peek-stream

Transform stream that lets you peek the first line before deciding how to parse it

npm install peek-stream

Usage

var peek = require('peek-stream')
var ldjson = require('ldjson-stream')
var csv = require('csv-parser')
 
var isCSV = function(data) {
  return data.toString().indexOf(',') > -1
}
 
var isJSON = function(data) {
  try {
    JSON.parse(data)
    return true
  } catch (err) {
    return false
  }
}
 
// call parser to create a new parser
var parser = function() {
  return peek(function(data, swap) {
    // maybe it is JSON?
    if (isJSON(data)) return swap(null, ldjson())
 
    // maybe it is CSV?
    if (isCSV(data)) return swap(null, csv())
 
    // we do not know - bail
    swap(new Error('No parser available'))
  })
}

The above parser will be able to parse both line delimited JSON and CSV

var parse = parser()
 
parse.write('{"hello":"world"}\n{"hello":"another"}\n')
parse.on('data', function(data) {
  console.log(data) // prints {hello:'world'} and {hello:'another'}
})

Or

var parse = parser()
 
parse.write('test,header\nvalue-1,value-2\n')
parse.on('data', function(data) {
  console.log(data) // prints {test:'value-1', header:'value-2'}
})

Per default data is the first line (or the first 65535 bytes if no newline is found). To change the max buffer pass an options map to the constructor

var parse = peek({
  maxBuffer: 10000
}, function(data, swap) {
  ...
})

If you want to emit an error if no newline is found set strict: true as well.

License

MIT