web/gui/src/main/java/org/onlab/onos/gui/TopologyViewMessages.java

/*
 * Copyright 2014 Open Networking Laboratory
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.onlab.onos.gui;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.node.ObjectNode;
import org.onlab.onos.cluster.ClusterEvent;
import org.onlab.onos.cluster.ClusterService;
import org.onlab.onos.cluster.ControllerNode;
import org.onlab.onos.cluster.NodeId;
import org.onlab.onos.core.CoreService;
import org.onlab.onos.mastership.MastershipService;
import org.onlab.onos.net.Annotated;
import org.onlab.onos.net.Annotations;
import org.onlab.onos.net.ConnectPoint;
import org.onlab.onos.net.DefaultEdgeLink;
import org.onlab.onos.net.Device;
import org.onlab.onos.net.DeviceId;
import org.onlab.onos.net.EdgeLink;
import org.onlab.onos.net.Host;
import org.onlab.onos.net.HostId;
import org.onlab.onos.net.HostLocation;
import org.onlab.onos.net.Link;
import org.onlab.onos.net.PortNumber;
import org.onlab.onos.net.device.DeviceEvent;
import org.onlab.onos.net.device.DeviceService;
import org.onlab.onos.net.flow.FlowEntry;
import org.onlab.onos.net.flow.FlowRuleService;
import org.onlab.onos.net.flow.TrafficTreatment;
import org.onlab.onos.net.flow.instructions.Instruction;
import org.onlab.onos.net.flow.instructions.Instructions.OutputInstruction;
import org.onlab.onos.net.host.HostEvent;
import org.onlab.onos.net.host.HostService;
import org.onlab.onos.net.intent.Intent;
import org.onlab.onos.net.intent.IntentService;
import org.onlab.onos.net.intent.LinkCollectionIntent;
import org.onlab.onos.net.intent.OpticalConnectivityIntent;
import org.onlab.onos.net.intent.OpticalPathIntent;
import org.onlab.onos.net.intent.PathIntent;
import org.onlab.onos.net.link.LinkEvent;
import org.onlab.onos.net.link.LinkService;
import org.onlab.onos.net.provider.ProviderId;
import org.onlab.onos.net.statistic.Load;
import org.onlab.onos.net.statistic.StatisticService;
import org.onlab.onos.net.topology.Topology;
import org.onlab.onos.net.topology.TopologyService;
import org.onlab.osgi.ServiceDirectory;
import org.onlab.packet.IpAddress;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Strings.isNullOrEmpty;
import static org.onlab.onos.cluster.ClusterEvent.Type.INSTANCE_ADDED;
import static org.onlab.onos.cluster.ClusterEvent.Type.INSTANCE_REMOVED;
import static org.onlab.onos.cluster.ControllerNode.State.ACTIVE;
import static org.onlab.onos.net.DeviceId.deviceId;
import static org.onlab.onos.net.HostId.hostId;
import static org.onlab.onos.net.PortNumber.P0;
import static org.onlab.onos.net.PortNumber.portNumber;
import static org.onlab.onos.net.device.DeviceEvent.Type.DEVICE_ADDED;
import static org.onlab.onos.net.device.DeviceEvent.Type.DEVICE_REMOVED;
import static org.onlab.onos.net.host.HostEvent.Type.HOST_ADDED;
import static org.onlab.onos.net.host.HostEvent.Type.HOST_REMOVED;
import static org.onlab.onos.net.link.LinkEvent.Type.LINK_ADDED;
import static org.onlab.onos.net.link.LinkEvent.Type.LINK_REMOVED;

/**
 * Facility for creating messages bound for the topology viewer.
 */
public abstract class TopologyViewMessages {

    protected static final Logger log = LoggerFactory.getLogger(TopologyViewMessages.class);

    private static final ProviderId PID = new ProviderId("core", "org.onlab.onos.core", true);
    private static final String COMPACT = "%s/%s-%s/%s";

    private static final double KB = 1024;
    private static final double MB = 1024 * KB;
    private static final double GB = 1024 * MB;

    private static final String GB_UNIT = "GB";
    private static final String MB_UNIT = "MB";
    private static final String KB_UNIT = "KB";
    private static final String B_UNIT = "B";

    private static final String ANIMATED = "animated";

    protected final ServiceDirectory directory;
    protected final ClusterService clusterService;
    protected final DeviceService deviceService;
    protected final LinkService linkService;
    protected final HostService hostService;
    protected final MastershipService mastershipService;
    protected final IntentService intentService;
    protected final FlowRuleService flowService;
    protected final StatisticService statService;
    protected final TopologyService topologyService;

    protected final ObjectMapper mapper = new ObjectMapper();
    private final String version;

