Message Protocol

This section descbribes the DPS message protocol encodings. DPS messages are encoded in CBOR.

DPS Message types

DPS has four messages types.

message = pub / sub / ack / sak

Common types

These are types common across the various message types.

UUID

UUIDs identify publications and are also used as key identifiers for encrypted messages.

uuid = bstr .size 16

Bit vector control flags

Bits vectors are usually run-length encoded unless the raw unencoded bit vector is more compact than the rle-encoded representation. The rle-encoded flag indicates if the bit vector is encoded or raw.

The rle-complement flags indicates if the complement of the bit vector was was encoded. The bit vector complement is encoded if this results in a more compact encoding. This flag is only useful with run-length encoding.

bit-vector-flags = &(
  rle-encoded: 1,
  rle-complement: 2
)

Bit vector encoding

The bit vector encoding includes control flags, the bit vector length expressed in bits and the raw or run-length encoded bit vector data.

bit-vector = [
  flags: uint .bits bit-vector-flags, ; # bit vector control flags
  len: uint,                          ; # bit vector length in bits
  bits: bstr                          ; # raw or rle-encoded bit vector
]

### Subscription flags

sub-flags = &(
  delta: 1,        ; # indicate interests is a delta
  mute: 2          ; # mute has been indicated
)

Header field member keys.

For compactness the member keys are encoded as integers as listed below.

header-field = (
  ? 1 => uint,        ; # port number sender is listening on
  ? 2 => int,         ; # ttl - time to live in seconds
  ? 3 => uuid,        ; # pub-id - unique indentifier for a publication
  ? 4 => uint,        ; # seq-num - sequence number for a publication
  ? 5 => bool,        ; # ack-req - indicates if an publisher is requesting an acknowledgement
  ? 6 => bit-vector,  ; # bloom-filter -the bloom filter for a publication
  ? 7 => sub-flags,   ; # sub-flags - indicates delta or mute
  ? 8 => uuid,        ; # mesh-id - the mesh ID
  ? 9 => bit-vector,  ; # needs - the needs bit vector
  ? 10 => bit-vector  ; # interests - the interests bit vector
)

DPS message types

Publication message encoding

The encoding of a publication.

pub = [
  type: 1,
  headers: { * header-field }, ; # port, ttl
  body: { * header-field },    ; # ttl, pub-id, seq-num, ack-req, bloom-filter
  payload: [
    topics: [ + topic: tstr ]
    payload: bstr
  ]
]

Subscription message encoding

The encoding of a subscription.

sub = [
  type: 2,
  headers: { * header-field }, ; # port, seq-num
  body: { * header-field }     ; # sub-flags, mesh-id, needs, interests or empty for unlink
]

Acknowledgement message encoding

The encoding of an acknowledgement message.

ack = [
  type: 3,
  body: { * header-field },    ; # pub-id, seq-num
  payload: bstr
]

Subscription acknowledgement message encoding

The encoding of a subscription acknowledgement message.

sak = [
  type: 4,
  headers: { * header-field }  ; # port, seq-num
]