JS function using aws-sdk to download json map from s3 and use it to map request uri to redirect url

fn-uri-map-in-s3.js

const AWS = require('aws-sdk')
const s3 = new AWS.S3()

function fetchJson (bucket, key) {
  return new Promise((resolve, reject) => {
    s3.getObject({ Bucket: bucket, Key: key }, (err, data) => {
      if (err) return reject(err)

      try {
        const bodyString = data.Body.toString('utf8')
        const obj = JSON.parse(bodyString)
        resolve(obj)
      } catch (e) {
        reject(err)
      }
    })
  })
}

function mapRequestToRedirect (requestUri, redirectMap) {
  // FIXME implement mapping logic here
  return '_default_url_'
}

function getRedirectUrl (requestUri, bucket, key) {
  return new Promise((resolve, reject) => {
    fetchJson(bucket, key)
      .then(redirectMap => {
        const redirectUrl = mapRequestToRedirect(requestUri, redirectMap)
        resolve(redirectUrl)
      })
  })
}

const requestUri = '/go/some-ico'
const bucket = 'example.com'
const key = 'redirect-map.json'

getRedirectUrl(requestUri, bucket, key)
  .then(redirectUrl => {
    console.log(`Redirect to: ${redirectUrl}`)
  })
  .catch(err => {
    console.error(err)
  })