support multi transaction

router.go

@@ -1,23 +1,27 @@
 package godis
 
-import "strings"
+import (
+	"strings"
+)
 
 var cmdTable = make(map[string]*command)
 
 type command struct {
 	executor ExecFunc
-	prepare  PreFunc // return related keys and rollback command
-	arity    int     // allow number of args, arity < 0 means len(args) >= -arity
+	prepare  PreFunc // return related keys command
+	undo     UndoFunc
+	arity    int // allow number of args, arity < 0 means len(args) >= -arity
 }
 
 // RegisterCommand registers a new command
 // arity means allowed number of cmdArgs, arity < 0 means len(args) >= -arity.
 // for example: the arity of `get` is 2, `mget` is -2
-func RegisterCommand(name string, executor ExecFunc, prepare PreFunc, arity int) {
+func RegisterCommand(name string, executor ExecFunc, prepare PreFunc, rollback UndoFunc, arity int) {
 	name = strings.ToLower(name)
 	cmdTable[name] = &command{
 		executor: executor,
 		prepare:  prepare,
+		undo:     rollback,
 		arity:    arity,
 	}
 }