Data Messages
Data messages carry application-specific data defined by a DML Protocol. However, DML as a serialization system is not inherently related to the framing protocol itself, and should be considered a separate entity which is chosen due to its flexibility.
Along with the encoded DML payload, a small header provides the metadata needed for the peer to understand the message.
The "message" terminology can either stand for a data message as part of the framing protocol, which is documented here, or a DML message as a data structure encoded inside a data message. These are not to be confused with each other, see Data Management Layer for more details on the serialization system.
Structure
An encoded message always follows a fixed structure. The opcode in the
frame body is always set to 0 for data messages.
| Offset | Type | Description |
|---|---|---|
| 0x0 | uint8 | The service ID the message belongs to |
| 0x1 | uint8 | The order number within the protocol |
| 0x2 | uint16 | The length of the entire DML message data, including this header |
| 0x4 | uint8[len] | The serialized DML message data |
len | uint8 | Trailing null byte; not considered by the length field |