fs.cpSync / fs.cp / fs.promises.cp fails when src/dest args are Buffer

Version

All

Platform

All

Subsystem

fs

What steps will reproduce the bug?

const { cpSync, cp, promises } = require('node:fs');

cpSync(Buffer.from('dirA'), Buffer.from('dirB'), { recursive: true, filter(...args) { console.log(...args); return true; } });  // throws

cp(Buffer.from('dirA'), Buffer.from('dirB'), { recursive: true, filter(...args) { console.log(...args); return true; } }, (err) => {
  console.log(err);  // errors
});

promises.cp(Buffer.from('dirA'), Buffer.from('dirB'), { recursive: true, filter(...args) { console.log(...args); return true; } });  // rejects

How often does it reproduce? Is there a required condition?

Always

What is the expected behavior? Why is that the expected behavior?

It should just work without throwing. The filter function should be called with the option to receive the path as either a string, Buffer, or URL.

What do you see instead?

It throws.

Additional information

The issue here is that the underlying implementation assumes that the paths are strings and tries to use the path.join function to concatenate them, which obviously does not work for Buffer and URL. The implementation has to be able to support Buffer and URL paths in order to properly support arbitrary text encodings in file names etc. Unfortunately, because of the way the callback is designed, it's not clear that there is an immediate non-breaking fix ready available.

@dario-piotrowicz @cjihrig @anonrig

Start with the fs.cpSync, fs.cp, and fs.promises.cp entry points and reproduce the Buffer-path example from the issue. Trace the path handling and filter callback arguments for string, Buffer, and URL inputs. Done means all three APIs accept Buffer and URL paths without throwing, and the filter receives a supported path value.