chore: establish local platform baseline

internal/httpapi/metrics.go

@@ -0,0 +1,66 @@
+package httpapi
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+var (
+	httpRequests = promauto.NewCounterVec(prometheus.CounterOpts{
+		Namespace: "voice_platform", Subsystem: "http", Name: "requests_total",
+		Help: "Total HTTP requests by service, method, route and status.",
+	}, []string{"service", "method", "route", "status"})
+	httpDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Namespace: "voice_platform", Subsystem: "http", Name: "request_duration_seconds",
+		Help:    "HTTP request duration by service, method and route.",
+		Buckets: []float64{0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5},
+	}, []string{"service", "method", "route"})
+	httpInflight = promauto.NewGaugeVec(prometheus.GaugeOpts{
+		Namespace: "voice_platform", Subsystem: "http", Name: "inflight_requests",
+		Help: "Current in-flight HTTP requests by service.",
+	}, []string{"service"})
+)
+
+func MetricsHandler() http.Handler { return promhttp.Handler() }
+
+func metricsMiddleware(serviceName string, next http.Handler) http.Handler {
+	return http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
+		startedAt := time.Now()
+		httpInflight.WithLabelValues(serviceName).Inc()
+		defer httpInflight.WithLabelValues(serviceName).Dec()
+		recorder := &statusRecorder{ResponseWriter: writer, status: http.StatusOK}
+		defer func() {
+			route := request.Pattern
+			if route == "" {
+				route = "unmatched"
+			}
+			httpRequests.WithLabelValues(serviceName, request.Method, route, strconv.Itoa(recorder.status)).Inc()
+			httpDuration.WithLabelValues(serviceName, request.Method, route).Observe(time.Since(startedAt).Seconds())
+		}()
+		next.ServeHTTP(recorder, request)
+	})
+}
+
+type statusRecorder struct {
+	http.ResponseWriter
+	status int
+	bytes  int
+}
+
+func (r *statusRecorder) WriteHeader(status int) {
+	r.status = status
+	r.ResponseWriter.WriteHeader(status)
+}
+
+func (r *statusRecorder) Write(body []byte) (int, error) {
+	written, err := r.ResponseWriter.Write(body)
+	r.bytes += written
+	return written, err
+}
+
+func (r *statusRecorder) Unwrap() http.ResponseWriter { return r.ResponseWriter }