记得朋友圈看到过一句话，如果Defi是以太坊的皇冠，那么Uniswap就是这顶皇冠中的明珠。当前,Uniswap已经发行了自己的ERC20代币，本文就是学习其代币合约的记录。
一、UNI Token 介绍
UNI Token 为 Uniswap团队自己发行的以太坊上的ERC20代币，其合约源码在etherscan上已经开源可查。在UniswapV2相关合约学习完之后（学习期间），我们抽空来学习一下它发行的ERC20代币合约。
UNI Token 代币合约并不属于Uniswap交易所的一部分，所以没有把它像以前那样归类到核心合约或者周边合约。但是它的某些实现上，和核心合约中的交易对流动性代币合约的相应实现有些类似。
二、合约源码
因为合约源码直接从ethersacn上复制而来，它将所有导入都写在一个源文件里，因此篇幅较长。笔者稍微整理了一下，将SafeMath库放在外面以减少篇幅。修改后的源码为：
pragma solidity ^0.5.16;
pragma experimental ABIEncoderV2;
import "./SafeMath.sol";
contract Uni {
/// @notice EIP-20 token name for this token
string public constant name = "Uniswap";
/// @notice EIP-20 token symbol for this token
string public constant symbol = "UNI";
/// @notice EIP-20 token decimals for this token
uint8 public constant decimals = 18;
/// @notice Total number of tokens in circulation
uint public totalSupply = 1_000_000_000e18; // 1 billion Uni
/// @notice Address which may mint new tokens
address public minter;
/// @notice The timestamp after which minting may occur
uint public mintingAllowedAfter;
/// @notice Minimum time between mints
uint32 public constant minimumTimeBetweenMints = 1 days * 365;
/// @notice Cap on the percentage of totalSupply that can be minted at each mint
uint8 public constant mintCap = 2;
/// @notice Allowance amounts on behalf of others
mapping (address => mapping (address => uint96)) internal allowances;
/// @notice Official record of token balances for each account
mapping (address => uint96) internal balances;
/// @notice A record of each accounts delegate
mapping (address => address) public delegates;
/// @notice A checkpoint for marking number of votes from a given block
struct Checkpoint {
uint32 fromBlock;
uint96 votes;
}
/// @notice A record of votes checkpoints for each account, by index
mapping (address => mapping (uint32 => Checkpoint)) public checkpoints;
/// @notice The number of checkpoints for each account
mapping (address => uint32) public numCheckpoints;
/// @notice The EIP-712 typehash for the contract's domain
bytes32 public constant DOMAIN_TYPEHASH = keccak256("EIP712Domain(string name,uint256 chainId,address verifyingContract)");
/// @notice The EIP-712 typehash for the delegation struct used by the contract
bytes32 public constant DELEGATION_TYPEHASH = keccak256("Delegation(address delegatee,uint256 nonce,uint256 expiry)");
/// @notice The EIP-712 typehash for the permit struct used by the contract
bytes32 public constant PERMIT_TYPEHASH = keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
/// @notice A record of states for signing / validating signatures
mapping (address => uint) public nonces;
/// @notice An event thats emitted when the minter address is changed
event MinterChanged(address minter, address newMinter);
/// @notice An event thats emitted when an account changes its delegate
event DelegateChanged(address indexed delegator, address indexed fromDelegate, address indexed toDelegate);
/// @notice An event thats emitted when a delegate account's vote balance changes
event DelegateVotesChanged(address indexed delegate, uint previousBalance, uint newBalance);
/// @notice The standard EIP-20 transfer event
event Transfer(address indexed from, address indexed to, uint256 amount);
/// @notice The standard EIP-20 approval event
event Approval(address indexed owner, address indexed spender, uint256 amount);
/**
* @notice Construct a new Uni token
* @param account The initial account to grant all the tokens
* @param minter_ The account with minting ability
* @param mintingAllowedAfter_ The timestamp after which minting may occur
*/
constructor(address account, address minter_, uint mintingAllowedAfter_) public {
