Flow Core Smart Contracts

These are the smart contracts that define the core functionality of the Flow protocol.

The version of the contracts in the master branch is the Cadence 1.0 version of the contracts and is not the same as the ones that are currently deployed to testnet and mainnet. See the cadence-0.42 branch for the currently deployed versions.

What is Flow?

Flow is a new blockchain for open worlds. Read more about it here.

What is Cadence?

Cadence is a new Resource-oriented programming language for developing smart contracts for the Flow Blockchain. Read more about it here

We recommend that anyone who is reading this should have already completed the Cadence Tutorials so they can build a basic understanding of the programming language.

FlowToken

contracts/FlowToken.cdc

Network	Contract Address
Emulator	0x0ae53cb6e3f42a79
Testnet	0x7e60df042a9c0868
Mainnet	0x1654653399040a61

This is the contract that defines the network token for Flow. This token is used for account creation fees, transaction fees, staking, and more. It is implemented as a regular smart contract so that it can be easily used just like any other token in the network. See the flow fungible token repository for more information.

You can find transactions for using the Flow Token in the transactions/flowToken directory.

Flow Transaction Fee Contract

contracts/FlowFees.cdc

Network	Contract Address
Emulator	0xe5a8b7f23e8b548f
Testnet	0x912d5440f7e3769e
Mainnet	0xf919ee77447b7497

This contract defines fees that are spent for executing transactions and creating accounts.

Storage Fee Contract

contracts/FlowStorageFees.cdc

Network	Contract Address
Emulator	0xf8d6e0586b0a20c7
Testnet	0x8c5303eaa26202d6
Mainnet	0xe467b9dd11fa00df

This contract defines fees that are spent to pay for the storage that an account uses. There is a minimum balance that an account needs to maintain in its main FlowToken Vault in order to pay for the storage it uses. You can see more docs about storage capacity and fees here.

Service Account Contract

contracts/FlowServiceAccount.cdc

Network	Contract Address
Emulator	0xf8d6e0586b0a20c7
Testnet	0x8c5303eaa26202d6
Mainnet	0xe467b9dd11fa00df

This contract manages account creation and flow token initialization. It enforces temporary requirements for which accounts are allowed to create other accounts, and provides common functionality for flow tokens.

You can find transactions for interacting with the service account contract in the transactions/FlowServiceAccount directory.

Random Beacon History Contract

contracts/RandomBeaconHistory.cdc

Network	Contract Address
Emulator	0xf8d6e0586b0a20c7
Testnet	0x8c5303eaa26202d6
Mainnet	0xe467b9dd11fa00df

This contract stores the history of random sources generated by the Flow network. The defined Heartbeat resource is updated by the Flow Service Account at the end of every block with that block's source of randomness.

You can find transactions for interacting with the random beacon history contract in the transactions/randomBeaconHistory directory.

Node Version Beacon Contract

contracts/NodeVersionBeacon.cdc

Network	Contract Address
Emulator	0xf8d6e0586b0a20c7
Testnet	0x8c5303eaa26202d6
Mainnet	0xe467b9dd11fa00df

The NodeVersionBeacon contract holds the past and future protocol versions that should be used to execute/handle blocks at a given block height.

You can find transactions for interacting with the node version beacon history contract in the transactions/nodeVersionBeacon directory.

Flow Epochs, Identity Table, and Staking Contracts

contracts/FlowIDTableStaking.cdc contracts/epochs/FlowEpoch.cdc

Network	Contract Address
Emulator	0xf8d6e0586b0a20c7
Testnet	0x9eca2b38b18b5dfe
Mainnet	0x8624b52f9ddcd04a

These contract manages the list of identities that correspond to node operators in the Flow network as well as the process for adding and removing nodes from the network via Epochs. Each node identity stakes tokens with these contracts, and also gets paid rewards with their contracts. This contract also manages the logic for users to delegate their tokens to a node operator and receive their own rewards. You can see an explanation of this process in the staking section of the Flow Docs website.

You can find all the transactions for interacting with the IDTableStaking contract with unlocked FLOW in the transactions/idTableStaking directory, though it is recommended to use the staking collection transactions instead. These are described in the "Flow Staking Collection" section below.

