René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"buffer: UTF-16LE indexOf can hang on unaligned Buffer views","articleBody":"### Version\n\nv27.0.0-pre (`b805fb5158a`)\n\n### Platform\n\n```text\nDarwin 24.6.0 arm64\n```\n\n### Subsystem\n\nbuffer\n\n### What steps will reproduce the bug?\n\n`Buffer#indexOf()` can hang when its receiver is an unaligned view. The child process timeout prevents the reproduction from hanging indefinitely.\n\n```js\n'use strict';\n\nconst { spawnSync } = require('node:child_process');\n\nfor (const prefixLength of [0, 1]) {\n  const source = `\n    const data = Buffer.from('abc', 'utf16le');\n    const backing = Buffer.alloc(data.length + ${prefixLength});\n    data.copy(backing, ${prefixLength});\n\n    const view = backing.subarray(${prefixLength});\n    console.log(view.indexOf('a', 0, 'utf16le'));\n  `;\n\n  const result = spawnSync(process.execPath, ['-e', source], {\n    encoding: 'utf8',\n    timeout: 2000,\n  });\n\n  console.log({\n    prefixLength,\n    status: result.status,\n    error: result.error?.code,\n    stdout: result.stdout.trim(),\n  });\n}\n```\n\n### How often does it reproduce? Is there a required condition?\n\nIt's consistent when the receiver view starts at an odd byte offset. The aligned control returns normally.\n\n### What is the expected behavior? Why is that the expected behavior?\n\nBoth searches should terminate and return `0`.\nThe 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.\n\n### What do you see instead?\n\nThe aligned view returns `0`. The view starting at byte offset 1 does not complete before the timeout:\n\n```\n{ prefixLength: 0, status: 0, error: undefined, stdout: '0' }\n{ prefixLength: 1, status: null, error: 'ETIMEDOUT', stdout: '' }\n```\n\n### Additional information\n\n`Buffer#indexOf()` [passes the receiver data to the 16-bit search](https://github.com/nodejs/node/blob/b805fb5158a33f6dc0c213165edddc35045f4eb3/src/node_buffer.cc#L1119-L1124), while `nbytes` [aligns matched addresses down](https://github.com/nodejs/node/blob/b805fb5158a33f6dc0c213165edddc35045f4eb3/deps/nbytes/include/nbytes.h#L459-L465). For an odd-offset view, this can move before the start of the view and appears to cause the hang.\n\nThis is distinct from #26448, which concerns search-offset rounding, and remains reproducible after #65905, which affects UTF-16LE decoding rather than `Buffer#indexOf()`.\n\nCopying the view or using a `Buffer` needle avoids the hang. Both workarounds return `0` locally:\n```js\nBuffer.from(view).indexOf('a', 0, 'utf16le');\nview.indexOf(Buffer.from('a', 'utf16le'));\n```","author":{"url":"https://github.com/inoway46","@type":"Person","name":"inoway46"},"datePublished":"2026-09-10T11:52:06Z","url":"https://github.com/nodejs/node/issues/65959"}