class Seahorse::Client::Plugins::RequestCallback::ReadCallbackHandler

def call(context)
  if (callback = context[:on_chunk_sent])
    context.http_request.body = ReadCallbackIO.new(
      context.http_request.body,
      callback
    )
    @handler.call(context).tap do
      unwrap_callback_body(context)
    end
  else
    @handler.call(context)
  end
end

def unwrap_callback_body(context)
  body = context.http_request.body
  if body.is_a? ReadCallbackIO
    context.http_request.body = body.io
  end
end