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refactor: token refunds cleanup #9943

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merged 3 commits into from
Nov 13, 2024
Merged

refactor: token refunds cleanup #9943

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dcc5b7f
refactor: token refunds cleanup
benesjan Nov 13, 2024
9cb93a8
fix: fmt
benesjan Nov 13, 2024
4bb0b7d
WIP
benesjan Nov 13, 2024
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64 changes: 8 additions & 56 deletions noir-projects/noir-contracts/contracts/token_contract/src/main.nr
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Original file line number Diff line number Diff line change
Expand Up @@ -666,62 +666,14 @@ contract Token {
user,
));

// 4. Now we get the partial payloads
// TODO(#7775): Manually fetching the randomness here is not great. If we decide to include randomness in all
// notes we could just inject it in macros.
let fee_payer_randomness = unsafe { random() };
let user_randomness = unsafe { random() };

let fee_payer_setup_payload = UintNote::setup_payload().new(
fee_payer,
fee_payer_randomness,
storage.balances.at(fee_payer).set.storage_slot,
);

let user_setup_payload = UintNote::setup_payload().new(
user,
user_randomness,
storage.balances.at(user).set.storage_slot,
);

// 5. We get transient storage slots
// Using the x-coordinate as a hiding point slot is safe against someone else interfering with it because
// we have a guarantee that the public functions of the transaction are executed right after the private ones
// and for this reason the protocol guarantees that nobody can front-run us in consuming the hiding point.
// This guarantee would break if `finalize_transfer_to_private` was not called in the same transaction. This
// however is not the flow we are currently concerned with. To support the multi-transaction flow we could
// introduce a `from` function argument, hash the x-coordinate with it and then repeat the hashing in
// `finalize_transfer_to_private`.
//
// We can also be sure that the `hiding_point_slot` will not overwrite any other value in the storage because
// in our state variables we derive slots using a different hash function from multi scalar multiplication
// (MSM).
let fee_payer_point_slot = fee_payer_setup_payload.hiding_point.x;
let user_point_slot = user_setup_payload.hiding_point.x;

// 6. We compute setup logs
let fee_payer_setup_log =
fee_payer_setup_payload.encrypt_log(&mut context, user_ovpk, fee_payer, fee_payer);
let user_setup_log =
user_setup_payload.encrypt_log(&mut context, user_ovpk, user, fee_payer);

// 7. We store the hiding points an logs in transients storage
Token::at(context.this_address())
._store_payload_in_transient_storage_unsafe(
fee_payer_point_slot,
fee_payer_setup_payload.hiding_point,
fee_payer_setup_log,
)
.enqueue(&mut context);
Token::at(context.this_address())
._store_payload_in_transient_storage_unsafe(
user_point_slot,
user_setup_payload.hiding_point,
user_setup_log,
)
.enqueue(&mut context);

// 8. Set the public teardown function to `complete_refund(...)`. Public teardown is the only time when a public
// 4. We prepare the partial notes
// TODO(#9887): In each `_prepare_transfer_to_private` call we fetch the user's ovpk_m 2 more times. This is
// very inefficient.
let fee_payer_point_slot =
_prepare_transfer_to_private(user, fee_payer, &mut context, storage);
let user_point_slot = _prepare_transfer_to_private(user, user, &mut context, storage);

// 5. Set the public teardown function to `complete_refund(...)`. Public teardown is the only time when a public
// function has access to the final transaction fee, which is needed to compute the actual refund amount.
context.set_public_teardown_function(
context.this_address(),
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