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Table of Contents

Status

subtle	true
colour	Yellow
title	Work in Progress

This page documents the existing Yang Parser used in ONAP and OpenDayLight and will investigate if they can be used for it fulfill the needs of the C&PS.

Resources

*Although this documentation link is to the latest ODL doc revision, it is very outdated and the code examples need significant updates, see findings in Mini-PoC below (bug reported: https://jira.opendaylight.org/browse/DOCS-126)

Overview

The Yang parser used in ONAP (CCSDK / SDNC) was developed (and still is) a OpenDayLight Library.

...

In ccsdk/sli/plugins, there is a plugin called restconf-client which was contributed by Huawei. That code uses the yangtool parser more directly so that it can interpret the results being returned when it calls a restconf interface.

Resources

Additional Resources (still to be examined)

https://github.com/PANTHEONtech/lighty-core

_{*Although this documentation link is to the latest ODL doc revision, it is very outdated and the code examples need significant updates, see findings in Mini-PoC below (bug reported: https://jira.opendaylight.org/browse/DOCS-126)}

Mini-PoC

To help this evaluation I will create a small sample project with the goal to pare a yang file using the ODL Yang Tools. I will report my findings here

...

The documentation mentioned above lists many modules but the code examples do not clarify which exactly are needed to parse a Yang model and Yang file data files in java code.

...

Code Block

language	xml
theme	Midnight
title	pom.xml
collapse	true

    <parent>    <properties>
        <maven.compiler.version>3.8.1</maven.compiler.version>
        <maven.compiler.release>11</maven.compiler.release>
        <odl.yangtools.version>5.0.5</odl.yangtools.version>
    </properties>

    <build>
        <plugins>
            <plugin>
                <groupId>org.opendaylightapache.maven.mdsal<plugins</groupId>
                <artifactId>binding<artifactId>maven-compiler-parent<plugin</artifactId>
        <version>3.0.8</version>        <version>${maven.compiler.version}</version>
                <configuration>
                    <release>${maven.compiler.release}</release>
                </configuration>
            <relativePath/></plugin>
        </plugins>
    </parent>build>
	:
    <dependencies>
        <dependency>
            <groupId>org.opendaylight.yangtools</groupId>
            <artifactId>yang-parser-api</artifactId>
            <version>${odl.yangtools.version}</version>
        </dependency>
        <dependency>
            <groupId>org.opendaylight.yangtools</groupId>
            <artifactId>yang-parser-impl</artifactId>
            <version>${odl.yangtools.version}</version>
        </dependency>
        <dependency>
            <groupId>org.opendaylight.yangtools</groupId>
            <artifactId>yang-model-util</artifactId>
            <version>${odl.yangtools.version}</version>
        </dependency>

        <dependency>
            <groupId>org.opendaylight.yangtools</groupId>
            <artifactId>yang-data-codec-xml</artifactId>
            <version>${odl.yangtools.version}</version>
        </dependency>
        <dependency>
            <groupId>org.opendaylight.yangtools</groupId>
            <artifactId>yang-data-codec-gson</artifactId>
            <version>5<version>${odl.0yangtools.3<version}</version>
        </dependency>
        <!-- SLF4J API -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.6.1</version>
        </dependency>
        <!-- LOG4J -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.6.1</version>
        </dependency>
    </dependencies>

Note. SLF4J has also been added as the implementation requires an enabled logger

Documentation Code Updates

...

Code Block

language	java
theme	Midnight
title	Corrected Code
linenumbers	true
collapse	true

    static YangParserFactory PARSER_FACTORY;

    static {
        final YangTextSchemaSourceIterator<YangParserFactory> sourceit = YangTextSchemaSource.forFile(new File("/example.yang"));
   ServiceLoader.load(YangParserFactory.class).iterator();
        if (!it.hasNext()) {
            throw new IllegalStateException("No YangParserFactory found");
        }
     StatementStreamSource yangModuleSource   PARSER_FACTORY = YangStatementStreamSourceit.createnext(source);
    }

   CrossSourceStatementReactor.BuildAction reactor = defaultReactor().newBuild(); ...

        File file = new File(ClassLoader.getSystemClassLoader().getResource("example.yang").getFile());
        YangTextSchemaSource source = reactorYangTextSchemaSource.addSourceforFile(yangModuleSourcefile);
        
SchemaContext schemaContext        final YangParser yangParser = reactorPARSER_FACTORY.buildEffectivecreateParser(StatementParserMode.DEFAULT_MODE);
         Set<Module> modulesyangParser.addSource(source);
        SchemaContext schemaContext = schemaContextyangParser.getModulesbuildEffectiveModel();
 

     Set<DataSchemaNode> dataSchemaNodes = schemaContext.getDataDefinitionsgetModules();

This is the kind of object (module) that gets created:

Image RemovedImage Added

Generated Java Object Structures per Yang concept

Object Structure

The SchemaContext object generated by the Yang Parser in java has the following possible structures (java collections)

Gliffy

macroId	8eafa348-6609-4eae-a733-beb5a2766488
name	Yang Parser Java Object View
pagePin	35

