cmd/bitcask: recovery tool (#92)

* cmd/bitcask: recovery tool

* refactor configuration & use it in recover tool

cmd/bitcask/recover.go

@@ -0,0 +1,84 @@
+package main
+
+import (
+	"os"
+
+	"github.com/prologic/bitcask"
+	"github.com/prologic/bitcask/internal/config"
+	"github.com/prologic/bitcask/internal/index"
+	log "github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+	"github.com/spf13/viper"
+)
+
+var recoveryCmd = &cobra.Command{
+	Use:     "recover",
+	Aliases: []string{"recovery"},
+	Short:   "Analyzes and recovers the index file for corruption scenarios",
+	Long: `This analyze files to detect different forms of persistence corruption in 
+persisted files. It also allows to recover the files to the latest point of integrity.
+Recovered files have the .recovered extension`,
+	Args: cobra.ExactArgs(0),
+	PreRun: func(cmd *cobra.Command, args []string) {
+		viper.BindPFlag("dry-run", cmd.Flags().Lookup("dry-run"))
+	},
+	Run: func(cmd *cobra.Command, args []string) {
+		path := viper.GetString("path")
+		dryRun := viper.GetBool("dry-run")
+		os.Exit(recover(path, dryRun))
+	},
+}
+
+func init() {
+	RootCmd.AddCommand(recoveryCmd)
+	recoveryCmd.Flags().BoolP("dry-run", "n", false, "Will only check files health without applying recovery if unhealthy")
+}
+
+func recover(path string, dryRun bool) int {
+	maxKeySize := bitcask.DefaultMaxKeySize
+	if cfg, err := config.Decode(path); err == nil {
+		maxKeySize = cfg.MaxKeySize
+	}
+
+	t, found, err := index.ReadFromFile(path, maxKeySize)
+	if err != nil && !index.IsIndexCorruption(err) {
+		log.WithError(err).Info("error while opening the index file")
+	}
+	if !found {
+		log.Info("index file doesn't exist, will be recreated on next run.")
+		return 0
+	}
+
+	if err == nil {
+		log.Debug("index file is not corrupted")
+		return 0
+	}
+	log.Debugf("index file is corrupted: %v", err)
+
+	if dryRun {
+		log.Debug("dry-run mode, not writing to a file")
+		return 0
+	}
+
+	fi, err := os.OpenFile("index.recovered", os.O_WRONLY|os.O_CREATE, 0600)
+	if err != nil {
+		log.WithError(err).Info("error while creating recovered index file")
+		return 1
+	}
+
+	// Leverage that t has the partiatially read tree even on corrupted files
+	err = index.WriteIndex(t, fi)
+	if err != nil {
+		log.WithError(err).Info("error while writing the recovered index file")
+
+		fi.Close()
+		return 1
+	}
+	err = fi.Close()
+	if err != nil {
+		log.WithError(err).Info("the recovered file index coudn't be saved correctly")
+	}
+	log.Debug("the index was recovered in the index.recovered new file")
+
+	return 0
+}