From e341f67b682a51b46b205c489a150c077bf119ce Mon Sep 17 00:00:00 2001
From: MabinGo <bin.ma@huawei.com>
Date: Wed, 12 Aug 2015 02:03:46 +0800
Subject: [PATCH] Add V2 convert to V1 function

---
 utils/digest.go | 130 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 130 insertions(+)
 create mode 100644 utils/digest.go

diff --git a/utils/digest.go b/utils/digest.go
new file mode 100644
index 0000000..75aaf52
--- /dev/null
+++ b/utils/digest.go
@@ -0,0 +1,130 @@
+package utils
+
+import (
+	"bytes"
+	"crypto"
+	"fmt"
+	"hash"
+	"io"
+	"strings"
+
+	"github.com/docker/libtrust"
+)
+
+//port from distribution in order to match the digest that generated by docker client
+
+// Algorithm identifies and implementation of a digester by an identifier.
+// Note the that this defines both the hash algorithm used and the string
+// encoding.
+type Algorithm string
+
+// supported digest types
+const (
+	SHA256         Algorithm = "sha256"           // sha256 with hex encoding
+	SHA384         Algorithm = "sha384"           // sha384 with hex encoding
+	SHA512         Algorithm = "sha512"           // sha512 with hex encoding
+	TarsumV1SHA256 Algorithm = "tarsum+v1+sha256" // supported tarsum version, verification only
+
+	// Canonical is the primary digest algorithm used with the distribution
+	// project. Other digests may be used but this one is the primary storage
+	// digest.
+	Canonical = SHA256
+)
+
+var (
+	// TODO(stevvooe): Follow the pattern of the standard crypto package for
+	// registration of digests. Effectively, we are a registerable set and
+	// common symbol access.
+
+	// algorithms maps values to hash.Hash implementations. Other algorithms
+	// may be available but they cannot be calculated by the digest package.
+	algorithms = map[Algorithm]crypto.Hash{
+		SHA256: crypto.SHA256,
+		SHA384: crypto.SHA384,
+		SHA512: crypto.SHA512,
+	}
+)
+
+// Available returns true if the digest type is available for use. If this
+// returns false, New and Hash will return nil.
+func (a Algorithm) Available() bool {
+	h, ok := algorithms[a]
+	if !ok {
+		return false
+	}
+
+	// check availability of the hash, as well
+	return h.Available()
+}
+
+func (a Algorithm) New() Digester {
+	return &digester{
+		alg:  a,
+		hash: a.Hash(),
+	}
+}
+
+func (a Algorithm) Hash() hash.Hash {
+	if !a.Available() {
+		return nil
+	}
+
+	return algorithms[a].New()
+}
+
+type Digester interface {
+	Hash() hash.Hash // provides direct access to underlying hash instance.
+	Digest() string
+}
+
+// digester provides a simple digester definition that embeds a hasher.
+type digester struct {
+	alg  Algorithm
+	hash hash.Hash
+}
+
+func (d *digester) Hash() hash.Hash {
+	return d.hash
+}
+
+func (d *digester) Digest() string {
+	return string(fmt.Sprintf("%s:%x", d.alg, d.hash.Sum(nil)))
+}
+
+func FromReader(rd io.Reader) (string, error) {
+	digester := Canonical.New()
+
+	if _, err := io.Copy(digester.Hash(), rd); err != nil {
+		return "", err
+	}
+
+	return digester.Digest(), nil
+}
+
+func Payload(data []byte) ([]byte, error) {
+	jsig, err := libtrust.ParsePrettySignature(data, "signatures")
+	if err != nil {
+		return nil, err
+	}
+
+	// Resolve the payload in the manifest.
+	return jsig.Payload()
+}
+
+func DigestManifest(data []byte) (string, error) {
+	p, err := Payload(data)
+	if err != nil {
+		if !strings.Contains(err.Error(), "missing signature key") {
+			return "", err
+		}
+
+		p = data
+	}
+
+	digest, err := FromReader(bytes.NewReader(p))
+	if err != nil {
+		return "", err
+	}
+
+	return digest, err
+}