Adding OpenTelemetry Metrics and Tracing

internal/telemetry/telemetry_golden_test.go

@@ -0,0 +1,76 @@
+package telemetry
+
+import (
+	"bufio"
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+// Golden test that /metrics contains expected metric names.
+func TestMetricsGoldenContains(t *testing.T) {
+	ctx := context.Background()
+	resetMetricsForTest()
+	t.Setenv("NEWT_METRICS_INCLUDE_SITE_LABELS", "true")
+	cfg := Config{ServiceName: "newt", PromEnabled: true, AdminAddr: "127.0.0.1:0", BuildVersion: "test"}
+	tel, err := Init(ctx, cfg)
+	if err != nil {
+		t.Fatalf("telemetry init error: %v", err)
+	}
+	defer func() { _ = tel.Shutdown(context.Background()) }()
+
+	if tel.PrometheusHandler == nil {
+		t.Fatalf("prom handler nil")
+	}
+	ts := httptest.NewServer(tel.PrometheusHandler)
+	defer ts.Close()
+
+	// Trigger counters to ensure they appear in the scrape
+	IncConnAttempt(ctx, "websocket", "success")
+	IncWSReconnect(ctx, "io_error")
+	IncProxyConnectionEvent(ctx, "", "tcp", ProxyConnectionOpened)
+	if tel.MeterProvider != nil {
+		_ = tel.MeterProvider.ForceFlush(ctx)
+	}
+	time.Sleep(100 * time.Millisecond)
+
+	var body string
+	for i := 0; i < 5; i++ {
+		resp, err := http.Get(ts.URL)
+		if err != nil {
+			t.Fatalf("GET metrics failed: %v", err)
+		}
+		b, _ := io.ReadAll(resp.Body)
+		_ = resp.Body.Close()
+		body = string(b)
+		if strings.Contains(body, "newt_connection_attempts_total") {
+			break
+		}
+		time.Sleep(100 * time.Millisecond)
+	}
+
+	f, err := os.Open(filepath.Join("testdata", "expected_contains.golden"))
+	if err != nil {
+		t.Fatalf("read golden: %v", err)
+	}
+	defer f.Close()
+	s := bufio.NewScanner(f)
+	for s.Scan() {
+		needle := strings.TrimSpace(s.Text())
+		if needle == "" {
+			continue
+		}
+		if !strings.Contains(body, needle) {
+			t.Fatalf("expected metrics body to contain %q. body=\n%s", needle, body)
+		}
+	}
+	if err := s.Err(); err != nil {
+		t.Fatalf("scan golden: %v", err)
+	}
+}