When a HTTP 1.1 request is routed through a HTTP router and the upstream server responds with status 304 and no content. The upstream's content-type header is removed from the outgoing response.
This does not happen if the request is HTTP 2.0, nor does it happen when the request is HTTP 1.1 but upstream respond status 200 (with content).
I've temporarily worked around this by using a TCP router instead of the HTTP router (since I need that header even when there's no response content) but is the stripping of the content-type header expected behavior when the upstream server doesn't respond with any content?
EDIT:
According to the MDN page on how 304 should be handled, I think this would be considered a bug.
The response must not contain a body and must include the headers that would have been sent in an equivalent
200response