_DB_DIR + "/layerdb/sha256/" + id + "/parent")
+	if os.IsNotExist(err) {
+		node.parent = ""
+	} else if err != nil {
+		panic(err)
+	} else {
+		node.parent = strings.Replace(string(buf), "sha256:", "", 1)
+	}
+	return node
+}
+
+func readLayerInfo() map[string]Node {
+	files, err := ioutil.ReadDir(DOCKER_DB_DIR + "/layerdb/sha256/")
+    if err != nil {
+        panic(err)
+	}
+	nodes := make(map[string]Node)
+	for i, _ := range files {
+		id := files[i].Name()
+		nodes[id] = getNode(id)
+	}
+	return nodes
+}
+
+func searchForCacheId(diffIds []string, layers map[string]Node) string {
+	candidates := make([]string, 0, len(layers))
+	last := diffIds[len(diffIds)-1]
+	for i, v := range layers {
+		if v.diff == last {
+			sz := len(candidates)
+			candidates = candidates[:sz+1]
+			candidates[sz] = i
+		}
+	}
+	candidatesCurrent := make([]string, len(candidates))
+	for i, v := range candidates {
+		candidatesCurrent[i] = layers[v].parent
+	}
+	for i := len(diffIds)-2; i>=0; i-- {
+		for j := 0; j < len(candidates); {
+			if layers[candidatesCurrent[j]].diff == diffIds[i] {
+				candidatesCurrent[j] = layers[candidatesCurrent[j]].parent
+				j++;
+			} else {
+				oldLen := len(candidates)
+				candidates[j] = candidates[oldLen-1]
+				candidatesCurrent[j] = candidatesCurrent[oldLen-1]
+				candidates = candidates[:oldLen-1]
+				candidatesCurrent = candidatesCurrent[:oldLen - 1]
+			}
+		}
+	}
+	return candidates[0]
+}
+
+func main() {
+	image, tag := getImageTag()
+	imgId := getImageId(image, tag)
+	diffIds := getDiffIds(imgId)
+	layers := readLayerInfo()
+	cacheId := searchForCacheId(diffIds, layers)
+	fmt.Print(cacheId)
+}