steno

Super fast and safe non-blocking file writer for Node

var steno = require('steno')
steno('file.txt').write('data')

Example

If you need to write to file, you either use writeFileSync or writeFile. The first is blocking and the second doesn't prevent race condition.

For example:

// Very slow but file's content will always be 10000
for (var i = 0; i < 10000; i++) {
  fs.writeFileSync('file.txt', i)
}

// Very fast but file's content may be 5896, 2563, 9856, ...
for (var i = 0; i < 10000; i++) {
  fs.writeFile('file.txt', i, function() {})
}

With steno:

// Very fast and file's content will always be 10000
for (var i = 0; i < 10000; i++) {
  steno('file.txt').write(i)
}

Race condition is prevented and it runs in 2ms versus ~5500ms with fs.writeFileSync.

How it works

steno('file.txt').write('A') // starts writing A to file
steno('file.txt').write('B') // still writing A, B is buffered
steno('file.txt').write('C') // still writing A, B is replaced by C
                             // ...
                             // A has been written to file
                             // starts writting C (B has been skipped)

When file is being written, data is stored in memory and flushed to disk as soon as possible. Please note also that steno skips intermediate data (B in this example).

Methods

steno(filename)

Returns writer for filename.

writer.write(data, [cb])

Writes data to file. If file is already being written, data is buffered until it can be written. An optional callback can also be set to be notified when data has been written to disk.

writer.setCallback(cb)

Sets a writer level callback that is called only after file has been written. Useful for creating atomic writers, logging, delaying, ...

var atomicWriter = steno('tmp-file.txt').setCallback(function(err, data, next) {
  if (err) throw err
  fs.rename('tmp-file.txt', 'file.txt', function(err) {
    if (err) throw err
    next()
  })
})

atomicWriter.write('Hello world')

License

MIT - Typicode