Support auto-enable --stream when meet server sent events

[daleione]

#httpie/cli#376

[ducaale]

I think httpie/cli#376 (comment) is something we can implement easily in xh:

Actually, the best behaviour is to auto-enable --stream when you see Transfer-Encoding: chunked because the length is indeterminate.

[blyxxyz]

I don't think that's right. Nginx sends me Transfer-Encoding: chunked for a static page, and Flask doesn't send it when I have an endpoint that yields lines at one-second intervals.

There are apparently other mimetypes for streaming besides text/event-stream. But we shouldn't just check whether it has the word "stream" in it, application/octet-stream is the usual fallback for binary data.

It might actually make sense to just always enable streaming. The encoding detection and the binary content detection would suffer but I'm not sure anything else would. I haven't thought about it for very long though.

[ducaale]

It might actually make sense to just always enable streaming. The encoding detection and the binary content detection would suffer but I'm not sure anything else would. I haven't thought about it for very long though.

Do you know if enabling streaming comes with any noticeable performance degradation?

[blyxxyz]

Hmm. It seems that writing formatted JSON is much slower when streaming because the output isn't buffered. That's probably fixable by adding buffering but flushing it after each read (to make sure there's no delay).

There might be other cases.

[ducaale]

As of HTTPie 3.0, --stream is enabled if content-type equals text/event-stream. See httpie/cli#1226