Create a WSGI app which serves the metrics from a registry.

def make_wsgi_app(registry=REGISTRY):
    """Create a WSGI app which serves the metrics from a registry."""

    def prometheus_app(environ, start_response):
        params = parse_qs(environ.get('QUERY_STRING', ''))
        r = registry
        encoder, content_type = choose_encoder(environ.get('HTTP_ACCEPT'))
        if 'name[]' in params:
            r = r.restricted_registry(params['name[]'])
        output = encoder(r)

        status = str('200 OK')
        headers = [(str('Content-type'), content_type)]
        start_response(status, headers)
        return [output]

    return prometheus_app