use sync.OnceValue for various regular expressions

normalize.go

@@ -64,7 +64,7 @@ type normalizedNamed interface {
 //		_ "crypto/sha256"
 //	)
 func ParseNormalizedNamed(s string) (Named, error) {
-	if ok := anchoredIdentifierRegexp.MatchString(s); ok {
+	if ok := anchoredIdentifierRegexp().MatchString(s); ok {
 		return nil, fmt.Errorf("invalid repository name (%s), cannot specify 64-byte hexadecimal strings", s)
 	}
 	domain, remainder := splitDockerDomain(s)
@@ -274,7 +274,7 @@ func TagNameOnly(ref Named) Named {
 //		_ "crypto/sha256"
 //	)
 func ParseAnyReference(ref string) (Reference, error) {
-	if ok := anchoredIdentifierRegexp.MatchString(ref); ok {
+	if ok := anchoredIdentifierRegexp().MatchString(ref); ok {
 		return digestReference("sha256:" + ref), nil
 	}
 	if dgst, err := digest.Parse(ref); err == nil {

reference.go

@@ -207,7 +207,7 @@ func Path(named Named) (name string) {
 // If no valid hostname is found, the hostname is empty and the full value
 // is returned as name
 func splitDomain(name string) (string, string) {
-	match := anchoredNameRegexp.FindStringSubmatch(name)
+	match := anchoredNameRegexp().FindStringSubmatch(name)
 	if len(match) != 3 {
 		return "", name
 	}
@@ -232,9 +232,9 @@ func Parse(s string) (Reference, error) {
 		return nil, ErrNameEmpty
 	}
 
-	matches := referenceRegexp.FindStringSubmatch(s)
+	matches := referenceRegexp().FindStringSubmatch(s)
 	if matches == nil {
-		if sl := strings.ToLower(s); sl != s && referenceRegexp.FindStringSubmatch(sl) != nil {
+		if sl := strings.ToLower(s); sl != s && referenceRegexp().FindStringSubmatch(sl) != nil {
 			// Succeeds when lower-casing, so input contains an invalid repository name.
 			return nil, ErrNameContainsUppercase
 		}
@@ -243,7 +243,7 @@ func Parse(s string) (Reference, error) {
 
 	var repo repository
 
-	nameMatch := anchoredNameRegexp.FindStringSubmatch(matches[1])
+	nameMatch := anchoredNameRegexp().FindStringSubmatch(matches[1])
 	if len(nameMatch) == 3 {
 		repo.domain = nameMatch[1]
 		repo.path = nameMatch[2]
@@ -294,7 +294,7 @@ func ParseNamed(s string) (Named, error) {
 // WithName returns a named object representing the given string. If the input
 // is invalid ErrReferenceInvalidFormat will be returned.
 func WithName(name string) (Named, error) {
-	match := anchoredNameRegexp.FindStringSubmatch(name)
+	match := anchoredNameRegexp().FindStringSubmatch(name)
 	if match == nil || len(match) != 3 {
 		return nil, ErrReferenceInvalidFormat
 	}
@@ -312,7 +312,7 @@ func WithName(name string) (Named, error) {
 // WithTag combines the name from "name" and the tag from "tag" to form a
 // reference incorporating both the name and the tag.
 func WithTag(name Named, tag string) (NamedTagged, error) {
-	if !anchoredTagRegexp.MatchString(tag) {
+	if !anchoredTagRegexp().MatchString(tag) {
 		return nil, ErrTagInvalidFormat
 	}
 	var repo repository
@@ -338,7 +338,7 @@ func WithTag(name Named, tag string) (NamedTagged, error) {
 // WithDigest combines the name from "name" and the digest from "digest" to form
 // a reference incorporating both the name and the digest.
 func WithDigest(name Named, digest digest.Digest) (Canonical, error) {
-	if !anchoredDigestRegexp.MatchString(digest.String()) {
+	if !anchoredDigestRegexp().MatchString(digest.String()) {
 		return nil, ErrDigestInvalidFormat
 	}
 	var repo repository

regexp.go

@@ -3,6 +3,7 @@ package reference
 import (
 	"regexp"
 	"strings"
+	"sync"
 )
 
