One-transaction TBTC to BTC

solidity/contracts/bank/Bank.sol

@@ -141,7 +141,7 @@ contract Bank is Ownable {
     function approveBalanceAndCall(
         address spender,
         uint256 amount,
-        bytes memory extraData
+        bytes calldata extraData
     ) external {
         _approveBalance(msg.sender, spender, amount);
         IReceiveBalanceApproval(spender).receiveBalanceApproval(

solidity/contracts/bank/IReceiveBalanceApproval.sol

@@ -30,7 +30,7 @@ interface IReceiveBalanceApproval {
     /// @param amount The amount of the Bank balance approved by the owner
     ///        to be used by the contract.
     /// @param extraData The `extraData` passed to `Bank.approveBalanceAndCall`.
-    // @dev The implementation must ensure this function can only be called
+    /// @dev The implementation must ensure this function can only be called
     ///      by the Bank. The Bank does _not_ guarantee that the `amount`
     ///      approved by the `owner` currently exists on their balance. That is,
     ///      the `owner` could approve more balance than they currently have.
@@ -40,6 +40,6 @@ interface IReceiveBalanceApproval {
     function receiveBalanceApproval(
         address owner,
         uint256 amount,
-        bytes memory extraData
+        bytes calldata extraData
     ) external;
 }

solidity/contracts/vault/TBTCVault.sol

@@ -110,7 +110,7 @@ contract TBTCVault is IVault, Governable {
     function receiveBalanceApproval(
         address owner,
         uint256 amount,
-        bytes memory
+        bytes calldata
     ) external override onlyBank {
         require(
             bank.balanceOf(owner) >= amount,
@@ -136,7 +136,7 @@ contract TBTCVault is IVault, Governable {
         }
     }
 
-    /// @notice Burns `amount` of TBTC from the caller's account and transfers
+    /// @notice Burns `amount` of TBTC from the caller's balance and transfers
     ///         `amount` back to the caller's balance in the Bank.
     /// @dev Caller must have at least `amount` of TBTC approved to
     ///       TBTC Vault.
@@ -145,23 +145,51 @@ contract TBTCVault is IVault, Governable {
         _unmint(msg.sender, amount);
     }
 
-    /// @notice Burns `amount` of TBTC from the caller's account and transfers
-    ///         `amount` back to the caller's balance in the Bank.
-    /// @dev This function is doing the same as `unmint` but it allows to
-    ///      execute unminting without an additional approval transaction.
-    ///      The function can be called only via `approveAndCall` of TBTC token.
+    /// @notice Burns `amount` of TBTC from the caller's balance and transfers
+    ///         `amount` of Bank balance to the Bridge requesting redemption
+    ///         based on the provided `redemptionData`.
+    /// @dev Caller must have at least `amount` of TBTC approved to
+    ///       TBTC Vault.
+    /// @param amount Amount of TBTC to unmint and request to redeem in Bridge.
+    /// @param redemptionData Redemption data in a format expected from
+    ///        `redemptionData` parameter of Bridge's `receiveBalanceApproval`
+    ///        function.
+    function unmintAndRedeem(uint256 amount, bytes calldata redemptionData)
+        external
+    {
+        _unmintAndRedeem(msg.sender, amount, redemptionData);
+    }
+
+    /// @notice Burns `amount` of TBTC from the caller's balance. If `extraData`
+    ///         is empty, transfers `amount` back to the caller's balance in the
+    ///         Bank. If `extraData` is not empty, requests redemption in the
+    ///         Bridge using the `extraData` as a `redemptionData` parameter to
+    ///         Bridge's `receiveBalanceApproval` function.
+    /// @dev This function is doing the same as `unmint` or `unmintAndRedeem`
+    ///      (depending on `extraData` parameter) but it allows to execute
+    ///      unminting without a separate approval transaction. The function can
+    ///      be called only via `approveAndCall` of TBTC token.
     /// @param from TBTC token holder executing unminting.
     /// @param amount Amount of TBTC to unmint.
     /// @param token TBTC token address.
+    /// @param extraData Redemption data in a format expected from
+    ///        `redemptionData` parameter of Bridge's `receiveBalanceApproval`
+    ///        function. If empty, `receiveApproval` is not requesting a
+    ///        redemption of Bank balance but is instead performing just TBTC
+    ///        unminting to a Bank balance.
     function receiveApproval(
         address from,
         uint256 amount,
         address token,
-        bytes calldata
+        bytes calldata extraData
     ) external {
         require(token == address(tbtcToken), "Token is not TBTC");
         require(msg.sender == token, "Only TBTC caller allowed");
-        _unmint(from, amount);
+        if (extraData.length == 0) {
+            _unmint(from, amount);
+        } else {
+            _unmintAndRedeem(from, amount, extraData);
+        }
     }
 
     // slither-disable-next-line calls-loop
@@ -175,4 +203,14 @@ contract TBTCVault is IVault, Governable {
         tbtcToken.burnFrom(unminter, amount);
         bank.transferBalance(unminter, amount);
     }
+
+    function _unmintAndRedeem(
+        address redeemer,
+        uint256 amount,
+        bytes calldata redemptionData
+    ) internal {
+        emit Unminted(redeemer, amount);
+        tbtcToken.burnFrom(redeemer, amount);
+        bank.approveBalanceAndCall(bank.bridge(), amount, redemptionData);
+    }
 }

solidity/test/bridge/VendingMachine.test.ts

@@ -9,7 +9,7 @@ import {
   to1ePrecision,
   getBlockTime,
 } from "../helpers/contract-test-helpers"
-import vendingMachineFixture from "../fixtures/vendingMachine"
+import bridgeFixture from "../fixtures/bridge"
 
 const ZERO_ADDRESS = ethers.constants.AddressZero
 
@@ -41,10 +41,10 @@ describe("VendingMachine", () => {
       thirdParty,
     ] = await helpers.signers.getUnnamedSigners()
 
-    // eslint-disable-next-line @typescript-eslint/no-extra-semi
-    ;({ tbtcV1, tbtcV2, vendingMachine } = await waffle.loadFixture(
-      vendingMachineFixture
-    ))
+    await waffle.loadFixture(bridgeFixture)
+    tbtcV1 = await helpers.contracts.getContract("TBTCToken")
+    tbtcV2 = await helpers.contracts.getContract("TBTC")
+    vendingMachine = await helpers.contracts.getContract("VendingMachine")
 
     await tbtcV1
       .connect(deployer)

solidity/test/fixtures/bridge.ts

@@ -7,6 +7,8 @@ import type {
   BridgeStub,
   IWalletRegistry,
   TestRelay,
+  TBTC,
+  TBTCVault,
 } from "../../typechain"
 
 /**
@@ -19,6 +21,10 @@ export default async function bridgeFixture() {
     await helpers.signers.getNamedSigners()
   const [thirdParty] = await helpers.signers.getUnnamedSigners()
 
+  const tbtc: TBTC = await helpers.contracts.getContract("TBTC")
+
+  const tbtcVault: TBTCVault = await helpers.contracts.getContract("TBTCVault")
+
   const bank: Bank & BankStub = await helpers.contracts.getContract("Bank")
 
   const bridge: Bridge & BridgeStub = await helpers.contracts.getContract(
@@ -58,6 +64,8 @@ export default async function bridgeFixture() {
     governance,
     thirdParty,
     treasury,
+    tbtc,
+    tbtcVault,
     bank,
     relay,
     walletRegistry,