Move tarsum utilities out of common package

In preparation for removing the common package, the tarsum utilities are being
moved to the more relevant digest package. This functionality will probably go
away in the future, but it's maintained here for the time being.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

digest/digest.go

@@ -10,7 +10,6 @@ import (
 	"regexp"
 	"strings"
 
-	"github.com/docker/distribution/common"
 	"github.com/docker/docker/pkg/tarsum"
 )
 
@@ -105,7 +104,7 @@ func FromBytes(p []byte) (Digest, error) {
 func (d Digest) Validate() error {
 	s := string(d)
 	// Common case will be tarsum
-	_, err := common.ParseTarSum(s)
+	_, err := ParseTarSum(s)
 	if err == nil {
 		return nil
 	}

digest/tarsum.go

@@ -1,4 +1,4 @@
-package common
+package digest
 
 import (
 	"fmt"

digest/tarsum_test.go

@@ -1,4 +1,4 @@
-package common
+package digest
 
 import (
 	"reflect"

storage/paths.go

@@ -5,7 +5,6 @@ import (
 	"path"
 	"strings"
 
-	"github.com/docker/distribution/common"
 	"github.com/docker/distribution/digest"
 )
 
@@ -189,7 +188,7 @@ func digestPathComoponents(dgst digest.Digest) ([]string, error) {
 		hex,
 	}
 
-	if tsi, err := common.ParseTarSum(dgst.String()); err == nil {
+	if tsi, err := digest.ParseTarSum(dgst.String()); err == nil {
 		// We have a tarsum!
 		version := tsi.Version
 		if version == "" {