fileswap-stream

Write to a writable file-stream that swaps out it's underlying file resources according to swapper and naming functions. This can be used for a persistent log stream - just stream to it 24/7 and let it swap out to new files whenever you trigger it to.

Example

var swapStream = require('../.')
var RandomStream = require('random-stream')

var options = {
  namer : namer
, swapper : swapper
, tdelta : 1000
, path : "."
, fsops : {
    flags: "a"
  , encoding: "utf8"
  }
}

var ss = swapStream(options)

RandomStream().pipe(ss)

function namer () {
  return "t-" + getSecond() + "-" + getMinute()
}

function swapper () {
  return Math.round(parseInt(getSecond()) / 5)
}

function getMinute () {
  var d = new Date()
  return ('0' + d.getMinutes() ).slice(-2)
}

function getSecond () {
  var d = new Date()
  return ('0' + d.getSeconds() ).slice(-2)
}

this will produce the files full of random junk

t-27-07  t-28-07  t-33-07  t-38-07  t-43-07

every five seconds as determined by swapper.

Other useful ideas for swapper would be function that returns a different value every day:

function swapper () {
  var d = new Date()
  return ('0' + d.getUTCDate() ).slice(-2)
}

Another way to think about swapper is that it is a function that is repeatedly called to check it's return value against the last value. When the return value changes, the underlying file resource being written to is swapped out with a new name given by namer. In this way the fileswap could be controlled by anything, such as time, network or CPU heat.

Options

The options object has the following fields

options.namer

Called to name the new file. This function is called everytime the internal swapper is triggered. The function should return a string.

options.swapper

Called every tdelta milliseconds and compared to the previous return value of swapper. If it is different, a new file resource is contructed with name supplied by namer.

options.tdelta

The delay time for checking the swapper states.

options.path

Optional path parameter for creating new files.

options.fsops

options passed to fs.createWriteStream(fsops)

Install

npm install swapfile-stream

License

MIT