random-access-file

Continuous reading or writing to a file using random offsets and lengths

npm install random-access-file

Why?

If you are receiving a file in multiple pieces in a distributed system it can be useful to write these pieces to disk one by one in various places throughout the file without having to open and close a file descriptor all the time.

random-access-file allows you to do just this.

Usage

const RandomAccessFile = require('random-access-file')

const file = new RandomAccessFile('my-file.txt')

file.write(10, Buffer.from('hello'), function(err) {
  // write a buffer to offset 10
  file.read(10, 5, function(err, buffer) {
    console.log(buffer) // read 5 bytes from offset 10
    file.close(function() {
      console.log('file is closed')
    })
  })
})

file will use an open file descriptor. When you are done with the file you should call file.close().

API

const file = new RandomAccessFile(filename, [options])

Create a new file. Options include:

{
  truncate: false, // truncate the file before reading / writing
  size: someSize, // truncate the file to this size first
  readable: true, // should the file be opened as readable?
  writable: true,  // should the file be opened as writable?
  lock: false, // lock the file
  sparse: false // mark the file as sparse
}

file.write(offset, buffer, [callback])

Write a buffer at a specific offset.

file.read(offset, length, callback)

Read a buffer at a specific offset. Callback is called with the buffer read.

file.del(offset, length, callback)

Delete a portion of the file. Any partial file blocks in the deleted portion are zeroed and, if the file is sparse, the remaining file blocks unlinked in-place.

file.truncate(offset, callback)

Truncate the file length to this offset.

file.stat(callback)

Stat the storage. Should return an object with useful information about the underlying storage, including:

{
  size: number // how many bytes of data is stored?
}

file.close([callback])

Close the underlying file descriptor.

file.unlink([callback])

Unlink the underlying file.

file.on('open')

Emitted when the file descriptor has been opened. You can access the fd using file.fd. You do not need to wait for this event before doing any reads/writes.

file.on('close')

Emitted when the file has been closed.

License

MIT