require(mintingAllowedAfter_ >= block.timestamp, "Uni::constructor: minting can only begin after deployment");
balances[account] = uint96(totalSupply);
emit Transfer(address(0), account, totalSupply);
minter = minter_;
emit MinterChanged(address(0), minter);
mintingAllowedAfter = mintingAllowedAfter_;
}
/**
* @notice Change the minter address
* @param minter_ The address of the new minter
*/
function setMinter(address minter_) external {
require(msg.sender == minter, "Uni::setMinter: only the minter can change the minter address");
emit MinterChanged(minter, minter_);
minter = minter_;
}
/**
* @notice Mint new tokens
* @param dst The address of the destination account
* @param rawAmount The number of tokens to be minted
*/
function mint(address dst, uint rawAmount) external {
require(msg.sender == minter, "Uni::mint: only the minter can mint");
require(block.timestamp >= mintingAllowedAfter, "Uni::mint: minting not allowed yet");
require(dst != address(0), "Uni::mint: cannot transfer to the zero address");
// record the mint
mintingAllowedAfter = SafeMath.add(block.timestamp, minimumTimeBetweenMints);
// mint the amount
uint96 amount = safe96(rawAmount, "Uni::mint: amount exceeds 96 bits");
require(amount <= SafeMath.div(SafeMath.mul(totalSupply, mintCap), 100), "Uni::mint: exceeded mint cap");
totalSupply = safe96(SafeMath.add(totalSupply, amount), "Uni::mint: totalSupply exceeds 96 bits");
// transfer the amount to the recipient
balances[dst] = add96(balances[dst], amount, "Uni::mint: transfer amount overflows");
emit Transfer(address(0), dst, amount);
// move delegates
_moveDelegates(address(0), delegates[dst], amount);
}
/**
* @notice Get the number of tokens `spender` is approved to spend on behalf of `account`
* @param account The address of the account holding the funds
* @param spender The address of the account spending the funds
* @return The number of tokens approved
*/
function allowance(address account, address spender) external view returns (uint) {
return allowances[account][spender];
}
/**
* @notice Approve `spender` to transfer up to `amount` from `src`
* @dev This will overwrite the approval amount for `spender`
* and is subject to issues noted [here](https://eips.ethereum.org/EIPS/eip-20#approve)
* @param spender The address of the account which may transfer tokens
* @param rawAmount The number of tokens that are approved (2^256-1 means infinite)
* @return Whether or not the approval succeeded
*/
function approve(address spender, uint rawAmount) external returns (bool) {
uint96 amount;
if (rawAmount == uint(-1)) {
amount = uint96(-1);
} else {
amount = safe96(rawAmount, "Uni::approve: amount exceeds 96 bits");
}
allowances[msg.sender][spender] = amount;
emit Approval(msg.sender, spender, amount);
return true;
}
/**
* @notice Triggers an approval from owner to spends
* @param owner The address to approve from
* @param spender The address to be approved
* @param rawAmount The number of tokens that are approved (2^256-1 means infinite)
* @param deadline The time at which to expire the signature
* @param v The recovery byte of the signature
* @param r Half of the ECDSA signature pair
* @param s Half of the ECDSA signature pair
*/
function permit(address owner, address spender, uint rawAmount, uint deadline, uint8 v, bytes32 r, bytes32 s) external {
uint96 amount;
if (rawAmount == uint(-1)) {
amount = uint96(-1);
} else {
amount = safe96(rawAmount, "Uni::permit: amount exceeds 96 bits");
}
bytes32 domainSeparator = keccak256(abi.encode(DOMAIN_TYPEHASH, keccak256(bytes(name)), getChainId(), address(this)));
bytes32 structHash = keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, rawAmount, nonces[owner]++, deadline));
