Private & Public token contract
In this tutorial we will go through writing an L2 native token contract for the Aztec Network, using the Aztec.nr contract libraries.
This tutorial is intended to help you get familiar with the Aztec.nr library, Aztec contract syntax and some of the underlying structure of the Aztec network.
In this tutorial you will learn how to:
- Write public functions that update public state
- Write private functions that update private state
- Implement access control on public and private functions
- Handle math operations safely
- Handle different private note types
- Pass data between private and public state
We are going to start with a blank project and fill in the token contract source code defined here (GitHub Link), and explain what is being added as we go.
Requirements
You will need to have aztec-nargo installed in order to compile Aztec.nr contracts.
Project setup
Create a new project with:
aztec-nargo new --contract token_contract
Your file structure should look something like this:
.
|--private_voting
| |--src
| | |--main.nr
| |--Nargo.toml
Inside Nargo.toml paste the following:
[dependencies]
aztec = { git="https://github.com/AztecProtocol/aztec-packages/", tag="aztec-packages-v0.62.0", directory="noir-projects/aztec-nr/aztec" }
authwit={ git="https://github.com/AztecProtocol/aztec-packages/", tag="aztec-packages-v0.62.0", directory="noir-projects/aztec-nr/authwit"}
compressed_string = {git="https://github.com/AztecProtocol/aztec-packages/", tag="aztec-packages-v0.62.0", directory="noir-projects/aztec-nr/compressed-string"}
We will be working within main.nr for the rest of the tutorial.
How this will work
Before writing the functions, let's go through them to see how this contract will work:
Initializer
There is one initializer function in this contract, and it will be selected and executed once when the contract is deployed, similar to a constructor in Solidity. This is marked private, so the function logic will not be transparent. To execute public function logic in the constructor, this function will call _initialize (marked internal, more detail below).
Public functions
These are functions that have transparent logic, will execute in a publicly verifiable context and can update public storage.
set_adminenables the admin to be updatedset_minterenables accounts to be added / removed from the approved minter listmint_publicenables tokens to be minted to the public balance of an accountmint_privateenables tokens to be minted to the private balance of an account (with some caveats we will dig into)shieldenables tokens to be moved from a public balance to a private balance, not necessarily the same account (step 1 of a 2 step process)transfer_publicenables users to transfer tokens from one account's public balance to another account's public balanceburn_publicenables users to burn tokens
Private functions
These are functions that have private logic and will be executed on user devices to maintain privacy. The only data that is submitted to the network is a proof of correct execution, new data commitments and nullifiers, so users will not reveal which contract they are interacting with or which function they are executing. The only information that will be revealed publicly is that someone executed a private transaction on Aztec.
redeem_shieldenables accounts to claim tokens that have been made private viamint_privateorshieldby providing the secrettransfer_to_publicenables an account to send tokens from their private balance to any other account's public balancetransferenables an account to send tokens from their private balance to another account's private balancetransfer_fromenables an account to send tokens from another account's private balance to another account's private balancecancel_authwitenables an account to cancel an authorization to spend tokensburnenables tokens to be burned privately
Internal functions
Internal functions are functions that can only be called by the contract itself. These can be used when the contract needs to call one of it's public functions from one of it's private functions.
_increase_public_balanceincreases the public balance of an account whentransfer_to_publicis called_reduce_total_supplyreduces the total supply of tokens when a token is privately burned
To clarify, let's review some details of the Aztec transaction lifecycle, particularly how a transaction "moves through" these contexts.
Execution contexts
Transactions are initiated in the private context, then move to the L2 public context, then to the Ethereum L1 context.
Step 1. Private Execution
Users provide inputs and execute locally on their device for privacy reasons. Outputs of the private execution are commitment and nullifier updates, a proof of correct execution and any return data to pass to the public execution context.
Step 2. Public Execution
This happens remotely by the sequencer, which takes inputs from the private execution and runs the public code in the network virtual machine, similar to any other public blockchain.
Step 3. Ethereum execution
Aztec transactions can pass data to Ethereum contracts through the rollup via the outbox. The data can consumed by Ethereum contracts at a later time, but this is not part of the transaction flow for an Aztec transaction. The technical details of this are beyond the scope of this tutorial, but we will cover them in an upcoming piece.
Unconstrained functions
Unconstrained functions can be thought of as view functions from Solidity--they only return information from the contract storage or compute and return data without modifying contract storage.
