through2-spy

A through2 wrapper to for simple stream.PassThrough spies.

npm install through2-spy
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through2-spy

NPM

This is a super thin wrapper around through2 for creating simple stream.PassThrough spies.

Saves you a tiny bit of boilerplate compared to through2 for writing stream spies.

Note you will NOT be able to do anything but spy and abort the stream pipeline. To do any filtering or transformations you should consider through2 through2-filter or through2-map.

Pass a function to run as each chunk goes through your stream pipeline. Return an Error to abort the pipeline.


var spy = require("through2-spy")

var count = 0
var countChunks = spy(function (chunk) {
  count++
})

// vs. with through2:
var countChunks = through2(function (chunk, encoding, callback) {
  count++
  this.push(chunk)
  return callback()
})

// Then use your spy:
source.pipe(countChunks).pipe(sink)

// Additionally accepts `wantStrings` argument to conver buffers into strings
var nsaregex = /(open source)|(foss)|(node\.js)/i
var prizm = spy({wantStrings: true}, function (str) {
  var wiretap = str.match(nsaregex)
  if (wiretap) this.emit("OMGTERRIST", wiretap[0], str)
})

prizm.on("OMGTERRIST", sendDrone(/* ... */))

internet.pipe(prizm).pipe(internet)

// Return an Error to abort the pipeline
var Meter = spy.ctor({maxBytes: 1024, bytes: 0}, function (chunk) {
  this.options.bytes += chunk.length
  if (this.options.bytes >= this.options.maxBytes) return new Error("Over 1024 byte limit!")
})

var meter = new Meter()

Options

  • wantStrings: Automatically call chunk.toString() for the super lazy.
  • all other through2 options

LICENSE

MIT

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