bytes32 digest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
address signatory = ecrecover(digest, v, r, s);
require(signatory != address(0), "Uni::permit: invalid signature");
require(signatory == owner, "Uni::permit: unauthorized");
require(now <= deadline, "Uni::permit: signature expired");
allowances[owner][spender] = amount;
emit Approval(owner, spender, amount);
}
/**
* @notice Get the number of tokens held by the `account`
* @param account The address of the account to get the balance of
* @return The number of tokens held
*/
function balanceOf(address account) external view returns (uint) {
return balances[account];
}
/**
* @notice Transfer `amount` tokens from `msg.sender` to `dst`
* @param dst The address of the destination account
* @param rawAmount The number of tokens to transfer
* @return Whether or not the transfer succeeded
*/
function transfer(address dst, uint rawAmount) external returns (bool) {
uint96 amount = safe96(rawAmount, "Uni::transfer: amount exceeds 96 bits");
_transferTokens(msg.sender, dst, amount);
return true;
}
/**
* @notice Transfer `amount` tokens from `src` to `dst`
* @param src The address of the source account
* @param dst The address of the destination account
* @param rawAmount The number of tokens to transfer
* @return Whether or not the transfer succeeded
*/
function transferFrom(address src, address dst, uint rawAmount) external returns (bool) {
address spender = msg.sender;
uint96 spenderAllowance = allowances[src][spender];
uint96 amount = safe96(rawAmount, "Uni::approve: amount exceeds 96 bits");
if (spender != src && spenderAllowance != uint96(-1)) {
uint96 newAllowance = sub96(spenderAllowance, amount, "Uni::transferFrom: transfer amount exceeds spender allowance");
allowances[src][spender] = newAllowance;
emit Approval(src, spender, newAllowance);
}
_transferTokens(src, dst, amount);
return true;
}
/**
* @notice Delegate votes from `msg.sender` to `delegatee`
* @param delegatee The address to delegate votes to
*/
function delegate(address delegatee) public {
return _delegate(msg.sender, delegatee);
}
/**
* @notice Delegates votes from signatory to `delegatee`
* @param delegatee The address to delegate votes to
* @param nonce The contract state required to match the signature
* @param expiry The time at which to expire the signature
* @param v The recovery byte of the signature
* @param r Half of the ECDSA signature pair
* @param s Half of the ECDSA signature pair
*/
function delegateBySig(address delegatee, uint nonce, uint expiry, uint8 v, bytes32 r, bytes32 s) public {
bytes32 domainSeparator = keccak256(abi.encode(DOMAIN_TYPEHASH, keccak256(bytes(name)), getChainId(), address(this)));
bytes32 structHash = keccak256(abi.encode(DELEGATION_TYPEHASH, delegatee, nonce, expiry));
bytes32 digest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
address signatory = ecrecover(digest, v, r, s);
require(signatory != address(0), "Uni::delegateBySig: invalid signature");
require(nonce == nonces[signatory]++, "Uni::delegateBySig: invalid nonce");
require(now <= expiry, "Uni::delegateBySig: signature expired");
return _delegate(signatory, delegatee);
}
/**
* @notice Gets the current votes balance for `account`
* @param account The address to get votes balance
* @return The number of current votes for `account`
*/
function getCurrentVotes(address account) external view returns (uint96) {
uint32 nCheckpoints = numCheckpoints[account];
return nCheckpoints > 0 ? checkpoints[account][nCheckpoints - 1].votes : 0;
}
/**
* @notice Determine the prior number of votes for an account as of a block number
* @dev Block number must be a finalized block or else this function will revert to prevent misinformation.
