web-check/api/carbon.js

import middleware from './_common/middleware.js'
import { createLogger } from './_common/logger.js'

const log = createLogger('carbon')

const TIMEOUT = 8000
const MAX_BYTES = 10 * 1024 * 1024
const USER_AGENT = 'Mozilla/5.0 (compatible; WebCheck/2.0; +https://web-check.xyz)'

// Sustainable Web Design model v3 constants, matches websitecarbon.com formula
const KWH_PER_GB = 0.81
const FIRST_VISIT = 0.25
const RETURN_VISIT = 0.75
const RETURN_DATA_PCT = 0.02
const GRID_INTENSITY = 442
const RENEWABLE_INTENSITY = 50
const LITRES_PER_GRAM = 0.5562

// Stream the response, cap at MAX_BYTES so huge pages can't blow memory or time
const fetchByteCount = async (url) => {
  const r = await fetch(url, {
    signal: AbortSignal.timeout(TIMEOUT),
    redirect: 'follow',
    headers: { 'user-agent': USER_AGENT, accept: 'text/html,*/*;q=0.1' },
  })
  if (!r.ok) throw new Error(`status ${r.status}`)
  if (!r.body) return 0
  const reader = r.body.getReader()
  let total = 0
  while (total < MAX_BYTES) {
    const { value, done } = await reader.read()
    if (done) break
    total += value.length
  }
  reader.cancel().catch(() => {})
  return total
}

// SWD-based stats matching websitecarbon /data response shape
const computeCarbon = (bytes) => {
  const adjustedBytes = bytes * (FIRST_VISIT + RETURN_VISIT * RETURN_DATA_PCT)
  const energy = (adjustedBytes / 1073741824) * KWH_PER_GB
  const gridGrams = energy * GRID_INTENSITY
  const renewableGrams = energy * RENEWABLE_INTENSITY
  return {
    adjustedBytes,
    energy,
    co2: {
      grid: { grams: gridGrams, litres: gridGrams * LITRES_PER_GRAM },
      renewable: {
        grams: renewableGrams,
        litres: renewableGrams * LITRES_PER_GRAM,
      },
    },
  }
}

// Fetch site, count bytes, compute SWD carbon stats locally, no third-party API
const carbonHandler = async (url) => {
  let bytes
  try {
    bytes = await fetchByteCount(url)
  } catch (error) {
    log.warn(`fetch failed for ${url}`, error.message)
    return { error: `Failed to fetch site: ${error.message}` }
  }
  if (!bytes) return { skipped: 'Site returned no content, cannot calculate carbon' }
  log.debug(`measured ${bytes} bytes for ${url}`)
  return {
    url,
    bytes,
    green: false,
    statistics: computeCarbon(bytes),
    scanUrl: url,
  }
}

export const handler = middleware(carbonHandler)
export default handler