send-payload.ts

import { ServerResponse } from 'http'
import { isResSent } from '../lib/utils'

export function sendPayload(
  res: ServerResponse,
  payload: any,
  type: 'html' | 'json',
  options?:
    | { private: true }
    | { private: boolean; stateful: true }
    | { private: boolean; stateful: false; revalidate: number | false }
): void {
  if (isResSent(res)) {
    return
  }

  // TODO: ETag headers?
  res.setHeader(
    'Content-Type',
    type === 'json' ? 'application/json' : 'text/html; charset=utf-8'
  )
  res.setHeader('Content-Length', Buffer.byteLength(payload))
  if (options != null) {
    if (options.private || options.stateful) {
      if (options.private || !res.hasHeader('Cache-Control')) {
        res.setHeader(
          'Cache-Control',
          `private, no-cache, no-store, max-age=0, must-revalidate`
        )
      }
    } else if (typeof options.revalidate === 'number') {
      if (options.revalidate < 1) {
        throw new Error(
          `invariant: invalid Cache-Control duration provided: ${options.revalidate} < 1`
        )
      }

      res.setHeader(
        'Cache-Control',
        `s-maxage=${options.revalidate}, stale-while-revalidate`
      )
    } else if (options.revalidate === false) {
      res.setHeader(
        'Cache-Control',
        `s-maxage=31536000, stale-while-revalidate`
      )
    }
  }
  res.end(payload)
}