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Cheat Codes

Introduction​

To help with testing, the sandbox is shipped with a set of cheatcodes.

Cheatcodes allow you to change the time of the Aztec block, load certain state or more easily manipulate Ethereum instead of having to write dedicated RPC calls to anvil or hardhat.

Prerequisites

If you aren't familiar with Anvil, we recommend reading up on that since Aztec Sandbox uses Anvil as the local Ethereum instance.

Aims​

The guide will cover how to manipulate the state of the:

  • Ethereum blockchain;
  • Aztec network.

Dependencies​

For this guide, the following Aztec packages are used:

  • @aztec/aztec.js

Initialization​

import { createPXEClient, CheatCodes } from "@aztec/aztec.js";
const pxeRpcUrl = "http://localhost:8080";
const ethRpcUrl = "http://localhost:8545";
const pxe = createPXEClient(pxeRpcUrl);
const cc = await CheatCodes.create(ethRpcUrl, pxe);

There are two properties of the CheatCodes class - eth and aztec for cheatcodes relating to the Ethereum blockchain (L1) and the Aztec network (L2) respectively.

These are cheatcodes exposed from anvil/hardhat conveniently wrapped for ease of use in the Sandbox.

Interface​

// Fetch current block number of Ethereum
public async blockNumber(): Promise<number>

// Fetch chain ID of the local Ethereum instance
public async chainId(): Promise<number>

// Fetch current timestamp on Ethereum
public async timestamp(): Promise<number>

// Mine a given number of blocks on Ethereum. Mines 1 block by default
public async mine(numberOfBlocks = 1): Promise<void>

// Set the timestamp for the next block on Ethereum.
public async setNextBlockTimestamp(timestamp: number): Promise<void>

// Dumps the current Ethereum chain state to a given file.
public async dumpChainState(fileName: string): Promise<void>

// Loads the Ethereum chain state from a file. You may use `dumpChainState()` to save the state of the Ethereum chain to a file and later load it.
public async loadChainState(fileName: string): Promise<void>

// Load the value at a storage slot of a contract address on Ethereum
public async load(contract: EthAddress, slot: bigint): Promise<bigint>

// Set the value at a storage slot of a contract address on Ethereum (e.g. modify a storage variable on your portal contract or even the rollup contract).
public async store(contract: EthAddress, slot: bigint, value: bigint): Promise<void>

// Computes the slot value for a given map and key on Ethereum. A convenient wrapper to find the appropriate storage slot to load or overwrite the state.
public keccak256(baseSlot: bigint, key: bigint): bigint

// Let you send transactions on Ethereum impersonating an externally owned or contract, without knowing the private key.
public async startImpersonating(who: EthAddress): Promise<void>

// Stop impersonating an account on Ethereum that you are currently impersonating.
public async stopImpersonating(who: EthAddress): Promise<void>

// Set the bytecode for a Ethereum contract
public async etch(contract: EthAddress, bytecode: `0x${string}`): Promise<void>

// Get the bytecode for a Ethereum contract
public async getBytecode(contract: EthAddress): Promise<`0x${string}`>

blockNumber​

Function Signature​

public async blockNumber(): Promise<number>

Description​

Fetches the current Ethereum block number.

Example​

const blockNumber = await cc.eth.blockNumber();

chainId​

Function Signature​

public async chainId(): Promise<number>

Description​

Fetches the Ethereum chain ID

Example​

const chainId = await cc.eth.chainId();

timestamp​

Function Signature​

public async timestamp(): Promise<number>

Description​

Fetches the current Ethereum timestamp.

Example​

const timestamp = await cc.eth.timestamp();

mine​

Function Signature​

public async mine(numberOfBlocks = 1): Promise<void>

Description​

Mines the specified number of blocks on Ethereum (default 1).

Example​

const blockNum = await cc.eth.blockNumber();
await cc.eth.mine(10); // mines 10 blocks
const newBlockNum = await cc.eth.blockNumber(); // = blockNum + 10.

setNextBlockTimestamp​

Function Signature​

public async setNextBlockTimestamp(timestamp: number): Promise<void>

Description​

Sets the timestamp (unix format in seconds) for the next mined block on Ethereum. Time can only be set in the future. If you set the timestamp to a time in the past, this method will throw an error.

