class Rack::Chunked

# No exception raised
[200, { ‘Trailer’ => ‘Expires’}, body]
end
{ ‘Expires’ => Time.now.to_s }
def body.trailers
body = [“Hello”, “World”]
# error raised
[200, { ‘Trailer’ => ‘Expires’}, [“Hello”, “World”]]
specify a response body that supports a trailers method. Example:
headers in the chunked encoding. However, using this requires you manually
This supports the Trailer response header to allow the use of trailing
when the response does not include a Content-Length header.
Middleware that applies chunked transfer encoding to response bodies

def call(env)

modify the response to use chunked Transfer-Encoding.
but does not have Content-Length or Transfer-Encoding headers,
If the rack app returns a response that should have a body, 
def call(env)
  status, headers, body = @app.call(env)
  headers = HeaderHash[headers]
  if chunkable_version?(env[SERVER_PROTOCOL]) &&
     !STATUS_WITH_NO_ENTITY_BODY.key?(status.to_i) &&
     !headers[CONTENT_LENGTH] &&
     !headers[TRANSFER_ENCODING]
    headers[TRANSFER_ENCODING] = 'chunked'
    if headers['Trailer']
      body = TrailerBody.new(body)
    else
      body = Body.new(body)
    end
  end
  [status, headers, body]
end

def chunkable_version?(ver)

Whether the HTTP version supports chunked encoding (HTTP 1.1 does). 
def chunkable_version?(ver)
  case ver
  # pre-HTTP/1.0 (informally "HTTP/0.9") HTTP requests did not have
  # a version (nor response headers)
  when 'HTTP/1.0', nil, 'HTTP/0.9'
    false
  else
    true
  end
end

def initialize(app) 

def initialize(app)
  @app = app
end