CDP Manager - Detailed Documentation
Managing Vaults to be transferred between users
Last updated
Managing Vaults to be transferred between users
Last updated
Contract Name: cdpManager.sol
Type/Category: Vault Management
Summary: The DssCdpManager
(aka manager
) was created to enable a formalized process for Vaults to be transferred between owners, much like assets are transferred. It is recommended that all interactions with Vaults be done through the CDP Manager. Once unlocked collateral has been deposited into the Maker Protocol, users can make use of the following features:
Multi Vault ownership and numerical identification (users can own N number of Vaults)
Vault transferability
Note: The MCD system diagram above shows that the Vault user goes through the proxy in order to interact with the CDP Manager but it is also possible to directly use the CDP Manager contract.
cdpAllow(uint cdp, address usr, uint ok)
: Allow/Disallow (ok
) a usr
address to manage the cdp
.
urnAllow(address usr, uint ok)
: Allow/Disallow (ok
) a usr
address to interact with an urn for the purposes of either entering (src
) or quitting (dst).
open(bytes32 ilk, address usr)
: Opens a new Vault for usr
to be used for an ilk
collateral type.
give(uint cdp, address dst)
: Transfers cdp
to dst
.
frob(uint cdp, int dink, int dart)
: Increments/decrements the ink
amount of collateral locked and increments/decrements the art
amount of debt in the cdp
depositing the generated DAI or collateral freed in the cdp
address.
frob(uint cdp, address dst, int dink, int dart)
: Increments/decrements the ink
amount of collateral locked and increments/decrements the art
amount of debt in the cdp
depositing the generated DAI or collateral freed into a specified dst
address.
flux(bytes32 ilk, uint cdp, address dst, uint wad)
: Moves wad
(precision 18) amount of collateral ilk
from cdp
to dst
.
flux(uint cdp, address dst, uint wad)
: Moves wad
amount of cdp
collateral from cdp
to dst
.
move(uint cdp, address dst, uint rad)
: Moves rad
(precision 45) amount of DAI from cdp
to dst
.
quit(uint cdp, address dst)
: Moves the collateral locked and debt generated from cdp
to dst
.
Note: dst
refers to the destination address.
vat
: core contract address that holds the Vaults.
cdpi
: Auto incremental id.
urns
: Mapping CDPId => UrnHandler
list
: Mapping CDPId => Prev & Next CDPIds
(double linked list)
owns
: Mapping CDPId => Owner
ilks
: Mapping CDPId => Ilk
(collateral type)
first
: Mapping Owner => First CDPId
last
: Mapping Owner => Last CDPId
count
: Mapping Owner => Amount of CDPs
allows
: Mapping Owner => CDPId => Allowed Addr => True/False
The CDP Manager was created as a way to enable Vaults to be treated more like assets that can be exchanged. Originally, the dss core contracts did not have the functionality to enable transferring Vault positions. The CDP Manager was created to wrap this functionality and enable transferring between users.
The manager
receives the vat
address in its creation and acts as an interface contract between it and the users.
The manager
keeps an internal registry of id => owner
and id => urn
allowing for the owner
to execute vat
functions for their urn
via the manager
.
The manager
keeps a double linked list structure that allows the retrieval of all the Vaults that an owner
has via on-chain calls.
In short, this is what the GetCdps
is for. This contract is a helper contract that allows the fetching of all the Vaults in just one call.
A User executes open
and gets a CDPId
in return.
After this, the CDPId
gets associated with an urn
with manager.urns(cdpId)
and then join
's collateral to it.
The user can then execute frob
to choose which dst
address they want to use to send the generated DAI to.
If the user executes frob
without dst
then the generated DAI will remain in the Vault's urn
. In this case, the user can move
it at a later point in time.
Note that this is the same process for collateral that is freed after frob
(for the frob
function that doesn't require the dst
address). The user can flux
it to another address at a later time.
In the case where a user wants to abandon the manager
, they can use quit
as a way to migrate their position of their Vault to another dst
address.
For the developers who want to integrate with the manager
, they will need to understand that the Vault actions are still in the urn
environment. Regardless of this, the manager
tries to abstract the urn
usage by a CDPId
. This means that developers will need to get the urn
(urn = manager.urns(cdpId)
) to allow the join
ing of collateral to that Vault.
As the manager
assigns a specific ilk
per CDPId
and doesn't allow others to use it for theirs, there is a second flux
function which expects an ilk
parameter. This function has the simple purpose of taking out collateral that was wrongly sent to a Vault that can't handle it/is incompatible.
Frob Function(s):
When you frob
in the CDP manager, you generate new DAI in the vat
via the CDP manager which is then deposited in the urn
that the CDP manager manages. This process depends on which frob
function you use (there exist two frob
functions). In short, one allows a destination address and the other doesn’t require it.
If you use the frob
function that has the destiny (dst
) address, you are saying that you can send any Dai generated or collateral that has been freed. The second frob
function is meant for leaving the collateral in the urn
address because the urn
is owned by the CDP manager. In this case, you would need to manually use the flux
or move
functions to get the DAI or collateral out. These functions (flux
and move
) may be more beneficial for a developer working with the proxy function, as it allows for more flexibility. For example, by using these functions you can move a specific amount of collateral and can use the other functions to do it. Overall, it can make working with it a little more flexible on specific developer needs.
As mentioned above in the summary, the dss core contracts originally did not have the functionality to enable the transfer of Vault positions. Since then, the core contracts have also implemented a native transfer functionality called fork
which allows the transferring of a Vault to another address. However, there is a restriction, which is that the address owner that will be receiving the Vault needs to provide authorization that they do in fact want to receive it. This was created for the situation when a user is transferring the collateral that is locked as well as the debt generated. If you are simply moving collateral to another address, there is no issue but in the case that you are also transferring the debt generated, there is a chance of putting a perfectly safe Vault in a risky position. This makes the contract functionality a little more restrictive. Therefore, the CDP manager is a good option to keep a simple way of transferring Vaults and recognizing them via a numeric ID.
When open
is executed, a new urn
is created and a cdpId
is assigned to it for a specific owner
. If the user uses join
to add collateral to the urn
immediately after the transaction is mined, there is a chance that a reorganization of the chain occurs. This would result in the user losing the ownership of that cdpId
/urn
pair, therefore losing their collateral. However, this issue can only arise when avoiding the use of the proxy functions via a profile proxy as the user will open
the cdp
and join
collateral in the same transaction.