Cloudflare Workers streaming response bodies example with unconditional 200

streaming-responses-200.js

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

/**
 * Make multiple requests, 
 * aggregate the responses and 
 * stream it back as a single response.
 */
async function fetchAndApply(request) {
  const requestInit = {
    headers: { "Authorization": "XXXXXX" }
  }
  const fetches = [
    "https://api.coinbase.com/v2/prices/BTC-USD/spot",
    "https://api.coinbase.com/v2/prices/ETH-USD/spot",
    "https://api.coinbase.com/v2/prices/LTC-USD/spot"
  ].map(url => fetch(url, requestInit))

  // Create a pipe and stream the response bodies out
  // as a JSON array.
  let { readable, writable } = new TransformStream()
  streamJsonResponseBodies(fetches, writable)

  return new Response(readable)
}

async function streamJsonResponseBodies(fetches, writable) {
  let writer = writable.getWriter()
  let encoder = new TextEncoder()

  await writer.write(encoder.encode("[\n"))

  for (let i = 0; i < fetches.length; ++i) {
    let response = await fetches[i]
    if (i > 0) await writer.write(encoder.encode(",\n"))
    await manualPipeTo(response.body.getReader(), writer)
  }

  await writer.write(encoder.encode("]"))

  await writer.close()
}

async function manualPipeTo(reader, writer) {
  while (true) {
    const { done, value } = await reader.read()
    if (done) break
    await writer.write(value)
  }
}