join.sol

// SPDX-License-Identifier: AGPL-3.0-or-later

/// join.sol -- Basic token adapters

// Copyright (C) 2018 Rain <rainbreak@riseup.net>
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

pragma solidity >=0.5.12;

import "./lib.sol";

interface GemLike {
    function decimals() external view returns (uint);
    function transfer(address,uint) external returns (bool);
    function transferFrom(address,address,uint) external returns (bool);
}

interface DSTokenLike {
    function mint(address,uint) external;
    function burn(address,uint) external;
}

interface VatLike {
    function slip(bytes32,address,int) external;
    function move(address,address,uint) external;
}

/*
    Here we provide *adapters* to connect the Vat to arbitrary external
    token implementations, creating a bounded context for the Vat. The
    adapters here are provided as working examples:

      - `GemJoin`: For well behaved ERC20 tokens, with simple transfer
                   semantics.

      - `ETHJoin`: For native Ether.

      - `DaiJoin`: For connecting internal Dai balances to an external
                   `DSToken` implementation.

    In practice, adapter implementations will be varied and specific to
    individual collateral types, accounting for different transfer
    semantics and token standards.

    Adapters need to implement two basic methods:

      - `join`: enter collateral into the system
      - `exit`: remove collateral from the system

*/
//ERC20 Token的适配器模块

//Join模块通过实现Token的抽象外部接口来连接Vat,为vat创建上下文
//Join由GemJoin和DaiJoin两个合约组成

//GemJoin允许标准的ERC20 Token存入系统以供使用
//DaiJoin允许用户提供dai到标准的ERC20 Token中。

//每个Join都专门的创建，以允许特定的Token被加入到到Vat中,因此每个Join合约都有略微不同的逻辑来说明系统中不同的Token.
contract GemJoin is LibNote {
    // --- Auth ---
    mapping (address => uint) public wards;
    function rely(address usr) external note auth { wards[usr] = 1; }
    function deny(address usr) external note auth { wards[usr] = 0; }
    modifier auth {
        require(wards[msg.sender] == 1, "GemJoin/not-authorized");
        _;
    }

    //vat合约的部署地址
    VatLike public vat;   // CDP Engine
    //GemJoin创建的Ilk的id
    bytes32 public ilk;   // Collateral Type
    //ERC20 Token合约的地址
    GemLike public gem;
    //ERC20 Token的精度
    uint    public dec;
    uint    public live;  // Active Flag

    //Join模块有4个公共函数，分别是构造函数， join, exit, and cage
    //join、exit为用户提供了特定Token加入到Vat的机制，每个Token略有不同，但是总的来说是对vat里面transfer和call函数的调用
    //exit函数允许用户移除在vat中的token
    constructor(address vat_, bytes32 ilk_, address gem_) public {
        wards[msg.sender] = 1;
        live = 1;
        vat = VatLike(vat_);
        ilk = ilk_;
        gem = GemLike(gem_);
        dec = gem.decimals();
    }
    function cage() external note auth {
        live = 0;
    }

    //将抵押物gem转移wad数量到当前合约下，在vat中记载数量
    function join(address usr, uint wad) external note {
        require(live == 1, "GemJoin/not-live");
        require(int(wad) >= 0, "GemJoin/overflow");
        vat.slip(ilk, usr, int(wad));
        require(gem.transferFrom(msg.sender, address(this), wad), "GemJoin/failed-transfer");
    }

    function exit(address usr, uint wad) external note {
        require(wad <= 2 ** 255, "GemJoin/overflow");
        vat.slip(ilk, msg.sender, -int(wad));
        require(gem.transfer(usr, wad), "GemJoin/failed-transfer");
    }
}

contract DaiJoin is LibNote {
    // --- Auth ---
    mapping (address => uint) public wards;
    function rely(address usr) external note auth { wards[usr] = 1; }
    function deny(address usr) external note auth { wards[usr] = 0; }
    modifier auth {
        require(wards[msg.sender] == 1, "DaiJoin/not-authorized");
        _;
    }

    VatLike public vat;      // CDP Engine
    DSTokenLike public dai;  // Stablecoin Token
    uint    public live;     // Active Flag

    constructor(address vat_, address dai_) public {
        wards[msg.sender] = 1;
        live = 1;
        vat = VatLike(vat_);
        dai = DSTokenLike(dai_);
    }
    function cage() external note auth {
        live = 0;
    }
    uint constant ONE = 10 ** 27;
    function mul(uint x, uint y) internal pure returns (uint z) {
        require(y == 0 || (z = x * y) / y == x);
    }
    
    function join(address usr, uint wad) external note {
        vat.move(address(this), usr, mul(ONE, wad));
        dai.burn(msg.sender, wad);
    }
    function exit(address usr, uint wad) external note {
        require(live == 1, "DaiJoin/not-live");
        vat.move(msg.sender, address(this), mul(ONE, wad));
        dai.mint(usr, wad);
    }
}