Fix errcheck linter for most of non-test files

Add handling errors where it was missing

.golangci.yaml

@@ -17,12 +17,5 @@ issues:
 linters-settings:
   errcheck:
     exclude-functions:
-      - fmt.Fprintf
-      - fmt.Fprint
-      - (net/http.ResponseWriter).Write
-      - (*net/http.Server).Shutdown
       - (*flag.FlagSet).Parse
-      - (*os.File).Close
-      - (io.Closer).Close
-      - (flag.Value).Set
       - k8s.io/apimachinery/pkg/util/wait.PollUntil

cmd/404-server-with-metrics/server-with-metrics.go

@@ -259,6 +259,12 @@ func gracefulShutdown(s *server) {
 		klog.Infof("received /shutdown message, doing a graceful shutdown of http and metrics servers: \n")
 	}
 
-	s.httpServer.Shutdown(context.Background())
-	s.metricsServer.Shutdown(context.Background())
+	err := s.httpServer.Shutdown(context.Background())
+	if err != nil {
+		klog.Errorf("Error shutting down httpServer: %v", err)
+	}
+	err = s.metricsServer.Shutdown(context.Background())
+	if err != nil {
+		klog.Errorf("Error shutting down metricsServer: %v", err)
+	}
 }

cmd/echo/app/handlers.go

@@ -67,7 +67,10 @@ func RunHTTPServer(ctx context.Context) {
 		}
 
 		<-ctx.Done()
-		server.Shutdown(ctx)
+		err = server.Shutdown(ctx)
+		if err != nil {
+			klog.Infof("Error on server shutdown %v", err)
+		}
 	}()
 
 	go func() {
@@ -82,15 +85,23 @@ func RunHTTPServer(ctx context.Context) {
 		}
 
 		<-ctx.Done()
-		server.Shutdown(ctx)
+
+		err = server.Shutdown(ctx)
+		if err != nil {
+			klog.Errorf("Error on server shutdown %v", err)
+		}
 	}()
 
 	<-ctx.Done()
 }
 
 func healthCheck(w http.ResponseWriter, r *http.Request) {
 	w.WriteHeader(http.StatusOK)
-	w.Write([]byte("health: OK"))
+	_, err := w.Write([]byte("health: OK"))
+	if err != nil {
+		klog.Errorf("Error writing bytes: %v, UserAgent: %v, RemoteAddr: %v", err, r.UserAgent(), r.RemoteAddr)
+		return
+	}
 	klog.V(3).Infof("healthcheck: %v, %v, %v", time.Now(), r.UserAgent(), r.RemoteAddr)
 }
 
@@ -123,7 +134,11 @@ func echo(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	w.Write(processedData)
+	_, err = w.Write(processedData)
+	if err != nil {
+		klog.Errorf("Error writing data: %v, UserAgent: %v, RemoteAddr: %v", err, r.UserAgent(), r.RemoteAddr)
+		return
+	}
 	klog.V(3).Infof("echo: %v, %v, %v", time.Now(), r.UserAgent(), r.RemoteAddr)
 }
 

cmd/fuzzer/fuzzer.go

@@ -24,12 +24,7 @@ import (
 	_ "k8s.io/client-go/plugin/pkg/client/auth/gcp"
 	_ "k8s.io/client-go/plugin/pkg/client/auth/oidc"
 	"k8s.io/ingress-gce/cmd/fuzzer/app"
-)
-
-var (
-	kubeconfig       *string
-	ingressNamespace *string
-	ingressName      *string
+	"k8s.io/klog/v2"
 )
 
 func main() {
@@ -43,7 +38,10 @@ func main() {
 
 	switch os.Args[1] {
 	case "validate":
-		app.ValidateFlagSet.Parse(os.Args[2:])
+		err := app.ValidateFlagSet.Parse(os.Args[2:])
+		if err != nil {
+			klog.Errorf("app.ValidateFlagSet.Parse(%v) returned error: %v", os.Args[2:], err)
+		}
 	default:
 		flag.Usage()
 		os.Exit(1)

cmd/glbc/app/handlers.go

@@ -85,11 +85,17 @@ func healthCheckHandler(checker func() context.HealthCheckResults) http.HandlerF
 		}
 
 		if s.Len() == 0 {
-			w.Write([]byte("OK - no running controllers"))
+			_, err := w.Write([]byte("OK - no running controllers"))
+			if err != nil {
+				klog.Errorf("Error writing bytes: %v", err)
+			}
 			return
 		}
 
-		w.Write([]byte(s.String()))
+		_, err := w.Write([]byte(s.String()))
+		if err != nil {
+			klog.Errorf("Error writing bytes: %v", err)
+		}
 		return
 	}
 }
@@ -129,8 +135,11 @@ func putFlag(w http.ResponseWriter, r *http.Request) {
 }
 
 func setVerbosity(v string) {
-	flag.Lookup("v").Value.Set(v)
 	klog.V(0).Infof("Setting verbosity level to %q", v)
+	err := flag.Lookup("v").Value.Set(v)
+	if err != nil {
+		klog.Errorf("flag.Lookup(\"v\").Value.Set(%v) returned error: %v", v, err)
+	}
 }
 
 func getFlagPage(w http.ResponseWriter, r *http.Request) {

cmd/workload-daemon/main.go

@@ -39,7 +39,10 @@ func main() {
 		outputHelp()
 		return
 	}
-	cmdSet.Parse(os.Args[2:])
+	err := cmdSet.Parse(os.Args[2:])
+	if err != nil {
+		klog.Errorf("Error parsing os.Args: %v", err)
+	}
 	if *provider != "gce" {
 		klog.Fatalf("Current implementation only supports gce provider.")
 	}