Reading the NETCONF section in the User Guide is likely useful as it contains an overview of NETCONF in OpenDaylight and a how-to for spawning and configuring NETCONF connectors.
This chapter is recommended for application developers who want to interact with mounted NETCONF devices from their application code. It tries to demonstrate all the use cases from user guide with RESTCONF but now from the code level. One important difference would be the demonstration of NETCONF notifications and notification listeners. The notifications were not shown using RESTCONF because RESTCONF does not support notifications from mounted NETCONF devices.
It may also be useful to read the generic OpenDaylight MD-SAL app development tutorial before diving into this chapter. This guide assumes awareness of basic OpenDaylight application development.
All the examples presented here are implemented by a sample OpenDaylight application called ncmount in the coretutorials OpenDaylight project. It can be found on the github mirror of OpenDaylight’s repositories:
or checked out from the official OpenDaylight repository:
The application was built using the `project startup maven archetype `__ and demonstrates how to:
The code in ncmount is fully binding aware (works with generated java APIs from provided YANG models). However it is also possible to perform the same operations in binding independent manner.
The NcmountProvider class (found in NcmountProvider.java) is the central point of the ncmount application and all the application logic is contained there. The following sections will detail its most interesting pieces.
The MountPointService is a central registry of all available mount points in OpenDaylight. It is just another MD-SAL service and is available from the session attribute passed by onSessionInitiated callback:
@Override public void onSessionInitiated(ProviderContext session) LOG.info("NcmountProvider Session Initiated"); // Get references to the data broker and mount service this.mountService = session.getSALService(MountPointService.class); . > >
It is important to know when a mount point appears, when it is fully connected and when it is disconnected or removed. The exact states of a mount point are:
To receive this kind of information, an application has to register itself as a notification listener for the preconfigured netconf-topology subtree in MD-SAL’s datastore. This can be performed in the onSessionInitiated callback as well:
@Override public void onSessionInitiated(ProviderContext session) . this.dataBroker = session.getSALService(DataBroker.class); // Register ourselves as the REST API RPC implementation this.rpcReg = session.addRpcImplementation(NcmountService.class, this); // Register ourselves as data change listener for changes on Netconf // nodes. Netconf nodes are accessed via "Netconf Topology" - a special // topology that is created by the system infrastructure. It contains // all Netconf nodes the Netconf connector knows about. NETCONF_TOPO_IID // is equivalent to the following URL: // . /restconf/operational/network-topology:network-topology/topology/topology-netconf if (dataBroker != null) this.dclReg = dataBroker.registerDataChangeListener(LogicalDatastoreType.OPERATIONAL, NETCONF_TOPO_IID.child(Node.class), this, DataChangeScope.SUBTREE); > >
The implementation of the callback from MD-SAL when the data change can be found in the onDataChanged(AsyncDataChangeEvent, DataObject> change) callback of NcmountProvider class.
The first step when trying to interact with the device is to get the exact mount point instance (identified by an instance identifier) from the MountPointService:
@Override public FutureRpcResultShowNodeOutput>> showNode(ShowNodeInput input) LOG.info("showNode called, input <>", input); // Get the mount point for the specified node // Equivalent to '. /restconf//opendaylight-inventory:nodes/node//yang-ext:mount/' // Note that we can read both config and operational data from the same // mount point final OptionalMountPoint> xrNodeOptional = mountService.getMountPoint(NETCONF_TOPO_IID .child(Node.class, new NodeKey(new NodeId(input.getNodeName())))); Preconditions.checkArgument(xrNodeOptional.isPresent(), "Unable to locate mountpoint: %s, not mounted yet or not configured", input.getNodeName()); final MountPoint xrNode = xrNodeOptional.get(); . >
The triggering method in this case is called showNode . It is a YANG-defined RPC and NcmountProvider serves as an MD-SAL RPC implementation among other things. This means that showNode an be triggered using RESTCONF.
The next step is to retrieve an instance of the DataBroker API from the mount point and start a read transaction:
@Override public FutureRpcResultShowNodeOutput>> showNode(ShowNodeInput input) . // Get the DataBroker for the mounted node final DataBroker xrNodeBroker = xrNode.getService(DataBroker.class).get(); // Start a new read only transaction that we will use to read data // from the device final ReadOnlyTransaction xrNodeReadTx = xrNodeBroker.newReadOnlyTransaction(); . >
Finally, it is possible to perform the read operation:
@Override public FutureRpcResultShowNodeOutput>> showNode(ShowNodeInput input) . InstanceIdentifierInterfaceConfigurations> iid = InstanceIdentifier.create(InterfaceConfigurations.class); OptionalInterfaceConfigurations> ifConfig; try // Read from a transaction is asynchronous, but a simple // get/checkedGet makes the call synchronous ifConfig = xrNodeReadTx.read(LogicalDatastoreType.CONFIGURATION, iid).checkedGet(); > catch (ReadFailedException e) throw new IllegalStateException("Unexpected error reading data from " + input.getNodeName(), e); > . >
The instance identifier is used here again to specify a subtree to read from the device. At this point application can process the data as it sees fit. The ncmount app transforms the data into its own format and returns it from showNode .