refactoring prometheus endpoint

command/agent/metrics_endpoint.go

@@ -2,12 +2,28 @@ package agent
 
 import (
 	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 // MetricsRequest returns metrics in JSON format
 func (s *HTTPServer) MetricsRequest(resp http.ResponseWriter, req *http.Request) (interface{}, error) {
-	if req.Method == "GET" {
-		return s.agent.InmemSink.DisplayMetrics(resp, req)
+	if req.Method != "GET" {
+		return nil, CodedError(405, ErrInvalidMethod)
 	}
-	return nil, CodedError(405, ErrInvalidMethod)
+
+	if format := req.URL.Query().Get("format"); format == "prometheus" {
+		handlerOptions := promhttp.HandlerOpts{
+			ErrorLog:           s.logger,
+			ErrorHandling:      promhttp.ContinueOnError,
+			DisableCompression: true,
+		}
+
+		handler := promhttp.HandlerFor(prometheus.DefaultGatherer, handlerOptions)
+		handler.ServeHTTP(resp, req)
+		return nil, nil
+	}
+
+	return s.agent.InmemSink.DisplayMetrics(resp, req)
 }