terminus

An abstraction for making stream.Writable streams without all the boilerplate.

npm install terminus
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terminus

NPM

david-dm david-dm

terminus makes it easier to create streams2 Writable streams. You can either use it like through2 to eliminate subclassing boilerplate, or use one of the provided helper terminus streams.

var terminus = require("terminus")
var through2 = require("through2")
var spigot = require("stream-spigot")

// Streams2 all the way down...

function uc(chunk, encoding, callback) {
  this.push(chunk.toString().toUpperCase())
  callback()
}

function log(chunk, encoding, callback) {
  // This example is very contrived, you're likely better off directly piping to `process.stdout`
  console.log(chunk.toString())
  callback()
}

spigot(["my ", "dog ", "has ", "fleas"])
  .pipe(through2(uc))
  .pipe(terminus(log))

/*
MY 
DOG 
HAS 
FLEAS
*/

// devnull

var spy = require("through2-spy")

spigot(["my ", "dog ", "has ", "fleas"])
  .pipe(spy({highWaterMark: 2}, function (buf) {console.log(buf.toString())}))
  .pipe(terminus.devnull())

/*
my 
dog 
has 
fleas
*/

// concat

function reverse(contents) {
  console.log(contents.toString().split("").reverse().join(""))
}

spigot(["my ", "dog ", "has ", "fleas"])
  .pipe(terminus.concat(reverse))

/*
saelf sah god ym
*/

// tail

var chunkLengths = []
function logLength(chunk) {
  chunkLengths.push(chunk.length)
}

var ws = terminus.tail(logLength)
ws.on("finish", function () {
  console.log(chunkLengths)
})

spigot(["my ", "dog ", "has ", "fleas"])
  .pipe(ws)

/*
[ 3, 4, 4, 5 ]
*/

// objectMode

var s = spigot({objectMode: true}, [
  {foo: 1},
  {foo: 2},
  {foo: 3},
  {foo: 4},
])

function timesTwo(record, encoding, callback) {
  record.foo *= 2
  this.push(record)
  callback()
}

function logRecords(records) {
  console.log(records)
}

s.pipe(through2({objectMode: true}, timesTwo))
 .pipe(terminus.concat({objectMode: true}, logRecords))

/*
[ { foo: 2 }, { foo: 4 }, { foo: 6 }, { foo: 8 } ]
*/

API

terminus([options,] _writeFunction)

Create a streams.Writable instance that will call _writeFunction on every chunk. Consult the stream.Writable documentation for instructions on creating a _write function.

terminus.ctor([options,] _writeFunction)

Create a streams.Writable Subclass that can be used to re-create stream.Writable instances with the same _writeFunction.

terminus.devnull([options])

Create a stream.Writable instance that is akin to writing to dev/null i.e. it doesn't do anything except give your stream somewhere to go.

Why? Because if your pipeline doesn't terminate on a Writable stream, it will get paused at the High Water Mark with nothing to unpause it. I've most often seen this when people are using PassThrough streams, or Transforms that incorporate all required behavior.

terminus.concat([options], fn)

Collect the entire stream and when it is done, call fn(contents). This is similar to the stream behavior of concat-stream without the extra Array/Buffer concat behavior and entirely in streams2.

terminus.tail([options], fn)

A slightly less complicated version of terminus([options,] _writeFunction) that only requries you to provide a function that operates as fn(chunk, encoding).

options

All functions accept standard streams.Writable options, that is:

  • highWaterMark [Number] Buffer level when write() starts returning false. Default=16kb
  • decodeStrings [Boolean] Whether not to decode strings into Buffers before passing them to _write() Default=true
  • objectMode [Boolean] If the content is Javascript objects versus strings/buffers. Default=false

objectMode

The most common option you'll be setting is objectMode which will enable you to stream Javascript objects, e.g. records. Unfortunately this is currently required and ALL streams2 parts of your stream pipeline must be in objectMode or you'll get errors. It's annoying, I know.

LICENSE

MIT

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