kafka-dance-api/query.js

const buildMatcher = code => new Function('message', 'value', code)

const deepCopy = obj => JSON.parse(JSON.stringify(obj))

const realTimeMessageSearch = async ({ kafka, topic, onMessage, searchCode, immutable = true }) => {
  const consumer = kafka.consumer({ groupId: 'sage-testing-group' })

  console.log({ topic, onMessage, searchCode, immutable })
  await consumer.connect()
  await consumer.subscribe({ topic, fromBeginning: true })
  const matcher = searchCode && buildMatcher(searchCode)

  const messages = []

  console.log('consumer.run')
  await consumer.run({
    autoCommit: false,
    eachMessage: async ({ topic, partition, message }) => {
      const s = message.value.toString()
      let value
      try {
        value = JSON.parse(s)
      } catch (e) {
        value = '' + s
      }
      message.value = value
      const workingMessage = immutable ? deepCopy(message) : message
      if (!matcher || matcher(workingMessage, workingMessage.value)) {
        onMessage(message)
        messages.push(message)
        //console.log(message)
      }
    },
  })

  for (let i = 0; i <= 5; i++) {
    //console.log(`seek on partition ${i}`)
    await consumer.seek({topic, partition: i, offset: 0})
  }
  console.log('return consumer')
  return consumer
}

const searchMessages = async ({ kafka, maxItems, topic, onDone, searchCode, onBatchDone, immutable = true }) => {
  const consumer = kafka.consumer({ groupId: 'sage-testing-group' })

  await consumer.connect()
  await consumer.subscribe({ topic, fromBeginning: true })
  const matcher = searchCode && buildMatcher(searchCode)

  const messages = []

  await consumer.run({
    autoCommit: false,
    eachMessage: async ({ topic, partition, message }) => {
      const s = message.value.toString()
      const value = JSON.parse(s)
      delete value.Data
      message.value = value
      let workingMessage = immutable ? deepCopy(message) : message
      if (!matcher || matcher(workingMessage, workingMessage.value)) {
        messages.push(message)
        if (messages.length < maxItems) {
          onBatchDone(messages.length)
        } else {
          onBatchDone(maxItems)
          await consumer.stop()
          await consumer.disconnect()
          onDone(messages.slice(0, maxItems))
        }
        //console.log(message)
      }
    },
  })

  /*
   * 1. We need to know which partitions we are assigned.
   * 2. Which partitions have we consumed the last offset for
   * 3. If all partitions have 0 lag, we exit.
   */

  /*
   * `consumedTopicPartitions` will be an object of all topic-partitions
   * and a boolean indicating whether or not we have consumed all
   * messages in that topic-partition. For example:
   *
   * {
   *   "topic-test-0": false,
   *   "topic-test-1": false,
   *   "topic-test-2": false
   * }
   */
  let consumedTopicPartitions = {}
  consumer.on(consumer.events.GROUP_JOIN, async ({ payload }) => {
    //console.log('GROUP_JOIN')
    const { memberAssignment } = payload
    consumedTopicPartitions = Object.entries(memberAssignment).reduce(
      (topics, [topic, partitions]) => {
        for (const partition in partitions) {
          topics[`${topic}-${partition}`] = false
        }
        return topics
      },
      {}
    )
  })

  /*
   * This is extremely unergonomic, but if we are currently caught up to the head
   * of all topic-partitions, we won't actually get any batches, which means we'll
   * never find out that we are actually caught up. So as a workaround, what we can do
   * is to check in `FETCH_START` if we have previously made a fetch without
   * processing any batches in between. If so, it means that we received empty
   * fetch responses, meaning there was no more data to fetch.
   *
   * We need to initially set this to true, or we would immediately exit.
   */
  //let processedBatch = true
  consumer.on(consumer.events.FETCH_START, async () => {
    //console.log('FETCH_START')
    // This was part of the original code, but seems to cause a near-immediate exit
    //if (processedBatch === false) {
    //  console.log('I DIE AT FETCH')
    //  await consumer.disconnect()
    //  process.exit(0)
    //}

    //processedBatch = false
  })

  /*
   * Now whenever we have finished processing a batch, we'll update `consumedTopicPartitions`
   * and exit if all topic-partitions have been consumed,
   */
  consumer.on(consumer.events.END_BATCH_PROCESS, async ({ payload }) => {
    //console.log('END_BATCH_PROCESS')
    const { topic, partition, offsetLag } = payload
    consumedTopicPartitions[`${topic}-${partition}`] = offsetLag === '0'

    if (Object.values(consumedTopicPartitions).every(Boolean)) {
      await consumer.stop()
      await consumer.disconnect()
      console.log(`I DIE AT BATCH with ${messages.length} messages`)
      onDone(messages)
      //process.exit(0)
    }

    //processedBatch = true
  })

  return consumer
}

//run()
//  .then(() => console.log('DONE'))
//  .catch(e => console.error(`[example/consumer] ${e.message}`, e))

module.exports = {
  searchMessages,
  realTimeMessageSearch,
}