feat: add IM service health and metrics endpoints

server/metrics/metrics.go

@@ -0,0 +1,61 @@
+package metrics
+
+import (
+	"expvar"
+	"strconv"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	Registry = prometheus.NewRegistry()
+
+	HTTPRequestsTotal = prometheus.NewCounterVec(prometheus.CounterOpts{
+		Name: "http_requests_total",
+		Help: "Total number of HTTP requests by method, normalized path, and status.",
+	}, []string{"method", "path", "status"})
+
+	HTTPRequestDuration = prometheus.NewHistogramVec(prometheus.HistogramOpts{
+		Name:    "http_request_duration_seconds",
+		Help:    "HTTP request duration by method, normalized path, and status.",
+		Buckets: []float64{0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10},
+	}, []string{"method", "path", "status"})
+
+	DBQueryDuration = prometheus.NewHistogramVec(prometheus.HistogramOpts{
+		Name:    "db_query_duration_seconds",
+		Help:    "Database operation duration by driver, operation, and status.",
+		Buckets: []float64{0.001, 0.003, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5},
+	}, []string{"driver", "operation", "status"})
+
+	WSConnectionsActive = prometheus.NewGaugeFunc(prometheus.GaugeOpts{
+		Name: "ws_connections_active",
+		Help: "Current active WebSocket connections.",
+	}, func() float64 {
+		return float64(expvarIntValue("LiveSessions"))
+	})
+)
+
+func init() {
+	Registry.MustRegister(WSConnectionsActive, HTTPRequestsTotal, HTTPRequestDuration, DBQueryDuration)
+}
+
+func ObserveDB(driverName, operation string, started time.Time, err error) {
+	status := "ok"
+	if err != nil {
+		status = "error"
+	}
+	DBQueryDuration.WithLabelValues(driverName, operation, status).Observe(time.Since(started).Seconds())
+}
+
+func expvarIntValue(name string) int64 {
+	value := expvar.Get(name)
+	if value == nil {
+		return 0
+	}
+	n, err := strconv.ParseInt(value.String(), 10, 64)
+	if err != nil {
+		return 0
+	}
+	return n
+}