DDM Objects (Distributed Data Management)

Inside each DSS frame, DDM objects carry the actual protocol commands and data. DDM uses a recursive TLV (Type-Length-Value) structure.

Object Format

+-------------------------------------+
|  DDM Header (4 bytes)               |
|  +------------+-------------------+ |
|  |  Length     |  Code Point       | |
|  |  2 bytes   |  2 bytes          | |
|  |  (BE)      |  (identifies cmd) | |
|  +------------+-------------------+ |
|  Nested DDM parameters...           |
|  Each parameter:                    |
|    Length (2) + CodePoint (2) + Data |
+-------------------------------------+

Fields

Offset	Size	Field	Description
0	2 bytes	Length	Total object length including header (big-endian)
2	2 bytes	Code Point	Identifies the command or parameter type
4	variable	Data	Nested parameters or raw data

Nested Structure

DDM objects are recursively nested. A command like EXCSAT contains multiple parameters, each with their own length, code point, and value:

EXCSAT (0x1041)
  +-- EXTNAM (0x115E): "db2-node-client"
  +-- SRVNAM (0x116D): "db2-node"
  +-- SRVRLSLV (0x115A): "db2node00100"
  +-- SRVCLSNM (0x1147): "db2-node"
  +-- MGRLVLLS (0x1404):
        +-- AGENT (0x1403): level 7
        +-- SQLAM (0x2407): level 7
        +-- RDB (0x240F): level 7
        +-- SECMGR (0x1440): level 7
        +-- CMNTCPIP (0x1474): level 5

Building DDM Objects

The DDM builder creates properly framed objects:

let excsat = DdmBuilder::new(EXCSAT)
    .add_string(EXTNAM, "db2-node-client")
    .add_string(SRVNAM, "db2-node")
    .add_string(SRVRLSLV, "db2node00100")
    .add_string(SRVCLSNM, "db2-node")
    .add_bytes(MGRLVLLS, &mgrlvlls_bytes)
    .build();

Parsing DDM Objects

Parsing walks the byte buffer, reading length + code point pairs:

let ddm = DdmObject::parse(&bytes)?;
assert_eq!(ddm.code_point, EXCSAT);

for param in ddm.parameters() {
    match param.code_point {
        EXTNAM => { /* handle external name */ }
        SRVNAM => { /* handle server name */ }
        MGRLVLLS => { /* handle manager levels */ }
        _ => { /* unknown parameter, skip */ }
    }
}

Manager Level List (MGRLVLLS)

The MGRLVLLS parameter is specially encoded as pairs of (code_point: u16, level: u16):

MGRLVLLS data:
  0x1403 0x0007   -- AGENT level 7
  0x2407 0x0007   -- SQLAM level 7
  0x240F 0x0007   -- RDB level 7
  0x1440 0x0007   -- SECMGR level 7
  0x1474 0x0005   -- CMNTCPIP level 5

These levels negotiate protocol capabilities between client and server. Higher levels enable newer features.