    // TODO: extract into an external & durable state; good enough for now and demo
    private static Map<String, ObjectNode> metaUi = new ConcurrentHashMap<>();

    /**
     * Creates a messaging facility for creating messages for topology viewer.
     *
     * @param directory service directory
     */
    protected TopologyViewMessages(ServiceDirectory directory) {
        this.directory = checkNotNull(directory, "Directory cannot be null");
        clusterService = directory.get(ClusterService.class);
        deviceService = directory.get(DeviceService.class);
        linkService = directory.get(LinkService.class);
        hostService = directory.get(HostService.class);
        mastershipService = directory.get(MastershipService.class);
        intentService = directory.get(IntentService.class);
        flowService = directory.get(FlowRuleService.class);
        statService = directory.get(StatisticService.class);
        topologyService = directory.get(TopologyService.class);

        version = directory.get(CoreService.class).version().toString();
    }

    // Retrieves the payload from the specified event.
    protected ObjectNode payload(ObjectNode event) {
        return (ObjectNode) event.path("payload");
    }

    // Returns the specified node property as a number
    protected long number(ObjectNode node, String name) {
        return node.path(name).asLong();
    }

    // Returns the specified node property as a string.
    protected String string(ObjectNode node, String name) {
        return node.path(name).asText();
    }

    // Returns the specified node property as a string.
    protected String string(ObjectNode node, String name, String defaultValue) {
        return node.path(name).asText(defaultValue);
    }

    // Returns the specified set of IP addresses as a string.
    private String ip(Set<IpAddress> ipAddresses) {
        Iterator<IpAddress> it = ipAddresses.iterator();
        return it.hasNext() ? it.next().toString() : "unknown";
    }

    // Produces JSON structure from annotations.
    private JsonNode props(Annotations annotations) {
        ObjectNode props = mapper.createObjectNode();
        if (annotations != null) {
            for (String key : annotations.keys()) {
                props.put(key, annotations.value(key));
            }
        }
        return props;
    }

    // Produces an informational log message event bound to the client.
    protected ObjectNode info(long id, String message) {
        return message("info", id, message);
    }

    // Produces a warning log message event bound to the client.
    protected ObjectNode warning(long id, String message) {
        return message("warning", id, message);
    }

    // Produces an error log message event bound to the client.
    protected ObjectNode error(long id, String message) {
        return message("error", id, message);
    }

    // Produces a log message event bound to the client.
    private ObjectNode message(String severity, long id, String message) {
        return envelope("message", id,
                        mapper.createObjectNode()
                                .put("severity", severity)
                                .put("message", message));
    }

    // Puts the payload into an envelope and returns it.
    protected ObjectNode envelope(String type, long sid, ObjectNode payload) {
        ObjectNode event = mapper.createObjectNode();
        event.put("event", type);
        if (sid > 0) {
            event.put("sid", sid);
        }
        event.set("payload", payload);
        return event;
    }

    // Produces a set of all hosts listed in the specified JSON array.
    protected Set<Host> getHosts(ArrayNode array) {
        Set<Host> hosts = new HashSet<>();
        if (array != null) {
            for (JsonNode node : array) {
                try {
                    addHost(hosts, hostId(node.asText()));
                } catch (IllegalArgumentException e) {
                    log.debug("Skipping ID {}", node.asText());
                }
            }
        }
        return hosts;
    }

    // Adds the specified host to the set of hosts.
    private void addHost(Set<Host> hosts, HostId hostId) {
        Host host = hostService.getHost(hostId);
        if (host != null) {
            hosts.add(host);
        }
    }


