Takes the response data as well as any additional headers and returns a
    tuple of tuples of headers suitable for passing to start_response()

def get_headers(data, extra_headers=None):
    '''
    Takes the response data as well as any additional headers and returns a
    tuple of tuples of headers suitable for passing to start_response()
    '''
    response_headers = {
        'Content-Length': str(len(data)),
    }

    if extra_headers:
        response_headers.update(extra_headers)

    return list(response_headers.items())