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FireFly Tokens Microservice for ERC20 & ERC721

This project provides a thin shim between FireFly and ERC20/ERC721 contracts exposed via ethconnect or evmconnect.

Based on Node.js and Nest.

This service is entirely stateless - it maps incoming REST operations directly to blockchain calls, and maps blockchain events to outgoing websocket events.

Smart Contracts

This connector is designed to interact with ERC20 and ERC721 smart contracts on an Ethereum blockchain which conform to a few different patterns. The repository includes sample Solidity contracts that conform to some of the ABIs expected.

At the very minimum, all contracts must implement the events and methods defined in the ERC20 or ERC721 standards, including all optional methods such as name() and symbol(), decimals() (for ERC20), and tokenURI() (for ERC721).

Beyond this, there are a few methods for creating a contract that the connector can utilize.

FireFly Interface Parsing

The most flexible and robust token functionality is achieved by teaching FireFly about your token contract, then allowing it to teach the token connector. This is optional in the sense that there are additional methods used by the token connector to guess at the contract ABI (detailed later), but is the preferred method for most use cases.

To leverage this capability in a running FireFly environment, you must:

  1. Upload the token contract ABI to FireFly as a contract interface.
  2. Include the interface parameter when creating the pool on FireFly.

This will cause FireFly to parse the interface and provide ABI details to this connector, so it can determine the best methods from the ABI to be used for each operation. When this procedure is followed, the connector can find and call any variant of mint/burn/transfer/approval that is listed in the source code for erc20.ts and erc721.ts. This list includes methods in the base standards, methods in the IERC20WithData and IERC721WithData interfaces defined in this repository, and common method variants from the OpenZeppelin Wizard. Additional variants can be added to the list by building a custom version of this connector or by proposing them via pull request.

If implementing a new contract, the signatures in IERC20WithData and IERC721WithData will provide the most complete FireFly functionality by allowing FireFly transactions and messages to be pinned to the blockchain alongside token operations. The sample ERC20WithData and ERC721WithData contracts may be used to get up and running with simple token support, and may provide a starting point for developing production contracts that can be used with this connector.

Solidity Interface Support

In the absence of being provided with ABI details, the token connector will attempt to guess the contract ABI in use. It does this by using ERC165 supportsInterface() to query the contract's support for IERC20WithData or IERC721WithData, as defined in this repository. If the query succeeds, the connector will leverage the methods on that interface to perform token operations. Therefore it is possible to use these contracts without the extra step of teaching FireFly about the contract interface first.

Fallback Functionality (not recommended)

If neither of the above procedures is followed for a given contract, the connector will fall back to assuming that the ABI looks like ERC20NoData.json or ERC721NoData.json, which are based on common OpenZeppelin patterns. This behavior can also be tweaked to assume ERC20NoDataLegacy.json or ERC721NoDataLegacy.json by setting USE_LEGACY_ERC20_SAMPLE=true or USE_LEGACY_ERC721_SAMPLE=true in the connector environment (these sample ABIs were provided in an older version of this repository but are now deprecated). However, relying on this fallback functionality may be unreliable and is not recommended.

API Extensions

The APIs of this connector conform to the FireFly fftokens standard, and are designed to be called by FireFly. They should generally not be called directly by anything other than FireFly.

Below are some of the specific considerations and extra requirements enforced by this connector on top of the fftokens standard.

/createpool

If config.address is specified, the connector will index the token contract at the specified address (must be an ERC20 contract if type is fungible, or an ERC721 contract if type is nonfungible). config.blockNumber may also be supplied to begin indexing from a specific block (if it is not specified, indexing will begin from block 0). Any name provided from FireFly will be ignored by the connector. If a symbol is provided from FireFly, it must match the symbol() defined on the underlying contract.

If config.address is not specified, and FACTORY_CONTRACT_ADDRESS is set in the connector's environment, the factory contract will be invoked to deploy a new instance of ERC20 or ERC721. The factory contract must conform to ITokenFactory to be usable. Any name and symbol provided from FireFly will be passed into the factory create() method.

