From b783f57e0135a033eeedae913473a4c07a7bc0fe Mon Sep 17 00:00:00 2001
From: "Alessandro (Ale) Segala" <43508+ItalyPaleAle@users.noreply.github.com>
Date: Tue, 15 Sep 2020 06:39:35 +0000
Subject: [PATCH] writeConfig operations are atomic

---
 viper.go | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/viper.go b/viper.go
index c3130c2..cc1a4f1 100644
--- a/viper.go
+++ b/viper.go
@@ -1490,17 +1490,27 @@ func (v *Viper) writeConfig(filename string, force bool) error {
 	if v.config == nil {
 		v.config = make(map[string]interface{})
 	}
-	flags := os.O_CREATE | os.O_TRUNC | os.O_WRONLY
-	if !force {
-		flags |= os.O_EXCL
-	}
-	f, err := v.fs.OpenFile(filename, flags, v.configPermissions)
+
+	exists, err := afero.Exists(v.fs, filename)
+	if err != nil {
+		return err
+	}
+	if exists && !force {
+		return fmt.Errorf("file already exists: %s", filename)
+	}
+	f, err := afero.TempFile(v.fs, filepath.Dir(filename), filepath.Base(filename)+"-")
 	if err != nil {
 		return err
 	}
-	defer f.Close()
 
 	if err := v.marshalWriter(f, configType); err != nil {
+		f.Close()
+		return err
+	}
+	f.Close()
+
+	err = v.fs.Rename(f.Name(), filename)
+	if err != nil {
 		return err
 	}