    // Produces a set of all devices listed in the specified JSON array.
    protected Set<Device> getDevices(ArrayNode array) {
        Set<Device> devices = new HashSet<>();
        if (array != null) {
            for (JsonNode node : array) {
                try {
                    addDevice(devices, deviceId(node.asText()));
                } catch (IllegalArgumentException e) {
                    log.debug("Skipping ID {}", node.asText());
                }
            }
        }
        return devices;
    }

    private void addDevice(Set<Device> devices, DeviceId deviceId) {
        Device device = deviceService.getDevice(deviceId);
        if (device != null) {
            devices.add(device);
        }
    }

    protected void addHover(Set<Host> hosts, Set<Device> devices, String hover) {
        try {
            addHost(hosts, hostId(hover));
        } catch (IllegalArgumentException e) {
            try {
                addDevice(devices, deviceId(hover));
            } catch (IllegalArgumentException ne) {
                log.debug("Skipping ID {}", hover);
            }
        }
    }

    // Produces a cluster instance message to the client.
    protected ObjectNode instanceMessage(ClusterEvent event) {
        ControllerNode node = event.subject();
        ObjectNode payload = mapper.createObjectNode()
                .put("id", node.id().toString())
                .put("online", clusterService.getState(node.id()) == ACTIVE)
                .put("uiAttached", event.subject().equals(clusterService.getLocalNode()));

        ArrayNode labels = mapper.createArrayNode();
        labels.add(node.id().toString());
        labels.add(node.ip().toString());

        // Add labels, props and stuff the payload into envelope.
        payload.set("labels", labels);
        addMetaUi(node.id().toString(), payload);

        String type = (event.type() == INSTANCE_ADDED) ? "addInstance" :
                ((event.type() == INSTANCE_REMOVED) ? "removeInstance" : "updateInstance");
        return envelope(type, 0, payload);
    }

    // Produces a device event message to the client.
    protected ObjectNode deviceMessage(DeviceEvent event) {
        Device device = event.subject();
        ObjectNode payload = mapper.createObjectNode()
                .put("id", device.id().toString())
                .put("type", device.type().toString().toLowerCase())
                .put("online", deviceService.isAvailable(device.id()))
                .put("master", master(device.id()));

        // Generate labels: id, chassis id, no-label, optional-name
        String name = device.annotations().value("name");
        ArrayNode labels = mapper.createArrayNode();
        labels.add("");
        labels.add(isNullOrEmpty(name) ? device.id().toString() : name);
        labels.add(device.id().toString());

        // Add labels, props and stuff the payload into envelope.
        payload.set("labels", labels);
        payload.set("props", props(device.annotations()));
        addGeoLocation(device, payload);
        addMetaUi(device.id().toString(), payload);

        String type = (event.type() == DEVICE_ADDED) ? "addDevice" :
                ((event.type() == DEVICE_REMOVED) ? "removeDevice" : "updateDevice");
        return envelope(type, 0, payload);
    }

    // Produces a link event message to the client.
    protected ObjectNode linkMessage(LinkEvent event) {
        Link link = event.subject();
        ObjectNode payload = mapper.createObjectNode()
                .put("id", compactLinkString(link))
                .put("type", link.type().toString().toLowerCase())
                .put("online", link.state() == Link.State.ACTIVE)
                .put("linkWidth", 1.2)
                .put("src", link.src().deviceId().toString())
                .put("srcPort", link.src().port().toString())
                .put("dst", link.dst().deviceId().toString())
                .put("dstPort", link.dst().port().toString());
        String type = (event.type() == LINK_ADDED) ? "addLink" :
                ((event.type() == LINK_REMOVED) ? "removeLink" : "updateLink");
        return envelope(type, 0, payload);
    }

    // Produces a host event message to the client.
    protected ObjectNode hostMessage(HostEvent event) {
        Host host = event.subject();
        String hostType = host.annotations().value("type");
        ObjectNode payload = mapper.createObjectNode()
                .put("id", host.id().toString())
                .put("type", isNullOrEmpty(hostType) ? "endstation" : hostType)
                .put("ingress", compactLinkString(edgeLink(host, true)))
                .put("egress", compactLinkString(edgeLink(host, false)));
        payload.set("cp", hostConnect(mapper, host.location()));
        payload.set("labels", labels(mapper, ip(host.ipAddresses()),
                                     host.mac().toString()));
        payload.set("props", props(host.annotations()));
        addGeoLocation(host, payload);
        addMetaUi(host.id().toString(), payload);

        String type = (event.type() == HOST_ADDED) ? "addHost" :
                ((event.type() == HOST_REMOVED) ? "removeHost" : "updateHost");
        return envelope(type, 0, payload);
    }

