Does adding Access-Contr-Expose-Headers increase the size of the headers returned?

Question

I work for a large company that is already pushing the boundaries of header size limits on AWS Lambda among other things. If I were to expose additional headers aside from the CORS safe-listed headers, does that increase the size of the headers sent in a response? Reason I'm asking is because Expose makes me think they're already included in the Response, but they are just inaccessible or invisible on the browser/app.

Answer 1

Your problem is that you treat Node as a synchronous / sequential language.

I recommend that you learn about callbacks (you use it here), Promises and async / await. (And TypeScript by the way)

Fortunately, with node v10 you can easily avoid the pitfalls of async and * callback hell * - using async / await

A modern solution should look similar to:

import { readFile } from 'fs/promises'; //Modern fersion of `fs`

const main = async () => { // modern way to define function (async)
  let response = ''; // Variables defined by `var` are available in global context, and may cause problems 
  response = await readFile('test.txt', {encoding: 'utf8' })
  return response
}

try { // `try {} catch() {}` - error handling
  console.log(await main())//It will work 90% of the time.
} catch (ex) {
  console.error(ex)
}

//If you cannot define an asychronic function then use: 
main().then((res) =>{
  console.log(res)
  //Here you can use `res`
}).catch(ex => console.error(ex)) // error handling
// not here