1 环境搭建

1.1 安装Substrate节点

$ git clone [email protected]:paritytech/substrate.git
$ cd substrate
(master)$ git checkout -b v2.0.0-rc4 v2.0.0-rc4
切换到一个新分支 'v2.0.0-rc4'
(v2.0.0-rc4)$ cargo build --release

1.2 安装cargo contract插件

•安装命令

$ cargo install cargo-contract --vers 0.6.1 --force

•帮助手册

$ cargo contract --help
cargo-contract 0.6.1
Utilities to develop Wasm smart contracts

USAGE:
    cargo contract <SUBCOMMAND>

OPTIONS:
    -h, --help       Prints help information
    -V, --version    Prints version information

SUBCOMMANDS:
    new                  Setup and create a new smart contract project
    build                Compiles the smart contract
    generate-metadata    Generate contract metadata artifacts
    test                 Test the smart contract off-chain
    help                 Prints this message or the help of the given subcommand(s)

2 ERC20合约介绍

2.1 什么是ERC20标准

ERC20 通证标准（ERC20 Token Standard）是通过以太坊创建通证时的一种规范。按照 ERC20 的规范可以编写一个智能合约，创建“可互换通证”。它并非强制要求，但遵循这个标准，所创建的通证可以与众多交易所、钱包等进行交互，它现在已被行业普遍接受。

ERC20定义了一些标准的接口函数：balanceOf 、 totalSupply 、transfer 、transferFrom 、approve和allowance 。以及一些可选的字段，例如通证名称、符号以及小数保留位数等。

详见：https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md

2.2 ERC20接口

contract ERC20 {
   function totalSupply() constant returns (uint theTotalSupply);
   function balanceOf(address _owner) constant returns (uint balance);
   function transfer(address _to, uint _value) returns (bool success);
   function transferFrom(address _from, address _to, uint _value) returns (bool success);
   function approve(address _spender, uint _value) returns (bool success);
   function allowance(address _owner, address _spender) constant returns (uint remaining);
   event Transfer(address indexed _from, address indexed _to, uint _value);
   event Approval(address indexed _owner, address indexed _spender, uint _value);
}

•功能介绍：

3 ERC20合约开发

3.1 创建合约工程

执行命令后，会生成2个文件，其中lib.rs会包括一些基础框架，我们可以在此基础上开发我们的合约。

$ cargo contract new erc20
    Created contract erc20

$ tree erc20/
erc20/
├── Cargo.toml
└── lib.rs

3.2 合约存储创建

    #[ink(storage)]
    struct Erc20 {
        /// 代币发行总量
        total_supply: storage::Value<Balance>,
        /// 用户及余额映射
        balances: storage::HashMap<AccountId, Balance>,
    }

3.3 合约构造方法创建

        #[ink(constructor)]
        fn new(&mut self, initial_supply: Balance) {
            // 获取合约创建者
            let caller = self.env().caller();
            // 设置发行总量
            self.total_supply.set(initial_supply);
            // 合约创建者拥有所有发行代币
            self.balances.insert(caller, initial_supply);
        }

3.4 合约接口方法创建

（1）查询代币发行总量接口

        #[ink(message)]
        fn total_supply(&self) -> Balance {
            *self.total_supply
        }

（2）查询用户代币余额接口

        #[ink(message)]
        fn balance_of(&self, owner: AccountId) -> Balance {
            self.balance_of_or_zero(&owner)
        }

        // 工具方法：若用户未被初始化，代币余额置为0
        fn balance_of_or_zero(&self, owner: &AccountId) -> Balance {
            *self.balances.get(owner).unwrap_or(&0)

（3）转账接口

        #[ink(message)]
        fn transfer(&mut self, to: AccountId, value: Balance) -> bool {
            // 获取合约接口调用者地址
            let from = self.env().caller();
            // 给接收地址转出指定金额代币
            self.transfer_from_to(from, to, value)
        }

        fn transfer_from_to(&mut self, from: AccountId, to: AccountId, value: Balance) -> bool {
            // 获取合约调用者账户余额
            let from_balance = self.balance_of_or_zero(&from);
            if from_balance < value {
                return false
            }
            // 获取合约接受者账户余额（代币接收者账户可能未被初始化，通过此方法将其余额初始化为0）
            let to_balance = self.balance_of_or_zero(&to);
            // 发送者余额减少指定数量
            self.balances.insert(from, from_balance - value);
            // 接收者余额增加指定数量
            self.balances.insert(to, to_balance + value);
            true
        }

