compat: `/range` endpoint does not suppport `chunk_size` or `duration` parameters

[yanjieee]

Correct:
curl -v "http://httpbin.org/range/100?duration=6&chunk_size=5" -r1-67 -N

The content is returned in sections.

Wrong:
curl -v "http://httpbingo.org/range/100?duration=6&chunk_size=5" -r1-67 -N

The content is returned at once

[mccutchen]

Thanks for the report! It turns out this is an undocumented departure from the original httpbin, according to this note I left and then forgot about:

go-httpbin/httpbin/handlers.go

Lines 702 to 706 in 8f905de

	// Range returns up to N bytes, with support for HTTP Range requests.
	//
	// This departs from httpbin by not supporting the chunk_size or duration
	// parameters.
	func (h *HTTPBin) Range(w http.ResponseWriter, r *http.Request) {

I think I took this shortcut just to rely on http.ServeContent's automatic handling of HTTP Range requests … I guess I might have to do some actual work to implement this correctly now.

[mccutchen]

Took a quick pass at this, but decided that — for now, at least — it's not worth the effort and additional complexity to implement properly chunked and streamed range responses, especially given questions about how chunk_size would interact with multiple range requests (which we do support and original httpbin does not support).

Wrote a bit more context on #203.

Leaving this open in case someone does want to take it on down the road, because I do get why it would be handy to simulate slow/streamed range requests!