    // Encodes the specified host location into a JSON object.
    private ObjectNode hostConnect(ObjectMapper mapper, HostLocation location) {
        return mapper.createObjectNode()
                .put("device", location.deviceId().toString())
                .put("port", location.port().toLong());
    }

    // Encodes the specified list of labels a JSON array.
    private ArrayNode labels(ObjectMapper mapper, String... labels) {
        ArrayNode json = mapper.createArrayNode();
        for (String label : labels) {
            json.add(label);
        }
        return json;
    }

    // Returns the name of the master node for the specified device id.
    private String master(DeviceId deviceId) {
        NodeId master = mastershipService.getMasterFor(deviceId);
        return master != null ? master.toString() : "";
    }

    // Generates an edge link from the specified host location.
    private EdgeLink edgeLink(Host host, boolean ingress) {
        return new DefaultEdgeLink(PID, new ConnectPoint(host.id(), portNumber(0)),
                                   host.location(), ingress);
    }

    // Adds meta UI information for the specified object.
    private void addMetaUi(String id, ObjectNode payload) {
        ObjectNode meta = metaUi.get(id);
        if (meta != null) {
            payload.set("metaUi", meta);
        }
    }

    // Adds a geo location JSON to the specified payload object.
    private void addGeoLocation(Annotated annotated, ObjectNode payload) {
        Annotations annotations = annotated.annotations();
        if (annotations == null) {
            return;
        }

        String slat = annotations.value("latitude");
        String slng = annotations.value("longitude");
        try {
            if (slat != null && slng != null && !slat.isEmpty() && !slng.isEmpty()) {
                double lat = Double.parseDouble(slat);
                double lng = Double.parseDouble(slng);
                ObjectNode loc = mapper.createObjectNode()
                        .put("type", "latlng").put("lat", lat).put("lng", lng);
                payload.set("location", loc);
            }
        } catch (NumberFormatException e) {
            log.warn("Invalid geo data latitude={}; longiture={}", slat, slng);
        }
    }

    // Updates meta UI information for the specified object.
    protected void updateMetaUi(ObjectNode event) {
        ObjectNode payload = payload(event);
        metaUi.put(string(payload, "id"), (ObjectNode) payload.path("memento"));
    }

    // Returns summary response.
    protected ObjectNode summmaryMessage(long sid) {
        Topology topology = topologyService.currentTopology();
        return envelope("showSummary", sid,
                        json("ONOS Summary", "node",
                             new Prop("Devices", format(topology.deviceCount())),
                             new Prop("Links", format(topology.linkCount())),
                             new Prop("Hosts", format(hostService.getHostCount())),
                             new Prop("Topology SCCs", format(topology.clusterCount())),
                             new Prop("Paths", format(topology.pathCount())),
                             new Separator(),
                             new Prop("Intents", format(intentService.getIntentCount())),
                             new Prop("Flows", format(flowService.getFlowRuleCount())),
                             new Prop("Version", version.replace(".SNAPSHOT", "*"))));
    }

    // Returns device details response.
    protected ObjectNode deviceDetails(DeviceId deviceId, long sid) {
        Device device = deviceService.getDevice(deviceId);
        Annotations annot = device.annotations();
        String name = annot.value("name");
        int portCount = deviceService.getPorts(deviceId).size();
        int flowCount = getFlowCount(deviceId);
        return envelope("showDetails", sid,
                        json(isNullOrEmpty(name) ? deviceId.toString() : name,
                             device.type().toString().toLowerCase(),
                             new Prop("URI", deviceId.toString()),
                             new Prop("Vendor", device.manufacturer()),
                             new Prop("H/W Version", device.hwVersion()),
                             new Prop("S/W Version", device.swVersion()),
                             new Prop("Serial Number", device.serialNumber()),
                             new Separator(),
                             new Prop("Master", master(deviceId)),
                             new Prop("Latitude", annot.value("latitude")),
                             new Prop("Longitude", annot.value("longitude")),
                             new Separator(),
                             new Prop("Ports", Integer.toString(portCount)),
                             new Prop("Flows", Integer.toString(flowCount))));
    }

    protected int getFlowCount(DeviceId deviceId) {
        int count = 0;
        Iterator<FlowEntry> it = flowService.getFlowEntries(deviceId).iterator();
        while (it.hasNext()) {
            count++;
            it.next();
        }
        return count;
    }

