Re: [whatwg/fetch] Trailer support in the API (#981)

Could deferred proxying take place if the Response object took a promise
for trailer headers rather than a callback? Not sure it’s actually worth it
as I suspect trailer cases require processing the entire body, but just
highlighting the possibility.

On Wed, Jul 19, 2023 at 1:46 PM James M Snell ***@***.***>
wrote:

> Keep in mind that these are reversed on client and server sides.
>
> On the client side, a trailers callback would need to be provided in the
> RequestInit, while on the server-side, it needs to be on the ResponseInit.
>
> On the receiving side, setting up an "on trailers" callback would avoid
> the issue of ordering when consuming the body.
>
> // client side fetch api
> const resp = await fetch('http://example.org', {
>   headers: { 'trailers': 'foo' },
>   // Called when sending the headers...
>   trailers(headers) {
>     headers.set('foo', 'bar');
>   }
> }
>
> resp.ontrailers = (headers) => {
>   // Called when trailers are received.
> };
>
> // server side fetch api
> export default {
>   async fetch(req) {
>     req.ontrailers = (headers) => {
>      // Called when trailers are received
>     };
>     // ...
>    return new Response(stream, {
>     headers: { 'trailers': 'foo' },
>     trailers(headers) {
>       headers.set('foo', 'bar');
>     }
>    });
>   }
> }
>
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