feat: Add MaybeTagStr method to Digest type

pkg/name/digest.go

@@ -31,6 +31,7 @@ type Digest struct {
 	Repository
 	digest   string
 	original string
+	tag      *string
 }
 
 var _ Reference = (*Digest)(nil)
@@ -64,6 +65,15 @@ func (d Digest) String() string {
 	return d.original
 }
 
+// MaybeTagStr returns the tag string (if one was provided).  Use bool return value to determine if a tag was present.
+func (d Digest) MaybeTagStr() (string, bool) {
+	if d.tag != nil {
+		return *d.tag, true
+	} else {
+		return "", false
+	}
+}
+
 // MarshalJSON formats the digest into a string for JSON serialization.
 func (d Digest) MarshalJSON() ([]byte, error) {
 	return json.Marshal(d.String())
@@ -116,8 +126,17 @@ func NewDigest(name string, opts ...Option) (Digest, error) {
 		return Digest{}, err
 	}
 
+	var tagStr *string
 	tag, err := NewTag(base, opts...)
 	if err == nil {
+
+		// Check and see if the TagStr was provided in the original base
+		// If not then it's a default tag and should be ignored
+		maybeTag := tag.TagStr()
+		if strings.HasSuffix(base, tagDelim+maybeTag) {
+			tagStr = &maybeTag
+		}
+
 		base = tag.Repository.Name()
 	}
 
@@ -129,5 +148,6 @@ func NewDigest(name string, opts ...Option) (Digest, error) {
 		Repository: repo,
 		digest:     dig,
 		original:   name,
+		tag:        tagStr,
 	}, nil
 }

pkg/name/digest_test.go

@@ -132,6 +132,15 @@ func TestDigestComponents(t *testing.T) {
 	if actualDigest != validDigest {
 		t.Errorf("DigestStr() was incorrect for %v. Wanted: `%s` Got: `%s`", digest, validDigest, actualDigest)
 	}
+
+	expectedTagStr := ""
+	expectedOk := false
+
+	tagStr, ok := digest.MaybeTagStr()
+	if tagStr != expectedTagStr || ok != expectedOk {
+		t.Errorf("MaybeTagStr() was incorrect for %v. Wanted: (`%s`, `%t`) Got: (`%s`, `%t`)", digest, expectedTagStr, expectedOk, tagStr, ok)
+	}
+
 }
 
 func TestDigestScopes(t *testing.T) {
@@ -154,6 +163,46 @@ func TestDigestScopes(t *testing.T) {
 	}
 }
 
+func TestMaybeTagStr(t *testing.T) {
+	t.Parallel()
+
+	testRegistry := "gcr.io"
+	testRepo := "project-id/image"
+	testTag := "1.0"
+
+	validations := map[string]Option{"strict": StrictValidation, "weak": WeakValidation}
+
+	digestNameStrWithTag := testRegistry + "/" + testRepo + ":" + testTag + "@" + validDigest
+	for valName, opt := range validations {
+		digest, err := NewDigest(digestNameStrWithTag, opt)
+		if err != nil {
+			t.Fatalf("`%s` should be a valid Digest name with validation: `%s`, got error: %v", digestNameStrWithTag, valName, err)
+		}
+
+		tagStr, ok := digest.MaybeTagStr()
+		expectedTagStr := testTag
+		expectedOk := true
+		if tagStr != expectedTagStr || ok != expectedOk {
+			t.Errorf("MaybeTagStr() was incorrect for %v with validation: `%s`. Wanted: (`%s`, `%t`) Got: (`%s`, `%t`)", digest, valName, expectedTagStr, expectedOk, tagStr, ok)
+		}
+	}
+
+	digestNameStrWithoutTag := testRegistry + "/" + testRepo + "@" + validDigest
+	for valName, opt := range validations {
+		digest, err := NewDigest(digestNameStrWithoutTag, opt)
+		if err != nil {
+			t.Fatalf("`%s` should be a valid Digest name with validation: `%s`, got error: %v", digestNameStrWithoutTag, valName, err)
+		}
+
+		tagStr, ok := digest.MaybeTagStr()
+		expectedTagStr := ""
+		expectedOk := false
+		if tagStr != expectedTagStr || ok != expectedOk {
+			t.Errorf("MaybeTagStr() was incorrect for %v with validation: `%s`. Wanted: (`%s`, `%t`) Got: (`%s`, `%t`)", digest, valName, expectedTagStr, expectedOk, tagStr, ok)
+		}
+	}
+}
+
 func TestJSON(t *testing.T) {
 	t.Parallel()
 	digestNameStr := "gcr.io/project-id/image@" + validDigest