class Aws::Binary::EventBuilder

def _event_stream_message(event_ref, params)
  es_headers = {}
  payload = ""
  es_headers[":message-type"] = Aws::EventStream::HeaderValue.new(
    type: "string", value: "event")
  es_headers[":event-type"] = Aws::EventStream::HeaderValue.new(
    type: "string", value: event_ref.location_name)
  explicit_payload = false
  implicit_payload_members = {}
  event_ref.shape.members.each do |member_name, member_ref|
    unless member_ref.eventheader
      if member_ref.eventpayload
        explicit_payload = true
      else
        implicit_payload_members[member_name] = member_ref
      end
    end
  end
  # implict payload
  if !explicit_payload && !implicit_payload_members.empty?
    if implicit_payload_members.size > 1
      payload_shape = Shapes::StructureShape.new
      implicit_payload_members.each do |m_name, m_ref|
        payload_shape.add_member(m_name, m_ref)
      end
      payload_ref = Shapes::ShapeRef.new(shape: payload_shape)
      payload = build_payload_members(payload_ref, params)
    else
      m_name, m_ref = implicit_payload_members.first
      streaming, content_type = _content_type(m_ref.shape)
      es_headers[":content-type"] = Aws::EventStream::HeaderValue.new(
        type: "string", value: content_type)
      payload = _build_payload(streaming, m_ref, params[m_name])
    end
  end
  event_ref.shape.members.each do |member_name, member_ref|
    if member_ref.eventheader && params[member_name]
      header_value = params[member_name]
      es_headers[member_ref.shape.name] = Aws::EventStream::HeaderValue.new(
        type: _header_value_type(member_ref.shape, header_value),
        value: header_value
      )
    elsif member_ref.eventpayload && params[member_name]
      # explicit payload
      streaming, content_type = _content_type(member_ref.shape)
      es_headers[":content-type"] = Aws::EventStream::HeaderValue.new(
        type: "string", value: content_type)
      payload = _build_payload(streaming, member_ref, params[member_name])
    end
  end
  Aws::EventStream::Message.new(
    headers: es_headers,
    payload: StringIO.new(payload)
  )
end