Rack streamed proxy causing Net::HTTPOK#read_body called twice

[Fabio Kreusch <fabiokr@gmail.com>]

So, I have a Rack application which acts as a proxy. I have
implemented a net/http api to deal with the communication, so the rack
app basically calls it like this:

api.new(request_method, rack_request, options).response
.response returns a valid rack response [status, headers, body].

Body is an instance of the api, and it its implementation is like this
(simplified version):

def initialize
  ...
  @proxy_connection = Net::HTTP.start(proxied_uri.host,
proxied_uri.port)
  @proxy_connection.request(@proxy_request) do |response|
    @proxy_response = response
  end
end

def each(&block)
  @proxy_response.read_body(&block)
end

def to_s
  @proxy_response.read_body
end
The rack app can then call the proxied service with a full response
with to_s, or as a streaming and receive the response in chunks with
each.

The thing is, when I return the response in rack, I'm getting the
following stack trace: https://gist.github.com/1879724

Apparently, the server or rack is calling 'each' more than once, but
I'm not sure what might be causing it.

The Rack app is running under rails 3.2.1.