feat: Do not send metrics if the client used DNT or GPC

internal/metrics/metrics.go

@@ -16,12 +16,18 @@ type MetricConfig struct {
 	Enabled       bool
 }
 
-// Checks if we should send a metric ping to Loki based on the served path.
-func (c *MetricConfig) ShouldSendMetrics(path, userAgent string) bool {
+// Checks if we should send a metric ping to page-metrics based on the served path.
+func (c *MetricConfig) ShouldSendMetrics(path, userAgent, dnt, gpc string) bool {
 	if !strings.HasSuffix(path, ".html") || !c.Enabled {
 		return false
 	}
 
+	// Ignore requests where the user have set "Do-Not-Track" or "Do-Not-Sell-My-Data", even though
+	// there is no user data and we're not selling it.
+	if dnt == "1" || gpc == "1" {
+		return false
+	}
+
 	// Filter out bots
 	for _, pattern := range *c.BotUserAgents {
 		if pattern.MatchString(userAgent) {

internal/metrics/metrics_test.go

@@ -14,11 +14,19 @@ func TestShouldPing(t *testing.T) {
 		},
 	}
 
-	if cfg.ShouldSendMetrics("/index.html", "random-bot/v23.5") {
+	if cfg.ShouldSendMetrics("/index.html", "random-bot/v23.5", "", "") {
 		t.Fatalf("Accepted bot user-agent")
 	}
 
-	if !cfg.ShouldSendMetrics("/index.html", "Firefox/...") {
+	if !cfg.ShouldSendMetrics("/index.html", "Firefox/...", "", "") {
 		t.Fatalf("Rejected real user-agent")
 	}
+
+	if cfg.ShouldSendMetrics("/index.html", "Firefox/...", "1", "") {
+		t.Fatalf("Ignored DNT")
+	}
+
+	if cfg.ShouldSendMetrics("/index.html", "Firefox/...", "", "1") {
+		t.Fatalf("Ignored GPC")
+	}
 }