Contract dependencies
Before we can implement the functions, we need set up the contract storage, and before we do that we need to import the appropriate dependencies.
We will be going over the code in main.nr here (GitHub link). If you are following along and want to compile main.nr yourself, you need to add the other files in the directory as they contain imports that are used in main.nr.
Paste these imports:
mod types;
mod test;
use dep::aztec::macros::aztec;
// Minimal token implementation that supports `AuthWit` accounts.
// The auth message follows a similar pattern to the cross-chain message and includes a designated caller.
// The designated caller is ALWAYS used here, and not based on a flag as cross-chain.
// message hash = H([caller, contract, selector, ...args])
// To be read as `caller` calls function at `contract` defined by `selector` with `args`
// Including a nonce in the message hash ensures that the message can only be used once.
#[aztec]
contract Token {
// Libs
use std::meta::derive;
use dep::compressed_string::FieldCompressedString;
use dep::aztec::{
context::{PrivateCallInterface, PrivateContext},
encrypted_logs::{
encrypted_event_emission::encode_and_encrypt_event_unconstrained,
encrypted_note_emission::{
encode_and_encrypt_note, encode_and_encrypt_note_unconstrained,
},
},
hash::compute_secret_hash,
keys::getters::get_public_keys,
macros::{
events::event,
functions::{initializer, internal, private, public, view},
storage::storage,
},
oracle::random::random,
prelude::{
AztecAddress, FunctionSelector, Map, NoteGetterOptions, PrivateSet, PublicContext,
PublicMutable, SharedImmutable,
},
protocol_types::{point::Point, traits::Serialize},
utils::comparison::Comparator,
};
use dep::uint_note::uint_note::UintNote;
use dep::authwit::auth::{
assert_current_call_valid_authwit, assert_current_call_valid_authwit_public,
compute_authwit_nullifier,
};
use crate::types::{balance_set::BalanceSet, transparent_note::TransparentNote};
}
We are importing:
CompressedStringto hold the token symbol- Types from
aztec::prelude - Types for storing note types
Types files
We are also importing types from a types.nr file, which imports types from the types folder. You can view them here (GitHub link).
The main thing to note from this types folder is the TransparentNote definition. This defines how the contract moves value from the public domain into the private domain. It is similar to the value_note that we imported, but with some modifications namely, instead of a defined nullifier key, it allows anyone that can produce the pre-image to the stored secret_hash to spend the note.
Note on private state
Private state in Aztec is all UTXOs.
Contract Storage
Now that we have dependencies imported into our contract we can define the storage for the contract.
Below the dependencies, paste the following Storage struct:
#[storage]
struct Storage<Context> {
admin: PublicMutable<AztecAddress, Context>,
minters: Map<AztecAddress, PublicMutable<bool, Context>, Context>,
balances: Map<AztecAddress, BalanceSet<Context>, Context>,
total_supply: PublicMutable<U128, Context>,
pending_shields: PrivateSet<TransparentNote, Context>,
public_balances: Map<AztecAddress, PublicMutable<U128, Context>, Context>,
symbol: SharedImmutable<FieldCompressedString, Context>,
name: SharedImmutable<FieldCompressedString, Context>,
decimals: SharedImmutable<u8, Context>,
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L75-L98
Reading through the storage variables:
adminan Aztec address stored in public state.mintersis a mapping of Aztec addresses in public state. This will store whether an account is an approved minter on the contract.balancesis a mapping of private balances. Private balances are stored in aPrivateSetofUintNotes. The balance is the sum of all of an account'sUintNotes.total_supplyis an unsigned integer (max 128 bit value) stored in public state and represents the total number of tokens minted.pending_shieldsis aPrivateSetofTransparentNotes stored in private state. What is stored publicly is a set of commitments toTransparentNotes.public_balancesis a mapping of Aztec addresses in public state and represents the publicly viewable balances of accounts.symbol,name, anddecimalsare similar in meaning to ERC20 tokens on Ethereum.
Functions
Copy and paste the body of each function into the appropriate place in your project if you are following along.
Constructor
This function sets the creator of the contract (passed as msg_sender from the constructor) as the admin and makes them a minter, and sets name, symbol, and decimals.
