static Tuple2<HttpResponse, Integer> doCheckProtocolVersion(List<String> clientSupportedVersions) {
        List<String> washedClientVersions = splitVersions(clientSupportedVersions);

        if (washedClientVersions == null || washedClientVersions.isEmpty()) {
            return new Tuple2<>(new ErrorHttpResponse(
                    Headers.HTTP_NOT_ACCEPTABLE,
                    "Request did not contain " + Headers.VERSION
                    + "header. Server supports protocol versions "
                    + serverSupportedVersions), -1);
        }

        //select the highest version supported by both parties
        //this could be extended when we support a gazillion versions - but right now: keep it simple.
        int version;
        if (washedClientVersions.contains("3")) {
            version = 3;
        } else {
            return new Tuple2<>(new ErrorHttpResponse(
                    Headers.HTTP_NOT_ACCEPTABLE,
                    "Could not parse " + Headers.VERSION
                    + "header of request (values: " + washedClientVersions +
                    "). Server supports protocol versions "
                    + serverSupportedVersions), -1);
        }
        return new Tuple2<>(null, version);
    }
Accept feeds from outside the Vespa cluster.

@author Steinar Knutsen
vespaclient-container-plugin/src/main/java/com/yahoo/vespa/http/server/FeedHandler.java