Revision as of 11:14, 24 January 2011 by Dloman (talk | contribs) (More details in libPKG header part.)

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


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)
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


List of NetMsgTypes.

List of Common NetMsg Exchanges