How nignx handled the header to the client in this situation

[allenhe]

I understand the nginx would proxy the header first and then the body, in
the case the connection with the upstream is broken during the transfer of
body, what status code the client would get? since the nginx would proxy the
200 OK from upstream first to the client, but will nginx send another 5xx
header to the client if the upstream connetction is broken?

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,287990,287990#msg-287990