What is your issue?

How did you get this error?

HTTP/2 doesn't have connection-level headers, like the other bug says.

@bradfitz I made a proxy for some urls

example code https://gist.github.com/suconghou/50dd30df10bd6faa2abe1805afe3216f

notice it works well then you use chrome , because chrome send keep-alive header

but some other software and services may send Keep-Alive header , eg: cloudflare , IE ( https://stackoverflow.com/questions/9650236/how-to-send-lower-case-keep-alive-header-through-httpwebrequest/30071784 the answers mentioned IE )

use curl -H "Connection:Keep-Alive" http://127.0.0.1:8080/ simulate this behavior

@bradfitz

please replace this

(v != "" && v != "close" && v != "keep-alive") 

with

(v != "" && v != "close" && v != "keep-alive" && v != "Keep-Alive") 

in checkConnHeaders function

Please read https://httpwg.org/specs/rfc7230.html#rfc.section.6.1

A proxy or gateway MUST parse a received Connection header field before a message is forwarded and, for each connection-option in this field, remove any header field(s) from the message with the same name as the connection-option, and then remove the Connection header field itself (or replace it with the intermediary's own connection options for the forwarded message).

I don't know why Go accepts Connection: keep-alive, which I think is the same as Connection: Keep-Alive. But this is a bug in your proxy, not in http package.

I think it is better to use httputil.ReverseProxy for this.

Doesn't it makes sense to handle this transparently?
I think Go should just drop the Connection header if H2 does not support Connection headers.
I see the same problem if I use plain http.Transport.RoundTrip(req) in case Connection: Keep-Alive is set and the backend called specified in the http.Request supports H2.

For me it sounds really weird to argue you should use httputil.ReverseProxy, instead of fixing this.

Change https://golang.org/cl/122588 mentions this issue: http2: compare Connection header value case-insensitively