Because files matter!

Prefer posix_fallocate over fallocate as it is more portable. offset and length have po be integers.

const {posix_fallocate, fallocate /* linux only */} = require("fallocate");

posix_fallocate("some_file", 0 /* offset */, 1<<20).
  then(console.log).
  catch(console.error);
posix_fallocate("some_file", 0 /* offset */, 1<<20, (err, path) => {
  if (err) {
    console.error(err);
  }
  else {
    console.log(path);
  }
});

fallocate("some_file", 0 /* offset */, 1<<20, 0 /* mode */).
  then(console.log).
  catch(console.error);
fallocate("some_file", 0 /* offset */, 1<<20, 0 /* mode */, (err, path) => {
  if (err) {
    console.error(err);
  }
  else {
    console.log(path);
  }
});

posix_fallocateSync("some_file", 0 /* offset */, 1<<20);
fallocateSync("some_file", 0 /* offset */, 1<<20, 0 /* mode */);

const fd = fs.openSync("some_file", "w", {encoding: null});
try {
  fposix_fallocateSync(fd, 0 /* offset */, 1<<20);
  ffallocateSync(fd, 0 /* offset */, 1<<20, 0 /* mode */);
}
finally {
  fs.closeSync(fd);
}

Errors are either errors as returned by underlying APIs, or FallocateErrors. FallocateError additionally exposes .errno and .code.

Unfortunately the fposix_allocateSync and ffallocateSync functions cannot be implemented in an async variant, due to node not offering a proper way to pass file descriptors to child processes (only sockets and such).

If your OS or rather libc doesn't provide *64 implementations for offsets, the off_t sizes are guesses.

At the moment only Linux is supported. BSDs might be supported when they provide a posix_fallocate implementation.

Windows are not supported for lack of support of this API. However, maxos offers APIs which can be used to simulate the functionality. This is not implemented at the moment, tho.

Unsupported plaforms will always raise an error.

• Implemented using ffi, no binary components.
• Async functions implemented using a child_process performing the actual allocation. That worker is started on demand and kept alive until the parent process exits. If you're messing with the working directory after the first fallocate call make sure to pass a qualified path.
• Files will be opened with a (unless using the function taking an fd).