index.js

const { Transform } = require('stream')
const { EOL } = require('os')

module.exports = BinarySplit

function firstMatch (buf, offset, matcher) {
  if (offset >= buf.length) return -1
  let i
  for (i = offset; i < buf.length; i++) {
    if (buf[i] === matcher[0]) {
      if (matcher.length > 1) {
        let fullMatch = true
        let j = i
        for (let k = 0; j < i + matcher.length; j++, k++) {
          if (buf[j] !== matcher[k]) {
            fullMatch = false
            break
          }
        }
        if (fullMatch) return j - matcher.length
      } else {
        break
      }
    }
  }

  const idx = i + matcher.length - 1
  return idx
}

function BinarySplit (splitOn = EOL) {
  const matcher = Buffer.from(splitOn)
  let buffered

  return new Transform({
    readableObjectMode: true,

    transform (buf, enc, done) {
      let offset = 0
      let lastMatch = 0
      if (buffered) {
        buf = Buffer.concat([buffered, buf])
        offset = buffered.length
        buffered = undefined
      }

      while (true) {
        const idx = firstMatch(buf, offset - matcher.length + 1, matcher)
        if (idx !== -1 && idx < buf.length) {
          if (lastMatch !== idx) {
            this.push(buf.slice(lastMatch, idx))
          }
          offset = idx + matcher.length
          lastMatch = offset
        } else {
          buffered = buf.slice(lastMatch)
          break
        }
      }

      done()
    },

    flush (done) {
      if (buffered && buffered.length > 0) this.push(buffered)
      done()
    }
  })
}