join-4.sol

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

/// join-4.sol -- Non-standard token adapters

// Copyright (C) 2018 Rain <rainbreak@riseup.net>
// Copyright (C) 2018-2020 Maker Ecosystem Growth Holdings, INC.
//
// 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 "dss/lib.sol";

interface VatLike {
    function slip(bytes32, address, int256) external;
}

interface GemLike {
    function decimals() external view returns (uint256);
    function balanceOf(address) external returns (uint256);
    function transfer(address, uint256) external returns (bool);
}

// For tokens that do not implement transferFrom (like GNT), meaning the usual adapter
// approach won't work: the adapter cannot call transferFrom and therefore
// has no way of knowing when users deposit gems into it.

// To work around this, we introduce the concept of a bag, which is a trusted
// (it's created by the adapter), personalized component (one for each user).

// Users first have to create their bag with `GemJoin4.make`, then transfer
// gem to it, and then call `GemJoin4.join`, which transfer the gems from the
// bag to the adapter.

contract GemBag {
    address public ada;
    address public lad;
    GemLike public gem;

    constructor(address lad_, address gem_) public {
        ada = msg.sender;
        lad = lad_;
        gem = GemLike(gem_);
    }

    function exit(address usr, uint256 wad) external {
        require(msg.sender == ada || msg.sender == lad, "GemBag/invalid-caller");
        require(gem.transfer(usr, wad), "GemBag/failed-transfer");
    }
}

contract GemJoin4 is LibNote {
    // --- Auth ---
    mapping (address => uint256) 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); _; }

    VatLike public vat;
    bytes32 public ilk;
    GemLike public gem;
    uint256 public dec;
    uint256 public live;  // Access Flag

    mapping(address => address) public bags;

    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;
    }

    // -- admin --
    function make() external returns (address bag) {
        bag = make(msg.sender);
    }

    function make(address usr) public note returns (address bag) {
        require(bags[usr] == address(0), "GemJoin4/bag-already-exists");

        bag = address(new GemBag(address(usr), address(gem)));
        bags[usr] = bag;
    }

    // -- gems --
    function join(address urn, uint256 wad) external note {
        require(live == 1, "GemJoin4/not-live");
        require(int256(wad) >= 0, "GemJoin4/negative-amount");

        GemBag(bags[msg.sender]).exit(address(this), wad);
        vat.slip(ilk, urn, int256(wad));
    }

    function exit(address usr, uint256 wad) external note {
        require(int256(wad) >= 0, "GemJoin4/negative-amount");

        vat.slip(ilk, msg.sender, -int256(wad));
        require(gem.transfer(usr, wad), "GemJoin4/failed-transfer");
    }
}