third-party cookiesを無効にしつつニコニコ動画の埋め込みを再生するやつ(未完成)

background.js

(function() {
  'use strict'
  let nicosid = ''
  let nicohistory = ''


  const assignFromSetCookieHeader = (cookie) => {
    const values = cookie.split(';')
    for (const value of values) {
      const sid = /^nicosid=([0-9.]+)$/.exec(value)
      if (sid) nicosid = sid[1]

      const history = /^nicohistory=([a-zA-Z0-9%]+)$/.exec(value)
      if (history) nicohistory = history[1]
    }
  }


  const onHeadersReceived = (details) => {
    for (const header of details.responseHeaders) {
      if (header.name.toLowerCase() === 'set-cookie') {
        assignFromSetCookieHeader(header.value)
        break
      }
    }
    return {'responseHeaders': details.responseHeaders}
  }


  const toPass = (details) => {
    const isNicoVideo = /^https?:\/\/[^\/]+\.nicovideo\.jp\//.test(details.url)
    if (!isNicoVideo) return true
    if (details.url === 'https://nmsg.nicovideo.jp/api.json/') return true
    if (details.method === 'OPTIONS') return true
    return false
  }


  const getNicoCookieValues = () => {
    if (nicosid.length > 0 && nicohistory.length > 0) {
      return `nicosid=${nicosid}; nicohistory=${nicohistory}`
    } else if (nicosid.length > 0) {
      return `nicosid=${nicosid}`
    } else if (nicohistory.length > 0) {
      return `nicohistory=${nicohistory}`
    } else {
      return null
    }
  }


  const onBeforeSendHeaders = (details) => {
    if (toPass(details)) return details

    const setCookie = getNicoCookieValues()
    if (setCookie === null) return details

    let isCookieSet = false
    for (const header of details.requestHeaders) {
      if (header.name.toLowerCase() !== 'cookie') continue

      if (header.value) header.value = `${header.value}; ${setCookie}`
      else header.value = setCookie
      isCookieSet = true
      break
    }

    if (!isCookieSet) details.requestHeaders.push({name: 'Cookie', value: setCookie})
    return details
  }


  browser.webRequest.onHeadersReceived.addListener(
    onHeadersReceived,
    {urls: ['https://*.nicovideo.jp/*']},
    ['blocking', 'responseHeaders']
  )

  browser.webRequest.onBeforeSendHeaders.addListener(
    onBeforeSendHeaders,
    {urls: ['https://*.nicovideo.jp/*']},
    ['blocking', 'requestHeaders']
  )
})()

manifest.json

{
  "manifest_version": 2,
  "name": "Watch",
  "version": "0.1",
  "applications": {
    "gecko": {
      "strict_min_version": "57.0a1",
      "id": "watch@example.com"
    }
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "tabs",
    "https://friends.nico/web/*",
    "https://friends.nico/nicomment",
    "https://*.nicovideo.jp/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  }
}