我们注意到，在进行余额的增减时，并未像以太坊的solidity智能合约，使用额外的SafeMath接口，这是因为ink!提供了内置防溢出保护，通过在Cargo.toml 配置文件中，添加如下配置来提供该安全机制：

[profile.release]
panic = "abort"           <-- Panics shall be treated as aborts: reduces binary size
lto = true                <-- enable link-time-optimization: more efficient codegen
opt-level = "z"           <-- Optimize for small binary output
overflow-checks = true    <-- Arithmetic overflow protection

（4）授权转账——授权接口

通过授权转账，调用方可以授权指定账户，从其地址中安全的消费指定数量的代币。

需完善合约存储：

    #[ink(storage)]
    struct Erc20 {
        ......
        // (代币所有者, 代币授权使用者) -> 代币授权使用者可支配余额
        allowances: storage::HashMap<(AccountId, AccountId), Balance>,
    }
        #[ink(message)]
        fn approve(&mut self, spender: AccountId, value: Balance) -> bool {
            let owner = self.env().caller();
            // 代币所有者(owner)授权代币使用者(spender)可支配余额(value)
            self.allowances.insert((owner, spender), value);
            true
        }

（5）授权转账——余额查询

获取代币授权使用者剩余被允许转移的代币数量。

        #[ink(message)]
        fn allowance(&self, owner: AccountId, spender: AccountId) -> Balance {
            self.allowance_of_or_zero(&owner, &spender)
        }

（6）授权转账——转账接口

允许智能合约自动执行转账流程并代表所有者发送给定数量的代币

        #[ink(message)]
        fn transfer_from(&mut self, from: AccountId, to: AccountId, value: Balance) -> bool {
            let caller = self.env().caller();
            let allowance = self.allowance_of_or_zero(&from, &caller);
            if allowance < value {
                return false
            }
            self.allowances.insert((from, caller), allowance - value);
            self.transfer_from_to(from, to, value)
        }

        fn allowance_of_or_zero(&self, owner: &AccountId, spender: &AccountId) -> Balance {
            *self.allowances.get(&(*owner, *spender)).unwrap_or(&0)
        }

3.5 合约事件创建

•事件定义

    #[ink(event)]
    struct Transfer {
        #[ink(topic)]
        from: Option<AccountId>,
        #[ink(topic)]
        to: Option<AccountId>,
        #[ink(topic)]
        value: Balance,
    }

    #[ink(event)]
    struct Approval {
        #[ink(topic)]
        owner: AccountId,
        #[ink(topic)]
        spender: AccountId,
        #[ink(topic)]
        value: Balance,
    }

•合约构造事件

            self.env().emit_event(Transfer {
                from: None,
                to: Some(caller),
                value: initial_supply,
            });

•转账事件

            self.env().emit_event(Transfer {
                from: Some(from),
                to: Some(to),
                value,
            });

•授权事件

            self.env().emit_event(Approval {
                owner,
                spender,
                value,
            });

3.6 单元测试用例编写

        #[test]
        fn new_works() {
            let contract = Erc20::new(777);
            assert_eq!(contract.total_supply(), 777);
        }

        #[test]
        fn balance_works() {
            let contract = Erc20::new(100);
            assert_eq!(contract.total_supply(), 100);
            assert_eq!(contract.balance_of(AccountId::from([0x1; 32])), 100);
            assert_eq!(contract.balance_of(AccountId::from([0x0; 32])), 0);
        }

        #[test]
        fn transfer_works() {
            let mut contract = Erc20::new(100);
            assert_eq!(contract.balance_of(AccountId::from([0x1; 32])), 100);
            assert!(contract.transfer(AccountId::from([0x0; 32]), 10));
            assert_eq!(contract.balance_of(AccountId::from([0x0; 32])), 10);
            assert!(!contract.transfer(AccountId::from([0x0; 32]), 100));
        }

