cmd/main: Prevent to load syncthing along with new config file (fixes s…

…yncthing#4921)

cmd/syncthing/main.go

@@ -9,6 +9,7 @@ package main
 import (
 	"bytes"
 	"crypto/tls"
+	"encoding/json"
 	"errors"
 	"flag"
 	"fmt"
@@ -225,34 +226,35 @@ var (
 )
 
 type RuntimeOptions struct {
-	confDir        string
-	resetDatabase  bool
-	resetDeltaIdxs bool
-	showVersion    bool
-	showPaths      bool
-	showDeviceId   bool
-	doUpgrade      bool
-	doUpgradeCheck bool
-	upgradeTo      string
-	noBrowser      bool
-	browserOnly    bool
-	hideConsole    bool
-	logFile        string
-	auditEnabled   bool
-	auditFile      string
-	verbose        bool
-	paused         bool
-	unpaused       bool
-	guiAddress     string
-	guiAPIKey      string
-	generateDir    string
-	noRestart      bool
-	profiler       string
-	assetDir       string
-	cpuProfile     bool
-	stRestarting   bool
-	logFlags       int
-	showHelp       bool
+	confDir                     string
+	resetDatabase               bool
+	resetDeltaIdxs              bool
+	showVersion                 bool
+	showPaths                   bool
+	showDeviceId                bool
+	doUpgrade                   bool
+	doUpgradeCheck              bool
+	upgradeTo                   string
+	noBrowser                   bool
+	browserOnly                 bool
+	hideConsole                 bool
+	logFile                     string
+	auditEnabled                bool
+	auditFile                   string
+	verbose                     bool
+	paused                      bool
+	unpaused                    bool
+	guiAddress                  string
+	guiAPIKey                   string
+	generateDir                 string
+	noRestart                   bool
+	profiler                    string
+	assetDir                    string
+	cpuProfile                  bool
+	stRestarting                bool
+	logFlags                    int
+	showHelp                    bool
+	allowConfigurationDowngrade bool
 }
 
 func defaultRuntimeOptions() RuntimeOptions {
@@ -306,6 +308,7 @@ func parseCommandLineOptions() RuntimeOptions {
 	flag.BoolVar(&options.unpaused, "unpaused", false, "Start with all devices and folders unpaused")
 	flag.StringVar(&options.logFile, "logfile", options.logFile, "Log file name (still always logs to stdout). Cannot be used together with -no-restart/STNORESTART environment variable.")
 	flag.StringVar(&options.auditFile, "auditfile", options.auditFile, "Specify audit file (use \"-\" for stdout, \"--\" for stderr)")
+	flag.BoolVar(&options.allowConfigurationDowngrade, "allow-configuration-downgrade", false, "Downgrade configuration to current Syncthing configuration version")
 	if runtime.GOOS == "windows" {
 		// Allow user to hide the console window
 		flag.BoolVar(&options.hideConsole, "no-console", false, "Hide console window")
@@ -663,7 +666,12 @@ func syncthingMain(runtimeOptions RuntimeOptions) {
 		"myID": myID.String(),
 	})
 
-	cfg := loadConfigAtStartup()
+	var cfg *config.Wrapper
+	if runtimeOptions.allowConfigurationDowngrade {
+		cfg = downgradeConfig()
+	} else {
+		cfg = loadConfigAtStartup()
+	}
 
 	if err := checkShortIDs(cfg); err != nil {
 		l.Fatalln("Short device IDs are in conflict. Unlucky!\n  Regenerate the device ID of one of the following:\n  ", err)
@@ -748,7 +756,13 @@ func syncthingMain(runtimeOptions RuntimeOptions) {
 	curParts := strings.Split(Version, "-")
 	if prevParts[0] != curParts[0] {
 		if prevVersion != "" {
-			l.Infoln("Detected upgrade from", prevVersion, "to", Version)
+			// Check Syncthing version
+			checkRelation := upgrade.CompareVersions(curParts[0], prevParts[0])
+			if checkRelation == upgrade.Older || checkRelation == upgrade.MajorOlder {
+				l.Warnf("Downgrade detected: %s to %s", prevVersion, Version)
+			} else {
+				l.Infoln("Detected upgrade from", prevVersion, "to", Version)
+			}
 		}
 
