Rack::Request - how do I get all headers?

The HTTP headers are available in the Rack environment passed to your app:

HTTP_ Variables: Variables corresponding to the client-supplied HTTP request headers (i.e., variables whose names begin with HTTP_). The presence or absence of these variables should correspond with the presence or absence of the appropriate HTTP header in the request.

So the HTTP headers are prefixed with "HTTP_" and added to the hash.

Here's a little program that extracts and displays them:

require 'rack'app = Proc.new do |env|  headers = env.select {|k,v| k.start_with? 'HTTP_'}    .collect {|key, val| [key.sub(/^HTTP_/, ''), val]}    .collect {|key, val| "#{key}: #{val}<br>"}    .sort  [200, {'Content-Type' => 'text/html'}, headers]endRack::Server.start :app => app, :Port => 8080

When I run this, in addition to the HTTP headers as shown by Chrome or Firefox, there is a "VERSION: HTPP/1.1" (i.e. an entry with key "HTTP_VERSION" and value "HTTP/1.1" is being added to the env hash).

Based on @matt's answer, but this really gives you the request headers in a hash as requested in the question:

headers = Hash[*env.select {|k,v| k.start_with? 'HTTP_'}  .collect {|k,v| [k.sub(/^HTTP_/, ''), v]}  .collect {|k,v| [k.split('_').collect(&:capitalize).join('-'), v]}  .sort  .flatten]

Depending on what key convention you prefer you might want to use something else instead of :capitalize.

Like @Gavriel's answer, but using transform_keys (simpler):

class Request  def headers    env.select { |k,v| k.start_with? 'HTTP_'}.      transform_keys { |k| k.sub(/^HTTP_/, '').split('_').map(&:capitalize).join('-') }  endend

You can even make it so lookups still work even if the case is different:

  def headers    env.      select { |k,v| k.start_with? 'HTTP_'}.      transform_keys { |k| k.sub(/^HTTP_/, '').split('_').map(&:capitalize).join('-') }.      sort.to_h.      tap do |headers|        headers.define_singleton_method :[] do |k|          super(k.split(/[-_]/).map(&:capitalize).join('-'))        end      end  end

So for example, even if headers normalizes the keys so it returns this:

{  Dnt: '1',  Etag: 'W/"ec4454af5ae1bacff1afc5a06a2133f4"',  'X-Xss-Protection': '1; mode=block',}

you can still look up headers using the more natural/common names for these headers:

headers['DNT']headers['ETag']headers['X-XSS-Protection']