#[public]
#[initializer]
fn constructor(admin: AztecAddress, name: str<31>, symbol: str<31>, decimals: u8) {
assert(!admin.is_zero(), "invalid admin");
storage.admin.write(admin);
storage.minters.at(admin).write(true);
storage.name.initialize(FieldCompressedString::from_string(name));
storage.symbol.initialize(FieldCompressedString::from_string(symbol));
storage.decimals.initialize(decimals);
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L100-L113
Public function implementations
Public functions are declared with the #[public] macro above the function name.
As described in the execution contexts section above, public function logic and transaction information is transparent to the world. Public functions update public state, but can be used to prepare data to be used in a private context, as we will go over below (e.g. see the shield function).
Storage is referenced as storage.variable.
set_admin
After storage is initialized, the contract checks that the msg_sender is the admin. If not, the transaction will fail. If it is, the new_admin is saved as the admin.
#[public]
fn set_admin(new_admin: AztecAddress) {
assert(storage.admin.read().eq(context.msg_sender()), "caller is not admin");
storage.admin.write(new_admin);
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L114-L122
set_minter
This function allows the admin to add or a remove a minter from the public minters mapping. It checks that msg_sender is the admin and finally adds the minter to the minters mapping.
#[public]
fn set_minter(minter: AztecAddress, approve: bool) {
assert(storage.admin.read().eq(context.msg_sender()), "caller is not admin");
storage.minters.at(minter).write(approve);
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L186-L196
mint_public
This function allows an account approved in the public minters mapping to create new public tokens owned by the provided to address.
First, storage is initialized. Then the function checks that the msg_sender is approved to mint in the minters mapping. If it is, a new U128 value is created of the amount provided. The function reads the recipients public balance and then adds the amount to mint, saving the output as new_balance, then reads to total supply and adds the amount to mint, saving the output as supply. new_balance and supply are then written to storage.
#[public]
fn mint_public(to: AztecAddress, amount: Field) {
assert(storage.minters.at(context.msg_sender()).read(), "caller is not minter");
let amount = U128::from_integer(amount);
let new_balance = storage.public_balances.at(to).read().add(amount);
let supply = storage.total_supply.read().add(amount);
storage.public_balances.at(to).write(new_balance);
storage.total_supply.write(supply);
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L197-L209
mint_private
This public function allows an account approved in the public minters mapping to create new private tokens that can be claimed by anyone that has the pre-image to the secret_hash.
First, public storage is initialized. Then it checks that the msg_sender is an approved minter. Then a new TransparentNote is created with the specified amount and secret_hash. You can read the details of the TransparentNote in the types.nr file here (GitHub link). The amount is added to the existing public total_supply and the storage value is updated. Then the new TransparentNote is added to the pending_shields using the insert_from_public function, which is accessible on the PrivateSet type. Then it's ready to be claimed by anyone with the secret_hash pre-image using the redeem_shield function.
// TODO(benesjan): To be nuked in a followup PR.
#[public]
fn mint_private_old(amount: Field, secret_hash: Field) {
assert(storage.minters.at(context.msg_sender()).read(), "caller is not minter");
let pending_shields = storage.pending_shields;
let mut note = TransparentNote::new(amount, secret_hash);
let supply = storage.total_supply.read().add(U128::from_integer(amount));
storage.total_supply.write(supply);
pending_shields.insert_from_public(&mut note);
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L210-L223
shield
This public function enables an account to stage tokens from it's public_balance to be claimed as a private TransparentNote by any account that has the pre-image to the secret_hash.
First, storage is initialized. Then it checks whether the calling contract (context.msg_sender) matches the account that the funds will be debited from.
Authorizing token spends
If the msg_sender is NOT the same as the account to debit from, the function checks that the account has authorized the msg_sender contract to debit tokens on its behalf. This check is done by computing the function selector that needs to be authorized (in this case, the shield function), computing the hash of the message that the account contract has approved. This is a hash of the contract that is approved to spend (context.msg_sender), the token contract that can be spent from (context.this_address()), the selector, the account to spend from (from.address), the amount, the secret_hash and a nonce to prevent multiple spends. This hash is passed to assert_valid_public_message_for to ensure that the Account Contract has approved tokens to be spent on it's behalf.
If the msg_sender is the same as the account to debit tokens from, the authorization check is bypassed and the function proceeds to update the account's public_balance and adds a new TransparentNote to the pending_shields.
It returns 1 to indicate successful execution.
