refactor: addition of a generic server to use for health, metrics etc

Author: dimakis

cmd/kar-controllers/app/generic-server.go

@@ -0,0 +1,107 @@
+package app
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/http"
+	"strconv"
+	"time"
+
+	logger "k8s.io/klog/v2"
+)
+
+type ServerOption func(*Server)
+
+// WithTimeout sets the shutdown timeout for the server.
+func WithTimeout(timeout time.Duration) ServerOption {
+	return func(s *Server) {
+		s.shutdownTimeout = timeout
+	}
+}
+
+type Server struct {
+	httpServer      http.Server
+	listener        net.Listener
+	endpoint        string
+	shutdownTimeout time.Duration
+}
+
+func NewServer(port int, endpoint string, handler http.Handler, options ...ServerOption) (*Server, error) {
+	addr := "0"
+	if port != 0 {
+		addr = ":" + strconv.Itoa(port)
+	}
+
+	listener, err := newListener(addr)
+	if err != nil {
+		return nil, err
+	}
+
+	mux := http.NewServeMux()
+	mux.Handle(endpoint, handler)
+
+	s := &Server{
+		endpoint:        endpoint,
+		listener:        listener,
+		httpServer:      http.Server{Handler: mux},
+		shutdownTimeout: 30 * time.Second,  // Default value
+	}
+
+	for _, opt := range options {
+		opt(s)
+	}
+
+	return s, nil
+}
+
+func (s *Server) Start() (err error) {
+	if s.listener == nil {
+		logger.Infof("Serving endpoint %s is disabled", s.endpoint)
+		return
+	}
+	
+	defer func() {
+		if r := recover(); r != nil {
+			err = fmt.Errorf("serving endpoint %s failed: %v", s.endpoint, r)
+		}
+	}()
+	
+	logger.Infof("Started serving endpoint %s at %s", s.endpoint, s.listener.Addr())
+	if e := s.httpServer.Serve(s.listener); e != http.ErrServerClosed {
+		return fmt.Errorf("serving endpoint %s failed: %v", s.endpoint, e)
+	}
+	return
+}
+
+func (s *Server) Shutdown() error {
+	if s.listener == nil {
+		return nil
+	}
+	
+	logger.Info("Stopping server")
+
+	shutdownCtx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+	defer cancel()
+
+	// Try graceful shutdown
+	if err := s.httpServer.Shutdown(shutdownCtx); err != nil {
+		return fmt.Errorf("failed to shutdown server gracefully: %v", err)
+	}
+	return s.httpServer.Shutdown(shutdownCtx)
+}
+
+// newListener creates a new TCP listener bound to the given address.
+func newListener(addr string) (net.Listener, error) {
+	// Add a case to disable serving altogether
+	if addr == "0" {
+		return nil, nil
+	}
+
+	listener, err := net.Listen("tcp", addr)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create listener: %v", err)
+	}
+
+	return listener, nil
+}