buffer: UTF-16LE indexOf can hang on unaligned Buffer views

Version

v27.0.0-pre (b805fb5158a)

Platform

Darwin 24.6.0 arm64

Subsystem

buffer

What steps will reproduce the bug?

Buffer#indexOf() can hang when its receiver is an unaligned view. The child process timeout prevents the reproduction from hanging indefinitely.

'use strict';

const { spawnSync } = require('node:child_process');

for (const prefixLength of [0, 1]) {
  const source = `
    const data = Buffer.from('abc', 'utf16le');
    const backing = Buffer.alloc(data.length + ${prefixLength});
    data.copy(backing, ${prefixLength});

    const view = backing.subarray(${prefixLength});
    console.log(view.indexOf('a', 0, 'utf16le'));
  `;

  const result = spawnSync(process.execPath, ['-e', source], {
    encoding: 'utf8',
    timeout: 2000,
  });

  console.log({
    prefixLength,
    status: result.status,
    error: result.error?.code,
    stdout: result.stdout.trim(),
  });
}

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

It's consistent when the receiver view starts at an odd byte offset. The aligned control returns normally.

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

Both searches should terminate and return 0.
The views contain the same bytes, and the UTF-16LE value begins at index 0 of each view. The result should not depend on the underlying memory address.

What do you see instead?

The aligned view returns 0. The view starting at byte offset 1 does not complete before the timeout:

{ prefixLength: 0, status: 0, error: undefined, stdout: '0' }
{ prefixLength: 1, status: null, error: 'ETIMEDOUT', stdout: '' }

Additional information

Buffer#indexOf() passes the receiver data to the 16-bit search, while nbytes aligns matched addresses down. For an odd-offset view, this can move before the start of the view and appears to cause the hang.

This is distinct from #26448, which concerns search-offset rounding, and remains reproducible after #65905, which affects UTF-16LE decoding rather than Buffer#indexOf().

Copying the view or using a Buffer needle avoids the hang. Both workarounds return 0 locally:

Buffer.from(view).indexOf('a', 0, 'utf16le');
view.indexOf(Buffer.from('a', 'utf16le'));

Run the provided reproduction first, then inspect Buffer#indexOf in src/node_buffer.cc around lines 1119-1124 and the 16-bit search alignment in deps/nbytes/include/nbytes.h around lines 459-465. Trace how an odd-offset view is passed to the search and add regression coverage for aligned and unaligned views. Done means both UTF-16LE searches terminate and return 0.