Add simple username validation

internal/backend.go

@@ -16,6 +16,7 @@ type Backend interface {
 	GetRoomByID(id string) Room
 	Sync(token string, request sync.SyncRequest) (response *sync.SyncReply, err models.ApiError)
 	PublicRooms() []Room
+	ValidateUsernameFunc() func(string) error
 }
 
 type Room interface {

internal/backends/memory/backend.go

@@ -1,6 +1,8 @@
 package memory
 
 import (
+	"fmt"
+	"regexp"
 	"sort"
 	"sync"
 
@@ -15,6 +17,7 @@ type Backend struct {
 	data                 map[string]internal.User
 	rooms                map[string]internal.Room
 	hostname             string
+	validateUsernameFunc func(string) error // TODO: create ability to redefine validation func
 	mutex                sync.Mutex         // TODO: replace with RW mutex
 }
 
@@ -25,6 +28,7 @@ type Token struct {
 func NewBackend(hostname string) *Backend {
 	return &Backend{
 		hostname:             hostname,
+		validateUsernameFunc: defaultValidationUsernameFunc,
 		rooms:                make(map[string]internal.Room),
 		data:                 make(map[string]internal.User)}
 }
@@ -32,6 +36,13 @@ func NewBackend(hostname string) *Backend {
 func (backend *Backend) Register(username, password, device string) (user internal.User, token string, err models.ApiError) {
 	backend.mutex.Lock()
 
+	if backend.validateUsernameFunc != nil {
+		err := backend.validateUsernameFunc(username)
+		if err != nil {
+			return nil, "", models.NewError(models.M_INVALID_USERNAME, err.Error())
+		}
+	}
+
 	if _, ok := backend.data[username]; ok {
 		backend.mutex.Unlock()
 		return nil, "", models.NewError(models.M_USER_IN_USE, "trying to register a user ID which has been taken")
@@ -131,3 +142,20 @@ func (backend *Backend) PublicRooms() []internal.Room {
 
 	return rooms
 }
+
+func (backend *Backend) ValidateUsernameFunc() func(string) error {
+	backend.mutex.Lock()
+	defer backend.mutex.Unlock()
+
+	return backend.validateUsernameFunc
+}
+
+func defaultValidationUsernameFunc(userName string) error {
+	const re = `\w{5,}`
+
+	if !regexp.MustCompile(re).MatchString(userName) {
+		return fmt.Errorf("username does not match %s", re)
+	}
+
+	return nil
+}