Builds HTTPResponse object for streaming.

def _BuildStreamingResponse(self, binary_stream, method_name=None):
    """Builds HTTPResponse object for streaming."""
    precondition.AssertType(method_name, Text)

    # We get a first chunk of the output stream. This way the likelihood
    # of catching an exception that may happen during response generation
    # is much higher.
    content = binary_stream.GenerateContent()
    try:
      peek = content.next()
      stream = itertools.chain([peek], content)
    except StopIteration:
      stream = []

    response = werkzeug_wrappers.Response(
        response=stream,
        content_type="binary/octet-stream",
        direct_passthrough=True)
    response.headers["Content-Disposition"] = ((
        "attachment; filename=%s" % binary_stream.filename).encode("utf-8"))
    if method_name:
      response.headers["X-API-Method"] = method_name.encode("utf-8")

    if binary_stream.content_length:
      response.content_length = binary_stream.content_length

    return response