refactor: nuking pay_refund_with_shielded_rebate flow (#9639)

noir-projects/noir-contracts/Nargo.toml

@@ -29,7 +29,6 @@ members = [
     "contracts/parent_contract",
     "contracts/pending_note_hashes_contract",
     "contracts/price_feed_contract",
-    "contracts/private_fpc_contract",
     "contracts/router_contract",
     "contracts/schnorr_account_contract",
     "contracts/schnorr_hardcoded_account_contract",

noir-projects/noir-contracts/contracts/fpc_contract/src/main.nr

@@ -1,10 +1,12 @@
 mod lib;
+mod settings;
 
 use dep::aztec::macros::aztec;
 
 #[aztec]
 contract FPC {
     use crate::lib::compute_rebate;
+    use crate::settings::Settings;
     use dep::aztec::{
         macros::{functions::{initializer, internal, private, public}, storage::storage},
         protocol_types::{abis::function_selector::FunctionSelector, address::AztecAddress},
@@ -14,38 +16,27 @@ contract FPC {
 
     #[storage]
     struct Storage<Context> {
-        other_asset: SharedImmutable<AztecAddress, Context>,
+        settings: SharedImmutable<Settings, Context>,
     }
 
     #[public]
     #[initializer]
-    fn constructor(other_asset: AztecAddress) {
-        storage.other_asset.initialize(other_asset);
+    fn constructor(other_asset: AztecAddress, admin: AztecAddress) {
+        let settings = Settings { other_asset, admin };
+        storage.settings.initialize(settings);
     }
 
     #[private]
-    fn fee_entrypoint_private(
-        amount: Field,
-        asset: AztecAddress,
-        secret_hash: Field,
-        nonce: Field,
-    ) {
-        assert(asset == storage.other_asset.read_private());
-        Token::at(asset)
-            .transfer_to_public(context.msg_sender(), context.this_address(), amount, nonce)
-            .call(&mut context);
-        context.set_as_fee_payer();
-        // Would like to get back to
-        // FPC::at(context.this_address()).pay_refund_with_shielded_rebate(amount, asset, secret_hash).set_public_teardown_function(&mut context);
-        context.set_public_teardown_function(
-            context.this_address(),
-            comptime {
-                FunctionSelector::from_signature(
-                    "pay_refund_with_shielded_rebate(Field,(Field),Field)",
-                )
-            },
-            [amount, asset.to_field(), secret_hash],
+    fn fee_entrypoint_private(amount: Field, asset: AztecAddress, nonce: Field) {
+        // TODO(PR #8022): Once SharedImmutable performs only 1 merkle proof here, we'll save ~4k gates
+        let settings = storage.settings.read_private();
+
+        assert(asset == settings.other_asset);
+
+        Token::at(asset).setup_refund(settings.admin, context.msg_sender(), amount, nonce).call(
+            &mut context,
         );
+        context.set_as_fee_payer();
     }
 
     #[private]
@@ -82,11 +73,4 @@ contract FPC {
             &mut context,
         );
     }
-
-    #[public]
-    #[internal]
-    fn pay_refund_with_shielded_rebate(amount: Field, asset: AztecAddress, secret_hash: Field) {
-        let refund = compute_rebate(context, amount);
-        Token::at(asset).shield(context.this_address(), refund, secret_hash, 0).call(&mut context);
-    }
 }

noir-projects/noir-contracts/contracts/token_contract/src/main.nr

@@ -675,6 +675,7 @@ contract Token {
         fee_payer: AztecAddress, // Address of the entity which will receive the fee note.
         user: AztecAddress, // A user for which we are setting up the fee refund.
         funded_amount: Field, // The amount the user funded the fee payer with (represents fee limit).
+        nonce: Field, // A nonce to make authwitness unique.
     ) {
         // 1. This function is called by fee paying contract (fee_payer) when setting up a refund so we need to support
         // the authwit flow here and check that the user really permitted fee_payer to set up a refund on their behalf.