 		// Drop delta indexes in case we've changed random stuff we
@@ -972,15 +986,97 @@ func loadConfigAtStartup() *config.Wrapper {
 	}
 
 	if cfg.RawCopy().OriginalVersion != config.CurrentVersion {
+		// Check config version
+		if cfg.RawCopy().OriginalVersion > config.CurrentVersion {
+			// Config version is not compatible with installed version
+			if findOldConfig(cfg) {
+				archivePath := cfg.ConfigPath() + fmt.Sprintf(".v%d", config.CurrentVersion)
+				l.Infof("Compatible version of config was found in path %s, can be used manually.", archivePath)
+			}
+			l.Infof("Use `-allow-downgrade-config' flag to downgrade your config.")
+			l.Fatalf("Current Configuration Version: %d, Loading Configuration Version: %d (Configuration Version Mismatch)", cfg.RawCopy().OriginalVersion, config.CurrentVersion)
+		}
 		err = archiveAndSaveConfig(cfg)
 		if err != nil {
 			l.Fatalln("Config archive:", err)
 		}
 	}
+	return cfg
+}
+
+func downgradeConfig() *config.Wrapper {
+	cfgFile := locations[locConfigFile]
+	cfg, err := config.Load(cfgFile, myID)
+	if os.IsNotExist(err) {
+		cfg = defaultConfig(cfgFile)
+		cfg.Save()
+		l.Infof("Default config saved. Edit %s to taste or use the GUI\n", cfg.ConfigPath())
+	} else if err == io.EOF {
+		l.Fatalln("Failed to load config: unexpected end of file. Truncated or empty configuration?")
+	} else if err != nil {
+		l.Fatalln("Failed to load config:", err)
+	}
+
+	configVersion := cfg.RawCopy().OriginalVersion
 
+	// Check config version
+	if configVersion > config.CurrentVersion {
+		// Config version is not compatible with installed version
+		l.Infof("Current Configuration Version: %d, Loading Configuration Version: %d (Configuration Version Mismatch)", configVersion, config.CurrentVersion)
+		l.Infof("Wait for downgrading...")
+
+		fd, err := os.Open(cfgFile)
+		if err != nil {
+			l.Fatalln("Config not opened")
+		}
+		defer fd.Close()
+
+		// Read XML and set defaults (Check-1)
+		// In most cases everything should correct on here  except Version.
+		cfgXML, err := config.ReadXML(fd, myID)
+		if err != nil {
+			l.Fatalln("Config not read")
+		}
+
+		err = archiveAndSaveConfig(cfg)
+		if err != nil {
+			l.Fatalln("Config archive:", err)
+		}
+
+		// Read configuration second time and Unmarshal to configuration struct (Check-2)
+		var cfgConfig config.Configuration
+		var buf bytes.Buffer
+		err = json.NewEncoder(&buf).Encode(cfgXML)
+		if err != nil {
+			l.Fatalln("Config didn't downgrade: ", err)
+		}
+
+		cfgConfig, err = config.ReadJSON(&buf, myID)
+		if err != nil {
+			l.Fatalln("Config didn't downgrade: ", err)
+		}
+
+		// Change version
+		cfgConfig.Version = config.CurrentVersion
+		cfgConfig.OriginalVersion = config.CurrentVersion
+		cfgConfigWrapper := config.Wrap(cfgFile, cfgConfig)
+
+		cfgConfigWrapper.Save()
+		return cfgConfigWrapper
+	}
+	l.Infoln("No need to use `-allow-downgrade-config` flag")
 	return cfg
 }
 
+func findOldConfig(cfg *config.Wrapper) bool {
+	archivePath := cfg.ConfigPath() + fmt.Sprintf(".v%d", config.CurrentVersion)
+	// Check if file already exists
+	if _, err := os.Stat(archivePath); err == nil {
+		return true
+	}
+	return false
+}
+
 func archiveAndSaveConfig(cfg *config.Wrapper) error {
 	// Copy the existing config to an archive copy
 	archivePath := cfg.ConfigPath() + fmt.Sprintf(".v%d", cfg.RawCopy().OriginalVersion)
@@ -989,7 +1085,7 @@ func archiveAndSaveConfig(cfg *config.Wrapper) error {
 		return err
 	}
 
-	// Do a regular atomic config sve
+	// Do a regular atomic config save
 	return cfg.Save()
 }