Re: [dtn] BPv7 CDDL and CBOR tagging

[Brian Sipos <[e-mail]>]

Scott,
At the bottom of this email is a full CDDL that captures both the
encodings of extension / administrative data as well as the binding
between extension data types and extension block numbers.
I also added restrictions on CRC type code and CRC value data, and used
the socket convention and the "-structure" convention from the pre-RFC
CDDL draft.

I'll leave up to you to decide if this is an over-specialized use of
CDDL. Using the reference "cddl" program to generate randomized data
actually produces near-to-reasonable bundles to my eye, which is nice
validation of the CDDL itself.

The reference program can be tested as in:
$ gem install cddl
$ cddl bpv7.cddl.txt generate 
[[7, 17174, 0, [2, [3026, 451]], [1, 0], [2, [535, 2091]], [4044,
2891], 1070, h'FCDD'], [8, 2593, 229, 2, h'190836', h'C4F3'], [7, 2533,
177, 2, h'820100', h'0504'], [8, 3239, 179, 2, h'1850'], [8, 398, 237,
2, h'183E', h'31261138'], [1, 0, 175, 0,
h'8201848481F581F481F481F51901C6820166766F6C75707482190704190CDA',
h'AFA5']]

One issue that I ran into when testing this: I used this CDDL to
validate some test bundles which I had been generating separately to
test the TCPCL agent. The original CDDL in the draft contains the field
name "total-application-data-length" which also appears several times
in the draft as "total application data unit length" in the statments.
But I don't see that field listed in Section 4.2.2. Is there a missing
field in that section, or is that field no longer present and the other
text is inaccurate?

Thanks,
Brian S.

On Tue, 2019-04-09 at 01:24 +0000, Burleigh, Scott C (312B) wrote:
> Guys, please feel free to send me an updated CDDL expression of
> Bundle Protocol version 7; I will gladly include it in the document.
> 
> My one comment is that the type dtn-time is correctly defined as
> uint; it should NOT be changed to int, as negative values are not
> allowed.  If you can spot an instance in the spec where dtn-time is
> characterized as a signed integer, please let me know and I will
> correct it.
> 
> Scott

start = bundle / #6.55799(bundle)

; Times before 2000 are invalid
dtn-time = uint

; CRC enumerated type
crc-type = 0 / 1 / 2
; Either 16-bit or 32-bit
crc-value = (bstr .size 2) / (bstr .size 4)

creation-timestamp = [dtn-time, sequence: uint]

eid = $eid-choice .within eid-structure
eid-structure = [
  uri-code: uint,
  SSP: any
]
$eid-choice /= [
  uri-code: 1,
  SSP: (tstr / 0)
]
$eid-choice /= [
  uri-code: 2,
  SSP: [
    nodenum: uint,
    servicenum: uint
  ]
]

bundle-control-flags = uint .bits bundleflagbits
bundleflagbits = &(
  reserved: 15
  reserved: 14
  reserved: 13
  bundle-deletion-status-reports-are-requested: 12
  bundle-delivery-status-reports-are-requested: 11
  bundle-forwarding-status-reports-are-requested: 10
  reserved: 9
  bundle-reception-status-reports-are-requested: 8
  bundle-contains-a-Manifest-block: 7
  status-time-is-requested-in-all-status-reports: 6
  user-application-acknowledgement-is-requested: 5
  reserved: 4
  reserved: 3
  bundle-must-not-be-fragmented: 2
  payload-is-an-administrative-record: 1
  bundle-is-a-fragment: 0
)

block-control-flags = uint .bits blockflagbits
blockflagbits = &(
  reserved: 7
  reserved: 6
  reserved: 5
  reserved: 4
  bundle-must-be-deleted-if-block-cannot-be-processed: 3
  status-report-must-be-transmitted-if-block-cannot-be-processed: 2
  block-must-be-removed-from-bundle-if-it-cannot-be-processed: 1
  block-must-be-replicated-in-every-fragment: 0
)

bundle = [primary-block, *extension-block, payload-block]

primary-block = [
  version: 7,
  bundle-control-flags,
  crc-type,
  destination: eid,
  source-node: eid,
  report-to: eid,
  creation-timestamp,
  lifetime: uint,
  ? (
    fragment-offset: uint,
;    total-application-data-length: uint,
  )
  ? crc-value,
]

; Abstract shared structure of all non-primary blocks
canonical-block-structure = [
  block-type-code: uint,
  block-number: uint,
  block-control-flags,
  crc-type,
  ; Each block type defines the content within the bytestring
  block-type-specific-data,
  ? crc-value
]
block-type-specific-data = bstr / #6.24(bstr)
; Extension block type, which does not specialize any more than the
code/number
extension-block = $extension-block-structure .within canonical-block-
structure
$extension-block-structure = [
  block-type-code: (uint .gt 1),
  extension-block-number,
  block-control-flags,
  crc-type,
  ($extension-block-data .within block-type-specific-data)
  ? crc-value
]
extension-block-number = (uint .ne 0)
; Payload block type
payload-block = payload-block-structure .within canonical-block-
structure
payload-block-structure = [
  block-type-code: 1,
  block-number: 0,
  block-control-flags,
  crc-type,
  ($payload-block-data .within block-type-specific-data)
  ? crc-value
]

; Arbitrary payload data
$payload-block-data /= bstr


; Administrative record as a payload data specialization
$payload-block-data /= block-type-specific-data .cbor admin-record
admin-record = $admin-record .within admin-record-structure
admin-record-structure = [
  record-type-code: uint,
  record-content: any
]
; Only one defined record type
$admin-record /= [1, status-record-content]
status-record-content = [
  bundle-status-information,
  status-report-reason-code: uint,
  source-node-eid: eid,
  subject-creation-timestamp: creation-timestamp,
  ? (
    subject-payload-offset: uint,
    subject-payload-length: uint
  )
]
bundle-status-information = [
  reporting-node-received-bundle: status-info-content,
  reporting-node-forwarded-bundle: status-info-content,
  reporting-node-delivered-bundle: status-info-content,
  reporting-node-deleted-bundle: status-info-content
]
status-info-content = [
  status-indicator: bool,
  ? timestamp: dtn-time
]

; Previous Node extension block
$extension-block-structure /= [
  block-type-code: 7,
  extension-block-number,
  block-control-flags,
  crc-type,
  (block-type-specific-data .cbor ext-data-previous-node)
  ? crc-value
]
ext-data-previous-node = eid

; Bundle Age extension block
$extension-block-structure /= [
  block-type-code: 8,
  extension-block-number,
  block-control-flags,
  crc-type,
  (block-type-specific-data .cbor ext-data-bundle-age)
  ? crc-value
]
ext-data-bundle-age = uint

; Hop Count extension block
$extension-block-structure /= [
  block-type-code: 9,
  extension-block-number,
  block-control-flags,
  crc-type,
  (block-type-specific-data .cbor ext-data-hop-count)
  ? crc-value
]
ext-data-hop-count = [
  hop-limit: uint,
  hop-count: uint
]