*: add default value to 'database-id'

Fix https://github.com/coreos/dbtester/issues/312.

control/command.go

@@ -18,6 +18,7 @@ package control
 import (
 	"fmt"
 	"os"
+	"strings"
 	"time"
 
 	"github.com/coreos/dbtester"
@@ -55,7 +56,8 @@ func init() {
 		break
 	}
 
-	Command.PersistentFlags().StringVar(&databaseID, "database-id", "etcd__tip", "See dbtesterpb/database_id.pb.go")
+	ids := dbtesterpb.GetAllDatabaseIDs()
+	Command.PersistentFlags().StringVar(&databaseID, "database-id", ids[0], strings.Join(ids, ", "))
 	Command.PersistentFlags().StringVarP(&configPath, "config", "c", "", "YAML configuration file path.")
 	Command.PersistentFlags().StringVar(&diskDevice, "disk-device", dn, "Disk device to collect disk statistics metrics from.")
 	Command.PersistentFlags().StringVar(&networkInterface, "network-interface", nt, "Network interface to record in/outgoing packets.")

dbtesterpb/util.go

@@ -16,6 +16,7 @@ package dbtesterpb
 
 import (
 	"image/color"
+	"sort"
 
 	"github.com/gonum/plot/plotutil"
 )
@@ -26,6 +27,16 @@ func IsValidDatabaseID(id string) bool {
 	return ok
 }
 
+// GetAllDatabaseIDs returns all database ids.
+func GetAllDatabaseIDs() []string {
+	var ids []string
+	for k := range DatabaseID_value {
+		ids = append(ids, k)
+	}
+	sort.Strings(ids)
+	return ids
+}
+
 func GetRGBI(databaseID string, i int) color.Color {
 	switch databaseID {
 	case "etcd__v2_3":