Inspect Rack headers going through a middleware step

inspect_headers.rb

# Somehow Firefox 3 on Flame Oldest Linux In The Universe
# gets the .tgz files double-cooked compressed. This MW is
# intrduced to verify why that happens
class HeaderSniffer
  def initialize(app, path_regexp = /\.tgz/)
    @path_regexp = path_regexp
    @app = app
  end
  
  def call(env)
    return @app.call(env) unless env['PATH_INFO'].to_s =~ @path_regexp
    
    log "Request headers:"
    env.keys.each do | http_header_name |
      log "  #{http_header_name}: #{env[http_header_name]}"
    end
    
    status, headers, body = @app.call(env)
    log "Response headers:"
    headers.each_pair do |name, value|
      log "  #{name}: #{value}"
    end
    
    [status, headers, body]
  end
  private
  
  def log msg
    $stderr.puts msg
  end 
end