#[public]
fn shield(from: AztecAddress, amount: Field, secret_hash: Field, nonce: Field) {
if (!from.eq(context.msg_sender())) {
// The redeem is only spendable once, so we need to ensure that you cannot insert multiple shields from the same message.
assert_current_call_valid_authwit_public(&mut context, from);
} else {
assert(nonce == 0, "invalid nonce");
}
let amount = U128::from_integer(amount);
let from_balance = storage.public_balances.at(from).read().sub(amount);
let pending_shields = storage.pending_shields;
let mut note = TransparentNote::new(amount.to_field(), secret_hash);
storage.public_balances.at(from).write(from_balance);
pending_shields.insert_from_public(&mut note);
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L224-L240
transfer_public
This public function enables public transfers between Aztec accounts. The sender's public balance will be debited the specified amount and the recipient's public balances will be credited with that amount.
After storage is initialized, the authorization flow specified above is checked. Then the sender and recipient's balances are updated and saved to storage.
#[public]
fn transfer_public(from: AztecAddress, to: AztecAddress, amount: Field, nonce: Field) {
if (!from.eq(context.msg_sender())) {
assert_current_call_valid_authwit_public(&mut context, from);
} else {
assert(nonce == 0, "invalid nonce");
}
let amount = U128::from_integer(amount);
let from_balance = storage.public_balances.at(from).read().sub(amount);
storage.public_balances.at(from).write(from_balance);
let to_balance = storage.public_balances.at(to).read().add(amount);
storage.public_balances.at(to).write(to_balance);
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L241-L255
burn_public
This public function enables public burning (destroying) of tokens from the sender's public balance.
After storage is initialized, the authorization flow specified above is checked. Then the sender's public balance and the total_supply are updated and saved to storage.
#[public]
fn burn_public(from: AztecAddress, amount: Field, nonce: Field) {
if (!from.eq(context.msg_sender())) {
assert_current_call_valid_authwit_public(&mut context, from);
} else {
assert(nonce == 0, "invalid nonce");
}
let amount = U128::from_integer(amount);
let from_balance = storage.public_balances.at(from).read().sub(amount);
storage.public_balances.at(from).write(from_balance);
let new_supply = storage.total_supply.read().sub(amount);
storage.total_supply.write(new_supply);
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L256-L272
Private function implementations
Private functions are declared with the #[private] macro above the function name like so:
#[private]
fn redeem_shield(
As described in the execution contexts section above, private function logic and transaction information is hidden from the world and is executed on user devices. Private functions update private state, but can pass data to the public execution context (e.g. see the transfer_to_public function).
Storage is referenced as storage.variable.
redeem_shield
This private function enables an account to move tokens from a TransparentNote in the pending_shields mapping to a UintNote in private balances. The UintNote will be associated with a nullifier key, so any account that knows this key can spend this note.
Going through the function logic, first the secret_hash is generated from the given secret. This ensures that only the entity possessing the secret can use it to redeem the note. Following this, a TransparentNote is retrieved from the set, using the provided amount and secret. The note is subsequently removed from the set, allowing it to be redeemed only once. The recipient's private balance is then increased using the increment helper function from the value_note library (GitHub link).
The function returns 1 to indicate successful execution.
#[private]
fn redeem_shield(to: AztecAddress, amount: Field, secret: Field) {
let secret_hash = compute_secret_hash(secret);
// Pop 1 note (set_limit(1)) which has an amount stored in a field with index 0 (select(0, amount)) and
// a secret_hash stored in a field with index 1 (select(1, secret_hash)).
let mut options = NoteGetterOptions::new();
options = options
.select(TransparentNote::properties().amount, Comparator.EQ, amount)
.select(TransparentNote::properties().secret_hash, Comparator.EQ, secret_hash)
.set_limit(1);
let notes = storage.pending_shields.pop_notes(options);
assert(notes.len() == 1, "note not popped");
// Add the token note to user's balances set
// Note: Using context.msg_sender() as a sender below makes this incompatible with escrows because we send
// outgoing logs to that address and to send outgoing logs you need to get a hold of ovsk_m.
let from = context.msg_sender();
let from_ovpk_m = get_public_keys(from).ovpk_m;
storage.balances.at(to).add(to, U128::from_integer(amount)).emit(encode_and_encrypt_note(
&mut context,
from_ovpk_m,
to,
context.msg_sender(),
));
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L273-L298
transfer_to_public
This private function enables un-shielding of private UintNotes stored in balances to any Aztec account's public_balance.