* @param account The address of the account to check
* @param blockNumber The block number to get the vote balance at
* @return The number of votes the account had as of the given block
*/
function getPriorVotes(address account, uint blockNumber) public view returns (uint96) {
require(blockNumber < block.number, "Uni::getPriorVotes: not yet determined");
uint32 nCheckpoints = numCheckpoints[account];
if (nCheckpoints == 0) {
return 0;
}
// First check most recent balance
if (checkpoints[account][nCheckpoints - 1].fromBlock <= blockNumber) {
return checkpoints[account][nCheckpoints - 1].votes;
}
// Next check implicit zero balance
if (checkpoints[account][0].fromBlock > blockNumber) {
return 0;
}
uint32 lower = 0;
uint32 upper = nCheckpoints - 1;
while (upper > lower) {
uint32 center = upper - (upper - lower) / 2; // ceil, avoiding overflow
Checkpoint memory cp = checkpoints[account][center];
if (cp.fromBlock == blockNumber) {
return cp.votes;
} else if (cp.fromBlock < blockNumber) {
lower = center;
} else {
upper = center - 1;
}
}
return checkpoints[account][lower].votes;
}
function _delegate(address delegator, address delegatee) internal {
address currentDelegate = delegates[delegator];
uint96 delegatorBalance = balances[delegator];
delegates[delegator] = delegatee;
emit DelegateChanged(delegator, currentDelegate, delegatee);
_moveDelegates(currentDelegate, delegatee, delegatorBalance);
}
function _transferTokens(address src, address dst, uint96 amount) internal {
require(src != address(0), "Uni::_transferTokens: cannot transfer from the zero address");
require(dst != address(0), "Uni::_transferTokens: cannot transfer to the zero address");
balances[src] = sub96(balances[src], amount, "Uni::_transferTokens: transfer amount exceeds balance");
balances[dst] = add96(balances[dst], amount, "Uni::_transferTokens: transfer amount overflows");
emit Transfer(src, dst, amount);
_moveDelegates(delegates[src], delegates[dst], amount);
}
function _moveDelegates(address srcRep, address dstRep, uint96 amount) internal {
if (srcRep != dstRep && amount > 0) {
if (srcRep != address(0)) {
uint32 srcRepNum = numCheckpoints[srcRep];
uint96 srcRepOld = srcRepNum > 0 ? checkpoints[srcRep][srcRepNum - 1].votes : 0;
uint96 srcRepNew = sub96(srcRepOld, amount, "Uni::_moveVotes: vote amount underflows");
_writeCheckpoint(srcRep, srcRepNum, srcRepOld, srcRepNew);
}
if (dstRep != address(0)) {
uint32 dstRepNum = numCheckpoints[dstRep];
uint96 dstRepOld = dstRepNum > 0 ? checkpoints[dstRep][dstRepNum - 1].votes : 0;
uint96 dstRepNew = add96(dstRepOld, amount, "Uni::_moveVotes: vote amount overflows");
_writeCheckpoint(dstRep, dstRepNum, dstRepOld, dstRepNew);
}
}
}
function _writeCheckpoint(address delegatee, uint32 nCheckpoints, uint96 oldVotes, uint96 newVotes) internal {
uint32 blockNumber = safe32(block.number, "Uni::_writeCheckpoint: block number exceeds 32 bits");
if (nCheckpoints > 0 && checkpoints[delegatee][nCheckpoints - 1].fromBlock == blockNumber) {
checkpoints[delegatee][nCheckpoints - 1].votes = newVotes;
} else {
checkpoints[delegatee][nCheckpoints] = Checkpoint(blockNumber, newVotes);
