eth-block-tracker/test/polling.js

A block tracker for the Ethereum blockchain. Keeps track of the latest block.

const test = require('tape')
const GanacheCore = require('ganache-core')
const pify = require('pify')
const PollingBlockTracker = require('../src/polling')
const noop = () => {}

module.exports = (test, testLabel, PollingBlockTracker) => {

  test(`${testLabel} - latest`, async (t) => {
    const provider = GanacheCore.provider()
    const blockTracker = new PollingBlockTracker({
      provider,
      pollingInterval: 100,
    })

    try {
      t.equal(blockTracker.isRunning(), false, 'PollingBlockTracker should begin stopped')

      const blocks = []
      blockTracker.on('latest', (block) => blocks.push(block))
      t.equal(blockTracker.isRunning(), true, 'PollingBlockTracker should start after listener is added')
      t.equal(blocks.length, 0, 'no blocks so far')

      await newLatestBlock(blockTracker)
      t.equal(blocks.length, 1, 'saw 1st block')

      await triggerNextBlock(provider)
      await newLatestBlock(blockTracker)
      t.equal(blocks.length, 2, 'saw 2nd block')

      await triggerNextBlock(provider)
      await triggerNextBlock(provider)
      await triggerNextBlock(provider)
      const lastBlock = await newLatestBlock(blockTracker)
      t.equal(blocks.length, 3, 'saw only 5th block')
      t.equal(Number.parseInt(lastBlock, 16), 4, 'saw correct block, with number 4')

      blockTracker.removeAllListeners()
      t.equal(blockTracker.isRunning(), false, 'PollingBlockTracker stops after all listeners are removed')


    } catch (err) {
      t.ifError(err)
    }

    // cleanup
    blockTracker.removeAllListeners()
    t.end()
  })

  test(`${testLabel} - error catch`, async (t) => {
    const provider = GanacheCore.provider()
    const blockTracker = new PollingBlockTracker({
      provider,
      pollingInterval: 100,
    })

    // ignore our error if registered as an uncaughtException
    process.on('uncaughtException', ignoreError)
    function ignoreError(err) {
      // ignore our error
      if (err.message.includes('boom')) return
      // otherwise fail
      t.ifError(err)
    }

    try {
      // keep the block tracker polling
      blockTracker.on('latest', () => { })
      // throw error in handler in attempt to break block tracker
      blockTracker.once('latest', () => { throw new Error('boom') })

      // emit and observe a block
      const nextBlockPromise = nextBlockSeen(blockTracker)
      await triggerNextBlock(provider)
      await nextBlockPromise

      // emit and observe another block
      const nextNextBlockPromise = nextBlockSeen(blockTracker)
      await triggerNextBlock(provider)
      await nextNextBlockPromise

    } catch (err) {
      t.ifError(err)
    }

    // setTimeout so we dont remove the uncaughtException handler before
    // the SafeEventEmitter emits the event on next tick
    setTimeout(() => {
      // cleanup
      process.removeListener('uncaughtException', ignoreError)
      blockTracker.removeAllListeners()
      t.end()
    })
  })

  test(`${testLabel} - _fetchLatestBlock error handling`, async (t) => {
    const provider = GanacheCore.provider()
    const blockTracker = new PollingBlockTracker({
      provider,
      pollingInterval: 100,
    })

    // measure if errors are reported to the console
    const consoleErrors = []
    const originalConsoleErrorMethod = console.error
    console.error = (err) => consoleErrors.push(err)

    // override _fetchLatestBlock to throw an error
    const originalFetchLatestBlock = blockTracker._fetchLatestBlock
    blockTracker._fetchLatestBlock = async () => {
      // restore fetch method
      blockTracker._fetchLatestBlock = originalFetchLatestBlock
      // throw error to try and break block tracker
      throw new Error('TestError')
    }

    try {
      const latestBlock = await blockTracker.getLatestBlock()
      t.ok(latestBlock, 'got a block back')
      t.ok(consoleErrors.length, 1, 'saw expected console error')
    } catch (err) {
      t.ifError(err)
    }

    // setTimeout so we dont remove the uncaughtException handler before
    // the SafeEventEmitter emits the event on next tick
    setTimeout(() => {
      // cleanup
      console.error = originalConsoleErrorMethod
      blockTracker.removeAllListeners()
      t.end()
    })
  })

}

async function triggerNextBlock(provider) {
  await pify((cb) => provider.sendAsync({ id: 1, method: 'evm_mine', jsonrpc: '2.0', params: [] }, cb))()
}

async function newLatestBlock(blockTracker) {
  return await pify(blockTracker.once, { errorFirst: false }).call(blockTracker, 'latest')
}

async function nextBlockSeen(blockTracker) {
  return new Promise((resolve) => {
    blockTracker.once('latest', resolve)
  })
}