A Cloudflare Worker for session persistence

stick-session.js

addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
  event.passThroughOnException()
})

const ORIGINS = [
  'storage.googleapis.com',
  'frank-io.herokuapp.com'
]

class StickySession {
  constructor (request) {
    this.request = new Request(request)
    this.url = new URL(this.request.url)
    this.hdrs = new Headers(this.request.headers)
    this.clientCookie = {}
    if (this.hdrs.has('cookie')) {
      this.clientCookie = new URLSearchParams(this.hdrs.get('cookie').trim().split(';').join('&'))
    } else {
      this.clientCookie = new URLSearchParams('_lbid=null')
    }
    this.origin = null
    this.intercept = false
    this.domainParam = this.url.hostname.split('.').splice(-2,2).join('.')
    console.log(this)
  }
  
  // probably overkill to use SHA-1
  static async digest (msg) {
    const msgUint8 = new TextEncoder().encode(msg)
    const hashBuffer = await crypto.subtle.digest('SHA-1', msgUint8)
    const hashArray = Array.from(new Uint8Array(hashBuffer))
    const hashHex = hashArray.map(b => b.toString(16).padStart(2, '0')).join('')
    return hashHex
  }

  get sticker () {
    return this.origin
  }

  set sticker (param) {
    if (this.clientCookie.has(param) && this.clientCookie.get(param) != 'null') {
      this.origin = this.clientCookie.get(param)
      console.log(this.origin)
    } else {
      const random = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min
      const originToHash = ORIGINS[random(0, ORIGINS.length - 1)]
      this.intercept = true
      this.origin = StickySession.digest(originToHash)
    }
  }

  async selectOrigin () {
    for (let i = 0; i < ORIGINS.length; i++) {
      let server = await StickySession.digest(ORIGINS[i])
      if (server === await this.sticker) {
        console.log(server, this.sticker, ORIGINS[i])
        return ORIGINS[i]
      }
    }
  }
}

async function handleRequest (request) {
  let session = new StickySession(request)
  // session.sticker is the cookie parameter key name
  session.sticker = '_lbid'
  // reassign the hostname property only.
  session.url.hostname = await session.selectOrigin()
 
  let response = await fetch(session.url, session.request)
  response = new Response(response.body, response)
  // TODO - move intercept boolean into class definitiion
  if (!session.intercept) return response
  // optionally set domain name parameter. Be sure to including the "." prefix for subdomains
  response.headers.append('set-cookie', `_lbid=${await session.sticker}; domain=.${session.domainParam};`)
  return response
}