If-Range must compare date with exact match

[hnakamur]

https://tools.ietf.org/html/rfc7233#section-3.2

Note that this comparison by exact match,
including when the validator is an HTTP-date, differs from the
"earlier than or equal to" comparison used when evaluating an
If-Unmodified-Since conditional.

However trafficserver currently compares If-Range date with the Last-Modified using the less than operator.

trafficserver/proxy/http/HttpTransactCache.cc

Lines 1384 to 1395 in 15b0051

	// this a Date, similar to If-Unmodified-Since
	else {
	// lm_value is zero if Last-modified not exists
	ink_time_t lm_value = response->get_last_modified();
	// condition fails if Last-modified not exists
	if ((request->get_if_range_date() < lm_value) || (lm_value == 0)) {
	return HTTP_STATUS_RANGE_NOT_SATISFIABLE;
	} else {
	return response->status_get();
	}
	}

[hnakamur]

Thanks!