metamask-extension/ui/app/helpers/utils/fetch-with-cache.js

import {
  loadLocalStorageData,
  saveLocalStorageData,
} from '../../../lib/local-storage-helpers'
import fetchWithTimeout from '../../../../app/scripts/lib/fetch-with-timeout'

const fetchWithCache = async (url, fetchOptions = {}, { cacheRefreshTime = 360000, timeout = 30000 } = {}) => {
  if (fetchOptions.body || (fetchOptions.method && fetchOptions.method !== 'GET')) {
    throw new Error('fetchWithCache only supports GET requests')
  }
  if (!(fetchOptions.headers instanceof window.Headers)) {
    fetchOptions.headers = new window.Headers(fetchOptions.headers)
  }
  if (
    fetchOptions.headers &&
    fetchOptions.headers.has('Content-Type') &&
    fetchOptions.headers.get('Content-Type') !== 'application/json'
  ) {
    throw new Error('fetchWithCache only supports JSON responses')
  }

  const currentTime = Date.now()
  const cachedFetch = loadLocalStorageData('cachedFetch') || {}
  const { cachedResponse, cachedTime } = cachedFetch[url] || {}
  if (cachedResponse && currentTime - cachedTime < cacheRefreshTime) {
    return cachedResponse
  }
  fetchOptions.headers.set('Content-Type', 'application/json')
  const _fetch = timeout
    ? fetchWithTimeout({ timeout })
    : window.fetch
  const response = await _fetch(url, {
    referrerPolicy: 'no-referrer-when-downgrade',
    body: null,
    method: 'GET',
    mode: 'cors',
    ...fetchOptions,
  })
  if (!response.ok) {
    throw new Error(`Fetch failed with status '${response.status}': '${response.statusText}'`)
  }
  const responseJson = await response.json()
  const cacheEntry = {
    cachedResponse: responseJson,
    cachedTime: currentTime,
  }
  cachedFetch[url] = cacheEntry
  saveLocalStorageData(cachedFetch, 'cachedFetch')
  return responseJson
}

export default fetchWithCache