    // Counts all entries that egress on the given device links.
    protected Map<Link, Integer> getFlowCounts(DeviceId deviceId) {
        List<FlowEntry> entries = new ArrayList<>();
        Set<Link> links = new HashSet<>(linkService.getDeviceEgressLinks(deviceId));
        Set<Host> hosts = hostService.getConnectedHosts(deviceId);
        Iterator<FlowEntry> it = flowService.getFlowEntries(deviceId).iterator();
        while (it.hasNext()) {
            entries.add(it.next());
        }

        // Add all edge links to the set
        if (hosts != null) {
            for (Host host : hosts) {
                links.add(new DefaultEdgeLink(host.providerId(),
                                              new ConnectPoint(host.id(), P0),
                                              host.location(), false));
            }
        }

        Map<Link, Integer> counts = new HashMap<>();
        for (Link link : links) {
            counts.put(link, getEgressFlows(link, entries));
        }
        return counts;
    }

    // Counts all entries that egress on the link source port.
    private Integer getEgressFlows(Link link, List<FlowEntry> entries) {
        int count = 0;
        PortNumber out = link.src().port();
        for (FlowEntry entry : entries) {
            TrafficTreatment treatment = entry.treatment();
            for (Instruction instruction : treatment.instructions()) {
                if (instruction.type() == Instruction.Type.OUTPUT &&
                        ((OutputInstruction) instruction).port().equals(out)) {
                    count++;
                }
            }
        }
        return count;
    }


    // Returns host details response.
    protected ObjectNode hostDetails(HostId hostId, long sid) {
        Host host = hostService.getHost(hostId);
        Annotations annot = host.annotations();
        String type = annot.value("type");
        String name = annot.value("name");
        String vlan = host.vlan().toString();
        return envelope("showDetails", sid,
                        json(isNullOrEmpty(name) ? hostId.toString() : name,
                             isNullOrEmpty(type) ? "host" : type,
                             new Prop("MAC", host.mac().toString()),
                             new Prop("IP", host.ipAddresses().toString().replaceAll("[\\[\\]]", "")),
                             new Prop("VLAN", vlan.equals("-1") ? "none" : vlan),
                             new Separator(),
                             new Prop("Latitude", annot.value("latitude")),
                             new Prop("Longitude", annot.value("longitude"))));
    }


    // Produces JSON message to trigger traffic overview visualization
    protected ObjectNode trafficSummaryMessage(long sid) {
        ObjectNode payload = mapper.createObjectNode();
        ArrayNode paths = mapper.createArrayNode();
        payload.set("paths", paths);
        for (Link link : linkService.getLinks()) {
            Set<Link> links = new HashSet<>();
            links.add(link);
            addPathTraffic(paths, "plain", "secondary", links);
        }
        return envelope("showTraffic", sid, payload);
    }

    // Produces JSON message to trigger flow overview visualization
    protected ObjectNode flowSummaryMessage(long sid, Set<Device> devices) {
        ObjectNode payload = mapper.createObjectNode();
        ArrayNode paths = mapper.createArrayNode();
        payload.set("paths", paths);

        for (Device device : devices) {
            Map<Link, Integer> counts = getFlowCounts(device.id());
            for (Link link : counts.keySet()) {
                addLinkFlows(link, paths, counts.get(link));
            }
        }
        return envelope("showTraffic", sid, payload);
    }

    private void addLinkFlows(Link link, ArrayNode paths, Integer count) {
        ObjectNode pathNode = mapper.createObjectNode();
        ArrayNode linksNode = mapper.createArrayNode();
        ArrayNode labels = mapper.createArrayNode();
        boolean noFlows = count == null || count == 0;
        pathNode.put("class", noFlows ? "secondary" : "primary");
        pathNode.put("traffic", false);
        pathNode.set("links", linksNode.add(compactLinkString(link)));
        pathNode.set("labels", labels.add(noFlows ? "" : (count.toString() +
                (count == 1 ? " flow" : " flows"))));
        paths.add(pathNode);
    }


