Rudamentary Prometheus metrics support

server/prometheus.go

@@ -0,0 +1,51 @@
+package server
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+var httpRequestsTotal = prometheus.NewCounter(
+	prometheus.CounterOpts{
+		Name: "silverbullet_http_requests_total",
+		Help: "Total number of HTTP requests to SilverBullet",
+	},
+)
+
+func init() {
+	prometheus.MustRegister(httpRequestsTotal)
+}
+
+func httpStatsMiddleware(config *ServerConfig) func(http.Handler) http.Handler {
+	if config.MetricsPort == 0 {
+		// NOOP
+		return func(next http.Handler) http.Handler {
+			return next
+		}
+	} else {
+		return func(next http.Handler) http.Handler {
+			return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				httpRequestsTotal.Inc()
+				next.ServeHTTP(w, r)
+			})
+		}
+	}
+}
+
+func runMetricsServer(config *ServerConfig) {
+	if config.MetricsPort != 0 {
+		metricRouter := chi.NewRouter()
+		metricsServer := &http.Server{
+			Addr:    fmt.Sprintf("%s:%d", config.BindHost, config.MetricsPort),
+			Handler: metricRouter,
+		}
+		metricRouter.Handle("/metrics", promhttp.Handler())
+		log.Printf("Metrics server started on %s:%d", config.BindHost, config.MetricsPort)
+		metricsServer.ListenAndServe()
+	}
+}