Use accelerated link verification using only e-tag

links.go

@@ -4,6 +4,8 @@ import (
 	"errors"
 	"fmt"
 	"strings"
+	"crypto/md5"
+	"encoding/hex"
 )
 func analyzeLink(args []string) (string, error) {
@@ -40,3 +42,26 @@ func readLink(path string) (string, error) {
 	return link, nil
 }
+
+func verifyLink(link string, info fileInfo) error {
+	// If we have e-tag, let's verify e-tag
+	if info.etag != "" {
+		content := "sha256:" + link
+		hash := md5.Sum([]byte(content))
+		hex := hex.EncodeToString(hash[:])
+		if info.etag == hex {
+			return nil
+		}
+	}
+
+	readed, err := readLink(info.path)
+	if err != nil {
+		return err
+	}
+
+	if readed != link {
+		return fmt.Errorf("readed link for %s is not equal %s", link, readed)
+	}
+
+	return nil
+}

repositories.go

@@ -131,15 +131,11 @@ func (r *repositoryData) addLayer(args []string, info fileInfo) error {
 		return err
 	}
-	readLink, err := readLink(r.layerLinkPath(link))
+	err = verifyLink(link, info)
 	if err != nil {
 		return err
 	}
-	if readLink != link {
-		return fmt.Errorf("read link for %s is not equal %s", link, readLink)
-	}
-
 	r.layers[link] = 0
 	return nil
 }
@@ -151,15 +147,11 @@ func (r *repositoryData) addManifestRevision(args []string, info fileInfo) error
 		return err
 	}
-	readLink, err := readLink(r.manifestRevisionPath(link))
+	err = verifyLink(link, info)
 	if err != nil {
 		return err
 	}
-	if readLink != link {
-		return fmt.Errorf("read link for %s is not equal %s", link, readLink)
-	}
-
 	r.manifests[link] = 0
 	return nil
 }

tags.go

 package main
 import (
-	"fmt"
 	"path/filepath"
 )
@@ -54,15 +53,11 @@ func (t *tag) addVersion(args []string, info fileInfo) error {
 		return err
 	}
-	readLink, err := readLink(t.versionLinkPath(link))
+	err = verifyLink(link, info)
 	if err != nil {
 		return err
 	}
-	if readLink != link {
-		return fmt.Errorf("read link for %s is not equal %s", link, readLink)
-	}
-
 	t.versions = append(t.versions, link)
 	return nil
 }