Yanglint

Introduction

Yanglint is command-line tool for validating and converting YANG schemas and YANG modeled data. It is part of the libyang open source project and implemented in C.

Install Yanglint

Install yang-tools (which includes yanglint). On Ubuntu this can be done as follows:

$ sudo apt install -y yang-tools

Verify that yanglint is properly installed:

$ yanglint --version
yanglint 0.16.105

Validate a YANG data model

The simplest way of using yanglint is to validate the correctness of a YANG data model:

$ yanglint interfaces.yang

The fact that we get no output means that the YANG file was correct. In addition, the program returns status code zero, so you can do something like this:

$ if yanglint interfaces.yang; then echo "All good"; else "There are errors"; fi
All good

Validate YANG data model bad-interfaces.yang to see an example of the error messages produced by yanglint (note hat unlike pyang, yanglint stops after the first error).

$ yanglint bad-interfaces.yang
err : Invalid keyword "organisation".
err : Module "bad-interfaces" parsing failed.

Convert a YANG data model

YANG data models tend to be very long and verbose. Yanglint can produce a summary of the YANG data model in a tree format:

$ yanglint -f tree interfaces.yang
module: interfaces
  +--rw interfaces
     +--rw interface* [name]
        +--rw name                string
        +--rw ipv4-address?       string
        +--ro sent-packets?       uint64
        +--ro received-packets?   uint64

The command yanglint --tree-help displays an explanation of the symbols in the tree diagram.

In addition to producing a tree summary, Yanglint can also convert the YANG data model to several other formats:

$ yanglint --help
Usage:
    yanglint [options] [-f { yang | yin | tree | tree-rfc | jsons}] <file>...
        Validates the YANG module in <file>, and all its dependencies.

    yanglint [options] [-f { xml | json }] <schema>... <file>...
        Validates the YANG modeled data in <file> according to the <schema>.

    yanglint
        Starts interactive mode with more features.

Options:
  -h, --help            Show this help message and exit.

[...]

  -f FORMAT, --format=FORMAT
                        Convert to FORMAT. Supported formats: 
                        yang, yin, tree and jsons (JSON) for schemas,
                        xml, json for data.

[...]

As an example, the following example converts the YANG data model to JSON:

$ yanglint -f jsons interfaces.yang
{"interfaces":{"namespace":"http://remoteautonomy.com/yang-schemas/interfaces","prefix":"intf","description":{"text":"A simplistic tutorial data model for interfaces on a device."},"organization":{"text":"Remote Autonomy"},"contact":{"text":"Bruno Rijsman\u000Abrunorijsman@remoteautonomy.com"},"yang-version":{"value":"1.0"},"revision":{"2022-03-12":{"description":{"text":"Initial revision."}}},"data":{"interfaces":{"nodetype":"container"}}}}

The JSON output is more readable if you pretty print it using jq:

$ yanglint -f jsons interfaces.yang | jq
{
  "interfaces": {
    "namespace": "http://remoteautonomy.com/yang-schemas/interfaces",
    "prefix": "intf",
    "description": {
      "text": "A simplistic tutorial data model for interfaces on a device."
    },
    "organization": {
      "text": "Remote Autonomy"
    },
    "contact": {
      "text": "Bruno Rijsman\nbrunorijsman@remoteautonomy.com"
    },
    "yang-version": {
      "value": "1.0"
    },
    "revision": {
      "2022-03-12": {
        "description": {
          "text": "Initial revision."
        }
      }
    },
    "data": {
      "interfaces": {
        "nodetype": "container"
      }
    }
  }
}

Interactive mode

It is also possible to run yanglint in interactive mode:

$ yanglint
> load interfaces
> print interfaces
module: interfaces
  +--rw interfaces
     +--rw interface* [name]
        +--rw name                string
        +--rw ipv4-address?       string
        +--ro sent-packets?       uint64
        +--ro received-packets?   uint64
> print interfaces -f jsons
{"interfaces":{"namespace":"http://remoteautonomy.com/yang-schemas/interfaces","prefix":"intf","description":{"text":"A simplistic tutorial data model for interfaces on a device."},"organization":{"text":"Remote Autonomy"},"contact":{"text":"Bruno Rijsman\u000Abrunorijsman@remoteautonomy.com"},"yang-version":{"value":"1.0"},"revision":{"2022-03-12":{"description":{"text":"Initial revision."}}},"data":{"interfaces":{"nodetype":"container"}}}}
> quit

Validate and convert instance data

In addition to validating and converting data models, yanglint can also validate that instance data confirms to a given data model and convert instance data.

Consider the following instance data in XML format (these are the contents of file yanglint/data.xml in the YANG tutorial repo):

<interfaces xmlns="http://remoteautonomy.com/yang-schemas/interfaces">
    <interface>
        <name>eth1</name>
        <ipv4-address>1.1.1.1</ipv4-address>
    </interface>
    <interface>
        <name>eth2</name>
        <ipv4-address>2.2.2.2</ipv4-address>
    </interface>
</interfaces>

The following sequence of commends in yanglint interactive mode validates that the above instance data confirms to the interfaces.yang data model and converts the instance data from XML to JSON:

$ yanglint
> load interfaces
> data -s -t config yanglint/data.xml -f json
{
  "interfaces:interfaces": {
    "interface": [
      {
        "name": "eth1",
        "ipv4-address": "1.1.1.1"
      },
      {
        "name": "eth2",
        "ipv4-address": "2.2.2.2"
      }
    ]
  }
}

Here the -s option enables strict validation, the -t config option indicates that we are validating configuration data, and the -f json option indicates that the instance data must be converted to JSON.

We can also perform the instance data validation and conversion from the command-line:

$ yanglint -s -t config yanglint/data.xml -f json interfaces.yang
{
  "interfaces:interfaces": {
    "interface": [
      {
        "name": "eth1",
        "ipv4-address": "1.1.1.1"
      },
      {
        "name": "eth2",
        "ipv4-address": "2.2.2.2"
      }
    ]
  }
}

Now, to demonstration a validation failure, consider the following instance data in XML format (these are the contents of file yanglint/bad-data.xml in the YANG tutorial repo). Note that the IPv4 address is invalid (the first byte 300 is not in the range 0-255).

<interfaces xmlns="http://remoteautonomy.com/yang-schemas/interfaces">
    <interface>
        <name>eth</name>
        <ipv4-address>300.1.1.1</ipv4-address>
    </interface>
</interfaces>

Validating this instance data produces the following error message:

$ yanglint -s -t config yanglint/bad-data.xml -f json interfaces.yang
err : Value "300.1.1.1" does not satisfy the constraint "(([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])" (range, length, or pattern). (/interfaces:interfaces/interface[name='eth']/ipv4-address)

References