2 :rfc6020: https://tools.ietf.org/html/rfc6020
3 :lhotka-yang-json: https://tools.ietf.org/html/draft-lhotka-netmod-yang-json-01
6 YANG Tools is set of libraries and tooling providing support for use {rfc6020}[YANG] for Java (or other JVM-based language) projects and applications.
8 YANG Tools provides following features in OpenDaylight:
10 - parsing of YANG sources and
11 semantic inference of relationship across YANG models as defined in
13 - representation of YANG-modeled data in Java
14 ** *Normalized Node* representation - DOM-like tree model, which uses conceptual
15 meta-model more tailored to YANG and OpenDaylight use-cases than a standard XML
17 - serialization / deserialization of YANG-modeled data driven by YANG
19 ** XML - as defined in {rfc6020}[RFC6020]
20 ** JSON - as defined in {rfc6020}[draft-lhotka-netmod-yang-json-01]
21 ** support for third-party generators processing YANG models.
24 YANG Tools project consists of following logical subsystems:
26 - *Commons* - Set of general purpose code, which is not specific to YANG, but
27 is also useful outside YANG Tools implementation.
28 - *YANG Model and Parser* - YANG semantic model and lexical and semantic parser
29 of YANG models, which creates in-memory cross-referenced represenation of
30 YANG models, which is used by other components to determine their behaviour
32 - *YANG Data* - Definition of Normalized Node APIs and Data Tree APIs, reference
33 implementation of these APIs and implementation of XML and JSON codecs for
35 - *YANG Maven Plugin* - Maven plugin which integrates YANG parser into Maven
36 build lifecycle and provides code-generation framework for components, which
37 wants to generate code or other artefacts based on YANG model.
40 Project defines base concepts and helper classes which are project-agnostic and could be used outside of YANG Tools project scope.
46 - yang-data-codec-gson
53 - yang-maven-plugin-it
54 - yang-maven-plugin-spi
62 Class diagram of yang model API
64 image:models/yang-model-api.png[]
68 Yang Statement Parser works on the idea of statement concepts as defined in RFC6020, section 6.3. We come up here with basic ModelStatement and StatementDefinition, following RFC6020 idea of having sequence of statements, where
69 every statement contains keyword and zero or one argument. ModelStatement is extended by DeclaredStatement (as it comes from source, e.g. YANG source)
70 and EffectiveStatement, which contains other substatements and tends to represent result of semantic processing of other statements (uses, augment for YANG).
71 IdentifierNamespace represents common superclass for YANG model namespaces.
73 Input of the Yang Statement Parser is a collection of StatementStreamSource objects.
74 StatementStreamSource interface is used for inference of effective model
75 and is required to emit its statements using supplied StatementWriter.
76 Each source (e.g. YANG source) has to be processed in three steps
77 in order to emit different statements for each step.
78 This package provides support for various namespaces used across statement parser
79 in order to map relations during declaration phase process.
81 Currently, there are two implementations of StatementStreamSource in Yangtools:
83 - YangStatementSourceImpl - intended for yang sources
84 - YinStatementSourceImpl - intended for yin sources
87 Class diagram of yang data API
89 image:models/yang-data-api.png[]
92 Codecs which enable serialization of NormalizedNodes into YANG-modeled data in XML or JSON format and deserialization of YANG-modeled data in XML or JSON format into NormalizedNodes.
94 ==== YANG Maven Plugin
95 Maven plugin which integrates YANG parser into Maven
96 build lifecycle and provides code-generation framework for components, which
97 wants to generate code or other artefacts based on YANG model.
101 === Working with YANG Model
102 First thing you need to do if you want to work with YANG models is to instantiate a SchemaContext object. This object type describes one or more parsed YANG modules.
104 In order to create it you need to utilize YANG statement parser which takes one or more StatementStreamSource objects as input and then produces the SchemaContext object.
