Add ExtractDomain to pkg/uri for eTLD+1 extraction

Uses golang.org/x/net/publicsuffix to extract the effective
top-level domain plus one label from a URL. Used to populate
detected_trackers.initiator_domain for domain-based tracker
attribution.

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

pkg/uri/uri.go

@@ -18,6 +18,9 @@ import (
 	"database/sql/driver"
 	"fmt"
 	"net/url"
+	"strings"
+
+	"golang.org/x/net/publicsuffix"
 )
 
 // URI is a validated absolute URI (scheme + host required).
@@ -71,3 +74,28 @@ func (u *URI) Scan(value any) error {
 func (u URI) Value() (driver.Value, error) {
 	return u.String(), nil
 }
+
+// ExtractDomain returns the eTLD+1 (effective top-level domain plus one
+// label) from a raw URL string. For example:
+//
+//	"https://www.googletagmanager.com/gtag/js" → "googletagmanager.com"
+//	"https://cdn.segment.io/v1/projects"       → "segment.io"
+//
+// Returns an empty string when the URL cannot be parsed or has no valid
+// hostname (e.g. data: URIs, bare IP addresses without a public suffix).
+func ExtractDomain(rawURL string) string {
+	u, err := Parse(rawURL)
+	if err != nil {
+		return ""
+	}
+
+	parsed, _ := url.Parse(string(u))
+	hostname := strings.ToLower(parsed.Hostname())
+
+	domain, err := publicsuffix.EffectiveTLDPlusOne(hostname)
+	if err != nil {
+		return ""
+	}
+
+	return domain
+}

pkg/uri/uri_test.go

@@ -249,3 +249,39 @@ func TestURIValue(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, "https://example.com", v)
 }
+
+func TestExtractDomain(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name   string
+		rawURL string
+		want   string
+	}{
+		{"google tag manager", "https://www.googletagmanager.com/gtag/js?id=G-ABC123", "googletagmanager.com"},
+		{"google analytics", "https://www.google-analytics.com/analytics.js", "google-analytics.com"},
+		{"facebook pixel", "https://connect.facebook.net/en_US/fbevents.js", "facebook.net"},
+		{"segment cdn", "https://cdn.segment.io/v1/projects/abc/settings", "segment.io"},
+		{"hubspot", "https://js.hs-analytics.net/analytics/1234/abc.js", "hs-analytics.net"},
+		{"subdomain stripped", "https://static.ads.example.com/pixel.js", "example.com"},
+		{"co.uk tld", "https://tracker.example.co.uk/script.js", "example.co.uk"},
+		{"bare domain no path", "https://doubleclick.net", "doubleclick.net"},
+		{"case insensitive", "https://WWW.GoogleTagManager.COM/gtag/js", "googletagmanager.com"},
+		{"empty string", "", ""},
+		{"invalid url", "not a url at all", ""},
+		{"data uri", "data:text/html,<h1>Hello</h1>", ""},
+		{"ip address", "https://192.168.1.1/script.js", ""},
+		{"port number", "https://tracker.example.com:8443/pixel.js", "example.com"},
+		{"http scheme", "http://cdn.jsdelivr.net/npm/cookieconsent", "jsdelivr.net"},
+	}
+
+	for _, tt := range tests {
+		t.Run(
+			tt.name,
+			func(t *testing.T) {
+				t.Parallel()
+				assert.Equal(t, tt.want, ExtractDomain(tt.rawURL))
+			},
+		)
+	}
+}