Example​

// // Set next block timestamp to 16 Aug 2023 10:54:30 GMT
await cc.eth.setNextBlockTimestamp(1692183270);
// next transaction you will do will have the timestamp as 1692183270

dumpChainState​

Function Signature​

public async dumpChainState(fileName: string): Promise<void>

Description​

Dumps the current Ethereum chain state to a file. Stores a hex string representing the complete state of the chain in a file with the provided path. Can be re-imported into a fresh/restarted instance of Anvil to reattain the same state. When combined with loadChainState() cheatcode, it can be let you easily import the current state of mainnet into the Anvil instance of the sandbox.

Example​

await cc.eth.dumpChainState("chain-state.json");

loadChainState​

Function Signature​

public async loadChainState(fileName: string): Promise<void>

Description​

Loads the Ethereum chain state from a file which contains a hex string representing an Ethereum state. When given a file previously written to by cc.eth.dumpChainState(), it merges the contents into the current chain state. Will overwrite any colliding accounts/storage slots.

Example​

await cc.eth.loadChainState("chain-state.json");

load​

Function Signature​

public async load(contract: EthAddress, slot: bigint): Promise<bigint>

Description​

Loads the value at a storage slot of a Ethereum contract.

Example​

contract LeetContract {
    uint256 private leet = 1337; // slot 0
}
const leetContractAddress = EthAddress.fromString("0x1234...");
const value = await cc.eth.load(leetContractAddress, BigInt(0));
console.log(value); // 1337

store​

Function Signature​

public async store(contract: EthAddress, slot: bigint, value: bigint): Promise<void>

Description​

Stores the value in storage slot on a Ethereum contract.

Example​

contract LeetContract {
    uint256 private leet = 1337; // slot 0
}
const leetContractAddress = EthAddress.fromString("0x1234...");
await cc.eth.store(leetContractAddress, BigInt(0), BigInt(1000));
const value = await cc.eth.load(leetContractAddress, BigInt(0));
console.log(value); // 1000

keccak256​

Function Signature​

public keccak256(baseSlot: bigint, key: bigint): bigint

Description​

Computes the storage slot for a map key.

Example​

contract LeetContract {
    uint256 private leet = 1337; // slot 0
    mapping(address => uint256) public balances; // base slot 1
}
// find the storage slot for key `0xdead` in the balance map.
const address = BigInt("0x000000000000000000000000000000000000dead");
const slot = cc.eth.keccak256(1n, address);
// store balance of 0xdead as 100
await cc.eth.store(contractAddress, slot, 100n);

startImpersonating​

Function Signature​

public async startImpersonating(who: EthAddress): Promise<void>

Description​

Start impersonating an Ethereum account. This allows you to use this address as a sender.

Example​

await cc.eth.startImpersonating(EthAddress.fromString(address));

stopImpersonating​

Function Signature​

public async stopImpersonating(who: EthAddress): Promise<void>

Description​

Stop impersonating an Ethereum account. Stops an active impersonation started by startImpersonating.

Example​

await cc.eth.stopImpersonating(EthAddress.fromString(address));

getBytecode​

Function Signature​

public async getBytecode(contract: EthAddress): Promise<`0x${string}`>

Description​

Get the bytecode for an Ethereum contract.

Example​

const bytecode = await cc.eth.getBytecode(contract); // 0x6080604052348015610010...

etch​

Function Signature​

public async etch(contract: EthAddress, bytecode: `0x${string}`): Promise<void>

Description​

Set the bytecode for an Ethereum contract.

Example​

const bytecode = `0x6080604052348015610010...`;
await cc.eth.etch(contract, bytecode);
console.log(await cc.eth.getBytecode(contract)); // 0x6080604052348015610010...

These are cheatcodes specific to manipulating the state of Aztec rollup.