        #[test]
        fn transfer_from_works() {
            let mut contract = Erc20::new(100);
            assert_eq!(contract.balance_of(AccountId::from([0x1; 32])), 100);
            contract.approve(AccountId::from([0x1; 32]), 20);
            contract.transfer_from(AccountId::from([0x1; 32]), AccountId::from([0x0; 32]), 10);
            assert_eq!(contract.balance_of(AccountId::from([0x0; 32])), 10);
        }

跑测试用例：

$ cargo +nightly test

3.7 完整代码

#![cfg_attr(not(feature = "std"), no_std)]

use ink_lang as ink;

#[ink::contract(version = "0.1.0")]
mod erc20 {
    use ink_core::storage;

    #[ink(storage)]
    struct Erc20 {
        /// The total supply.
        total_supply: storage::Value<Balance>,
        /// The balance of each user.
        balances: storage::HashMap<AccountId, Balance>,
        /// Approval spender on behalf of the message's sender.
        allowances: storage::HashMap<(AccountId, AccountId), Balance>,
    }

    #[ink(event)]
    struct Transfer {
        #[ink(topic)]
        from: Option<AccountId>,
        #[ink(topic)]
        to: Option<AccountId>,
        #[ink(topic)]
        value: Balance,
    }

    #[ink(event)]
    struct Approval {
        #[ink(topic)]
        owner: AccountId,
        #[ink(topic)]
        spender: AccountId,
        #[ink(topic)]
        value: Balance,
    }

    impl Erc20 {
        #[ink(constructor)]
        fn new(&mut self, initial_supply: Balance) {
            let caller = self.env().caller();
            self.total_supply.set(initial_supply);
            self.balances.insert(caller, initial_supply);
            self.env().emit_event(Transfer {
                from: None,
                to: Some(caller),
                value: initial_supply,
            });
        }

        #[ink(message)]
        fn total_supply(&self) -> Balance {
            *self.total_supply
        }

        #[ink(message)]
        fn balance_of(&self, owner: AccountId) -> Balance {
            self.balance_of_or_zero(&owner)
        }

        #[ink(message)]
        fn approve(&mut self, spender: AccountId, value: Balance) -> bool {
            let owner = self.env().caller();
            self.allowances.insert((owner, spender), value);
            self.env().emit_event(Approval {
                owner,
                spender,
                value,
            });
            true
        }

        #[ink(message)]
        fn allowance(&self, owner: AccountId, spender: AccountId) -> Balance {
            self.allowance_of_or_zero(&owner, &spender)
        }

        #[ink(message)]
        fn transfer_from(&mut self, from: AccountId, to: AccountId, value: Balance) -> bool {
            let caller = self.env().caller();
            let allowance = self.allowance_of_or_zero(&from, &caller);
            if allowance < value {
                return false
            }
            self.allowances.insert((from, caller), allowance - value);
            self.transfer_from_to(from, to, value)
        }

        #[ink(message)]
        fn transfer(&mut self, to: AccountId, value: Balance) -> bool {
            let from = self.env().caller();
            self.transfer_from_to(from, to, value)
        }

        fn transfer_from_to(&mut self, from: AccountId, to: AccountId, value: Balance) -> bool {
            let from_balance = self.balance_of_or_zero(&from);
            if from_balance < value {
                return false
            }
            let to_balance = self.balance_of_or_zero(&to);
            self.balances.insert(from, from_balance - value);
            self.balances.insert(to, to_balance + value);
            self.env().emit_event(Transfer {
                from: Some(from),
                to: Some(to),
                value,
            });
            true
        }

        fn balance_of_or_zero(&self, owner: &AccountId) -> Balance {
            *self.balances.get(owner).unwrap_or(&0)
        }

        fn allowance_of_or_zero(&self, owner: &AccountId, spender: &AccountId) -> Balance {
            *self.allowances.get(&(*owner, *spender)).unwrap_or(&0)
        }
    }

    #[cfg(test)]
    mod tests {
        use super::*;

        #[test]
        fn new_works() {
            let contract = Erc20::new(777);
            assert_eq!(contract.total_supply(), 777);
        }

        #[test]
        fn balance_works() {
            let contract = Erc20::new(100);
            assert_eq!(contract.total_supply(), 100);
            assert_eq!(contract.balance_of(AccountId::from([0x1; 32])), 100);
            assert_eq!(contract.balance_of(AccountId::from([0x0; 32])), 0);
        }

        #[test]