You can also find transactions and scripts for interacting with all the epoch smart contracts in the following directories: transactions/epoch/ transactions/dkg/ transactions/quorumCertificate/

You can also find scripts for querying info about staking and stakers in the transactions/idTableStaking/scripts/ directory. These scripts are documented in the staking scripts section of the docs

Flow Locked Tokens contract

contracts/LockedTokens.cdc

Network	Contract Address
Emulator	0xf8d6e0586b0a20c7
Testnet	0x95e019a17d0e23d7
Mainnet	0x8d0e87b65159ae63

This contract manages the two year lockup of Flow tokens that backers purchased in the initial token sale in October of 2020. See more documentation about LockedTokens here.

Flow Staking Collection Contract

contracts/FlowStakingCollection.cdc

The StakingCollection contract has the same import addresses as the LockedTokens contract on all the networks.

A Staking Collection is a resource that allows its owner to manage multiple staking objects in a single account via a single storage path, and perform staking and delegation actions using both locked and unlocked Flow.

Before the staking collection, accounts could use the instructions in the unlocked staking guide to stake with tokens. This was a bit restrictive, because that guide (and the corresponding transactions) only supports one node and one delegator object per account. If a user wanted to have more than one per account, they would either have to use custom transactions with custom storage paths for each object, or they would have had to use multiple accounts, which comes with many hassles of its own.

The same applies to the locked tokens staking guide. We only built in support for one node and one delegator per account.

The staking collection is a solution to both of these deficiencies. When an account is set up to use a staking collection, the staking collection recognizes the existing locked account capabilities (if they exist) and unlocked account staking objects, and incorporates their functionality so any user can stake for a node or delegator through a single common interface, regardless of if they have a brand new account, or have been staking through the locked account or unlocked account before.

Is the staking collection mandatory

Flow Port uses staking collection transaction by default other services are encouraged to use it instead of any of the other account staking setups. If you provide a staking service for Ledger or Blocto users, you will need to upgrade to this if you want to give your users access to the entire functionality of their account if they are also using Flow Port. If their entire interaction with staking is through Flow Port, then all the changes are handled for them and there is nothing for you to worry about.

Staking Collection Technical features

• The staking collection contract stores a dictionary of staking objects from the staking contract that are used to manage the stakers tokens. Since they are dictionaries, there can be as many node or delegator objects per account as the user wants.
• The resource only has one set of staking methods, which route the call to the correct staking object based on the arguments that the caller specifies. (nodeID, delegatorID)
• The contract also stores an optional capability to the locked token vault and locked tokens TokenHolder resource. This is only used if the user already has a locked account. The staking collection does not change the locked account setup at all, it only has access to it and to the locked vault.
• The collection makes the staking objects and vault capability fields private, because since it has access to the locked tokens, it needs to mediate access to the staking objects so users cannot withdraw tokens that are still locked from the sale. The resource has fields unlockedTokensUsed and lockedTokensUsed, to keep track of how many locked and unlocked tokens are being used for staking in order to allow the user to withdraw the correct amount when they choose to.
• The staking collection contract is a brand new contract that will be deployed to the same account as the existing locked tokens contract. A few of the fields on the LockedTokens contract have been updated to have access(account) visibility instead of access(self) because the staking collection contract needs to be able to access to them in order to work properly.
• We also included a public interface and getters in the contract so you can easily query it with an address to get node or delegator information from a collection.

Looking for feedback on design decisions, implementation details, any events that would be useful to include in the contract, and whatever you feel is important!

We intend for this to be the method that all Flow Port users (ledger, blocto, etc) use for the forseeable future. When we enable it in Flow Port, we will ask every user to run a transaction to set up their account to use the staking collection from then on.

Testing

To run the tests in the repo, use make test.

These tests need to utilize the transaction templates that are contained in transactions/.

Audit

Flow Core Contracts were audited by Quantstamp in July 2021: final report.

Getting Transaction Templates

If you need to use the contracts and transaction templates we have provided in an app, you don't necessarily need to copy and paste them into your code. We plan on providing packages for different languages to import in order to use the transactions instead of copying and pasting.

We currently include the lib/go/templates package for getting templates in the Go programming language. To use this package, run go get github.com/onflow/flow-core-contracts/lib/go/templates@{latest version} in your Go project direcory. To use it in your Go code, you can simply call one of the many template getters in one of the *_templates.go files.

Packages in other languages

We would like to add new packages for other popular languages to get transaction templates. If you would like to contribute to add one of these new packages, please reach out to the team and we would be happy to help!

License

The works in these folders are under the Unlicense:

• src/contracts