From bcbd41102ce44dbf330f16a70c5a2a122613310e Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <bradfitz@tailscale.com>
Date: Tue, 14 Jul 2020 16:35:10 -0700
Subject: [PATCH] atomicfile: use ioutil.TempFile, sync

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
---
 atomicfile/atomicfile.go | 32 ++++++++++++++++++++++++--------
 1 file changed, 24 insertions(+), 8 deletions(-)

diff --git a/atomicfile/atomicfile.go b/atomicfile/atomicfile.go
index f2af37182..ec3025340 100644
--- a/atomicfile/atomicfile.go
+++ b/atomicfile/atomicfile.go
@@ -9,20 +9,36 @@
 package atomicfile // import "tailscale.com/atomicfile"
 
 import (
-	"fmt"
 	"io/ioutil"
 	"os"
+	"path/filepath"
 )
 
 // WriteFile writes data to filename+some suffix, then renames it
 // into filename.
-func WriteFile(filename string, data []byte, perm os.FileMode) error {
-	tmpname := filename + ".new.tmp"
-	if err := ioutil.WriteFile(tmpname, data, perm); err != nil {
-		return fmt.Errorf("%#v: %v", tmpname, err)
+func WriteFile(filename string, data []byte, perm os.FileMode) (err error) {
+	f, err := ioutil.TempFile(filepath.Dir(filename), filepath.Base(filename)+".tmp")
+	if err != nil {
+		return err
 	}
-	if err := os.Rename(tmpname, filename); err != nil {
-		return fmt.Errorf("%#v->%#v: %v", tmpname, filename, err)
+	tmpName := f.Name()
+	defer func() {
+		if err != nil {
+			f.Close()
+			os.Remove(tmpName)
+		}
+	}()
+	if _, err := f.Write(data); err != nil {
+		return err
 	}
-	return nil
+	if err := f.Chmod(perm); err != nil {
+		return err
+	}
+	if err := f.Sync(); err != nil {
+		return err
+	}
+	if err := f.Close(); err != nil {
+		return err
+	}
+	return os.Rename(tmpName, filename)
 }