self-stream

Sometimes you need to change something in a file and probably you will do:

const fs = require('fs')
fs.readFile('file.md', 'utf8', (readErr, data) => {
  if (readErr) return console.log(readErr)
  data = changeSomething(data)
  fs.writeFile('file.md', data, 'utf8', (writeErr) => {
    if (writeErr) return console.log(writeErr)
    console.log('done')
  })
})

And that's not a good thing, because you are loading the entire file in your working memory slowing down your application.
In the magic world of Nodejs for avoid this problem you can use streams. But as you probably know with streams you cannot read, transform and write the same file.
Here come to help self-stream, an "hack" solution to this problem.
The solution is not in-place, because in case of something fails during the transform process, you will not lose the original file.

Needs Node.js >= 4.4.1
If are using 4.4.1 <= Node.js < 5 you need --es_staging flag

Install

$ npm install self-stream --save

API

selfStream(filename, transform, callback)

filename: the file to change with the relative path
transform: is a function or an array of functions with all the transforms
callback: callback function

Example:

const selfStream = require('self-stream')
const through2 = require('through2')
 
const transform = through2(function (chunk, enc, cb) {
  for (var i = 0; i < chunk.length; i++) {
    if (chunk[i] === 97) chunk[i] = 122 // swap 'a' for 'z'
  }
  this.push(chunk)
  cb()
})
 
selfStream('file.md', transform, function (err) {
  if (err) return console.log(err)
})
 

As you can see in the source code self-stream uses pump to pipe all the streams and at the end it will rewrite the original file with the modified one.

Contributing

If you feel you can help in any way, be it with examples, extra testing, or new features please open a pull request or open an issue.

The code follows the Standard code style.

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License

The code is released under the MIT license.

The software is provided "as is", without warranty of any kind, express or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose and non infringement. In no event shall the authors or copyright holders be liable for any claim, damages or other liability, whether in an action of contract, tort or otherwise, arising from, out of or in connection with the software or the use or other dealings in the software.