cddl

Property References

Property references in CDDL allow referring to previously defined types, groups, literals, and other constructs. This document explains how property references are represented in the AST.

Property Reference Definition

In the AST, a property reference is represented by the following structure:

export type PropertyReferenceType = 'literal' | 'group' | 'group_array' | 'array' | 'range' | 'tag'

export type PropertyReference = {
    Type: PropertyReferenceType
    Value: string | number | boolean | Group | Array | Range | Tag
    Unwrapped: boolean
    Operator?: Operator
}

Where:

• Type: The type of reference
• Value: The value being referenced (can be various types)
• Unwrapped: A boolean indicating if this reference should be unwrapped (applicable for arrays and groups)
• Operator: An optional operator that modifies the referenced value

Reference Types

The AST supports several types of references:

1. literal: References a literal value (string, number, boolean)
2. group: References a named group
3. group_array: References a group that should be treated as an array
4. array: References a named array
5. range: References a range definition
6. tag: References a tag definition

Examples of Property References

Reference to a Named Group

person = {
    address: address
}

address = {
    street: tstr,
    city: tstr
}

AST representation of the reference:

{
  "Type": "group",
  "Value": "address",
  "Unwrapped": false
}

Reference to a Literal Value

status = "active" / "inactive" / "suspended"

AST representation:

{
  "Type": "variable",
  "Name": "status",
  "IsChoiceAddition": false,
  "PropertyType": [
    {
      "Type": "literal",
      "Value": "active",
      "Unwrapped": false
    },
    {
      "Type": "literal",
      "Value": "inactive",
      "Unwrapped": false
    },
    {
      "Type": "literal",
      "Value": "suspended",
      "Unwrapped": false
    }
  ],
  "Comments": []
}

Reference with Unwrapping

basic-header = [
    field1: int,
    field2: text
]

advanced-header = [
    ~basic-header,
    field3: bytes
]

AST representation of the unwrapped reference:

{
  "Type": "group",
  "Value": "basic-header",
  "Unwrapped": true
}

Reference to a Range

port = 0..65535

AST representation:

{
  "Type": "range",
  "Value": {
    "Min": 0,
    "Max": 65535,
    "Inclusive": true
  },
  "Unwrapped": false
}

Reference to a Tag

my_uri = #6.32(tstr) / tstr

AST representation:

{
  "Type": "tag",
  "Value": {
    "NumericPart": 6.32,
    "TypePart": "tstr"
  },
  "Unwrapped": false
}

Reference with Operator

ip4 = bstr .size 4
foo = ip4 .and nai

AST representation:

{
  "Type": {
    "Type": "group",
    "Value": "ip4",
    "Unwrapped": false
  },
  "Operator": {
    "Type": "and",
    "Value": {
      "Type": "group",
      "Value": "nai",
      "Unwrapped": false
    }
  }
}

References in Group Composition

References can be used for group composition, where one group incorporates all the properties of another:

person = {
    name: tstr,
    age: uint
}

employee = {
    person,
    employeeId: uint,
    department: tstr
}

AST representation of the composition:

{
  "Type": "group",
  "Name": "employee",
  "IsChoiceAddition": false,
  "Properties": [
    {
      "HasCut": false,
      "Occurrence": { "n": 1, "m": 1 },
      "Name": "",
      "Type": [
        {
          "Type": "group",
          "Value": "person",
          "Unwrapped": false
        }
      ],
      "Comments": []
    },
    {
      "HasCut": true,
      "Occurrence": { "n": 1, "m": 1 },
      "Name": "employeeId",
      "Type": ["uint"],
      "Comments": []
    },
    {
      "HasCut": true,
      "Occurrence": { "n": 1, "m": 1 },
      "Name": "department",
      "Type": ["tstr"],
      "Comments": []
    }
  ],
  "Comments": []
}

References in Array Elements

References can be used to define array elements:

people = [* person]

AST representation:

{
  "Type": "array",
  "Name": "people",
  "Values": [
    {
      "HasCut": false,
      "Occurrence": { "n": 0, "m": Infinity },
      "Name": "",
      "Type": [
        {
          "Type": "group",
          "Value": "person",
          "Unwrapped": false
        }
      ],
      "Comments": []
    }
  ],
  "Comments": []
}

Nested References

References can refer to complex nested structures:

location = {
    city: tstr,
    country: {
        name: tstr,
        code: tstr
    }
}

AST representation:

{
  "Type": "group",
  "Name": "location",
  "IsChoiceAddition": false,
  "Properties": [
    {
      "HasCut": true,
      "Occurrence": { "n": 1, "m": 1 },
      "Name": "city",
      "Type": ["tstr"],
      "Comments": []
    },
    {
      "HasCut": true,
      "Occurrence": { "n": 1, "m": 1 },
      "Name": "country",
      "Type": [
        {
          "Type": "group",
          "Name": "",
          "IsChoiceAddition": false,
          "Properties": [
            {
              "HasCut": true,
              "Occurrence": { "n": 1, "m": 1 },
              "Name": "name",
              "Type": ["tstr"],
              "Comments": []
            },
            {
              "HasCut": true,
              "Occurrence": { "n": 1, "m": 1 },
              "Name": "code",
              "Type": ["tstr"],
              "Comments": []
            }
          ],
          "Comments": []
        }
      ],
      "Comments": []
    }
  ],
  "Comments": []
}

By understanding these property reference representations in the AST, you can properly interpret and process CDDL references for further transformation or analysis.

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