* app: optimize config file reading

* read config file just once (even when upgrading)
* don't call os.Stat()

app.go

@@ -93,16 +93,17 @@ func run(args options) {
 		os.Exit(0)
 	}()
 
+	if !config.firstRun {
 		// Do the upgrade if necessary
 		err := upgradeConfig()
 		if err != nil {
 			log.Fatal(err)
 		}
 
-	// parse from config file
 		err = parseConfig()
 		if err != nil {
-		log.Fatal(err)
+			os.Exit(1)
+		}
 	}
 
 	if (runtime.GOOS == "linux" || runtime.GOOS == "darwin") &&
@@ -120,18 +121,20 @@ func run(args options) {
 
 	loadFilters()
 
+	if !config.firstRun {
 		// Save the updated config
-	err = config.write()
+		err := config.write()
 		if err != nil {
 			log.Fatal(err)
 		}
+	}
 
 	// Init the DNS server instance before registering HTTP handlers
 	dnsBaseDir := filepath.Join(config.ourWorkingDir, dataDir)
 	initDNSServer(dnsBaseDir)
 
 	if !config.firstRun {
-		err = startDNSServer()
+		err := startDNSServer()
 		if err != nil {
 			log.Fatal(err)
 		}

config.go

@@ -30,6 +30,10 @@ type logSettings struct {
 // configuration is loaded from YAML
 // field ordering is important -- yaml fields will mirror ordering from here
 type configuration struct {
+	// Raw file data to avoid re-reading of configuration file
+	// It's reset after config is parsed
+	fileData []byte
+
 	ourConfigFilename string // Config filename (can be overridden via the command line arguments)
 	ourWorkingDir     string // Location of our directory, used to protect against CWD being somewhere else
 	firstRun          bool   // if set to true, don't run any services except HTTP web inteface, and serve only first-run html
@@ -174,7 +178,7 @@ func (c *configuration) getConfigFilename() string {
 func getLogSettings() logSettings {
 	l := logSettings{}
 	yamlFile, err := readConfigFile()
-	if err != nil || yamlFile == nil {
+	if err != nil {
 		return l
 	}
 	err = yaml.Unmarshal(yamlFile, &l)
@@ -190,13 +194,9 @@ func parseConfig() error {
 	log.Debug("Reading config file: %s", configFile)
 	yamlFile, err := readConfigFile()
 	if err != nil {
-		log.Error("Couldn't read config file: %s", err)
 		return err
 	}
-	if yamlFile == nil {
-		log.Error("YAML file doesn't exist, skipping it")
-		return nil
-	}
+	config.fileData = nil
 	err = yaml.Unmarshal(yamlFile, &config)
 	if err != nil {
 		log.Error("Couldn't parse config file: %s", err)
@@ -213,22 +213,23 @@ func parseConfig() error {
 
 // readConfigFile reads config file contents if it exists
 func readConfigFile() ([]byte, error) {
-	configFile := config.getConfigFilename()
-	if _, err := os.Stat(configFile); os.IsNotExist(err) {
-		// do nothing, file doesn't exist
-		return nil, nil
+	if len(config.fileData) != 0 {
+		return config.fileData, nil
 	}
-	return ioutil.ReadFile(configFile)
+
+	configFile := config.getConfigFilename()
+	d, err := ioutil.ReadFile(configFile)
+	if err != nil {
+		log.Error("Couldn't read config file %s: %s", configFile, err)
+		return nil, err
+	}
+	return d, nil
 }
 
 // Saves configuration to the YAML file and also saves the user filter contents to a file
 func (c *configuration) write() error {
 	c.Lock()
 	defer c.Unlock()
-	if config.firstRun {
-		log.Debug("Silently refusing to write config because first run and not configured yet")
-		return nil
-	}
 	configFile := config.getConfigFilename()
 	log.Debug("Writing YAML file: %s", configFile)
 	yamlText, err := yaml.Marshal(&config)

upgrade.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 
@@ -16,21 +15,15 @@ const currentSchemaVersion = 3 // used for upgrading from old configs to new con
 // Performs necessary upgrade operations if needed
 func upgradeConfig() error {
 	// read a config file into an interface map, so we can manipulate values without losing any
-	configFile := config.getConfigFilename()
-	if _, err := os.Stat(configFile); os.IsNotExist(err) {
-		log.Printf("config file %s does not exist, nothing to upgrade", configFile)
-		return nil
-	}
 	diskConfig := map[string]interface{}{}
-	body, err := ioutil.ReadFile(configFile)
+	body, err := readConfigFile()
 	if err != nil {
-		log.Printf("Couldn't read config file '%s': %s", configFile, err)
 		return err
 	}
 
 	err = yaml.Unmarshal(body, &diskConfig)
 	if err != nil {
-		log.Printf("Couldn't parse config file '%s': %s", configFile, err)
+		log.Printf("Couldn't parse config file: %s", err)
 		return err
 	}
 
@@ -87,6 +80,7 @@ func upgradeConfigSchema(oldVersion int, diskConfig *map[string]interface{}) err
 		return err
 	}
 
+	config.fileData = body
 	err = file.SafeWrite(configFile, body)
 	if err != nil {
 		log.Printf("Couldn't save YAML config: %s", err)