x/net/http2: client should drop connection specific headers

[jmhodges]

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?
   1.6.0
2. What operating system and processor architecture are you using (go env)?
   OS X and Linux (but it affects any of them)
3. What did you do?

net/http2 errors when adding a connection-specific header to client requests.

For example, adding a Keep-Alive header to an HTTP request (as the Google certificate-transparency client does) and have it go over an HTTP/2 connection.

Per Section 8.1.2.2 of the HTTP/2 spec, connection-specific headers are to be dropped by HTTP/2 clients.

See this sample code that talks to www.google.com: http://play.golang.org/p/W2C9LfLBlO

1. What did you expect to see?

A working GET request to an HTTP/2 server that returns a 200

1. What did you see instead?

A 400 Bad Request response from the HTTP/2 server.

This was discovered in google/certificate-transparency#1136

[jmhodges]

(Original play.golang.org link in the issue went to a sample that hit google.com, instead of www.google.com. That would redirect on success, so I've swapped out the sample for one that went to www.google.com)

[bradfitz]

Thanks!