Extract shared NormalizeAlnum into pkg/strutil

The alphanumeric-normalisation helper was duplicated verbatim in the
common-third-party owned-domains resolver and the cookiebanner tracker
mapping worker. Hoist it into a new dependency-free strutil package so
both call sites share one implementation and one test.

Signed-off-by: Émile Ré <emile@probo.com>

pkg/cookiebanner/tracker_mapping_agent_test.go

@@ -130,32 +130,6 @@ func TestNameIsCookieDatabaseAggregator(t *testing.T) {
 	}
 }
 
-func TestNormalizeAlnum(t *testing.T) {
-	t.Parallel()
-
-	tests := []struct {
-		name     string
-		input    string
-		expected string
-	}{
-		{name: "letters lowercased", input: "Letaido", expected: "letaido"},
-		{name: "strips punctuation and spaces", input: "letaido.com - Inc", expected: "letaidocominc"},
-		{name: "keeps digits", input: "auth0", expected: "auth0"},
-		{name: "empty", input: "", expected: ""},
-		{name: "only punctuation", input: "-_.:", expected: ""},
-	}
-
-	for _, tt := range tests {
-		t.Run(
-			tt.name,
-			func(t *testing.T) {
-				t.Parallel()
-				assert.Equal(t, tt.expected, normalizeAlnum(tt.input))
-			},
-		)
-	}
-}
-
 func TestBuildAgentPrompt(t *testing.T) {
 	t.Parallel()
 

pkg/cookiebanner/tracker_mapping_worker.go

@@ -28,6 +28,7 @@ import (
 	"go.probo.inc/probo/pkg/coredata"
 	"go.probo.inc/probo/pkg/gid"
 	"go.probo.inc/probo/pkg/llm"
+	"go.probo.inc/probo/pkg/strutil"
 	"go.probo.inc/probo/pkg/thirdparty"
 	"go.probo.inc/probo/pkg/uri"
 )
@@ -715,15 +716,15 @@ func nameMatchesSiteDomain(name, siteOrigin string) bool {
 		return false
 	}
 
-	normalizedName := normalizeAlnum(name)
+	normalizedName := strutil.NormalizeAlnum(name)
 	if normalizedName == "" {
 		return false
 	}
 
 	label, _, _ := strings.Cut(domain, ".")
 
-	return normalizedName == normalizeAlnum(domain) ||
+	return normalizedName == strutil.NormalizeAlnum(domain) ||
-		normalizedName == normalizeAlnum(label)
+		normalizedName == strutil.NormalizeAlnum(label)
 }
 
 // cookieDatabaseAggregators holds alphanumeric-normalised names of pure
@@ -746,18 +747,18 @@ var cookieDatabaseAggregators = map[string]struct{}{
 // is a known cookie-database directory operator that must never be
 // attributed a tracker. The agent may return either a brand name
 // ("Cookiepedia") or a domain form ("cookiedatabase.org"); the latter
-// would survive a plain normalised lookup because normalizeAlnum folds
+// would survive a plain normalised lookup because NormalizeAlnum folds
 // the eTLD into the key (e.g. "cookiedatabaseorg"). To catch both forms
 // the candidate is also reduced to its primary domain label before the
 // alphanumeric-normalised lookup. The comparison is alphanumeric-
 // normalised so spacing, punctuation, and casing differences do not
 // matter.
 func nameIsCookieDatabaseAggregator(name string) bool {
-	if _, ok := cookieDatabaseAggregators[normalizeAlnum(name)]; ok {
+	if _, ok := cookieDatabaseAggregators[strutil.NormalizeAlnum(name)]; ok {
 		return true
 	}
 
-	label := normalizeAlnum(uri.DomainLabel(name))
+	label := strutil.NormalizeAlnum(uri.DomainLabel(name))
 	if label == "" {
 		return false
 	}
@@ -767,22 +768,6 @@ func nameIsCookieDatabaseAggregator(name string) bool {
 	return ok
 }
 
-// normalizeAlnum lowercases s and keeps only ASCII letters and digits,
-// so vendor names and domains can be compared free of spacing,
-// punctuation, and casing differences (e.g. "Letaido" and "letaido.com"
-// both reduce to a comparable form).
-func normalizeAlnum(s string) string {
-	var b strings.Builder
-
-	for _, r := range strings.ToLower(s) {
-		if (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9') {
-			b.WriteRune(r)
-		}
-	}
-
-	return b.String()
-}
-
 // persistAgentIdentification writes a confident agent identification:
 // it resolves or creates the catalog third party and upserts the
 // catalog pattern row that links to it. It runs inside the caller's

pkg/strutil/strutil.go

@@ -0,0 +1,35 @@
+// Copyright (c) 2026 Probo Inc <hello@probo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+// Package strutil holds small, dependency-free string helpers shared
+// across packages.
+package strutil
+
+import "strings"
+
+// NormalizeAlnum lowercases s and keeps only ASCII letters and digits, so
+// vendor names and domains can be compared free of spacing, punctuation,
+// and casing differences (e.g. "Letaido" and "letaido.com" both reduce to
+// a comparable form).
+func NormalizeAlnum(s string) string {
+	var b strings.Builder
+
+	for _, r := range strings.ToLower(s) {
+		if (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9') {
+			b.WriteRune(r)
+		}
+	}
+
+	return b.String()
+}

pkg/strutil/strutil_test.go

@@ -0,0 +1,48 @@
+// Copyright (c) 2026 Probo Inc <hello@probo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package strutil_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"go.probo.inc/probo/pkg/strutil"
+)
+
+func TestNormalizeAlnum(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name     string
+		input    string
+		expected string
+	}{
+		{name: "letters lowercased", input: "Letaido", expected: "letaido"},
+		{name: "strips punctuation and spaces", input: "letaido.com - Inc", expected: "letaidocominc"},
+		{name: "keeps digits", input: "auth0", expected: "auth0"},
+		{name: "empty", input: "", expected: ""},
+		{name: "only punctuation", input: "-_.:", expected: ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(
+			tt.name,
+			func(t *testing.T) {
+				t.Parallel()
+				assert.Equal(t, tt.expected, strutil.NormalizeAlnum(tt.input))
+			},
+		)
+	}
+}

pkg/thirdparty/common_third_party_owned_domains.go

@@ -18,6 +18,7 @@ import (
 	"slices"
 	"strings"
 
+	"go.probo.inc/probo/pkg/strutil"
 	"go.probo.inc/probo/pkg/uri"
 )
 
@@ -157,7 +158,7 @@ func vendorLabels(name, website string) []string {
 	}
 
 	add(uri.DomainLabel(website))
-	add(normalizeAlnum(name))
+	add(strutil.NormalizeAlnum(name))
 
 	return labels
 }
@@ -213,18 +214,3 @@ func normalizeToETLD1(raw string) string {
 
 	return uri.ExtractDomain(raw)
 }
-
-// normalizeAlnum lowercases a string and drops every non-alphanumeric
-// rune, so "Dark Reader" and "DarkReader, Inc." both reduce to a
-// comparable label root.
-func normalizeAlnum(s string) string {
-	var b strings.Builder
-
-	for _, r := range strings.ToLower(s) {
-		if (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9') {
-			b.WriteRune(r)
-		}
-	}
-
-	return b.String()
-}