Pass abort function to eventStream callback and accept headers option

[tugrul]

I needed to finalize the response in some cases like "job done" or "unauthorized access". I consider to access abort callback from from setup callback is good idea.

Nginx is waiting for buffer to fill and It not send events immediately. It disables buffering when response headers has X-Accel-Buffering: no field. I put an options field to control this case.

[sergiodxa]

I would prefer to give you a way to pass a Headers object so you can set custom headers instead of adding an option for every custom header a proxy may need.

For the close function, you can create a custom AbortController before sending the response, see https://sergiodxa.com/tutorials/close-sse-connection-from-the-server-in-remix

[tugrul]

I changed to use optional headers more generic way as you mentioned.

I already use AbortController as a wrapper as you mentioned for workaround. But I think this is more common requirements and abort callback must have.

if it was necessary to use it due to an unusual situation then I wouldn't think about it.