numCheckpoints[delegatee] = nCheckpoints + 1;
}
emit DelegateVotesChanged(delegatee, oldVotes, newVotes);
}
function safe32(uint n, string memory errorMessage) internal pure returns (uint32) {
require(n < 2**32, errorMessage);
return uint32(n);
}
function safe96(uint n, string memory errorMessage) internal pure returns (uint96) {
require(n < 2**96, errorMessage);
return uint96(n);
}
function add96(uint96 a, uint96 b, string memory errorMessage) internal pure returns (uint96) {
uint96 c = a + b;
require(c >= a, errorMessage);
return c;
}
function sub96(uint96 a, uint96 b, string memory errorMessage) internal pure returns (uint96) {
require(b <= a, errorMessage);
return a - b;
}
function getChainId() internal pure returns (uint) {
uint256 chainId;
assembly {
chainId := chainid() }
return chainId;
}
}
三、源码简介
-
第一行，指定了Solidity版本
-
第二行，指定使用了一个体验功能
ABIEncoderV2，到底哪个地方涉及到了体验功能，笔者目前还不清楚。 -
第三行，导入
SafeMath库。这个库和UniswapV2周边合约及我们平常使用的SafeMath库稍微有些不同，增加了自定义错误消息的重载函数。下面举一个add函数的代码示例：function add(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) { uint256 c = a + b; require(c >= a, errorMessage); return c; } -
合约定义头三项为元数据，分别为名称，符号与精度。第四项为发行总量，可以看到为10亿枚。
-
接下来四项从
minter到mintCap是增发相关，可以看出最小增发间隔为365天。 -
接下来是
allowances授权额度和balances余额，注意它们都为uint96类型，并不是常用的uint256类型。使用Python计算一下（2 ** 96 - 1）/(1e18)的结果为79228162514.26434，也就是79亿枚。而当前发行总量是10亿枚，是不会溢出的。 -
Checkpoint相关的部分是社区治理（投票）部分，暂时不研究。 -
接下来是三个
TYPEHASHP定义。计算方法是一致的，注意在学习UniswapV2中提到了permit使用线下签名消息授权功能，应用于其流动性代币中。这里UNI代币也支持这个功能。同样在学习UniswapV2中也提到了DOMAIN_TYPEHASH。 -
mapping (*address* => *uint*) public nonces;这一句是在permit函数中防重放的。 -
接下来是五个
event，大家从名字也能大致猜出它的含义。 -
构造器
constructor。发行所有代币到account地址，并且设置增发者和最早增发时间。 -
setMinter函数。更换增发者，这里是直接设置新增发者，不放心怕出错的可以考虑更换/接受模式。多一个接受操作，防止扣操作设置成错误的地址。 -
mint函数。增发代币。这里首先验证最早增发时间并更新。然后验证增发数量不能走过原总量的1/50（先乘于2再除于100）。最后进行增发操作（更新相关地址余额和发行总量），同时转移等量委托（投票）权。 -
allowance函数，很简单，获取授权额度，基本上所有ERC20代币实现相同 。 -
approve函数。授权函数，使用了和UniswapV2交易对流动性代币相似的授权实现，只不过数据大小从uint256变成了uint96（函数内进行了类型转换）。 -
permit，使用线下签名消息授权。参考我的另一篇文章UniswapV2核心合约学习（2）——UniswapV2ERC20.sol中的permit函数学习。 -
balanceOf函数，很简单，返回某个地址的代币余额。 -
transfer函数。也很简单，外部接口，调用内部_transferTokens来实现操作。注意它首先将转移数量转换成了uint96类型。 -
transferFrom函数，授权转移函数，也很简单，和UniswapV2交易对中流动性代币的transferFrom实现类似，只不过多了uint256转uint96。 -
delegate函数，委托投票，外部接口，直接调用内部函数。一种程序设计模式，使内部接口多处重用。 -
delegateBySig使用签名消息委托，同permit函数类似。和permit函数共用nonces。 -
getCurrentVotes，获得某地址当前投票数。看实现逻辑使用了检查点来记录不同时刻的投票数，未研究。 -
getPriorVotes函数，获得某地址历史投票数。参数分别为查询的地址和历史区块。具体实现逻辑未研究。 -
_delegate，委托函数。首先获取旧的委托地址、委托人代币余额，然后更新为新的委托地址。接着触发委托改变事件，最后将相应的委托值（和委托人代币余额数值等额）从旧委托地址转移到新委托地址。 -
_transferTokens函数。转移代币资产。这个要点有二处：1、资产的大小为uint96类型，2、是代币转移完成后转同时委托额度。这里SuShi项目在沿用Compound的治理协议时代币转移函数里就少了最后的委托（投票）转移，成为了一个众所周知的bug。 -
_moveDelegates，转移委托的具体实现。这里每次转移都写入了检查点，具体逻辑没有研究。 -
_writeCheckpoint写入检查点，具体逻辑没有研究。 -
接下来的
safe32，safe96，add96及sub96都是实现类似库函数的功能。防止数据上下溢出。 -
getChainId函数，使用内嵌汇编获取当前以太坊的区块链ID（区块链ID代表它是主链或者测链或者自定义链）。验证线下签名消息时使用，防止在错误的链上验证。
好了,Uniswap 发行的 UNI Token源码学习就到这结束了。由于主要是学习ERC20代币结构及函数（功能）介绍，所以一些函数的具体实现没有仔细研究。如果读者想参考其中的功能与实现，必须仔细研究清楚。
由于个人能力有限，难免有理解错误或者不正确的地方，还请大家多多留言指正。