noir-projects/noir-contracts/contracts/token_contract/src/test/refunds.nr

@@ -1,4 +1,5 @@
 use crate::{test::utils, Token};
+use aztec::oracle::random::random;
 
 use dep::authwit::cheatcodes as authwit_cheatcodes;
 use std::test::OracleMock;
@@ -14,14 +15,16 @@ unconstrained fn setup_refund_success() {
 
     let funded_amount = 1_000;
 
-    // We use the same randomness for both the fee payer and the user as we currently don't have `OracleMock::mock_once()`
+    // We use the same randomness for both the fee payer, the user and the nonce as we currently don't have
+    // `OracleMock::mock_once()`
     let fee_payer_randomness = 123;
     let user_randomness = fee_payer_randomness;
+    let nonce = fee_payer_randomness;
 
     let _ = OracleMock::mock("getRandomField").returns(fee_payer_randomness);
 
     let setup_refund_from_call_interface =
-        Token::at(token_contract_address).setup_refund(fee_payer, user, funded_amount);
+        Token::at(token_contract_address).setup_refund(fee_payer, user, funded_amount, nonce);
 
     authwit_cheatcodes::add_private_authwit_from_call_interface(
         user,
@@ -70,9 +73,10 @@ unconstrained fn setup_refund_insufficient_funded_amount() {
 
     // We set funded amount to 0 to make the transaction fee higher than the funded amount
     let funded_amount = 0;
+    let nonce = random();
 
     let setup_refund_from_call_interface =
-        Token::at(token_contract_address).setup_refund(fee_payer, user, funded_amount);
+        Token::at(token_contract_address).setup_refund(fee_payer, user, funded_amount, nonce);
 
     authwit_cheatcodes::add_private_authwit_from_call_interface(
         user,

scripts/ci/get_e2e_jobs.sh

@@ -29,7 +29,6 @@ allow_list=(
   "e2e_fees_failures"
   "e2e_fees_gas_estimation"
   "e2e_fees_private_payments"
-  "e2e_fees_private_refunds"
   "e2e_max_block_number"
   "e2e_nested_contract"
   "e2e_ordering"

yarn-project/aztec.js/src/fee/private_fee_payment_method.ts

@@ -1,6 +1,5 @@
 import { type FunctionCall } from '@aztec/circuit-types';
 import { type GasSettings } from '@aztec/circuits.js';
-import { computeSecretHash } from '@aztec/circuits.js/hash';
 import { FunctionSelector, FunctionType } from '@aztec/foundation/abi';
 import { type AztecAddress } from '@aztec/foundation/aztec-address';
 import { Fr } from '@aztec/foundation/fields';
@@ -28,10 +27,15 @@ export class PrivateFeePaymentMethod implements FeePaymentMethod {
     private wallet: Wallet,
 
     /**
-     * A secret to shield the rebate amount from the FPC.
-     * Use this to claim the shielded amount to private balance
+     * Address that the FPC sends notes it receives to.
      */
-    private rebateSecret = Fr.random(),
+    private feeRecipient: AztecAddress,
+
+    /**
+     * If true, the max fee will be set to 1.
+     * TODO(#7694): Remove this param once the lacking feature in TXE is implemented.
+     */
+    private setMaxFeeToOne = false,
   ) {}
 
   /**
@@ -52,31 +56,32 @@ export class PrivateFeePaymentMethod implements FeePaymentMethod {
    * @returns The function call to pay the fee.
    */
   async getFunctionCalls(gasSettings: GasSettings): Promise<FunctionCall[]> {
+    // We assume 1:1 exchange rate between fee juice and token. But in reality you would need to convert feeLimit
+    // (maxFee) to be in token denomination.
+    const maxFee = this.setMaxFeeToOne ? Fr.ONE : gasSettings.getFeeLimit();
     const nonce = Fr.random();
-    const maxFee = gasSettings.getFeeLimit();
+
     await this.wallet.createAuthWit({
       caller: this.paymentContract,
       action: {
-        name: 'transfer_to_public',
-        args: [this.wallet.getCompleteAddress().address, this.paymentContract, maxFee, nonce],
-        selector: FunctionSelector.fromSignature('transfer_to_public((Field),(Field),Field,Field)'),
+        name: 'setup_refund',
+        args: [this.feeRecipient, this.wallet.getAddress(), maxFee, nonce],
+        selector: FunctionSelector.fromSignature('setup_refund((Field),(Field),Field,Field)'),
         type: FunctionType.PRIVATE,
         isStatic: false,
         to: this.asset,
         returnTypes: [],
       },
     });
 
