Code Metadata

Introduction

Code metadata consists of flags representing the allowed actions of a smart contract after deployment. These flags include:

• upgradeable - indicating whether the contract can be upgraded in the future.
• readable - determining if the contract's storage can be read by other contracts.
• payable - specifying if the contract can receive funds without any endpoint being called, similar to user accounts. Note: A contract does NOT have to be payable to receive funds in payable endpoints.
• payable by smart contracts - similar to the payable flag but exclusively designed to receive funds from other smart contracts. User transfers will be rejected.

Usage

When deploying or upgrading a smart contract using koperator, the default code metadata flags are only upgradeable. These default values can be overwritten by using the following options with the koperator sc create or koperator sc upgrade commands:

• --upgradeable - marks the contract as non- upgradeable.
• --readable - marks the contract as non- readable.
• --payable - marks the contract as payable.
• --payableBySc - marks the contract as payable by smart contracts.

Bit-flag Layout

Internally, the metadata is stored as a 2-byte wide bit-flag. For clarity, let's define the flags in binary and hex representation:

bitflags! {
    struct CodeMetadata: u16 {
		const UPGRADEABLE = 0b0000_0001_0000_0000; // LSB of the first byte
		const READABLE = 0b0000_0100_0000_0000; // 3rd LSB of the first byte
		const PAYABLE = 0b0000_0000_0000_0010; // 2nd LSB of the second byte
		const PAYABLE_BY_SC = 0b0000_0000_0000_0100; // 3rd LSB of the second byte
    }
}

Alternatively, in hex representation:

const UPGRADEABLE: u16 = 0x01_00;
const READABLE: u16 = 0x04_00;
const PAYABLE: u16 = 0x00_02;
const PAYABLE_BY_SC = 0x00_04;

For example, if you wish to deploy a contract that is payable and upgradeable, the metadata would be 0x0102.

Conclusion

We believe that these flags will significantly simplify the process of creating and upgrading smart contracts.

For more examples of how Code Metadata is used, you can explore the Klever Go SDK Rust repository.