ChildNodes are SchemaTree is implemented as a Map <QName, DataSchemaNode>a ImmutableMap<QName, SchemaTreeEffectiveStatement<?>>

The Class DataSchemaNode SchemaTree can represent a tree of any Yang Leaf, List or Container. All leafs implement the LeafStatement interface which provides methods for many Yang Language features including

getType()
getUnits()
getMandatory()
getWhenStatement()
getMustStatments()

Main data types

The package org.opendaylight.yangtools.yang.model.util.type contains classes for all the possible data types including:

BaseBinaryType
BaseBitsType
BaseBooleanType
BaseDecimalType
BaseEnumerationType
BaseInt8Type
BaseInt16Type
BaseInt32Type
BaseInt64Type
BaseStringType
BaseUint8Type
BaseUint16Type
BaseUint32Type
BaseUint64Type

There are also some special data types such as:

BaseEmptyType
BaseIdentityrefType
BaseInstanceIdentifierType
BaseLeafrefType
BaseUnionType

And also 'restricted' versions of the base types such as:

RestrictedStringType
RestrictedUint64Type

Description	Yang	Java Object View	Notes	XML Validation	JSON Validation
Datatypes and basic constraints
Basic String	`leaf response-code {` `type string;` `}`

Image Removed

	Image Added	`TypeStatement TypeAwareDeclaredStatement.getType()`	Yes	Yes
Mandatory Basic String	`leaf response-code {925px` `type string;` `mandatory "true";` `}`

Image Removed

Image Added	`Optional<MandatoryStatement> MandatoryStatementAwareDeclaredStatement.getMandatory()`	No	No
Limited String	`leaf pnf-name {` `type string {` `length "0..256";` `}`

Image Removed

Specialized class to hold length limitation

Image Added

Optional<LengthConstraint> AbstractLengthRestrictedType.getLengthConstraint()

Yes

typedef (String) with pattern

typedef dotted-quad {
type string {
pattern
'(([0-9] ...';
}
}

leaf address {
type dotted-quad;
mandatory "true";
}

Image Removed

Image Added	`List<PatternConstraint> RestrictedStringType.getPatternConstraints()`	Yes	Yes
Limited

unint64

uint64 leaf cid {
type

string

uint64 {

length

range "0..

52

503";
}
}

Image Removed

	Image Added	`org.opendaylight.yangtools.yang.model.util.type.RestrictedUint64Type`	Yes	Yes
boolean with default value	`leaf blacklisted {` `type boolean;` `default 1;` `}`

Image Removed range

Image Added	`org.opendaylight.yangtools.yang.model.util.type.DerivedBooleanType`	N/A	N/A
Unique
Unique	`list server {` `key "name";` `unique "ip port";` `leaf name {` `type string;` `}` `leaf ip {` `type dotted-quad;` `}` `leaf port {` `type uint32;` `}}`	Image Added	`org.opendaylight.yangtools.yang.model.api.stmt.UniqueStatement`	No	No
Choice
Choice	`choice transfer-method {` `leaf transfer-interval {` `type uint64 {`

range "15..2880";

}
units minutes;

Image Removed

`}` `leaf transfer-on-commit {` `type empty;` `}}`	Image Added	`org.opendaylight.yangtools.yang.model.api.stmt.ChoiceStatement`	N/A	N/A
Must
Must	`leaf ifType {` `type enumeration {` `enum ethernet;` `enum atm;}`

`}` `leaf ifMTU {` `type uint32;}` `must "ifType != 'ethernet' or "` `+ "(ifType = 'ethernet' and ifMTU = 1500)" {error-message 466px"An ethernet MTU must be 1500";}`	Image Added	`org.opendaylight.yangtools.yang.model.api.stmt.ErrorMessageStatement`	No	No
When
When	leaf a { type boolean; } leaf b { type string; when "../a = 'true'"; }	Image Added	`org.opendaylight.yangtools.yang.model.api.stmt.WhenStatement`	No	No
Extension
Extension declaration	`extension store-state-ext {` `argument duration;` `description "An extension to enablestate-storage for any attribute. Use duration to specify how long:`

nnn h

nnn<h|d|

y

y>";
}

Image Added

Image Removed

	N/A
Extension usage	`leaf attribute-with-temporal-storage {` `type string;` `cm-notify-api:store-state-ext "`

3 d

`3d"; // store state 3 days` `}`	Image Added	`org.opendaylight.yangtools.yang.model.api.stmt.UnrecognizedStatement` which extends `UnknownStatement:` public interface UnknownStatement<A> extends DeclaredStatement<A> { default @Nullable A getArgument() { return argument(); } }	N/A
Augmentation
	`augment "server" {` `when "port = '8787'";` `leaf enable-debug {` `type boolean;` `}` `}`	Image Added	The additional leaf just appears in the SchemaTree (without any reference that it is an augmentation)	N/A
RPC
rpc	rpc nbrlist-change-notification { description "RAN Neighbor List change notification to configure RuntimeDB"; input { : } output { : } }	Image Added		N/A
rpc input	input { leaf fap-service-number-of-entries-changed { type uint64; description "Number of cells for which neighbor list has changed"; } list fap-service { key "alias"; leaf alias { type string { length "1..64"; } } leaf cid { type string { length "0..52"; } } uses x-0005b9-lte-g; leaf lte-cell-number-of-entries { type uint64; description

