How to stream to/from a file descriptor in node?

Question

The fs.createReadStream() and fs.createWriteStream() only support file paths but I need to read (or write) from a file descriptor (passed to/from a child process).

Note I need Streams, so fs.open/fs.read/fs.write are not sufficient.

Answer 1

When you call fs.createReadStream you can pass in a file descriptor:

var fs = require('fs');
var fd = fs.openSync('/tmp/tmp.js', 'r');
var s = fs.createReadStream(null, {fd: fd});
s.pipe(process.stdout);

If there is a fd option, the filename is ignored.

Answer 2

// Open &3:
process.oob1 = fs.createWriteStream(null, { fd: 3 });
// Write to &3 / oob1 (out-of-band 1)
process.oob1.write("Note: this will throw an exception without 3>&1 or something else declaring the existence of &3");