feat(exporter): add prometheus exporter for cache, database & webserver stats

internal/exporter/middleware.go

@@ -0,0 +1,68 @@
+package exporter
+
+import (
+	"net/http"
+	"sync"
+	"time"
+
+	"github.com/go-chi/chi/v5/middleware"
+)
+
+type RequestData struct {
+	Latency time.Duration
+	Request *http.Request
+	Start   time.Time
+}
+
+type RequestDataQueue struct {
+	mu   sync.Mutex
+	data []RequestData
+}
+
+func NewRequestDataQueue() *RequestDataQueue {
+	return &RequestDataQueue{
+		data: []RequestData{},
+	}
+}
+
+func (q *RequestDataQueue) Add(data RequestData) {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+	q.data = append(q.data, data)
+}
+
+func (q *RequestDataQueue) ConsumeAll() []RequestData {
+	q.mu.Lock()
+	defer q.mu.Unlock()
+	data := q.data
+	q.data = nil
+	return data
+}
+
+type Middleware struct {
+	queue *RequestDataQueue
+}
+
+func NewMiddleware(queue *RequestDataQueue) func(next http.Handler) http.Handler {
+	m := Middleware{
+		queue: queue,
+	}
+	return m.handler
+}
+
+func (m Middleware) handler(next http.Handler) http.Handler {
+	fn := func(w http.ResponseWriter, r *http.Request) {
+		start := time.Now()
+		ww := middleware.NewWrapResponseWriter(w, r.ProtoMajor)
+		next.ServeHTTP(ww, r)
+
+		m.queue.Add(
+			RequestData{
+				Latency: time.Since(start),
+				Request: r,
+				Start:   start,
+			},
+		)
+	}
+	return http.HandlerFunc(fn)
+}