Response.text() may twist underlying bytes

gistfile1.txt

res Response {
  [Symbol(realm)]: null,
  [Symbol(state)]: {
    aborted: false,
    rangeRequested: false,
    timingAllowPassed: true,
    requestIncludesCredentials: true,
    type: 'default',
    status: 200,
    timingInfo: {
      startTime: 74.42806800082326,
      redirectStartTime: 0,
      redirectEndTime: 0,
      postRedirectStartTime: 74.42806800082326,
      finalServiceWorkerStartTime: 0,
      finalNetworkResponseStartTime: 0,
      finalNetworkRequestStartTime: 0,
      endTime: 0,
      encodedBodySize: 538,
      decodedBodySize: 538,
      finalConnectionTimingInfo: null
    },
    cacheState: '',
    statusText: 'OK',
    headersList: HeadersList {
      cookies: null,
      [Symbol(headers map)]: [Map],
      [Symbol(headers map sorted)]: null
    },
    urlList: [ [URL] ],
    body: { stream: undefined }
  },
  [Symbol(headers)]: HeadersList {
    cookies: null,
    [Symbol(headers map)]: Map(8) {
      'date' => [Object],
      'content-type' => [Object],
      'content-length' => [Object],
      'connection' => [Object],
      'last-modified' => [Object],
      'etag' => [Object],
      'accept-ranges' => [Object],
      'server' => [Object]
    },
    [Symbol(headers map sorted)]: null
  }
}
textBytes [
  '3c68746d6c3e0a3c686561643e0a3c6d',
  '65746120687474702d65717569763d22',
  '436f6e74656e742d547970652220636f',
  '6e74656e743d22746578742f68746d6c',
  '3b20636861727365743d53686966745f',
  '4a4953223e0a3c6d657461206e616d65',
  '3d2247454e455241544f522220636f6e',
  '74656e743d224a75737453797374656d',
  '7320486f6d6570616765204275696c64',
  '65722056657273696f6e2032302e302e',
  '362e3020666f722057696e646f777322',
  '3e0a3c6d65746120687474702d657175',
  '69763d22436f6e74656e742d5374796c',
  '652d547970652220636f6e74656e743d',
  '22746578742f637373223e0a3c746974',
  '6c653eefbfbdefbfbdefbfbdefbfbdef',
         ^ "efbfbd" is U+FFFD "Replacement Character" in UTF8.
  'bfbdefbfbdefbfbdcc837aefbfbd5bef',
  'bfbdefbfbdefbfbd79efbfbd5befbfbd',
  '573c2f7469746c653e0a3c2f68656164',
  '3e0a3c6672616d6573657420636f6c73',
  '3d31382c38323e0a20203c6672616d65',
  '207372633d226d656e752e68746d2220',
  '6d617267696e6865696768743d223022',
  '206d617267696e77696474683d223022',
  '207363726f6c6c696e673d226175746f',
  '22206e616d653d226c656674223e0a20',
  '203c6672616d65207372633d22746f70',
  '2e68746d22206d617267696e68656967',
  '68743d223022206d617267696e776964',
  '74683d223022207363726f6c6c696e67',
  '3d226175746f22206e616d653d227269',
  '676874223e0a20203c6e6f6672616d65',
  '733e0a20203c626f64793e3c2f626f64',
  '793e0a20203c2f6e6f6672616d65733e',
  '0a3c2f6672616d657365743e0a3c2f68',
  '746d6c3e'
]
textBytes [
  { confidence: 100, name: 'UTF-8', lang: undefined },
  { confidence: 45, name: 'GB18030', lang: 'zh' },
  { confidence: 31, name: 'windows-1252', lang: 'fr' },
  { confidence: 18, name: 'windows-1250', lang: 'ro' },
  { confidence: 10, name: 'Shift_JIS', lang: 'ja' },
  { confidence: 10, name: 'Big5', lang: 'zh' },
  { confidence: 8, name: 'windows-1254', lang: 'tr' },
  { confidence: 0, name: 'ASCII', lang: undefined }
]
rawBytes [
  '3c68746d6c3e0a3c686561643e0a3c6d',
  '65746120687474702d65717569763d22',
  '436f6e74656e742d547970652220636f',
  '6e74656e743d22746578742f68746d6c',
  '3b20636861727365743d53686966745f',
  '4a4953223e0a3c6d657461206e616d65',
  '3d2247454e455241544f522220636f6e',
  '74656e743d224a75737453797374656d',
  '7320486f6d6570616765204275696c64',
  '65722056657273696f6e2032302e302e',
  '362e3020666f722057696e646f777322',
  '3e0a3c6d65746120687474702d657175',
  '69763d22436f6e74656e742d5374796c',
  '652d547970652220636f6e74656e743d',
  '22746578742f637373223e0a3c746974',
  '6c653e88a295948ab082cc837a815b83',
  '808379815b83573c2f7469746c653e0a',
  '3c2f686561643e0a3c6672616d657365',
  '7420636f6c733d31382c38323e0a2020',
  '3c6672616d65207372633d226d656e75',
  '2e68746d22206d617267696e68656967',
  '68743d223022206d617267696e776964',
  '74683d223022207363726f6c6c696e67',
  '3d226175746f22206e616d653d226c65',
  '6674223e0a20203c6672616d65207372',
  '633d22746f702e68746d22206d617267',
  '696e6865696768743d223022206d6172',
  '67696e77696474683d22302220736372',
  '6f6c6c696e673d226175746f22206e61',
  '6d653d227269676874223e0a20203c6e',
  '6f6672616d65733e0a20203c626f6479',
  '3e3c2f626f64793e0a20203c2f6e6f66',
  '72616d65733e0a3c2f6672616d657365',
  '743e0a3c2f68746d6c3e'
]
rawBytes [
  { confidence: 33, name: 'windows-1252', lang: 'fr' },
  { confidence: 20, name: 'windows-1250', lang: 'ro' },
  { confidence: 10, name: 'Shift_JIS', lang: 'ja' },
  { confidence: 10, name: 'Big5', lang: 'zh' },
  { confidence: 10, name: 'GB18030', lang: 'zh' },
  { confidence: 8, name: 'windows-1254', lang: 'tr' },
  { confidence: 0, name: 'ASCII', lang: undefined }
]

try-chardet.js

const { fetch } = require('undici');
const chardet = require('chardet');

/**
 * @param {Buffer} buffer 
 */
function dumpBuffer(buffer) {
  const lines = []
  const SPAN = 16;
  for (let i = 0; ; i += SPAN) {
    const slice = buffer.subarray(i, i + SPAN)
    if (!slice.length) break

    lines.push(slice.toString('hex'))
  }
  return lines

}

async function main() {
  const res = await fetch('http://abehiroshi.la.coocan.jp/')
  console.debug('res', res);

  const text = await res.clone().text()
  const textBytes = Buffer.from(text);

  console.debug(`textBytes`, dumpBuffer(textBytes))
  console.debug(`textBytes`, chardet.analyse(textBytes))
  const rawBytes = Buffer.from(await res.clone().arrayBuffer())

  console.debug(`rawBytes`, dumpBuffer(rawBytes))
  console.debug(`rawBytes`, chardet.analyse(rawBytes))
}

main().finally(() => process.exit(0));