Demonstration of ETag header casing issue

config.ru

require 'rack'

run lambda { |env|
  [
    200,
    { 'ETag' => 'some etag value', 'Content-Type' => 'text/plain' },
    ['ETag has been set']
  ]
}

curl output

curl -is http://localhost:9292/
HTTP/1.1 200 OK 
Etag: some etag value
Connection: Keep-Alive
Content-Type: text/plain
Date: Sat, 16 Jul 2011 23:17:23 GMT
Server: WEBrick/1.3.1 (Ruby/1.8.7/2011-02-18)
Content-Length: 17

ETag has been set              

Notice that the header is set as "ETag" but rack normalizes it to "Etag".