106 StatementStreamSource object contains the source file information. It has two implementations, one for YANG sources - YangStatementSourceImpl, and one for YIN sources - YinStatementSourceImpl.
108 Here is an example of creating StatementStreamSource objects for YANG files, providing them to the YANG statement parser and building the SchemaContext:
112 StatementStreamSource yangModuleSource = new YangStatementSourceImpl("/example.yang", false);
113 StatementStreamSource yangModuleSource2 = new YangStatementSourceImpl("/example2.yang", false);
115 CrossSourceStatementReactor.BuildAction reactor = YangInferencePipeline.RFC6020_REACTOR.newBuild();
116 reactor.addSources(yangModuleSource, yangModuleSource2);
118 SchemaContext schemaContext = reactor.buildEffective();
121 First, StatementStreamSource objects with two constructor arguments should be instantiated: path to the yang source file (which is a regular String object) and a boolean which determines if the path is absolute or relative.
123 Next comes the initiation of new yang parsing cycle - which is represented by CrossSourceStatementReactor.BuildAction object. You can get it by calling method newBuild() on CrossSourceStatementReactor object (RFC6020_REACTOR) in YangInferencePipeline class.
125 Then you should feed yang sources to it by calling method addSources() that takes one or more StatementStreamSource objects as arguments.
127 Finally you call the method buildEffective() on the reactor object which returns EffectiveSchemaContext (that is a concrete implementation of SchemaContext). Now you are ready to work with contents of the added yang sources.
129 Let us explain how to work with models contained in the newly created SchemaContext. If you want to get all the modules in the schemaContext, you have to call method getModules() which returns a Set of modules. If you want to get all the data definitions in schemaContext, you need to call method getDataDefinitions, etc.
132 Set<Module> modules = schemaContext.getModules();
133 Set<DataSchemaNodes> dataSchemaNodes = schemaContext.getDataDefinitions();
135 Usually you want to access specific modules. Getting a concrete module from SchemaContext is a matter of calling one of these methods:
137 * findModuleByName(),
138 * findModuleByNamespace(),
139 * findModuleByNamespaceAndRevision().
141 In the first case, you need to provide module name as it is defined in the yang source file and module revision date if it specified in the yang source file (if it is not defined, you can just pass a null value). In order to provide the revision date in proper format, you can use a utility class named SimpleDateFormatUtil.
144 Module exampleModule = schemaContext.findModuleByName("example-module", null);
146 Date revisionDate = SimpleDateFormatUtil.getRevisionFormat().parse("2015-09-02");
147 Module exampleModule = schemaContext.findModuleByName("example-module", revisionDate);
149 In the second case, you have to provide module namespace in form of an URI object.
151 Module exampleModule = schema.findModuleByNamespace(new URI("opendaylight.org/example-module"));
153 In the third case, you provide both module namespace and revision date as arguments.
155 Once you have a Module object, you can access its contents as they are defined in YANG Model API.
156 One way to do this is to use method like getIdentities() or getRpcs() which will give you a Set of objects. Otherwise you can access a DataSchemaNode directly via the method getDataChildByName() which takes a QName object as its only argument. Here are a few examples.
160 Set<AugmentationSchema> augmentationSchemas = exampleModule.getAugmentations();
161 Set<ModuleImport> moduleImports = exampleModule.getImports();
163 ChoiceSchemaNode choiceSchemaNode = (ChoiceSchemaNode) exampleModule.getDataChildByName(QName.create(exampleModule.getQNameModule(), "example-choice"));
165 ContainerSchemaNode containerSchemaNode = (ContainerSchemaNode) exampleModule.getDataChildByName(QName.create(exampleModule.getQNameModule(), "example-container"));
168 The YANG statement parser can work in three modes:
171 * mode with active resolution of if-feature statements
172 * mode with active semantic version processing
174 The default mode is active when you initialize the parsing cycle as usual by calling the method newBuild() without passing any arguments to it. The second and third mode can be activated by invoking the newBuild() with a special argument. You can either activate just one of them or both by passing proper arguments. Let us explain how these modes work.
