GeometryServiceNetworkProtocol

---

The Geometry Service Network (GSNet) Protocol is a TCP/IP based protocol designed to facilitate socketed communications between Geometry Service Nodes on a network. A Geometry Service Node is defined as any softwares that supports communication via the GSNet Protocol.

---

GSNet Msg (Visual) Breakdown

---

GSNet Msg Description

Header

The header of the GSNet Msg contains the information necessary for quickly determining authenticity, type and length. Geometry Service's network library, libNetwork, is built upon BRL-CAD's networking library: libPKG. This causes the header byte layout to look like this:

Element	Length	Value
Magic1	int16 (2 Bytes)	Always 0x41FE
Magic2	int16 (2 Bytes)	Always 0x5309
MessageLength	int32 (4 bytes)	Does *NOT* include the magic or length, so is packet size - 8
MsgType	int16 (2 bytes)
MessageUUID	String (Variable bytes)
HasRegardingUUID	Boolean (1 byte)
RegardingMessageUUID	String (Variable bytes)

libPKG Part

Due to some C and C++ incompatibilities, the libPKG "Type" parameter is used as "Magic2" in the GSNet Protocol. This is due to libPKG's need for each network connection to have a callback table that maps NetMsg types to pointers to the appropriate NetMsg handler function. The GSNetwork library uses a publish/subscription scheme to route NetMsg. LibPKG strips off the libPKG header before calling the appropriate callback function, thus making per class deserialization extremely complex. To address these issues, the GSNetwork library routes NetMsg based on the "GS Msg Type" parameter rather than the "libPKG Type" parameter.

Table showing modifications described above:

libPKG element	GSNet element
Magic	Magic01
Type	Magic02
Length	Length

• Magic01: 2 bytes of data designed to ensure integrity of data and mark NetMsg starting point.
• Magic02: 2 bytes of data designed to ensure integrity of data and mark NetMsg starting point.
• Length: 4 byte integer that represents the number of bytes in the message from the end of this value to the end.

GSNet Part

• MsgType: 2 byte integer value that tells what type of message this is.
• MessageUUID: Standard UUID for this message. Currently stored as a string.
• HasRegardingUUID: Boolean flag that indicates whether there is a Regarding UUID or not.
• RegardingMessageUUID: Standard UUID that indicates this NetMsg is a response to another NetMsg.

---

Data

---

The Data load of a NetMsg is, obivously, the important and unique part. Data Loads can be as small as zero (in the case of a TypeOnlyMsg) or many kilobytes long.

Here is a list of NetMsg types and here is a list of Common NetMsg Exchanges.