Interface​

// Get the current aztec block number
public async blockNumber(): Promise<number>

// Set time of the next execution on aztec. It also modifies time on Ethereum for next execution and stores this time as the last rollup block on the rollup contract.
public async warp(to: number): Promise<void>

// Loads the value stored at the given slot in the public storage of the given contract.
public async loadPublic(who: AztecAddress, slot: Fr | bigint): Promise<Fr>

// Loads the value stored at the given slot in the private storage of the given contract.
public async loadPrivate(owner: AztecAddress, contract: AztecAddress, slot: Fr | bigint): Promise<Note[]>

// Computes the slot value for a given map and key.
public computeSlotInMap(baseSlot: Fr | bigint, key: Fr | bigint): Fr

blockNumber​

Function Signature​

public async blockNumber(): Promise<number>

Description​

Get the current aztec block number.

Example​

const blockNumber = await cc.aztec.blockNumber();

warp​

Function Signature​

public async warp(to: number): Promise<void>

Description​

Sets the time on Ethereum and the time of the next block on Aztec. Like with the corresponding Ethereum cheatcode, time can only be set in the future, not the past. Otherwise, it will throw an error.

Example​

const timestamp = await cc.eth.timestamp();
const newTimestamp = timestamp + 100_000_000;
await cc.aztec.warp(newTimestamp);
// any Aztec.nr contract calls that make use of current timestamp
// and is executed in the next rollup block will now read `newTimestamp`

computeSlotInMap​

Function Signature​

public computeSlotInMap(baseSlot: Fr | bigint, key: Fr | bigint): Fr

Description​

Compute storage slot for a map key. The baseSlot is specified in the Aztec.nr contract.

Example​

#[aztec(storage)]
struct Storage {
    balances: Map<AztecAddress, PublicMutable<Field>>,
}

contract Token {
    ...
}
const slot = cc.aztec.computeSlotInMap(1n, key);

loadPublic​

Function Signature​

public async loadPublic(who: AztecAddress, slot: Fr | bigint): Promise<Fr>

Description​

Loads the value stored at the given slot in the public storage of the given contract.

Note: One Field element occupies a storage slot. Hence, structs with multiple field elements will be spread over multiple sequential slots. Using loadPublic will only load a single field of the struct (depending on the size of the attributes within it).

Example​

#[aztec(storage)]
struct Storage {
    balances: Map<AztecAddress, PublicMutable<Field>>,
}

contract Token {
    ...
}
const address = AztecAddress.fromString("0x123...");
const slot = cc.aztec.computeSlotInMap(1n, key);
const value = await cc.aztec.loadPublic(address, slot);

loadPrivate​

Function Signature​

public async loadPrivate(owner: AztecAddress, contract: AztecAddress, slot: Fr | bigint): Promise<Note[]>

Description​

Loads the value stored at the given slot in the private storage of the given contract.

Note: One Field element occupies a storage slot. Hence, structs with multiple field elements will be spread over multiple sequential slots. Using loadPublic will only load a single field of the struct (depending on the size of the attributes within it).

Example​

#[aztec(storage)]
struct Storage {
    ...
    pending_shields: Set<TransparentNote, TRANSPARENT_NOTE_LEN>,
}

contract Token {
    ...
}
load_private_cheatcode
const mintAmount = 100n;
const secret = Fr.random();
const secretHash = computeSecretHash(secret);
const receipt = await token.methods.mint_private(mintAmount, secretHash).send().wait();

const note = new Note([new Fr(mintAmount), secretHash]);
const extendedNote = new ExtendedNote(
  note,
  admin.address,
  token.address,
  TokenContract.storage.pending_shields.slot,
  TokenContract.notes.TransparentNote.id,
  receipt.txHash,
);
await pxe.addNote(extendedNote);

// check if note was added to pending shield:
const notes = await cc.aztec.loadPrivate(
  admin.address,
  token.address,
  TokenContract.storage.pending_shields.slot,
);
const values = notes.map(note => note.items[0]);
const balance = values.reduce((sum, current) => sum + current.toBigInt(), 0n);
expect(balance).toEqual(mintAmount);
Source code: yarn-project/end-to-end/src/e2e_cheat_codes.test.ts#L218-L246

Participate​

Keep up with the latest discussion and join the conversation in the Aztec forum.

You can also use the above link to request more cheatcodes.