176 Mode with active resolution of if-features makes yang statements containing an if-feature statement conditional based on the supported features. These features are provided in the form of a QName-based java.util.Set object. In the example below, only two features are supported: example-feature-1 and example-feature-2. The Set is passed to the method newBuild() and the mode is activated.
180 Set<QName> supportedFeatures = ImmutableSet.of(
181 QName.create("example-namespace", "2016-08-31", "example-feature-1"),
182 QName.create("example-namespace", "2016-08-31", "example-feature-2"));
184 CrossSourceStatementReactor.BuildAction reactor = YangInferencePipeline.RFC6020_REACTOR.newBuild(supportedFeatures);
187 In case when no features should be supported, you should provide an empty Set<QName> object.
191 Set<QName> supportedFeatures = ImmutableSet.of();
193 CrossSourceStatementReactor.BuildAction reactor = YangInferencePipeline.RFC6020_REACTOR.newBuild(supportedFeatures);
196 When this mode is not activated, all features in the processed YANG sources are supported.
198 Mode with active semantic version processing changes the way how YANG import statements work - each module import is processed based on the specified semantic version statement and the revision-date statement is ignored. In order to activate this mode, you have to provide StatementParserMode.SEMVER_MODE enum constant as argument to the method newBuild().
202 CrossSourceStatementReactor.BuildAction reactor = YangInferencePipeline.RFC6020_REACTOR.newBuild(StatementParserMode.SEMVER_MODE);
205 Before you use a semantic version statement in a YANG module, you need to define an extension for it so that the YANG statement parser can recognize it.
209 module semantic-version {
210 namespace "urn:opendaylight:yang:extension:semantic-version";
214 revision 2016-02-02 {
215 description "Initial version";
217 sv:semantic-version "0.0.1";
219 extension semantic-version {
220 argument "semantic-version" {
227 In the example above, you see a YANG module which defines semantic version as an extension. This extension can be imported to other modules in which we want to utilize the semantic versioning concept.
229 Below is a simple example of the semantic versioning usage. With semantic version processing mode being active, the foo module imports the bar module based on its semantic version. Notice how both modules import the module with the semantic-version extension.
238 import semantic-version { prefix sv; revision-date 2016-02-02; sv:semantic-version "0.0.1"; }
239 import bar { prefix bar; sv:semantic-version "0.1.2";}
241 revision "2016-02-01" {
242 description "Initial version";
244 sv:semantic-version "0.1.1";
257 import semantic-version { prefix sv; revision-date 2016-02-02; sv:semantic-version "0.0.1"; }
259 revision "2016-01-01" {
260 description "Initial version";
262 sv:semantic-version "0.1.2";
268 Every semantic version must have the following form: x.y.z. The x corresponds to a major version, the y corresponds to a minor version and the z corresponds to a patch version. If no semantic version is specified in a module or an import statement, then the default one is used - 0.0.0.
270 A major version number of 0 indicates that the model is still in development and is subject to change.
272 Following a release of major version 1, all modules will increment major version number when backwards incompatible changes to the model are made.
274 The minor version is changed when features are added to the model that do not impact current clients use of the model.
276 The patch version is incremented when non-feature changes (such as bugfixes or clarifications of human-readable descriptions that do not impact model functionality) are made that maintain backwards compatibility.
278 When importing a module with activated semantic version processing mode, only the module with the newest (highest) compatible semantic version is imported. Two semantic versions are compatible when all of the following conditions are met:
280 * the major version in the import statement and major version in the imported module are equal. For instance, 1.5.3 is compatible with 1.5.3, 1.5.4, 1.7.2, etc., but it is not compatible with 0.5.2 or 2.4.8, etc.
