overleaf/services/web/app/src/Features/Spelling/SpellingController.js

const request = require('request')
const Settings = require('settings-sharelatex')
const logger = require('logger-sharelatex')
const AuthenticationController = require('../Authentication/AuthenticationController')

const TEN_SECONDS = 1000 * 10

const languageCodeIsSupported = code =>
  Settings.languages.some(lang => lang.code === code)

module.exports = {
  proxyRequestToSpellingApi(req, res) {
    const { language } = req.body

    let url = req.url.slice('/spelling'.length)

    if (url === '/check') {
      if (!language) {
        logger.error('"language" field should be included for spell checking')
        return res.status(422).send(JSON.stringify({ misspellings: [] }))
      }

      if (!languageCodeIsSupported(language)) {
        // this log statement can be changed to 'error' once projects with
        // unsupported languages are removed from the DB
        logger.info({ language }, 'language not supported')
        return res.status(422).send(JSON.stringify({ misspellings: [] }))
      }
    }

    const userId = AuthenticationController.getLoggedInUserId(req)
    url = `/user/${userId}${url}`
    req.headers['Host'] = Settings.apis.spelling.host
    return request({
      url: Settings.apis.spelling.url + url,
      method: req.method,
      headers: req.headers,
      json: req.body,
      timeout: TEN_SECONDS
    })
      .on('error', function(error) {
        logger.error({ err: error }, 'Spelling API error')
        return res.status(500).end()
      })
      .pipe(res)
  }
}