testing: Test for and protect against circular accounts

internal/handlers/accounts.go

@@ -276,22 +276,55 @@ func (pame ParentAccountMissingError) Error() string {
 	return "Parent account missing"
 }
 
+type TooMuchNestingError struct{}
+
+func (tmne TooMuchNestingError) Error() string {
+	return "Too much nesting"
+}
+
+type CircularAccountsError struct{}
+
+func (cae CircularAccountsError) Error() string {
+	return "Would result in circular account relationship"
+}
+
 func insertUpdateAccount(db *DB, a *Account, insert bool) error {
 	transaction, err := db.Begin()
 	if err != nil {
 		return err
 	}
 
-	if a.ParentAccountId != -1 {
-		existing, err := transaction.SelectInt("SELECT count(*) from accounts where AccountId=?", a.ParentAccountId)
+	found := make(map[int64]bool)
+	if !insert {
+		found[a.AccountId] = true
+	}
+	parentid := a.ParentAccountId
+	depth := 0
+	for parentid != -1 {
+		depth += 1
+		if depth > 100 {
+			transaction.Rollback()
+			return TooMuchNestingError{}
+		}
+
+		var a Account
+		err := transaction.SelectOne(&a, "SELECT * from accounts where AccountId=?", parentid)
 		if err != nil {
-			transaction.Rollback()
-			return err
-		}
-		if existing != 1 {
 			transaction.Rollback()
 			return ParentAccountMissingError{}
 		}
+
+		// Insertion by itself can never result in circular dependencies
+		if insert {
+			break
+		}
+
+		found[parentid] = true
+		parentid = a.ParentAccountId
+		if _, ok := found[parentid]; ok {
+			transaction.Rollback()
+			return CircularAccountsError{}
+		}
 	}
 
 	if insert {
@@ -537,6 +570,8 @@ func AccountHandler(w http.ResponseWriter, r *http.Request, db *DB) {
 			if err != nil {
 				if _, ok := err.(ParentAccountMissingError); ok {
 					WriteError(w, 3 /*Invalid Request*/)
+				} else if _, ok := err.(CircularAccountsError); ok {
+					WriteError(w, 3 /*Invalid Request*/)
 				} else {
 					WriteError(w, 999 /*Internal Error*/)
 					log.Print(err)