Contract Name: join.sol
Type/Category: DSS —> Token Adapter Module
Join consists of three smart contracts:
GemJoin - allows standard ERC20 tokens to be deposited for use with the system.
ETHJoin - allows native Ether to be used with the system.
DaiJoin - allows users to withdraw their Dai from the system into a standard ERC20 token.
join contract is created specifically to allow the given token type to be
join'ed to the
vat. Because of this, each
join contract has slightly different logic to account for the different types of tokens within the system.
vat - storage of the
ilk - id of the Ilk for which a
GemJoin is created for.
gem - the address of the
ilk for transferring.
dai - the address of the
one - a 10^27 uint used for math in
live - an access flag for the
dec - decimals for the Gem.
join contract has 4 public functions: a constructor,
cage. The constructor is used on contract initialization and sets the core variables of that
exit are both true to their names.
Join provides a mechanism for users to add the given token type to the
vat. It has slightly different logic in each variation, but generally resolves down to a
transfer and a function call in the
Exit is very similar, but instead allows the the user to remove their desired token from the
Cage allows the adapter to be drained (allows tokens to move out but not in).
GemJoin contract serves a very specified and singular purpose which is relatively abstracted away from the rest of the core smart contract system. When a user desires to enter the system and interact with the
dss contracts, they must use one of the
join contracts. After they have finished with the
dss contracts, they must call
exit to leave the system and take out their tokens. When the
caged by an
authed address, it can
exit collateral from the Vat but it can no longer
join new collateral.
User balances for collateral tokens added to the system via
join are accounted for in the
Gem according to collateral type
Ilk until they are converted into locked collateral tokens (
ink) so the user can draw Dai.
DaiJoin contract serves a similar purpose. It manages the exchange of Dai that is tracked in the
Vat and ERC-20 Dai that is tracked by
Dai.sol. After a user draws Dai against their collateral, they will have a balance in
Vat.dai. This Dai balance can be
exit'ed from the Vat using the
DaiJoin contract which holds the balance of
mint's ERC-20 Dai. When a user wants to move their Dai back into the
Vat accounting system (to payback debt, participate in auctions, pack
bag's in the
End, or utilize the DSR, etc), they must call
DaiJoin.join. By calling
DaiJoin.join this effectively
burn's the ERC-20 Dai and transfers
Vat.dai from the
DaiJoin's balance to the User's account in the
Vat. Under normal operation of the system, the
Dai.totalSupply should equal the
Vat.dai(DaiJoin) balance. When the
DaiJoin contract gets
cage'd by an
auth'ed address, it can move Dai back into the Vat but it can no longer
exit Dai from the Vat.
The main source of user error with the
Join contract is that Users should never
transfer tokens directly to the contracts, they must use the
join functions or they will not be able to retrieve their tokens.
There are limited sources of user error in the
join contract system due to the limited functionality of the system. Barring a contract bug, should a user call
join by accident they could always get their tokens back through the corresponding
exit call on the given
The main issue to be aware of here would be a well-executed phishing attack. As the system evolves and potentially more
join contracts are created, or more user interfaces are made, there is the potential for a user to have their funds stolen by a malicious
join contract which does not actually send tokens to the
vat, but instead to some other contract or wallet.
There could potentially be a
vat upgrade that would require new
join contracts to be created.
gem contract were to go through a token upgrade or have the tokens frozen while a user's collateral was in the system, there could potentially be a scenario in which the users were unable to redeem their collateral after the freeze or upgrade was finished. This scenario likely presents little risk though because the token going through this upgrade would more than likely want to work alongside the Maker community to be sure this was not an issue.