Recently we had a bug report from the client that states they are unable to connect to WebSocket with Error during WebSocket Handshake: 'Connection' header value must contain 'Upgrade'.

Obviously we have this header so the only thing I can think of is that ours is downcased (people seem to have problems with that).

For this reason I wanted to capitalize “Upgrade” in the “Connection” header, but it’s trickier then it seems: When I run locally and analyze headers I can see that it is already capitalized, but behind the proxy it becomes downcase.

In nginx I capitalized the proxy_set_header Connection value which does nothing. I then tried both add_header Connection "Upgrade" always; and more_set_headers 'Connection: Upgrade'; from headers-more-nginx module, they work but add an extra “Connection” header instead of modifying the existing one which doesn’t seem solve the problem.

I also tried to clear the existing header before setting the new one, things like more_clear_headers 'Connection'; and such but they seem to “miss” the downcased header as if it didn’t exist.

Did anyone have a similar problem? Any info on how exactly the whole thing works? ideas how to solve it?

As I understand it headers go in, get proxied to the app and get downcased on their way back without much control over the whole thing.

At the moment I’m thinking about dropping nginx and using cap_net_bind_service or iptables to get to port 80 but I hope there is an easier solution.