}

Image Removed

extension is stored as 'UnknownNode' and refers back to the extension declarationAugmentation

           "Number of cells in a neighbor list that was changed";
       }
       list lte-ran-neighbor-list-in-use-lte-cell-changed {
         key "plmnid cid";
         uses lte-ran-neighbor-list-in-use-lte-cell-g;
         description
           "Changed/Modified List of cells

in a neighbor list for this fap service";

     }
   }
}

Image Added

N/A

rpc output

output {
    uses cm-notification-response;
}

Image Added

N/A

Yang Data Parsing and Validation

XML Parsing

Code Block

language	java
theme	Midnight
title	XML Parsing Example
linenumbers	true
collapse	true

		SchemaContext schemaContext = ... (see previous snippets)
        final Module module = schemaContext.findModules("ultraconfig-interfaces").iterator().next();
        QName qName = QName.create(module.getQNameModule(),"interfaces");
        final Optional<DataSchemaNode> node = module.findDataChildByName(qName);
        if (node.isPresent()) {
            final InputStream resourceAsStream = ClassLoader.getSystemClassLoader().getResourceAsStream("example2data.xml");
            final XMLStreamReader reader = UntrustedXML.createXMLStreamReader(resourceAsStream);
            final NormalizedNodeResult result = new NormalizedNodeResult();
            final NormalizedNodeStreamWriter streamWriter = ImmutableNormalizedNodeStreamWriter.from(result);
            final XmlParserStream xmlParser = XmlParserStream.create(streamWriter, schemaContext, node.get() );
            xmlParser.parse(reader);
            final NormalizedNode<?, ?> transformedInput = result.getResult();
        }

*Note: the DataSchemaNode being used when creating the XmlParserStream HAS to be the root node of the xml data!

XML Validation Findings

The XML Parser is found to do basic data type checks including range checks and (regex) pattern validation. If the dat input doesn't conform those a clear exception detailing the problem is thrown
Features such as 'mandatory' and 'unique' are to be validated
More advanced features such as 'must', 'when', 'choice' etc have not yet been tested

The table in the sections above has a column with the XML validation findings.

JSON Parsing

Code Block

language	java
theme	Midnight
title	JSON Parsing Example
linenumbers	true
collapse	true

		SchemaContext schemaContext = ... (see previous snippets)
        JSONCodecFactory jsonCodecFactory = JSONCodecFactorySupplier.DRAFT_LHOTKA_NETMOD_YANG_JSON_02.getShared(schemaContext);
        final NormalizedNodeResult result = new NormalizedNodeResult();
        final NormalizedNodeStreamWriter streamWriter = ImmutableNormalizedNodeStreamWriter.from(result);
        final JsonParserStream jsonParser = JsonParserStream.create(streamWriter, jsonCodecFactory);
        final InputStream resourceAsStream = ClassLoader.getSystemClassLoader().getResourceAsStream("example2data.json");
        final JsonReader jsonReader = new JsonReader(new InputStreamReader(resourceAsStream));
        jsonParser.parse(jsonReader);
        final NormalizedNode<?, ?> transformedInput = result.getResult();

JSON Validation Findings

As expected the parsing of string, originating form XML or JSON is done by the same code and the results are identical to those for XML Data Parsing

Conclusion

Pros

EXTENSIVE - The YangTools model parser is comprehensive and covers all possible Yang Language elements we might require
AVAILABLE - Extensively used throughout ONAP and ODL projects (able to convert to Java objects, code & API). These parsers are already used in many ONAP platform projects.
MATURE CODE - Mature code, dates back to 2013 with contributions from many companies including Cisco and Redhat and Pantheon Tech. (No need for licenses, these are also open source Yang parser). ODL is open source.
VALIDATION - Testing with parsing of JSON and XML data with validated for a (parsed) model included. Files to objects and vice versa is possible. Model violation & compilation validation is available.
OBJECTIVES - Meets our two high-level requirements & objectives. Parse models from SDC into Java objects relate to persistence of data. Parsing of documents compliant to those schemas.

Cons

LEARNING CURVE - Due to its completeness it also is a complicated piece of software which will take some time to get familiar with.
DOCUMENTATION - Documentation out of date, this page hopes to address that somewhat

Versions Compared

Old Version 18

New Version Current

Key

Resources

Overview

Resources

Mini-PoC

Documentation Code Updates

Generated Java Object Structures per Yang concept

Object Structure

Main data types

Datatypes and basic constraints

Unique

Choice

Must

When

Extension

Augmentation

RPC

Yang Data Parsing and Validation

XML Parsing

XML Validation Findings

JSON Parsing

JSON Validation Findings

Conclusion