282 * the combination of minor version and patch version in the import statement is not higher than the one in the imported module. For instance, 1.5.2 is compatible with 1.5.2, 1.5.4, 1.6.8 etc. In fact, 1.5.2 is also compatible with versions like 1.5.1, 1.4.9 or 1.3.7 as they have equal major version. However, they will not be imported because their minor and patch version are lower (older).
284 If the import statement does not specify a semantic version, then the default one is chosen - 0.0.0. Thus, the module is imported only if it has a semantic version compatible with the default one, for example 0.0.0, 0.1.3, 0.3.5 and so on.
286 === Working with YANG Data
287 If you want to work with YANG Data you are going to need NormalizedNode objects that are specified in the YANG Data API. NormalizedNode is an interface at the top of the YANG Data hierarchy. It is extended through sub-interfaces which define the behaviour of specific NormalizedNode types like AnyXmlNode, ChoiceNode, LeafNode, ContainerNode, etc. Concrete implemenations of these interfaces are defined in yang-data-impl module. Once you have one or more NormalizedNode instances, you can perform CRUD operations on YANG data tree which is an in-memory database designed to store normalized nodes in a tree-like structure.
289 In some cases it is clear which NormalizedNode type belongs to which yang statement (e.g. AnyXmlNode, ChoiceNode, LeafNode). However, there are some normalized nodes which are named differently from their yang counterparts. They are listed below:
291 * LeafSetNode - leaf-list
292 * OrderedLeafSetNode - leaf-list that is ordered-by user
293 * LeafSetEntryNode - concrete entry in a leaf-list
294 * MapNode - keyed list
295 * OrderedMapNode - keyed list that is ordered-by user
296 * MapEntryNode - concrete entry in a keyed list
297 * UnkeyedListNode - unkeyed list
298 * UnkeyedListEntryNode - concrete entry in an unkeyed list
300 In order to create a concrete NormalizedNode object you can use the utility class Builders or ImmutableNodes. These classes can be found in yang-data-impl module and they provide methods for building each type of normalized node. Here is a simple example of building a normalized node:
305 ContainerNode containerNode = Builders.containerBuilder().withNodeIdentifier(new YangInstanceIdentifier.NodeIdentifier(QName.create(moduleQName, "example-container")).build();
308 ContainerNode containerNode2 = Builders.containerBuilder(containerSchemaNode).build();
310 Both examples produce the same result. NodeIdentifier is one of the four types of YangInstanceIdentifier (these types are described in the javadoc of YangInstanceIdentifier). The purpose of YangInstanceIdentifier is to uniquely identify a particular node in the data tree. In the first example, you have to add NodeIdentifier before building the resulting node. In the second example it is also added using the provided ContainerSchemaNode object.
312 ImmutableNodes class offers similar builder methods and also adds an overloaded method called fromInstanceId() which allows you to create a NormalizedNode object based on YangInstanceIdentifier and SchemaContext. Below is an example which shows the use of this method.
316 YangInstanceIdentifier.NodeIdentifier contId = new YangInstanceIdentifier.NodeIdentifier(QName.create(moduleQName, "example-container");
318 NormalizedNode<?, ?> contNode = ImmutableNodes.fromInstanceId(schemaContext, YangInstanceIdentifier.create(contId));
321 Let us show a more complex example of creating a NormalizedNode. First, consider the following YANG module:
325 module example-module {
326 namespace "opendaylight.org/example-module";
329 container parent-container {
330 container child-container {
331 list parent-ordered-list {
334 key "parent-key-leaf";
336 leaf parent-key-leaf {
340 leaf parent-ordinary-leaf {
344 list child-ordered-list {
347 key "child-key-leaf";