    // Produces JSON message to trigger traffic visualization
    protected ObjectNode trafficMessage(long sid, TrafficClass... trafficClasses) {
        ObjectNode payload = mapper.createObjectNode();
        ArrayNode paths = mapper.createArrayNode();
        payload.set("paths", paths);

        for (TrafficClass trafficClass : trafficClasses) {
            for (Intent intent : trafficClass.intents) {
                boolean isOptical = intent instanceof OpticalConnectivityIntent;
                List<Intent> installables = intentService.getInstallableIntents(intent.id());
                if (installables != null) {
                    for (Intent installable : installables) {
                        String cls = isOptical ? trafficClass.type + " optical" : trafficClass.type;
                        if (installable instanceof PathIntent) {
                            addPathTraffic(paths, cls, ANIMATED,
                                           ((PathIntent) installable).path().links());
                        } else if (installable instanceof LinkCollectionIntent) {
                            addPathTraffic(paths, cls, ANIMATED,
                                           ((LinkCollectionIntent) installable).links());
                        } else if (installable instanceof OpticalPathIntent) {
                            addPathTraffic(paths, cls, ANIMATED,
                                           ((OpticalPathIntent) installable).path().links());
                        }

                    }
                }
            }
        }

        return envelope("showTraffic", sid, payload);
    }

    // Adds the link segments (path or tree) associated with the specified
    // connectivity intent
    protected void addPathTraffic(ArrayNode paths, String type, String trafficType,
                                  Iterable<Link> links) {
        ObjectNode pathNode = mapper.createObjectNode();
        ArrayNode linksNode = mapper.createArrayNode();

        if (links != null) {
            ArrayNode labels = mapper.createArrayNode();
            boolean hasTraffic = false;
            for (Link link : links) {
                if (isInfrastructureEgress(link)) {
                    linksNode.add(compactLinkString(link));
                    Load load = statService.load(link);
                    String label = "";
                    if (load.rate() > 0) {
                        hasTraffic = true;
                        label = format(load);
                    }
                    labels.add(label);
                }
            }
            pathNode.put("class", hasTraffic ? type + " " + trafficType : type);
            pathNode.put("traffic", hasTraffic);
            pathNode.set("links", linksNode);
            pathNode.set("labels", labels);
            paths.add(pathNode);
        }
    }

    // Poor-mans formatting to get the labels with byte counts looking nice.
    private String format(Load load) {
        long bytes = load.latest();
        String unit;
        double value;
        if (bytes > GB) {
            value = bytes / GB;
            unit = GB_UNIT;
        } else if (bytes > MB) {
            value = bytes / MB;
            unit = MB_UNIT;
        } else if (bytes > KB) {
            value = bytes / KB;
            unit = KB_UNIT;
        } else {
            value = bytes;
            unit = B_UNIT;
        }
        DecimalFormat format = new DecimalFormat("#,###.##");
        return format.format(value) + " " + unit;
    }

    // Formats the given number into a string.
    private String format(Number number) {
        DecimalFormat format = new DecimalFormat("#,###");
        return format.format(number);
    }

    private boolean isInfrastructureEgress(Link link) {
        return link.src().elementId() instanceof DeviceId;
    }

    // Produces compact string representation of a link.
    private static String compactLinkString(Link link) {
        return String.format(COMPACT, link.src().elementId(), link.src().port(),
                             link.dst().elementId(), link.dst().port());
    }

    // Produces JSON property details.
    private ObjectNode json(String id, String type, Prop... props) {
        ObjectMapper mapper = new ObjectMapper();
        ObjectNode result = mapper.createObjectNode()
                .put("id", id).put("type", type);
        ObjectNode pnode = mapper.createObjectNode();
        ArrayNode porder = mapper.createArrayNode();
        for (Prop p : props) {
            porder.add(p.key);
            pnode.put(p.key, p.value);
        }
        result.set("propOrder", porder);
        result.set("props", pnode);
        return result;
    }

    // Auxiliary key/value carrier.
    private class Prop {
        public final String key;
        public final String value;

        protected Prop(String key, String value) {
            this.key = key;
            this.value = value;
        }
    }

    // Auxiliary properties separator
    private class Separator extends Prop {
        protected Separator() {
            super("-", "");
        }
    }

    // Auxiliary carrier of data for requesting traffic message.
    protected class TrafficClass {
        public final String type;
        public final Set<Intent> intents;

        TrafficClass(String type, Set<Intent> intents) {
            this.type = type;
            this.intents = intents;
        }
    }

}