-    const secretHashForRebate = computeSecretHash(this.rebateSecret);
-
     return [
       {
         name: 'fee_entrypoint_private',
         to: this.paymentContract,
-        selector: FunctionSelector.fromSignature('fee_entrypoint_private(Field,(Field),Field,Field)'),
+        selector: FunctionSelector.fromSignature('fee_entrypoint_private(Field,(Field),Field)'),
         type: FunctionType.PRIVATE,
         isStatic: false,
-        args: [maxFee, this.asset, secretHashForRebate, nonce],
+        args: [maxFee, this.asset, nonce],
         returnTypes: [],
       },
     ];

yarn-project/cli-wallet/src/utils/options/fees.ts

@@ -76,7 +76,7 @@ export class FeeOpts implements IFeeOpts {
 
   static paymentMethodOption() {
     return new Option(
-      '--payment <method=name,asset=address,fpc=address,claimSecret=string,claimAmount=string,rebateSecret=string>',
+      '--payment <method=name,asset=address,fpc=address,claimSecret=string,claimAmount=string,feeRecipient=string>',
       'Fee payment method and arguments. Valid methods are: none, fee_juice, fpc-public, fpc-private.',
     );
   }
@@ -141,10 +141,15 @@ export function parsePaymentMethod(
     if (!parsed.asset) {
       throw new Error('Missing "asset" in payment option');
     }
+    if (!parsed.feeRecipient) {
+      // Recipient of a fee in the refund flow
+      throw new Error('Missing "feeRecipient" in payment option');
+    }
 
     const fpc = aliasedAddressParser('contracts', parsed.fpc, db);
+    const feeRecipient = AztecAddress.fromString(parsed.feeRecipient);
 
-    return [AztecAddress.fromString(parsed.asset), fpc];
+    return [AztecAddress.fromString(parsed.asset), fpc, feeRecipient];
   };
 
   return async (sender: AccountWallet) => {
@@ -180,12 +185,11 @@ export function parsePaymentMethod(
         return new PublicFeePaymentMethod(asset, fpc, sender);
       }
       case 'fpc-private': {
-        const [asset, fpc] = getFpcOpts(parsed, db);
-        const rebateSecret = parsed.rebateSecret ? Fr.fromString(parsed.rebateSecret) : Fr.random();
+        const [asset, fpc, feeRecipient] = getFpcOpts(parsed, db);
         log(
-          `Using private fee payment with asset ${asset} via paymaster ${fpc} with rebate secret ${rebateSecret.toString()}`,
+          `Using private fee payment with asset ${asset} via paymaster ${fpc} with rebate secret ${feeRecipient.toString()}`,
         );
-        return new PrivateFeePaymentMethod(asset, fpc, sender, rebateSecret);
+        return new PrivateFeePaymentMethod(asset, fpc, sender, feeRecipient);
       }
       case undefined:
         throw new Error('Missing "method" in payment option');

yarn-project/cli/src/cmds/devnet/bootstrap_network.ts

@@ -48,7 +48,8 @@ export async function bootstrapNetwork(
 
   await initPortal(pxe, l1Clients, erc20Address, portalAddress, bridge.address);
 
-  const fpc = await deployFPC(wallet, token.address);
+  const feeRecipient = wallet.getAddress();
+  const fpc = await deployFPC(wallet, token.address, feeRecipient);
 
   const counter = await deployCounter(wallet);
   // NOTE: Disabling for now in order to get devnet running
@@ -193,11 +194,15 @@ async function initPortal(
   await publicClient.waitForTransactionReceipt({ hash });
 }
 
