New idea for spec

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Aditya Sripal 2018-07-31 18:11:19 -07:00
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### Intro and Requirements
This paper specifies changes to the auth and bank modules to implement vested accounts for the Cosmos Hub.
The requirements for this vested account is that it should be capable of being initialized during genesis with
a starting balance X coins and a vesting blocktime T. The owner of this account should be able to delegate to validators and vote,
however they cannot send their coins to other accounts until the account has fully vested. Thus, the bank module's `MsgSend` handler
should error if a vested account is trying to send an amount before time T.
This paper specifies changes to the auth and bank modules to implement vesting accounts for the Cosmos Hub.
The requirements for this vesting account is that it should be capable of being initialized during genesis with
a starting balance X coins and a vesting blocktime T. The owner of this account should be able to delegate to validators
and vote with locked coins, however they cannot send locked coins to other accounts until those coins have been unlocked.
The vesting account should also be able to spend any coins it receives from other users or from fees/inflation rewards.
Thus, the bank module's `MsgSend` handler should error if a vesting account is trying to send an amount that exceeds their
unlocked coin amount.
### Implementation
##### Changes to x/auth Module
The `Account` interface will specify both the Account type and any parameters it needs.
##### Vesting Account implementation
```go
// Account is a standard account using a sequence number for replay protection
// and a pubkey for authentication.
type Account interface {
Type() string // returns the type of the account
type VestingAccount interface {
Account
AssertIsVestingAccount() // existence implies that account is vesting.
}
GetAddress() sdk.AccAddress
SetAddress(sdk.AccAddress) error // errors if already set.
// Implements Vesting Account
// Continuously vests by unlocking coins linearly with respect to time
type ContinuousVestingAccount struct {
BaseAccount
OriginalCoins sdk.Coins
ReceivedCoins sdk.Coins
StartTime int64
EndTime int64
}
GetPubKey() crypto.PubKey // can return nil.
SetPubKey(crypto.PubKey) error
GetAccountNumber() int64
SetAccountNumber(int64) error
GetSequence() int64
SetSequence(int64) error
GetCoins() sdk.Coins
SetCoins(sdk.Coins) error
// Getter and setter methods for account params
// Parameters can be understood to be a map[string]interface{} with encoded keys and vals in store
// It is upto handler to use these appropriately
GetParams([]byte) []byte
SetParams([]byte, []byte) error
func (vacc ContinuousVestingAccount) ConvertAccount() BaseAccount {
if T > vacc.EndTime {
// Convert to BaseAccount
}
}
```
The `Type` method will allow handlers to determine what type of account is sending the message, and the
handler can then call `GetParams` to handle the specific account type using the parameters it expects to
exist in the parameter map.
The `VestingAccount` interface is used purely to assert that an account is a vesting account like so:
The `VestedAccount` will be an implementation of `Account` interface that wraps `BaseAccount` with
`Type() => "vested` and params, `GetParams() => {"TimeLock": N (int64)}`.
`SetParams` will be disabled as we do not want to update params after vested account initialization.
```go
vacc, ok := acc.(VestingAccount); ok
```
The `ContinuousVestingAccount` struct implements the Vesting account interface. It uses `OriginalCoins`, `ReceivedCoins`,
`StartTime`, and `EndTime` to calculate how many coins are sendable at any given point. Once the account has fully vested,
the next `bank.MsgSend` will convert the account into a `BaseAccount` and store it in state as such from that point on.
Since the vesting restrictions need to be implemented on a per-module basis, the `ContinuouosVestingAccount` implements
the `Account` interface exactly like `BaseAccount`.
`auth.AccountMapper` will be modified handle vested accounts as well. Specific changes
are omitted in this doc for succinctness.
##### Changes to Keepers/Handler
##### Changes to bank MsgSend Handler
Since a vested account should be capable of doing everything but sending, the restriction should be
Since a vesting account should be capable of doing everything but sending with its locked coins, the restriction should be
handled at the `bank.Keeper` level. Specifically in methods that are explicitly used for sending like
`sendCoins` and `inputOutputCoins`. These methods must check an account's `Type` method; if it is a vested
account (i.e. `acc.Type() == "vested"`):
`sendCoins` and `inputOutputCoins`. These methods must check that an account is a vesting account using the check described above.
NOTE: `Now = ctx.BlockHeader().Time`
1. Check if `ctx.BlockHeader().Time < acc.GetParams()["BlockLock"]`
2. If `true`, the account is still vesting, return sdk.Error. Else, allow transaction to be processed as normal.
1. If `Now < vacc.EndTime`
1. Calculate `SendableCoins := ReceivedCoins + OriginalCoins * (Now - StartTime)/(EndTime - StartTime))`
- NOTE: `SendableCoins` may be greater than total coins in account. This is because coins can be subtracted by staking module.
`SendableCoins` denotes maximum coins allowed to be spent right now.
2. If `msg.Amount > SendableCoins`, return sdk.Error. Else, allow transaction to process normally.
2. Else:
1. Convert account to `BaseAccount` and process normally.
Coins that are sent to a vesting account after initialization either through users sending them coins or through fees/inflation rewards
should be spendable immediately after receiving them. Thus, handlers (like staking or bank) that send coins that a vesting account did not
originally own should increment `ReceivedCoins` by the amount sent.
WARNING: Handlers SHOULD NOT update `ReceivedCoins` if they were originally sent from the vesting account. For example, if a vesting account
unbonds from a validator, their tokens should be added back to account but `ReceivedCoins` SHOULD NOT be incremented.
However when the staking handler is handing out fees or inflation rewards, then `ReceivedCoins` SHOULD be incremented.
### Initializing at Genesis
To initialize both vested accounts and base accounts, the `GenesisAccount` struct will be:
To initialize both vesting accounts and base accounts, the `GenesisAccount` struct will be:
```go
type GenesisAccount struct {
Address sdk.AccAddress `json:"address"`
Coins sdk.Coins `json:"coins"`
Type string `json:"type"`
TimeLock int64 `json:"lock"`
Address sdk.AccAddress `json:"address"`
Coins sdk.Coins `json:"coins"`
EndTime int64 `json:"lock"`
}
```
During `InitChain`, the GenesisAccount's are decoded. If they have `Type == "vested`, a vested account with parameters =>
`{"TimeLock": N}` gets created and put in initial state. Otherwise if `Type == "base"` a base account is created
and the `TimeLock` attribute of corresponding `GenesisAccount` is ignored. `InitChain` will panic on any other account types.
### Pros and Cons
##### Pros
- Easily Extensible. If more account types need to get added in the future or if developers building on top of SDK
want to handle multiple custom account types, they simply have to implement the `Account` interface with unique `Type`
and their custom parameters.
- Handlers (and their associated keepers) get to determine what types of accounts they will handle and can use the parameters
in Account interface to handle different accounts appropriately.
##### Cons
- Changes to `Account` interface
- Slightly more complex code in `bank.Keeper` functions
During `InitChain`, the GenesisAccounts are decoded. If `EndTime == 0`, a BaseAccount gets created and put in Genesis state.
Otherwise a vesting account is created with `StartTime = RequestInitChain.Time`, `EndTime = gacc.EndTime`, and `OriginalCoins = Coins`.