After initializing storage, the function checks that the msg_sender is authorized to spend tokens. See the Authorizing token spends section above for more detail--the only difference being that assert_valid_message_for is modified to work specifically in the private context. After the authorization check, the sender's private balance is decreased using the decrement helper function for the value_note library. Then it stages a public function call on this contract (_increase_public_balance) to be executed in the public execution phase of transaction execution. _increase_public_balance is marked as an internal function, so can only be called by this token contract.
The function returns 1 to indicate successful execution.
#[private]
fn transfer_to_public(from: AztecAddress, to: AztecAddress, amount: Field, nonce: Field) {
if (!from.eq(context.msg_sender())) {
assert_current_call_valid_authwit(&mut context, from);
} else {
assert(nonce == 0, "invalid nonce");
}
let from_ovpk_m = get_public_keys(from).ovpk_m;
// TODO: constrain encryption below - we are using unconstrained here only becuase of the following Noir issue
// https://github.com/noir-lang/noir/issues/5771
storage.balances.at(from).sub(from, U128::from_integer(amount)).emit(
encode_and_encrypt_note_unconstrained(&mut context, from_ovpk_m, from, from),
);
Token::at(context.this_address())._increase_public_balance(to, amount).enqueue(&mut context);
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L299-L316
transfer
This private function enables private token transfers between Aztec accounts.
After initializing storage, the function checks that the msg_sender is authorized to spend tokens. See the Authorizing token spends section above for more detail--the only difference being that assert_valid_message_for is modified to work specifically in the private context. After authorization, the function gets the current balances for the sender and recipient and decrements and increments them, respectively, using the value_note helper functions.
#[private]
fn transfer(to: AztecAddress, amount: Field) {
let from = context.msg_sender();
let from_ovpk_m = get_public_keys(from).ovpk_m;
let amount = U128::from_integer(amount);
// We reduce `from`'s balance by amount by recursively removing notes over potentially multiple calls. This
// method keeps the gate count for each individual call low - reading too many notes at once could result in
// circuits in which proving is not feasible.
// Since the sum of the amounts in the notes we nullified was potentially larger than amount, we create a new
// note for `from` with the change amount, e.g. if `amount` is 10 and two notes are nullified with amounts 8 and
// 5, then the change will be 3 (since 8 + 5 - 10 = 3).
let change = subtract_balance(
&mut context,
storage,
from,
amount,
INITIAL_TRANSFER_CALL_MAX_NOTES,
);
storage.balances.at(from).add(from, change).emit(encode_and_encrypt_note_unconstrained(
&mut context,
from_ovpk_m,
from,
from,
));
storage.balances.at(to).add(to, amount).emit(encode_and_encrypt_note_unconstrained(
&mut context,
from_ovpk_m,
to,
from,
));
// We don't constrain encryption of the note log in `transfer` (unlike in `transfer_from`) because the transfer
// function is only designed to be used in situations where the event is not strictly necessary (e.g. payment to
// another person where the payment is considered to be successful when the other party successfully decrypts a
// note).
Transfer { from, to, amount: amount.to_field() }.emit(
encode_and_encrypt_event_unconstrained(&mut context, from_ovpk_m, to, from),
);
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L317-L358
transfer_from
This private function enables an account to transfer tokens on behalf of another account. The account that tokens are being debited from must have authorized the msg_sender to spend tokens on its behalf.
#[private]
fn transfer_from(from: AztecAddress, to: AztecAddress, amount: Field, nonce: Field) {
if (!from.eq(context.msg_sender())) {
assert_current_call_valid_authwit(&mut context, from);
} else {
assert(nonce == 0, "invalid nonce");
}
let from_ovpk_m = get_public_keys(from).ovpk_m;
let amount = U128::from_integer(amount);
// TODO: constrain encryption below - we are using unconstrained here only becuase of the following Noir issue
// https://github.com/noir-lang/noir/issues/5771
storage.balances.at(from).sub(from, amount).emit(encode_and_encrypt_note_unconstrained(
&mut context,
from_ovpk_m,
from,
from,
));
// TODO: constrain encryption below - we are using unconstrained here only becuase of the following Noir issue
// https://github.com/noir-lang/noir/issues/5771
storage.balances.at(to).add(to, amount).emit(encode_and_encrypt_note_unconstrained(
&mut context,
from_ovpk_m,
to,
from,
));
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L419-L453
burn
This private function enables accounts to privately burn (destroy) tokens.
