Fix registration socket removal on windows.

- Until the bug - golang/go#33357 is fixed, os.stat wouldn't return the
  right mode(socket) on windows. Hence deleting the file, without checking whether
  its a socket, on windows.

- Place os specific logic into util_{linux, windows} files and move util under pkg.

cmd/csi-node-driver-registrar/node_register.go

@@ -24,6 +24,7 @@ import (
 
 	"google.golang.org/grpc"
 
+	"github.com/kubernetes-csi/node-driver-registrar/pkg/util"
 	"k8s.io/klog"
 	registerapi "k8s.io/kubernetes/pkg/kubelet/apis/pluginregistration/v1alpha1"
 )
@@ -36,23 +37,15 @@ func nodeRegister(
 	// pluginswatcher infrastructure. Node labeling is done by kubelet's csi code.
 	registrar := newRegistrationServer(csiDriverName, *kubeletRegistrationPath, supportedVersions)
 	socketPath := fmt.Sprintf("/registration/%s-reg.sock", csiDriverName)
-	fi, err := os.Stat(socketPath)
-	if err == nil && (fi.Mode()&os.ModeSocket) != 0 {
-		// Remove any socket, stale or not, but fall through for other files
-		if err := os.Remove(socketPath); err != nil {
-			klog.Errorf("failed to remove stale socket %s with error: %+v", socketPath, err)
-			os.Exit(1)
-		}
-	}
-	if err != nil && !os.IsNotExist(err) {
-		klog.Errorf("failed to stat the socket %s with error: %+v", socketPath, err)
+	if err := util.CleanupSocketFile(socketPath); err != nil {
+		klog.Errorf("%+v", err)
 		os.Exit(1)
 	}
 
 	var oldmask int
 	if runtime.GOOS == "linux" {
 		// Default to only user accessible socket, caller can open up later if desired
-		oldmask, _ = umask(0077)
+		oldmask, _ = util.Umask(0077)
 	}
 
 	klog.Infof("Starting Registration Server at: %s\n", socketPath)
@@ -62,7 +55,7 @@ func nodeRegister(
 		os.Exit(1)
 	}
 	if runtime.GOOS == "linux" {
-		umask(oldmask)
+		util.Umask(oldmask)
 	}
 	klog.Infof("Registration Server started at: %s\n", socketPath)
 	grpcServer := grpc.NewServer()

cmd/csi-node-driver-registrar/util_linux.go → pkg/util/util_linux.go

@@ -16,12 +16,29 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package main
+package util
 
 import (
+	"fmt"
+	"os"
+
 	"golang.org/x/sys/unix"
 )
 
-func umask(mask int) (int, error) {
+func Umask(mask int) (int, error) {
 	return unix.Umask(mask), nil
 }
+
+func CleanupSocketFile(socketPath string) error {
+	fi, err := os.Stat(socketPath)
+	if err == nil && (fi.Mode()&os.ModeSocket) != 0 {
+		// Remove any socket, stale or not, but fall through for other files
+		if err := os.Remove(socketPath); err != nil {
+			return fmt.Errorf("failed to remove stale socket %s with error: %+v", socketPath, err)
+		}
+	}
+	if err != nil && !os.IsNotExist(err) {
+		return fmt.Errorf("failed to stat the socket %s with error: %+v", socketPath, err)
+	}
+	return nil
+}

pkg/util/util_windows.go

@@ -0,0 +1,47 @@
+// +build windows
+
+/*
+Copyright 2019 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package util
+
+import (
+	"errors"
+	"fmt"
+	"os"
+)
+
+func Umask(mask int) (int, error) {
+	return -1, errors.New("umask not supported in Windows")
+}
+
+func CleanupSocketFile(socketPath string) error {
+	if _, err := os.Lstat(socketPath); err != nil {
+		// If the file does not exist, then the cleanup can be considered successful.
+		if os.IsNotExist(err) {
+			return nil
+		}
+		return fmt.Errorf("failed to lstat the socket %s with error: %+v", socketPath, err)
+	}
+
+	// TODO: Until the bug - https://github.com/golang/go/issues/33357 is fixed, os.stat wouldn't return the
+	// right mode(socket) on windows. Hence deleting the file, without checking whether
+	// its a socket, on windows.
+	if err := os.Remove(socketPath); err != nil {
+		return fmt.Errorf("failed to remove stale socket %s with error: %+v", socketPath, err)
+	}
+	return nil
+}