 // DigestRegexp matches well-formed digests, including algorithm (e.g. "sha256:<encoded>").
@@ -31,7 +32,7 @@ var NameRegexp = regexp.MustCompile(namePat)
 // ReferenceRegexp is the full supported format of a reference. The regexp
 // is anchored and has capturing groups for name, tag, and digest
 // components.
-var ReferenceRegexp = referenceRegexp
+var ReferenceRegexp = referenceRegexp()
 
 // TagRegexp matches valid tag names. From [docker/docker:graph/tags.go].
 //
@@ -112,15 +113,21 @@ var (
 	// referenceRegexp is the full supported format of a reference. The regexp
 	// is anchored and has capturing groups for name, tag, and digest
 	// components.
-	referenceRegexp = regexp.MustCompile(referencePat)
+	referenceRegexp = sync.OnceValue(func() *regexp.Regexp {
+		return regexp.MustCompile(referencePat)
+	})
 
 	// anchoredTagRegexp matches valid tag names, anchored at the start and
 	// end of the matched string.
-	anchoredTagRegexp = regexp.MustCompile(anchored(tag))
+	anchoredTagRegexp = sync.OnceValue(func() *regexp.Regexp {
+		return regexp.MustCompile(anchored(tag))
+	})
 
 	// anchoredDigestRegexp matches valid digests, anchored at the start and
 	// end of the matched string.
-	anchoredDigestRegexp = regexp.MustCompile(anchored(digestPat))
+	anchoredDigestRegexp = sync.OnceValue(func() *regexp.Regexp {
+		return regexp.MustCompile(anchored(digestPat))
+	})
 
 	// pathComponent restricts path-components to start with an alphanumeric
 	// character, with following parts able to be separated by a separator
@@ -136,14 +143,18 @@ var (
 
 	// anchoredNameRegexp is used to parse a name value, capturing the
 	// domain and trailing components.
-	anchoredNameRegexp = regexp.MustCompile(anchoredNamePat)
-	anchoredNamePat    = anchored(optional(capture(domainAndPort), `/`), capture(remoteName))
+	anchoredNameRegexp = sync.OnceValue(func() *regexp.Regexp {
+		return regexp.MustCompile(anchoredNamePat)
+	})
+	anchoredNamePat = anchored(optional(capture(domainAndPort), `/`), capture(remoteName))
 
 	referencePat = anchored(capture(namePat), optional(`:`, capture(tag)), optional(`@`, capture(digestPat)))
 
 	// anchoredIdentifierRegexp is used to check or match an
 	// identifier value, anchored at start and end of string.
-	anchoredIdentifierRegexp = regexp.MustCompile(anchored(identifier))
+	anchoredIdentifierRegexp = sync.OnceValue(func() *regexp.Regexp {
+		return regexp.MustCompile(anchored(identifier))
+	})
 )
 
 // optional wraps the expression in a non-capturing group and makes the

regexp_test.go

@@ -179,7 +179,7 @@
 
 func TestFullNameRegexp(t *testing.T) {
 	t.Parallel()
-	if n := anchoredNameRegexp.NumSubexp(); n != 2 {
+	if n := anchoredNameRegexp().NumSubexp(); n != 2 {
 		t.Fatalf("anchored name regexp should have two submatches: %v, %v != 2", anchoredNamePat, n)
 	}
 
@@ -471,14 +471,14 @@
 		tc := tc
 		t.Run(tc.input, func(t *testing.T) {
 			t.Parallel()
-			checkRegexp(t, anchoredNameRegexp, tc)
+			checkRegexp(t, anchoredNameRegexp(), tc)
 		})
 	}
 }
 
 func TestReferenceRegexp(t *testing.T) {
 	t.Parallel()
-	if n := referenceRegexp.NumSubexp(); n != 3 {
+	if n := referenceRegexp().NumSubexp(); n != 3 {
 		t.Fatalf("anchored name regexp should have three submatches: %v, %v != 3", referencePat, n)
 	}
 
@@ -545,7 +545,7 @@
 		tc := tc
 		t.Run(tc.input, func(t *testing.T) {
 			t.Parallel()
 			checkRegexp(t, referenceRegexp, tc)
 		})
 	}
 }
@@ -581,7 +581,7 @@
 		tc := tc
 		t.Run(tc.input, func(t *testing.T) {
 			t.Parallel()
-			match := anchoredIdentifierRegexp.MatchString(tc.input)
+			match := anchoredIdentifierRegexp().MatchString(tc.input)
 			if match != tc.match {
 				t.Errorf("Expected match=%t, got %t", tc.match, match)
 			}