How to "pass through" the compressed body of a fetch() response in edge function?

Support
1

I’m using fetch() in an edge function, and I don’t understand why the response doesn’t have a Content-Encoding header even though visiting the request URL directly from a browser shows that it’s compressed using Brotli (and the Content-Encoding header is present).

const upstreamResponse = await fetch('https://example.com', {
  headers: {
    'Accept-Encoding': 'gzip, br',
  },
});

// Always null
console.log(upstreamResponse.headers.get('Content-Encoding'))

// Pass the response as-is to avoid automatic decompression,
// but the response body is always uncompressed
return new Response(upstreamResponse.body, {
  status: upstreamResponse.status,
  headers: {
    ...Object.fromEntries(upstreamResponse.headers),  // Preserve headers
  },
});

I can recompress it before sending it along, but that seems like a waste of computing resources. Anyone know how I can prevent the response from getting automatically uncompressed?

(I’m testing locally via Netlify CLI.)

2

Does this happen on production?

3

I haven’t actually deployed and tested it. Are you saying I should expect different behavior in production?

EDIT

FWIW, some reading I’ve done since posting this topic indicates that fetch() automatically decompreses the response body, and there’s no way to suppress it. So maybe this is expected behavior? (Seems kinda inefficient if one just wants to pass along the compressed response as is.)

4

If this happens outside of Netlify’s Edge Functions environment then there’s no much we can do about it.