349 leaf child-key-leaf {
353 leaf child-ordinary-leaf {
363 In the following example, two normalized nodes based on the module above are written to and read from the data tree.
367 TipProducingDataTree inMemoryDataTree = InMemoryDataTreeFactory.getInstance().create(TreeType.OPERATIONAL);
368 inMemoryDataTree.setSchemaContext(schemaContext);
370 // first data tree modification
371 MapEntryNode parentOrderedListEntryNode = Builders.mapEntryBuilder().withNodeIdentifier(
372 new YangInstanceIdentifier.NodeIdentifierWithPredicates(
373 parentOrderedListQName, parentKeyLeafQName, "pkval1"))
374 .withChild(Builders.leafBuilder().withNodeIdentifier(
375 new YangInstanceIdentifier.NodeIdentifier(parentOrdinaryLeafQName))
376 .withValue("plfval1").build()).build();
378 OrderedMapNode parentOrderedListNode = Builders.orderedMapBuilder().withNodeIdentifier(
379 new YangInstanceIdentifier.NodeIdentifier(parentOrderedListQName))
380 .withChild(parentOrderedListEntryNode).build();
382 ContainerNode parentContainerNode = Builders.containerBuilder().withNodeIdentifier(
383 new YangInstanceIdentifier.NodeIdentifier(parentContainerQName))
384 .withChild(Builders.containerBuilder().withNodeIdentifier(
385 new NodeIdentifier(childContainerQName)).withChild(parentOrderedListNode).build()).build();
387 YangInstanceIdentifier path1 = YangInstanceIdentifier.of(parentContainerQName);
389 DataTreeModification treeModification = inMemoryDataTree.takeSnapshot().newModification();
390 treeModification.write(path1, parentContainerNode);
392 // second data tree modification
393 MapEntryNode childOrderedListEntryNode = Builders.mapEntryBuilder().withNodeIdentifier(
394 new YangInstanceIdentifier.NodeIdentifierWithPredicates(
395 childOrderedListQName, childKeyLeafQName, "chkval1"))
396 .withChild(Builders.leafBuilder().withNodeIdentifier(
397 new YangInstanceIdentifier.NodeIdentifier(childOrdinaryLeafQName))
398 .withValue("chlfval1").build()).build();
400 OrderedMapNode childOrderedListNode = Builders.orderedMapBuilder().withNodeIdentifier(
401 new YangInstanceIdentifier.NodeIdentifier(childOrderedListQName))
402 .withChild(childOrderedListEntryNode).build();
404 ImmutableMap.Builder<QName, Object> builder = ImmutableMap.builder();
405 ImmutableMap<QName, Object> keys = builder.put(parentKeyLeafQName, "pkval1").build();
407 YangInstanceIdentifier path2 = YangInstanceIdentifier.of(parentContainerQName).node(childContainerQName)
408 .node(parentOrderedListQName).node(new NodeIdentifierWithPredicates(parentOrderedListQName, keys)).node(childOrderedListQName);
410 treeModification.write(path2, childOrderedListNode);
411 treeModification.ready();
412 inMemoryDataTree.validate(treeModification);
413 inMemoryDataTree.commit(inMemoryDataTree.prepare(treeModification));
415 DataTreeSnapshot snapshotAfterCommits = inMemoryDataTree.takeSnapshot();
416 Optional<NormalizedNode<?, ?>> readNode = snapshotAfterCommits.readNode(path1);
417 Optional<NormalizedNode<?, ?>> readNode2 = snapshotAfterCommits.readNode(path2);
419 First comes the creation of in-memory data tree instance. The schema context (containing the model mentioned above) of this tree is set. After that, two normalized nodes are built. The first one consists of a parent container, a child container and a parent ordered list which contains a key leaf and an ordinary leaf. The second normalized node is a child ordered list that also contains a key leaf and an ordinary leaf.
421 In order to add a child node to a node, method withChild() is used. It takes a NormalizedNode as argument. When creating a list entry, YangInstanceIdentifier.NodeIdentifierWithPredicates should be used as its identifier. Its arguments are the QName of the list, QName of the list key and the value of the key. Method withValue() specifies a value for the ordinary leaf in the list.
