Class ExitCodeUsage

A detector that identifies improper use of exit codes outside the developer-allowed range.

Why is it bad?

In the TON blockchain, exit codes are divided into specific ranges: 0 to 127 are reserved for the TVM or FunC, and 128 to 255 are reserved for Tact. This structure leaves the range from 256 to 65535 for developers to define custom exit codes.

When exit codes are defined outside this allowed range, it may lead to conflicts with existing reserved codes, causing unintended behavior or errors in the contract.

Example

contract Foo {
    receive("foobar") {
        // Bad: exit code defined in the reserved range for Tact
        let code: Int = 128;
        nativeThrowUnless(code, sender() == self.owner);
    }
}
Copy

Use instead:

contract Foo {
    receive("foobar") {
        // OK: using exit code from the allowed range
        let code: Int = 256;
        nativeThrowUnless(code, sender() == self.owner);
    }
}
Copy

Resources

1. Exit Codes | Tact Docs