From 859f1590dd25c633358bcc4182a0df66d7c35b09 Mon Sep 17 00:00:00 2001
From: Eugene Bujak <hmage@hmage.net>
Date: Thu, 6 Sep 2018 02:03:03 +0300
Subject: [PATCH] Be more atomic during writing of files -- this prevents other
 processes from seeing empty or impartial files

---
 config.go  | 13 +++++++++++--
 control.go |  8 +++++++-
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/config.go b/config.go
index b87429b1..f0923601 100644
--- a/config.go
+++ b/config.go
@@ -108,11 +108,16 @@ func writeConfig() error {
 		log.Printf("Couldn't generate YAML file: %s", err)
 		return err
 	}
-	err = ioutil.WriteFile(configfile, yamlText, 0644)
+	err = ioutil.WriteFile(configfile+".tmp", yamlText, 0644)
 	if err != nil {
 		log.Printf("Couldn't write YAML config: %s", err)
 		return err
 	}
+	err = os.Rename(configfile+".tmp", configfile)
+	if err != nil {
+		log.Printf("Couldn't rename YAML config: %s", err)
+		return err
+	}
 	return nil
 }
 
@@ -127,10 +132,14 @@ func writeCoreDNSConfig() error {
 		log.Printf("Couldn't generate DNS config: %s", err)
 		return err
 	}
-	err = ioutil.WriteFile(corefile, []byte(configtext), 0644)
+	err = ioutil.WriteFile(corefile+".tmp", []byte(configtext), 0644)
 	if err != nil {
 		log.Printf("Couldn't write DNS config: %s", err)
 	}
+	err = os.Rename(corefile+".tmp", corefile)
+	if err != nil {
+		log.Printf("Couldn't rename DNS config: %s", err)
+	}
 	return err
 }
 
diff --git a/control.go b/control.go
index e3d11119..57f83114 100644
--- a/control.go
+++ b/control.go
@@ -929,11 +929,17 @@ func writeFilterFile() error {
 		data = append(data, []byte(rule)...)
 		data = append(data, '\n')
 	}
-	err := ioutil.WriteFile(filterpath, data, 0644)
+	err := ioutil.WriteFile(filterpath+".tmp", data, 0644)
 	if err != nil {
 		log.Printf("Couldn't write filter file: %s", err)
 		return err
 	}
+
+	err = os.Rename(filterpath+".tmp", filterpath)
+	if err != nil {
+		log.Printf("Couldn't rename filter file: %s", err)
+		return err
+	}
 	return nil
 }