Mempool Wallet Connector Kit

(work in progress - relies on the multi-address tracking feature from mempool/mempool#4137)

A lightweight utility library for efficiently syncing Bitcoin wallet history from an instance of The Mempool Open Source Project® backend.

Mwck uses websocket push notifications to discover new address transaction events, eliminating the need to constantly poll the REST API.

Quick start

const mwck = require('mwck');
const wallet = new mwck.MempoolWallet({
  hostname: 'mempool.space'
});
wallet.connect();

wallet.subscribe('addressReady', ({ address, state }) => {
  // finished loading address transactions
});

wallet.subscribe('txEvent', ({event, address, tx}) => {
  switch (event) {
    'added': {
      // discovered a new transaction related to this address
    } break;

    'confirmed': {
      // a transaction related to this address was included in a block
    } break;

    'removed': {
      // a transaction related to this address was dropped from the mempool
    } break;
  }
});

wallet.trackAddresses([
  'bc1p...xyz',
  '3AB...123'
]);

API

MempoolWallet.connect() (async)

Starts the websocket connection to the configured Mempool server.

Regular ping/pong messages are sent to maintain the connection, and the websocket will attempt to automatically recover from interruptions.

MempoolWallet.disconnect()

Disconnect the websocket until connect() is called again

MempoolWallet.subscribe(event: WalletEvent, callback)

Subscribe to event notifications.

When an event of the requested type occurs, the provided callback is invoked.

See Events for a list of valid event topics and callback signatures.

MempoolWallet.getAddressState(address: string)

Returns an AddressState object representing the current state of an address.

If the address is invalid or not being tracked, returns null.

MempoolWallet.getWalletState(): WalletState

Returns a WalletState object representing the state of all currently tracked addresses and combined balances for the whole wallet.

MempoolWallet.restore(state: WalletState) (async)

Restores the state of a wallet from a snapshot previously obtained from getWalletState().

Useful for persisting a session across restarts/refreshes, or switching between different wallets.

MempoolWallet.async trackAddresses(addresses: string[]) (async)

Adds the list of addresses to the wallet, and attempts to sync their transaction history.

Returns once all new addresses are in sync, or immediately if the websocket is offline.

MempoolWallet.untrackAddresses(addresses: string[])

Removes the addresses from the wallet, unloads related state, and stops watching for new transaction activity involving these addresses.

MempoolWallet.destroy()

Call before discarding the MempoolWallet object to disconnect the websocket and clean up event handlers etc.

Events

The MempoolWallet class can either be used synchronously by fetching snapshots of address or wallet state, or via an observer-style subscription model.

Subscriptions are supported for the following event types:

wsConnected

Emitted when the websocket succeeds in connecting (or reconnecting) to the configured Mempool server.

Callback takes no arguments

wsDisconnected

Emitted when the websocket loses connection

Callback takes no arguments

addressReady

Emitted after the wallet finishes loading transaction history, and a tracked address is now in sync with the server.

Callback invoked with an argument of the form

{
  address: string,
  state: AddressState,
}

txAdded

Emitted every time a new transaction related to a tracked address is received.

Callback invoked with an argument of the form

{
  address: string,
  tx: Transaction,
}

txConfirmed

Emitted every time a transaction related to a tracked address is found to be confirmed in a mined block.

Callback invoked with an argument of the form

{
  address: string,
  tx: Transaction,
}

txRemoved

Emitted every time a transaction related to a tracked address is dropped from the mempool.

Callback invoked with an argument of the form

{
  address: string,
  tx: Transaction,
}

txEvent

Emitted for all of the above tx... events.

Callback invoked with an argument of the form

{
  event: 'added' | 'confirmed' | 'removed',
  address: string,
  tx: Transaction,
}

Types/Interfaces

Check src/interfaces.ts for the structure of return types and arguments.