-async function deployFPC(wallet: Wallet, tokenAddress: AztecAddress): Promise<ContractDeploymentInfo> {
+async function deployFPC(
+  wallet: Wallet,
+  tokenAddress: AztecAddress,
+  feeRecipient: AztecAddress,
+): Promise<ContractDeploymentInfo> {
   // eslint-disable-next-line @typescript-eslint/ban-ts-comment
   // @ts-ignore - Importing noir-contracts.js even in devDeps results in a circular dependency error. Need to ignore because this line doesn't cause an error in a dev environment
   const { FPCContract } = await import('@aztec/noir-contracts.js');
-  const fpc = await FPCContract.deploy(wallet, tokenAddress)
+  const fpc = await FPCContract.deploy(wallet, tokenAddress, feeRecipient)
     .send({ universalDeploy: true })
     .deployed({ proven: true, provenTimeout: 600 });
   const info: ContractDeploymentInfo = {

yarn-project/end-to-end/scripts/e2e_test_config.yml

@@ -49,8 +49,6 @@ tests:
     test_path: 'e2e_fees/gas_estimation.test.ts'
   e2e_fees_private_payments:
     test_path: 'e2e_fees/private_payments.test.ts'
-  e2e_fees_private_refunds:
-    test_path: 'e2e_fees/private_refunds.test.ts'
   e2e_keys: {}
   e2e_l1_with_wall_time: {}
   e2e_lending_contract: {}

yarn-project/end-to-end/src/benchmarks/bench_prover.test.ts

@@ -37,6 +37,7 @@ describe('benchmarks/proving', () => {
   let schnorrWalletAddress: CompleteAddress;
 
   let recipient: CompleteAddress;
+  let feeRecipient: CompleteAddress; // The address that receives the fees from the fee refund flow.
 
   let initialGasContract: FeeJuiceContract;
   let initialTestContract: TestContract;
@@ -89,7 +90,9 @@ describe('benchmarks/proving', () => {
       .send()
       .deployed();
     initialGasContract = await FeeJuiceContract.at(ProtocolContractAddress.FeeJuice, initialSchnorrWallet);
-    initialFpContract = await FPCContract.deploy(initialSchnorrWallet, initialTokenContract.address).send().deployed();
+    initialFpContract = await FPCContract.deploy(initialSchnorrWallet, initialTokenContract.address, feeRecipient)
+      .send()
+      .deployed();
 
     const feeJuiceBridgeTestHarness = await FeeJuicePortalTestingHarnessFactory.create({
       aztecNode: ctx.aztecNode,
@@ -112,6 +115,7 @@ describe('benchmarks/proving', () => {
     ]);
 
     recipient = CompleteAddress.random();
+    feeRecipient = CompleteAddress.random();
   });
 
   // remove the fake prover and setup the real one

yarn-project/end-to-end/src/benchmarks/bench_tx_size_fees.test.ts

@@ -47,7 +47,7 @@ describe('benchmarks/tx_size_fees', () => {
   beforeAll(async () => {
     feeJuice = await FeeJuiceContract.at(ProtocolContractAddress.FeeJuice, aliceWallet);
     token = await TokenContract.deploy(aliceWallet, aliceWallet.getAddress(), 'test', 'test', 18).send().deployed();
-    fpc = await FPCContract.deploy(aliceWallet, token.address).send().deployed();
+    fpc = await FPCContract.deploy(aliceWallet, token.address, sequencerAddress).send().deployed();
   });
 
   // mint tokens
@@ -94,7 +94,7 @@ describe('benchmarks/tx_size_fees', () => {
     ],
     [
       'private fee',
-      () => new PrivateFeePaymentMethod(token.address, fpc.address, aliceWallet),
+      () => new PrivateFeePaymentMethod(token.address, fpc.address, aliceWallet, sequencerAddress),
       // DA:
       // non-rev: 3 nullifiers, overhead; rev: 2 note hashes, 1168 B enc note logs, 0 B enc logs, 0 B unenc logs, teardown
       // L2: