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OpenDaylight Controller:MD-SAL:Toaster Tutorial

This content was created for the Helium release. The most recent release is Nitrogen. If you are interested in that, you might want to look for more recent content.


This tutorial presents a walk through of the MD-SAL based example of the Toaster capability ( this capability comes from the YANG module toaster.yang schema).


The main objective is to provide the reader a better understanding of the MD-SAL infrastructure within the OpenDaylight controller. The Toaster sample implementation is a suitable example because it provides the model of a programmable toaster, a sample consumer application that uses MD-SAL APIs, a sample service provider that implements Toaster, and a unit test suite.

Overview of Yang

If you are new to Yang, the below links contain various overviews that you may find useful.

Toaster Step-By-Step

We are putting together documentation where we build up the toaster from scratch to cover different scenarios ( much like the Ping example ).

The below documentation isn't a guide on how to write the toaster example from scratch. It provides an overview of the toaster example architecture, explanation of the API, the description of individual plugins, their configuration and interaction with the MD-SAL.

This page will help provide context about what code and configuration needs to be considered when you plan to develop your own application / plugin within ODL.

If you would like to see how we can progress from a simple Toaster model, to an advanced modeling structure, head over to OpenDaylight Controller:MD-SAL:Toaster Step-By-Step


The Toaster example is part of the OpenDaylight controller, so in order to access the source code with its dependencies please check ODL Installation Guide

It's located in controller.git under opendaylight/md-sal/samples.

YANG Data Model of Toaster

The definition of the Toaster capability is defined by it's yang data model ; the file is located in the sample-toaster project in: src/main/yang/toaster.yang

The yang schema defines the toaster service (YANG RPCs), the toaster description and state data (YANG Container), notifications from the toaster (YANG Notifications):

  1. DATA definitions for toaster: (YANG: container toaster)
    • (YANG: leaf toasterManufacturer)
    • (YANG: leaf toasterModelNumber)
    • (YANG: leaf toasterStatus)
  2. SERVICE RPCs: operations that can be done, they are defined through RPCs, there are two available:
    • (YANG: rpc make-toast) taking input parameters:
      • (YANG: leaf toasterDoneness)
      • (YANG: leaf toasterToastType)
    • (YANG: rpc cancel-toast)
    • (YANG: notification toastDone)
      • (YANG: leaf toastStatus)

Now that we have defined the functionality that has to be implemented, we have to consider the type of APIs that will have to be created:

API Types

MD-SAL provides three API types:

  • Java generated APIs :
In our example, from the Toaster's yang data model, the MD-SAL will generate a set of Java APIs against which the provider and consumer plugins will be developed.
  • DOM APIs - these are mostly used by infrastructure components and are useful for XML-driven plugin and application types
  • REST APIs - Restconf - these APIs are available to consumer type applications and provides access to RPC and data store - consumers invoke RPCs by invoking POST operation to /restconf/operations/model-name:rpc-name. Notifications aren't currently supported. We'll show how to invoke toaster's RPCs through the RESTCONF API in the Binding Independent context section.

Binding Aware vs Binding Independent

All providers and consumers that use Java generated APIs, whether they implement (providers) or make use of implemented functionality (consumers) are denoted as binding aware.

In our toaster example, we'll develop:

  • one binding aware provider (implementing the toaster service declared in the generated API) and
  • one binding aware consumer, which uses the service implemented by the above binding aware provider.

Binding independent consumers and providers are those which are not developed against a Java generated API, but use the Binding Independent Data format. This format is basically a normalized data tree derived/mapped (during system startup, when the .yang file is loaded ) from the YANG schema :

  • Simple Nodes - these are mappings of Yang leaf and items in a leaf-list
  • Composite Nodes - these are mappings of Yang container and items in a list

MD-SAL provides the infrastructure necessary to address the individual data tree nodes both from within binding aware and binding independent components through instance identifiers. The instance identifier is basically the path to a specific node in the data tree. In our example we'll use the instance identifier to update the status of the toaster in the data store.

The MD-SAL Data Store can be viewed as a binding independent provider that holds data (the state of the system, so it stores instances of classes not classes ) in the binding independent data format.

When ODL loads a bundle it searches that bundle (JAR) for files that end in “*.yang”. For each YANG file found it processes that file and builds several things dynamically including the structures to expose that as a RESTCONF compliant YANG interface.

In our toaster example, we'll see that we can access through RESTConf the individual toaster container items mapped from the YANG model( perform Create/Retrieve/Update/Delete -CRUD- operations on the toaster container) and even invoke the toaster's RPCs in the form of POST http requests.

Binding Aware context

Generated APIs and the Binding Model

In our example, the API that covers the toaster functionality (the Java generated API, we will refer to it as the 'Toaster SAL API') is generated from the Toaster Yang model using the YANG Tools.
This is achieved by using the yang-maven-plugin with the org.opendaylight.yangtools.maven.sal.api.gen.plugin.CodeGeneratorImpl code generator, called from the sample-toaster project build phase - section of the project's POM file:
  • the resulting generated SAL APIs are stored under 'src/main/yang-gen-sal (for a complete guide of the code generator mappings see [Yang to Java Mapping])
  • The src/main/yang/toaster.yang file is copied to target/classes/META-INF/yang/toaster.yang.
  • The org.opendaylight.yangtools.yang.binding.YangModelBindingProvider file is generated in target/classes/META-INF/services and contains the fully-qualfied name of the toaster's generated $YangModelBindingProvider class. This will be used by the MD-SAL's ModuleInfoBundleTracker class in the config subsystem (more details on this in the Config subsystem context section).

MD-SAL Bindings

The generated JAVA files constitute the Bindings that MD-SAL uses as part of its Binding Model. This is referred as 'Consumer & Provider binding' – A subset of the binding model which is directly visible to 'binding aware' Consumers and Providers.

There are three types of files that make up the binding:

  • Data Transfer Objects represent the instances of data nodes defined by YANG Schema and are used to store and transfer data (in our example Toaster,ToastDone,MakeToastInput)
  • interface ToasterData extends DataRoot (Toaster.java) <- DATA definitions for toaster
  • DTO Builders are objects that create DTOs (in our example ToasterBuilder,ToastDoneBuilder,MakeToastInputBuilder)
  • RPC interfaces represent the programmatic API to invoking RPCs (in our example ToasterService)
  • interface ToasterService extends RpcService (ToasterService.java) <- SERVICE RPCs
  • Listener interfaces:
  • interface ToasterListener extends NotificationListener (ToasterListener.java) <- NOTIFICATIONS

API OSGI bundle

Upon running a build of the sample-toaster project, the generated SAL APIs are bundled by maven creating an OSGI bundle, which will be referred as the 'API OSGI bundle'.

Toaster Provider

The set of generated JAVA interfaces (constituting the SAL API) from the Toaster's Yang data model (previous section) must be implemented, and this is the point where the provider plugin ( the sample-toaster-provider maven project) comes into play. The OpendaylightToaster class implements the generated interfaces and is instantiated and wired via blueprint XML.

The next section - the Toaster Consumer shows how we can access the Toaster Service programatically.

Toaster Consumer

The toaster consumer plugin uses the Toaster Service (API) implemented by the toaster provider to create a new service (API). This is in fact an example of 'service chaining' where a consumer using a provider, becomes itself a provider of another service.


The new service ( defined in the KitchenService API org.opendaylight.controller.sample.kitchen.api ) defines a new method makeBreakfast that uses makeToast from the Toaster Service API:

public interface KitchenService {
    boolean makeBreakfast( EggsType eggs, Class<? extends ToastType> toast, int toastDoneness );

Note that the makeBreakfast service includes also eggs, on top of the toast, for example the eggs could be made by another 'EggsService' defined similarly as the Toaster Service.

The Plugin

The KitchenServiceImpl class implements the KitchenService interface. Below we highlight the makeBreakfast(...) method belonging to the KitchenService API, using the makeToast(...) RPC

public boolean makeBreakfast( EggsType eggs, Class<? extends ToastType> toast, int toastDoneness ) {

            RpcResult<Void> result = toaster.makeToast( toastInput.build() ).get();
            return result.isSuccessful();



Binding Independent context

RESTConf and the DataStore

Create a toaster via Restconf

To create the controller you will do a REST post (you will need a rest client such as PostMan for google chrome).

HTTP Method => POST
URL => http://localhost:8080/restconf/config 
Header =>   Content-Type: application/yang.data+json  
Body =>  
   "toaster:toaster" :
     "toaster:toasterManufacturer" : "General Electric",
     "toaster:toasterModelNumber" : "123",
     "toaster:toasterStatus" : "up"

Note: You will likely see an exception on the OSGi terminal, and the return error code will be a 204, "No data returned". This means it succeeded!

Get the existing toaster via Restconf

To get the current toaster via REST conf you will do an HTTP get.

HTTP Method => GET
URL => http://localhost:8080/restconf/config/toaster:toaster 

This should return json defining the toaster, and should provide similar values to what you posted.

Modify the existing toaster

HTTP Method => PUT
URL => http://localhost:8080/restconf/config/toaster:toaster
Header =>   Content-Type: application/yang.data+json  
Body =>  
   "toaster": {
       "toasterStatus": "up",
       "toasterManufacturer": "kkoushik",
       "toasterModelNumber": "123"

To Delete the Toaster

To delete the current toaster via REST conf you will do an HTTP DELETE.

URL => http://localhost:8080/restconf/config/toaster:toaster 

To Make Toast (i.e. invoke the make-toast rpc call)

To make toast via the Restconf you will perform an HTTP POST to an operations URL.

HTTP Method => POST
URL => http://localhost:8080/restconf/operations/toaster:make-toast 
Header =>   Content-Type: application/yang.data+json  
Body =>  
  "input" :
     "toaster:toasterDoneness" : "10",

even thought the toast type is defaulted in the yang model, you still have to provide it.

To Cancel Toast (i.e. invoke the cancel-toast which hs no arguments)

You may want to cancel the make-toast operation part of the way through! You do this by invoking a restconf REST call in a very similar way as you invoke the make-toast.

URL => http://localhost:8080/restconf/operations/toaster:cancel-toast
HTTP Method => POST

Note: There is a bug in the way the RestconfImpl class processes / routes the REST requests. If you define the Content-Type header, then the rest call is routed to a method which expects a non-empty body. In this case though we don't have any input, so our body should be empty. Thus an exception is thrown. In order to make the cancel-toast call work successfully, you need to invoke the above call, with NO content-type define. By doing that you route the request to a different method, which expects an empty body.
Note 2: When you successfully invoke this call with no headers, you will still get an error. This is due to a null future being returned in our implementation above. You can though put a breakpoint in the cancel toast call at this point and have that breakpoint activated.

The unit test

The toaster example contains a unit test located under thesample-toaster-it project, src/main/test folder.

Controller configuration

  • It uses the Pax Exam to define a configuration of the controller in the OSGI container. This loads the minimum required bundles, standard MD-SAL bundles
  • + Toaster bundles:
                mavenBundle("org.opendaylight.controller.samples", "sample-toaster-provider").versionAsInProject(),
                mavenBundle("org.opendaylight.controller.samples", "sample-toaster-consumer").versionAsInProject(),
                mavenBundle("org.opendaylight.controller.samples", "sample-toaster").versionAsInProject()

Testing Consumer API through OSGI

The makeBreakfast is invoked:

kitchenService.makeBreakfast( EggsType.SCRAMBLED, HashBrown.class, 4);