423 Before writing a node to the data tree, a path (YangInstanceIdentifier) which determines its place in the data tree needs to be defined. The path of the first normalized node starts at the parent container. The path of the second normalized node points to the child ordered list contained in the parent ordered list entry specified by the key value "pkval1".
425 Write operation is performed with both normalized nodes mentioned earlier. It consist of several steps. The first step is to instantiate a DataTreeModification object based on a DataTreeSnapshot. DataTreeSnapshot gives you the current state of the data tree. Then comes the write operation which writes a normalized node at the provided path in the data tree. After doing both write operations, method ready() has to be called, marking the modification as ready for application to the data tree. No further operations within the modification are allowed. The modification is then validated - checked whether it can be applied to the data tree. Finally we commit it to the data tree.
427 Now you can access the written nodes. In order to do this, you have to create a new DataTreeSnapshot instance and call the method readNode() with path argument pointing to a particular node in the tree.
429 === Serialization / deserialization of YANG Data
430 If you want to deserialize YANG-modeled data which have the form of an XML document, you can use the XML parser found in the module yang-data-codec-xml. The parser walks through the XML document containing YANG-modeled data based on the provided SchemaContext and emits node events into a NormalizedNodeStreamWriter. The parser disallows multiple instances of the same element except for leaf-list and list entries. The parser also expects that the YANG-modeled data in the XML source are wrapped in a root element. Otherwise it will not work correctly.
432 Here is an example of using the XML parser.
435 InputStream resourceAsStream = ExampleClass.class.getResourceAsStream("/example-module.yang");
437 XMLInputFactory factory = XMLInputFactory.newInstance();
438 XMLStreamReader reader = factory.createXMLStreamReader(resourceAsStream);
440 NormalizedNodeResult result = new NormalizedNodeResult();
441 NormalizedNodeStreamWriter streamWriter = ImmutableNormalizedNodeStreamWriter.from(result);
443 XmlParserStream xmlParser = XmlParserStream.create(streamWriter, schemaContext);
444 xmlParser.parse(reader);
446 NormalizedNode<?, ?> transformedInput = result.getResult();
448 The XML parser utilizes the javax.xml.stream.XMLStreamReader for parsing an XML document. First, you should create an instance of this reader using XMLInputFactory and then load an XML document (in the form of InputStream object) into it.
450 In order to emit node events while parsing the data you need to instantiate a NormalizedNodeStreamWriter. This writer is actually an interface and therefore you need to use a concrete implementation of it. In this example it is the ImmutableNormalizedNodeStreamWriter, which constructs immutable instances of NormalizedNodes.
452 There are two ways how to create an instance of this writer using the static overloaded method from(). One version of this method takes a NormalizedNodeResult as argument. This object type is a result holder in which the resulting NormalizedNode will be stored. The other version takes a
453 NormalizedNodeContainerBuilder as argument. All created nodes will be written to this builder.
455 Next step is to create an instance of the XML parser. The parser itself is represented by a class named XmlParserStream. You can use one of two versions of the static overloaded method create() to construct this object. One version accepts a NormalizedNodeStreamWriter and a SchemaContext as arguments, the other version takes the same arguments plus a SchemaNode. Node events are emitted to the writer. The SchemaContext is used to check if the YANG data in the XML source comply with the provided YANG model(s). The last argument, a SchemaNode object, describes the node that is the parent of nodes defined in the XML data. If you do not provide this argument, the parser sets the SchemaContext as the parent node.
457 The parser is now ready to walk through the XML. Parsing is initiated by calling the method parse() on the XmlParserStream object with XMLStreamReader as its argument.
459 Finally you can access the result of parsing - a tree of NormalizedNodes containg the data as they are defined in the parsed XML document - by calling the method getResult() on the NormalizedNodeResult object.
461 === Introducing schema source repositories
463 === Writing YANG driven generators
465 === Introducing specific extension support for YANG parser