Overview

NOTE: The GUI architecture is migrating to use the AngularJS framework – some of the information on this page is deprecated (the topo events are still good).

The ONOS GUI is a single-page web-application with hash-navigation. The GUI system comprises client-side code (a single HTML page, javascript libraries and modules, CSS files, etc.) and server-side code (Java classes that interface to ONOS Server APIs). The GUI web page is served up by a web server running on an ONOS instance.

Client-Side Architecture (Deprecated)

The client side code is comprised of:

... along with their associated *.css stylesheets. 

The structure of the framework allows for the registration of multiple "views" and the subsequent navigation between them. 

For the first release, however, there is but a single view, the Topology View.

View Registration (Deprecated)

A view registers with the framework via a call to the addView(...) function.

onos.ui.addView('viewId', {
    init: init,
    reset: reset,
    load: load,
    unload: unload,
    resize: resize,
    theme: theme
});

The first argument to the function is a short string identifier for the view. 

The second argument to the function is an inline object block with the given keys, whose values are references to view life-cycle callback functions:

Topology View (Deprecated)

In the first release, the Topology View is the only view available; it is loaded at GUI startup. The following paragraphs summarize each of the view's callbacks:

Init

The init callback is used to initialize the view's SVG layer (including pan and zoom controls) and the Force Layout used to visualize the topology.

Reset

The reset callback is not needed, and thus not implemented.

Load

The load callback starts by injecting the radio button set into the masthead and registering key bindings and mouse gesture descriptions. After that, it performs an asynchronous load of the background GeoMap (Continental USA), before finally opening a websocket connection to the server.

Once the websocket is established, an initial requestSummary event is sent to the server. The UI then processes incoming events from the server to build up a view of the topology. See Event Descriptions below.

Unload

The unload callback cancels the background timer, if it is running.

Resize

The resize callback updates the size of the SVG layer.

Theme

The theme callback updates instance and device colors.

Topology Model

The UI maintains an internal model of the topology by storing data representing ONOS instances, nodes (devices and hosts) and links. The model is empty initially, but is augmented as events (such as addInstance, addDevice, addLink, etc.) come in from the server. As these events arrive, the model is updated and the visual representation modified to reflect the current model.

Client-Server Communication

The Topology View uses a websocket to establish communication with the server. This provides a dedicated TCP connection along which the client and the server can emit messages to the other side. The server sends messages to the client describing status updates and/or changes to the topology; the client sends messages to the server, in response to gestures made in the UI by the user, requesting actions to be performed or requesting additional data.

Event messages are structured JSON objects, with the following general format:

{
  "event": "eventType",
  "sid": ... ,
  "payload": {
    ...
  }
}

The event field is a string uniquely identifying the event type.

The sid field is an optional sequence identifier (monotonically increasing integers) which, if provided by the client, should be duplicated in the server's response to that event. Note that, in general,  server-initiated events do not include a sid field.

The payload field is an arbitrary JSON object the structure of which is implied by the event type. Many payloads include an id field at the top level, which holds the unique ID of the item being described by the event.

Event Descriptions

The following table enumerates the events, providing a high-level description of the payload. For explicit details of the payloads, see the source-code .

Note that the term "node" (in this context) is used to mean "device or host node" in the topology visualization.

Notes:

⁽¹⁾ Technically, only the ID field is required, but the server-side code is simplified by using the payload as is.

A Note about Links

The topology model on the server side represents links as unidirectional, with a source and destination. In the UI, each link model object abstracts away the directionality. This is to provide a single "link" element between two "nodes" in the visualization. However, this makes the link event processing a little more complex. Internally the links are modeled something like this:

When a link event arrives, a lookup is done to see if the "parent" object for that link already exists. 

Server-Side Architecture

Websocket Servlet

When the topology view is loaded it makes an HTTP request to ws://<server>/onos/ui/ws/topology URL. This requests gets upgraded into a Web-Socket, thus establishing a symmetric and persistent connection between the client and the server. On the server side, this process is facilitated by GuiWebSocketServlet, which extends Jetty WebSocketServlet and results in creation of a session-specific TopologyViewWebSocket instance. This instance holds the necessary session-state for interacting with this specific client.

Topology Resources

The following Java classes comprise the server-side code for the Topology View:

• TopologyResource - provides REST API for some auxiliary functionality, e.g. export of GEO location data
• TopologyViewIntentFilter - responsible for identifying list of intents which pertain to the specified sets of end-station hosts or infrastructure devices
• TopologyViewMessages - base class for composing various messages destined for the client and parsing those that were received from the client
• TopologyViewWebSocket - main controller for processing inbound messages and emitting appropriate responses

To see the server-side handling of the UI, take a look at TopologyViewWebSocket, in particular the web socket methods:

• onOpen()
• onMessage()
• onClose()

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