The AMM has an invariant for swaps where:
new_balance_1*new_balance_2 >= old_balance_1*old_balance_2
Due to rounding, this invariant could sometimes be violated (although by
very small amounts).
This patch introduces an amendment `fixAMMRounding` that changes the
rounding to always favor the AMM. Doing this should maintain the
invariant.
Co-authored-by: Bronek Kozicki
Co-authored-by: thejohnfreeman
Add `STObject` constructor to explicitly set the inner object template.
This allows certain AMM transactions to apply in the same ledger:
There is no issue if the trading fee is greater than or equal to 0.01%.
If the trading fee is less than 0.01%, then:
- After AMM create, AMM transactions must wait for one ledger to close
(3-5 seconds).
- After one ledger is validated, all AMM transactions succeed, as
appropriate, except for AMMVote.
- The first AMMVote which votes for a 0 trading fee in a ledger will
succeed. Subsequent AMMVote transactions which vote for a 0 trading
fee will wait for the next ledger (3-5 seconds). This behavior repeats
for each ledger.
This has no effect on the ultimate correctness of AMM. This amendment
will allow the transactions described above to succeed as expected, even
if the trading fee is 0 and the transactions are applied within one
ledger (block).
- Update amm_info to fetch AMM by amm account id.
- This is an additional way to retrieve an AMM object.
- Alternatively, AMM can still be fetched by the asset pair as well.
- Add owner directory entry for AMM object.
Context:
- Add back the AMM object directory entry, which was deleted by #4626.
- This fixes `account_objects` for `amm` type.
When an AMM account is deleted, the owner directory entries must be
deleted in order to ensure consistent ledger state.
* When deleting AMM account:
* Clean up AMM owner dir, linking AMM account and AMM object
* Delete trust lines to AMM
* Disallow `CheckCreate` to AMM accounts
* AMM cannot cash a check
* Constrain entries in AuthAccounts array to be accounts
* AuthAccounts is an array of objects for the AMMBid transaction
* SetTrust (TrustSet): Allow on AMM only for LP tokens
* If the destination is an AMM account and the trust line doesn't
exist, then:
* If the asset is not the AMM LP token, then fail the tx with
`tecNO_PERMISSION`
* If the AMM is in empty state, then fail the tx with `tecAMM_EMPTY`
* This disallows trustlines to AMM in empty state
* Add AMMID to AMM root account
* Remove lsfAMM flag and use sfAMMID instead
* Remove owner dir entry for ltAMM
* Add `AMMDelete` transaction type to handle amortized deletion
* Limit number of trust lines to delete on final withdraw + AMMDelete
* Put AMM in empty state when LPTokens is 0 upon final withdraw
* Add `tfTwoAssetIfEmpty` deposit option in AMM empty state
* Fail all AMM transactions in AMM empty state except special deposit
* Add `tecINCOMPLETE` to indicate that not all AMM trust lines are
deleted (i.e. partial deletion)
* This is handled in Transactor similar to deleted offers
* Fail AMMDelete with `tecINTERNAL` if AMM root account is nullptr
* Don't validate for invalid asset pair in AMMDelete
* AMMWithdraw deletes AMM trust lines and AMM account/object only if the
number of trust lines is less than max
* Current `maxDeletableAMMTrustLines` = 512
* Check no directory left after AMM trust lines are deleted
* Enable partial trustline deletion in AMMWithdraw
* Add `tecAMM_NOT_EMPTY` to fail any transaction that expects an AMM in
empty state
* Clawback considerations
* Disallow clawback out of AMM account
* Disallow AMM create if issuer can claw back
This patch applies to the AMM implementation in #4294.
Acknowledgements:
Richard Holland and Nik Bougalis for responsibly disclosing this issue.
Bug Bounties and Responsible Disclosures:
We welcome reviews of the project code and urge researchers to
responsibly disclose any issues they may find.
To report a bug, please send a detailed report to:
bugs@xrpl.org
Signed-off-by: Manoj Doshi <mdoshi@ripple.com>
Add AMM functionality:
- InstanceCreate
- Deposit
- Withdraw
- Governance
- Auctioning
- payment engine integration
To support this functionality, add:
- New RPC method, `amm_info`, to fetch pool and LPT balances
- AMM Root Account
- trust line for each IOU AMM token
- trust line to track Liquidity Provider Tokens (LPT)
- `ltAMM` object
The `ltAMM` object tracks:
- fee votes
- auction slot bids
- AMM tokens pair
- total outstanding tokens balance
- `AMMID` to AMM `RootAccountID` mapping
Add new classes to facilitate AMM integration into the payment engine.
`BookStep` uses these classes to infer if AMM liquidity can be consumed.
The AMM formula implementation uses the new Number class added in #4192.
IOUAmount and STAmount use Number arithmetic.
Add AMM unit tests for all features.
AMM requires the following amendments:
- featureAMM
- fixUniversalNumber
- featureFlowCross
Notes:
- Current trading fee threshold is 1%
- AMM currency is generated by: 0x03 + 152 bits of sha256{cur1, cur2}
- Current max AMM Offers is 30
---------
Co-authored-by: Howard Hinnant <howard.hinnant@gmail.com>
