def get_host(environ):
    """
    Return the real host for the given environment.
    """
    if 'HTTP_X_FORWARDED_HOST' in environ:
        return environ['HTTP_X_FORWARDED_HOST']
    elif 'HTTP_HOST' in environ:
        return environ['HTTP_HOST']
    result = environ['SERVER_NAME']
    if (environ['wsgi.url_scheme'], environ['SERVER_PORT']) not \
       in (('https', '443'), ('http', '80')):
        result += ':' + environ['SERVER_PORT']
    return result