Added ErrNotFound to storage interface

Author: vgarvardt

storage.go

@@ -1,6 +1,16 @@
 package osin
 
-import ()
+import (
+	"errors"
+)
+
+var (
+	// ErrNotFound is the error returned by Storage Get<...> and Load<...> functions in case
+	// no entity is found in the storage. E.g. Storage.GetClient() returns ErrNotFound when
+	// client is not found. All other returned errors must be treated as storage-specific errors,
+	// like "connection lost", "connection refused", etc.
+	ErrNotFound = errors.New("Entity not found")
+)
 
 // Storage interface
 type Storage interface {

storage_test.go

@@ -1,7 +1,6 @@
 package osin
 
 import (
-	"errors"
 	"strconv"
 	"time"
 )
@@ -74,7 +73,7 @@ func (s *TestingStorage) GetClient(id string) (Client, error) {
 	if c, ok := s.clients[id]; ok {
 		return c, nil
 	}
-	return nil, errors.New("Client not found")
+	return nil, ErrNotFound
 }
 
 func (s *TestingStorage) SetClient(id string, client Client) error {
@@ -91,7 +90,7 @@ func (s *TestingStorage) LoadAuthorize(code string) (*AuthorizeData, error) {
 	if d, ok := s.authorize[code]; ok {
 		return d, nil
 	}
-	return nil, errors.New("Authorize not found")
+	return nil, ErrNotFound
 }
 
 func (s *TestingStorage) RemoveAuthorize(code string) error {
@@ -111,7 +110,7 @@ func (s *TestingStorage) LoadAccess(code string) (*AccessData, error) {
 	if d, ok := s.access[code]; ok {
 		return d, nil
 	}
-	return nil, errors.New("Access not found")
+	return nil, ErrNotFound
 }
 
 func (s *TestingStorage) RemoveAccess(code string) error {
@@ -123,7 +122,7 @@ func (s *TestingStorage) LoadRefresh(code string) (*AccessData, error) {
 	if d, ok := s.refresh[code]; ok {
 		return s.LoadAccess(d)
 	}
-	return nil, errors.New("Refresh not found")
+	return nil, ErrNotFound
 }
 
 func (s *TestingStorage) RemoveRefresh(code string) error {