The example at examples/server.rs breaks when I add one more header after line 36,
https://github.com/stepancheg/rust-http2/blob/master/examples/server.rs#L36 :

resp_headers.add("ETag", "12345678901234567890");

Tested with Firefox 60.0.1 and Google Chrome 65.0, in both cases no response comes back with the above line added to the server example. Tried to debug but got all lost in futures.