After initializing storage, the function checks that the msg_sender is authorized to spend tokens. Then it gets the sender's current balance and decrements it. Finally it stages a public function call to _reduce_total_supply.
#[private]
fn burn(from: AztecAddress, amount: Field, nonce: Field) {
if (!from.eq(context.msg_sender())) {
assert_current_call_valid_authwit(&mut context, from);
} else {
assert(nonce == 0, "invalid nonce");
}
let from_ovpk_m = get_public_keys(from).ovpk_m;
// TODO: constrain encryption below - we are using unconstrained here only becuase of the following Noir issue
// https://github.com/noir-lang/noir/issues/5771
storage.balances.at(from).sub(from, U128::from_integer(amount)).emit(
encode_and_encrypt_note_unconstrained(&mut context, from_ovpk_m, from, from),
);
Token::at(context.this_address())._reduce_total_supply(amount).enqueue(&mut context);
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L454-L470
Internal function implementations
Internal functions are functions that can only be called by this contract. The following 3 functions are public functions that are called from the private execution context. Marking these as internal ensures that only the desired private functions in this contract are able to call them. Private functions defer execution to public functions because private functions cannot update public state directly.
_increase_public_balance
This function is called from transfer_to_public. The account's private balance is decremented in shield and the public balance is increased in this function.
#[public]
#[internal]
fn _increase_public_balance(to: AztecAddress, amount: Field) {
let new_balance = storage.public_balances.at(to).read().add(U128::from_integer(amount));
storage.public_balances.at(to).write(new_balance);
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L816-L823
_reduce_total_supply
This function is called from burn. The account's private balance is decremented in burn and the public total_supply is reduced in this function.
#[public]
#[internal]
fn _reduce_total_supply(amount: Field) {
// Only to be called from burn.
let new_supply = storage.total_supply.read().sub(U128::from_integer(amount));
storage.total_supply.write(new_supply);
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L824-L832
View function implementations
View functions in Aztec are similar to view functions in Solidity in that they only return information from the contract storage or compute and return data without modifying contract storage. These functions are different from unconstrained functions in that the return values are constrained by their definition in the contract.
Public view calls that are part of a transaction will be executed by the sequencer when the transaction is being executed, so they are not private and will reveal information about the transaction. Private view calls can be safely used in private transactions for getting the same information.
admin
A getter function for reading the public admin value.
#[public]
#[view]
fn get_admin() -> Field {
storage.admin.read().to_field()
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L158-L164
is_minter
A getter function for checking the value of associated with a minter in the public minters mapping.
#[public]
#[view]
fn is_minter(minter: AztecAddress) -> bool {
storage.minters.at(minter).read()
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L165-L171
total_supply
A getter function for checking the token total_supply.
#[public]
#[view]
fn total_supply() -> Field {
storage.total_supply.read().to_integer()
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L172-L178
balance_of_public
A getter function for checking the public balance of the provided Aztec account.
#[public]
#[view]
fn balance_of_public(owner: AztecAddress) -> Field {
storage.public_balances.at(owner).read().to_integer()
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L179-L185
Unconstrained function implementations
Unconstrained functions are similar to view functions in Solidity in that they only return information from the contract storage or compute and return data without modifying contract storage. They are different from view functions in that the values are returned from the user's PXE and are not constrained by the contract's definition--if there is bad data in the user's PXE, they will get bad data back.
balance_of_private
A getter function for checking the private balance of the provided Aztec account. Note that the Private Execution Environment (PXE) (GitHub link) must have ivsk (incoming viewing secret key) in order to decrypt the notes.
pub(crate) unconstrained fn balance_of_private(owner: AztecAddress) -> pub Field {
storage.balances.at(owner).balance_of().to_field()
}
Source code: noir-projects/noir-contracts/contracts/token_contract/src/main.nr#L834-L838
Compiling
Now that the contract is complete, you can compile it with aztec-nargo. See the Sandbox reference page for instructions on setting it up.
Run the following command in the directory where your Nargo.toml file is located:
aztec-nargo compile
Once your contract is compiled, optionally generate a typescript interface with the following command:
aztec codegen target -o src/artifacts
Next Steps
Token Bridge Contract
The token bridge tutorial is a great follow up to this one.
It builds on the Token contract described here and goes into more detail about Aztec contract composability and Ethereum (L1) and Aztec (L2) cross-chain messaging.