Encoding rules of YANG instance-identifier in the Concise Binary Object Representation (CBOR)

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Table of Contents

1. Introduction

The [RFC9254]: Encoding Rules of Data Modeled with YANG in the Concise Binary Object Representation (CBOR) defines rules for representing of YANG-modeled data [RFC7950] in CBOR [RFC8949]. The instance-identifier YANG data type is well-defined for instances that reference containers, lists with one or more keys, and leafs. The document fails to address cases when the instance-identifier instance points to entries in a list with no keys or a leaf-list. The YANG-CBOR refines encoding rules of two kinds. One variant, named as using names, is compatible with YANG-JSON [RFC7951] encoding. The second variant uses SIDs to compress the information needed to encode the instance-identifier. Only the SID-based encoding rules are incomplete. This documents aims to define the missing rules and to clarify the terminology used.¶

2. Terminology and Notation

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

The following terms are defined in [RFC7950]:¶

• list¶

• leaf-list¶

• leaf¶

• container¶

• instance-identifier¶

The following term is defined in [RFC8949]:¶

• data item¶

The following terms are defined in [RFC9254]:¶

• YANG Scheme Item iDentifier (YANG SID, or simply SID)¶

• delta (of YANG SIDs)¶

• absolute SID¶

The following terms are defined in [RFC9595]:¶

• item¶

Keyless list:

Is config false YANG list without any keys.¶

Keyed list:

Is YANG list that is not a keyless list. It is either a config true list or a config false list with at least one key. Note that a config true list must have at least one key.¶

3. Representing SIDs as YANG instance-identifier in CBOR

container system {
  ...
  leaf reporting-entity {
    type instance-identifier;
  }
}

// in module isis
container adjacencies {
  config false;
  list adjacency {
    leaf neighbor-sysid {  // SID 68000
      type string;
    }
    leaf more-data {
      type binary;
    }
  }
}

82              # array(2)
   1A 000109A0  # 68000
   02           # 2

container auth {
  leaf-list foreign-user { // SID 60000
    type string;
  }
}

82               # array(2)
   19 F6F6       # unsigned(60000)
   65            # text(5)
      616c696365 # "alice"

list user-group {
  config true;
  key "group-name"

  leaf group-name {
    type string;
  }

  leaf-list user { // SID 61000
    type string;
  }
}

83                         # array(3)
   19 EE48                 # 61000
   6A                      # text(10)
      72657374726963746564 # "resricted"
   63                      # text(3)
      657665               # "eve"

83                         # array(3)
   19 EE48                 # 61000
   6A                      # text(10)
      72657374726963746564 # "resricted"

list working-group {
  leaf name {
    type string;
  }

  leaf-list chair { // SID 62000
    type instance-identifier;
  }
}

83                                        # array(3)
   19 F230                                # 62000
   64                                     # text(4)
      636F7265                            # "core"
   82                                     # array(2)
      19 F6F6                             # 60000
      6F                                  # text(15)
         4361727374656E20426F726D616E6E   # "Carsten Bormann"

list device {
  key "id";

  leaf id {
    type string;
  }

  list security {
    config false;

    list user {
      key "name";
      leaf name;

      list access-token {
        leaf type {
          type identityref { base token; }
        }
        leaf token-data { // SID 61500
          type binary;
        }
      }
    }
  }
}

identity token;

84             # array(4)
   19 F03C     # 61500
   64          # text(4)
      69643031 # "id01"
   01          # 1
   63          # text(3)
      626F62   # "bob"
   02          # 2

4. Content-Types

TODO Is it possible to reuse the Content-types define in the [RFC9254]? It would be wasteful to assign new MIME content-type to basically the same format.¶

5. Security Considerations

The security considerations of [RFC8949], [RFC7950], [RFC9254] and [RFC9595] apply.¶

The implementations should be aware of possibly very large recursive nesting that occurs when instance-identifiers are chained.¶

TODO Security¶

6. IANA Considerations

This document has no IANA actions.¶

TODO Is it possible to keep the same IANA allocations of th [RFC9254]? This draft wants to be more of a bugfix document than new encoding scheme.¶

7. References

Acknowledgments

TODO acknowledge. thank Andy Bierman for his friendly responses on mailing list.¶

Author's Address