/mint

For fungible (ERC20) token pools, tokenIndex and uri will be ignored.

For non-fungible (ERC721) token pools, amount must be 1 (or unset). If the underlying contract expects an index to be provided, tokenIndex must be set (if it supports auto-indexing, tokenIndex will be ignored).

/burn

For non-fungible (ERC721) token pools, tokenIndex is required, and amount must be 1 (or unset).

/transfer

For non-fungible (ERC721) token pools, tokenIndex is required, and amount must be 1 (or unset).

/approval

For fungible (ERC20) token pools, if config.allowance is set, the approval will be valid for the specified number of tokens. If omitted, the approval has unlimited allowance.

For non-fungible (ERC721) token pools, if config.tokenIndex is set, the approval will be for that specific token. If omitted, the approval covers all tokens.

Extra APIs

The following APIs are not part of the fftokens standard, but are exposed under /api/v1:

  • GET /receipt/:id - Get receipt for a previous request

Running the service

The easiest way to run this service is as part of a stack created via firefly-cli.

To run manually, you first need to run an Ethereum blockchain node and an instance of firefly-ethconnect, and deploy the ERC20 smart contract.

Then, adjust your configuration to point at the deployed contract by editing .env or by setting the environment values directly in your shell.

Install and run the application using npm:

# install
$ npm install

# run in development mode
$ npm run start

# run in watch mode
$ npm run start:dev

# run in production mode
$ npm run start:prod

View the Swagger UI at http://localhost:3000/api
View the generated OpenAPI spec at http://localhost:3000/api-json

Manually deploy contracts

To deploy both ERC20 and ERC721 contracts to a FireFly network, use the provided deploy script powered by hardhat.

cd samples/solidity
npm install
npm run deploy

Note: firefly-cli will take care of contract deployment during stack creation.

Testing

# unit tests
$ npm run test

# e2e tests
$ npm run test:e2e

# lint
$ npm run lint

# formatting
$ npm run format

Blockchain retry behaviour

Most short-term outages should be handled by the blockchain connector. For example if the blockchain node returns HTTP 429 due to rate limiting it is the blockchain connector's responsibility to use appropriate back-off retries to attempt to make the required blockchain call successfully.

There are cases where the token connector may need to perform its own back-off retry for a blockchain action. For example if the blockchain connector microservice has crashed and is in the process of restarting just as the token connector is trying to query an NFT token URI to enrich a token event, if the token connector doesn't perform a retry then the event will be returned without the token URI populated.

The token connector has configurable retry behaviour for all blockchain related calls. By default the connector will perform up to 15 retries with a back-off interval between each one. The default first retry interval is 100ms and doubles up to a maximum of 10s per retry interval. Retries are only performed where the error returned from the REST call matches a configurable regular expression retry condition. The default retry condition is .*ECONN.* which ensures retries take place for common TCP errors such as ECONNRESET and ECONNREFUSED.

The configurable retry settings are:

  • RETRY_BACKOFF_FACTOR (default 2)
  • RETRY_BACKOFF_LIMIT_MS (default 10000)
  • RETRY_BACKOFF_INITIAL_MS (default 100)
  • RETRY_CONDITION (default .*ECONN.*)
  • RETRY_MAX_ATTEMPTS (default 15)

Setting RETRY_CONDITION to "" disables retries. Setting RETRY_MAX_ATTEMPTS to -1 causes it to retry indefinitely.

Note, the token connector will make a total of RETRY_MAX_ATTEMPTS + 1 calls for a given retryable call (1 original attempt and RETRY_MAX_ATTEMPTS retries)

TLS

Mutual TLS can be enabled by providing three environment variables:

  • TLS_CA
  • TLS_CERT
  • TLS_KEY

Each should be a path to a file on disk. Providing all three environment variables will result in a token connector running with TLS enabled, and requiring all clients to provide client certificates signed by the certificate authority.