Flow Transaction Service

A middleware microservice for admin backend and Flow blockchain interaction.

Scripts

Development

1. git clone the repository to your local machine.
2. run npm install to install dependencies.
3. remove the .example extension at the end of the .env.example file and adjust environment variables to your needs.
4. run redis-stack-server to run a local redis instance
5. run npm run dev-server to start the local development server.

GCP KMS Setup

The @fcl-kms-gcp-authorizer library requires authentication with google. It is recommended to use an environment variable to set up the authentication using a google account authentication JSON file. This variable only applies to the current shell session, so if a new session is open, the variable must be set again.

$ export GOOGLE_APPLICATION_CREDENTIALS= "PATH"
# -> PATH = /home/user/Downloads/service-account-file.json

Google Cloud Documentation for authentication: https://cloud.google.com/docs/authentication/getting-started

Source Files

.
├── cadence            # Flow (Cadence) transactions and import address map
├── commands           # Processing flow commands (transactions) received from Google Pub/Sub
├── config             # Project configuration variables, imported from .env
├── event              # Processing flow events received from Google Pub/Sub
├── keys               # Proposer key handling logic
├── logger             # Winston logger configuration
├── redis              # Functions used to interact with Redis
├── typings            # Typescript module declarations
├── subscribe          # Receive/Send Google Pub/Sub messages
└── index.ts

Google Pub/Sub

This service is subscribed to two Google Pub/Sub topics defined inside the .env file:

COMMAND_TOPIC=test.blockchain.flow.commands-sub
EVENT_TOPIC=test.blockchain.flow.events-sub

The expected message format for the Flow Command Topic defined inside the ICommand interface (command/command.i.ts)

export default interface ICommand {
  id: string; // Backend generated unique id
  type: TransactionName; // The name of the transaction
  callbackTopic: string; // Callback topic used to publish transaction id after succesful command processing
  payload: Array<any>; // Transaction arguments
}

The expected message format for the Flow Event Topic defined inside the IEvent interface (event/event.i.ts)

export default interface IEvent {
  flowTrasactionId: string; // Transaction id of an event
}

Implementing New Transactions

To add a new transaction that interacts with a Flow Smart Contract, only files inside the cadence folder should be changed, if necessary, files inside the config/env can be changed. Follow this checklist to add a new transaction:

1. If the .env and config files do not contain the contract address, add the contract address to the .env and config files, as well as to the getImports method inside the cadence/index.ts file
2. Add the new transaction to the cadence/transactions folder, the folder name should match the contract name
3. Add a new line containing the path to your newly added transaction inside the codes.ts file, making sure to keep the following format:

const EXAMPLE_CONTRRACT_TEST = read("./transactions/example/test.cdc"); // Path to the new file

export { .../*previous exports*/ EXAMPLE_CONTRRACT_TEST}

4. Add your new tranasction to the TransactioName enum and the switch case inside the getTransaction function, in the index.ts file (cadence folder)

export enum TransactionName {
  EXAMPLE_CONTRACT_TEST = "EXAMPLE_CONTRACT_TEST"
}

export const getTransaction = (name: TransactionName): string => {
  switch (name) {
    case TransactionName.EXAMPLE_CONTRACT_TEST:
      return codes.EXAMPLE_CONTRACT_TEST;
  }
};

5. Try sending a pubsub message with the type field set as the name of your newly added transaction, if you've been following the tutorial closely, it should be EXAMPLE_CONTRACT_TEST

Dependencies

• @google-cloud/logging-winston: Used to log messages to Google Stackdriver.
• @google-cloud/pubsub: Used to receive/send messages to Google Pub/Sub topics.
• @onflow/fcl: Library to interact with the Flow blockchain.
• chalk: Used to add color to console logs.
• dotenv: Used to load environment variables from the .env file.
• fcl-gcp-kms-authorizer: Library to authenticate with Google Cloud KMS.
• flow-cadut: Library to compile Flow (Cadence) code.
• fs: The Node.js file system module.
• ioredis: A Redis client for Node.js.
• path: The Node.js path module.
• redis: Redis client for Node.js.
• winston: A logger for Node.js.
• winston-transport: Transport for winston logger.