Improve usability of the user registration

lib/database/users.go

@@ -8,10 +8,13 @@ import (
 	"bytes"
 	"crypto/rand"
 	"errors"
+	"regexp"
 
 	"golang.org/x/crypto/scrypt"
 )
 
+var alphaNumeric = regexp.MustCompile(`^[a-zA-Z0-9_\-\.]+$`).MatchString
+
 type User struct {
 	ID        int    `sql:"type:serial"`
 	Username  string `sql:"type:varchar(255),unique"`
@@ -23,7 +26,7 @@ type User struct {
 
 func (db *pgDB) AddUser(name string, pass string) error {
 	if !validUserName(name) {
-		return errors.New("Invalid user name")
+		return errors.New("Invalid user name. Username needs to have at least 3 characters and can only be letters, numbers, '-', '_' and '.'.")
 	}
 	num, err := db.sql.Model(&User{}).Where("lower(username) = lower(?)", name).Count()
 	if err != nil {
@@ -118,8 +121,14 @@ func (db *pgDB) getUser(name string) (User, error) {
 }
 
 func validUserName(name string) bool {
+	if len(name) < 3 {
+		return false
+	}
+	if !alphaNumeric(name) {
+		return false
+	}
 	switch name {
-	case "", "admin", "webmaster", "postmaster", "info", "root", "news":
+	case "", "admin", "webmaster", "postmaster", "info", "root", "news", "trantor", "librarian", "library", "imperial":
 		return false
 	default:
 		return true