Use common httpserver across fission (#2409)

* Defining httpserver package to capture httpserver shutdown and
introduces uniform running of http server across codebase.
* Add unit tests for httpserver

Signed-off-by: Sanket Sudake <sanketsudake@gmail.com>

pkg/utils/metrics/server.go

@@ -23,34 +23,16 @@ import (
 
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"go.uber.org/zap"
+
+	"github.com/fission/fission/pkg/utils/httpserver"
 )
 
 func ServeMetrics(ctx context.Context, logger *zap.Logger) {
 	metricsAddr := os.Getenv("METRICS_ADDR")
 	if metricsAddr == "" {
-		metricsAddr = ":8080"
+		metricsAddr = "8080"
 	}
 	mux := http.NewServeMux()
 	mux.Handle("/metrics", promhttp.Handler())
-	s := &http.Server{
-		Addr:    metricsAddr,
-		Handler: mux,
-	}
-	logger.Info("Starting metrics server", zap.String("address", metricsAddr))
-	go func() {
-		if err := s.ListenAndServe(); err != nil {
-			if err != http.ErrServerClosed {
-				logger.Error("Metrics server error", zap.Error(err))
-			}
-		}
-	}()
-	<-ctx.Done()
-	logger.Info("Shutting down metrics server")
-	err := s.Shutdown(ctx)
-	if err == context.DeadlineExceeded || err == context.Canceled {
-		return
-	}
-	if err != nil {
-		logger.Error("Failed to shutdown metrics server", zap.Error(err))
-	}
+	httpserver.StartServer(ctx, logger, "metrics", metricsAddr, mux)
 }