Validity check for Exonum blockchain

• Browser Support
• Core concepts
  • Driver
  • Provider
• Check validity of blocks and transactions
• Config
  • driver
  • provider
  • cache
  • syncTimeout
• Events
  • initialized
  • loaded
  • stopped
  • synchronized
  • error
• Custom drivers
  • getAddressTransactions
  • getOpReturnFromTx
  • txLoadLimit
• Instance methods
  • blockStatus
  • txStatus
  • getStatus
  • syncStop
  • on
  • off
• Driver example
• Changelog
• Big Thanks
• License

Browser Support

Core concepts

When you initialize a new instance of exonum-anchoring, it automatically starts loading anchoring transactions from the Bitcoin blockchain using driver. Loading of every part of the transactions causes a loaded event to be dispatched. When all anchoring transactions are loaded a synchronized event is dispatched. After all anchoring transactions are loaded, exonum-anchoring checks availability of new transactions at regular intervals.

Driver

Driver is a class, which provides (anchoring transactions) from Bitcoin blockchain by using HTTP API.

By default there is one driver is implemented:

• Smartbit API

If you need a driver for another HTTP API, you can implement it yourself by extending the Driver class. For this purpose use API with Bech32 addresses support. See example to get details.

Provider

Provider is a class, which transactions and blocks from your Exonum blockchain by using HTTP API.

Check validity of blocks and transactions

import exonum from 'exonum-client-anchoring'

const config = {
  driver: exonum.drivers.Smartbit({
    network: 'testnet', // use testnet for testnet, mainnet by default
    version: 'v1' // Version of smartbit API. Optional
  }),
  provider: {
    nodes: ['http://192.168.1.1:8000', 'http://192.168.1.2:8000'] // list of IP addresses of Exonum nodes
  }
}

const anchoring = new exonum.Anchoring(config)

const blockHeight = 10000
anchoring.blockStatus(blockHeight)
  .then(data => /* work here with data object */) // data will contain status of block and proof
  .catch(err => /* error handler */) //err will be returned in case of network or unexpected errors

const transactionHash = 'b0459b712bca9a95bcb09b922f90f8a8bd28270475b169b7bcc281270ab38338'
anchoring.txStatus(transactionHash)
  .then(data => /* work here with data object */) // data will contain status of transaction and proof
  .catch(err => /* error handler */) //err will be returned in case of network or unexpected errors

Config

driver - instance of Driver class, required

An instance of the Driver class, which provides anchoring transactions from the bitcoin blockchain to exonum-anchoring.

provider - object, optional

Includes a set of parameters about your Exonum blockchain.

• nodes - Array of IPs, optional
  List of IP addresses of your Exonum nodes with a port. All nodes in this list should be with HTTP module and CORS enabled.
  Default: ['http://localhost:8000']
• version - string, optional
  Exonum API version.
  Default: v1

cache - boolean, optional

If cache is disabled, exonum-anchoring will ignore the cache and begin loading from the first transaction.
Default: false

syncTimeout - number, optional

When all anchoring transactions are loaded, exonum-anchoring checks availability of new transactions at regular intervals. syncTimeout sets these intervals in seconds.
Default: 120 seconds

Events

During work exonum-anchoring will be dispatching events; to subscribe to/ unsubscribe from the event you can use standard API:

const eventHandler = event => {/* work here with event */}
anchoring.on('loaded', eventHandler) // subscribe
anchoring.off('loaded', eventHandler) // unsubscribe

initialized

Fires after cache is loaded (if cache loading is enabled), when anchoring transactions synchronization starts.

loaded

Fires when a list of anchoring transactions according to the request is loaded.

stopped

Fires when synchronization stops after syncStop method is called. On dispatching this event exonum-anchoring instance deactivates.

synchronized

Fires when all anchoring transactions from Provider are synchronized. Also will fire after every check for new transactions according to syncTimeout config parameter.

error

Fires when an unexpected error occurs. Such errors include cache boot errors, cache saving errors, network connection errors.

Custom drivers

To create a custom driver you should extend standard Driver class. Your custom driver should have two methods and one parameter inside:

getAddressTransactions

A method which takes an object parameter with three fields {address, pagesize, page} and returns a promise, where address is a bitcoin address from which a transactions list needs to be obtained, pagesize and page are pagination data. Note, transactions are sorted from the oldest to the newest.

getOpReturnFromTx

A method which takes a single transaction and returns OP_RETURN from this transaction.

txLoadLimit

A maximum number of transactions that can be obtained by a single request according to provider limitations.

Driver example

Here you can see an example of a driver to BTC.com API. This driver is provided for your information only, but non-operating because it doesn't support Bech32 addresses:

import { drivers } from 'exonum-client-anchoring'
import http from 'http' // your HTTP client library
const Driver = drivers.Driver

class BtcDotCom extends Driver {
  constructor (params) {
    super()

    const { version, token } = Object.assign({
      version: 'v3',
      token: null,
      network: 'chain' // use chain for main network or tchain to testnet
    }, params)

    this.params = { api_key: token }
    this.api = `https://chain.api.btc.com/${version}`
    this.txLoadLimit = 50
  }

  getOpReturnFromTx (tx) {
    return tx.outputs[1] && tx.outputs[1].script_hex // return OP_RETURN
  }

  getAddressTransactions ({ address, limit, page }) {
    return http.get({
      url: `${this.api}/address/${address}/tx`,
      params: Object.assign({}, this.params, {
        page,
        pagesize
      })
    }).then((data) => data.data.list)
  }
}

An example of how to use exonum-client-anchoring can be found here

Instance methods

blockStatus(blockHeight)

Returns a promise with the block status, message and proof (if exists), can return an error in case of unexpected troubles.

txStatus(txHash)

Returns a promise with the transaction status, message and proof (if exists), can return an error in case of unexpected troubles.

getStatus()

Returns a current status of anchoring check.

syncStop()

Stops anchoring synchronization. Dispatches stopped event after stop.

on(eventName, callback)

Adds a new event listener by the event name.

off(eventName, callback)

Removes event listener by the event name and callback. Returns a boolean status of an operation.

Changelog

Detailed changes for each release are documented in the CHANGELOG file.

Big Thanks

Cross-browser Testing Platform and Open Source <3 Provided by Sauce Labs

License

Exonum Anchoring Check library is licensed under the Apache License (Version 2.0). See LICENSE for details.