We have our own protocol for communication between devices. It is based on protobuf structures over websocket.
PacketMessage.proto :
syntax = "proto3"; package pb_pm;
enum BodyType { BodyType_UNSPECIFIED = 0; RESPONSE = 1; HANDSHAKE = 2; V2X = 3; RTK = 4; SYSTEM = 5; }
enum BodyCompressType { BodyCompressType_UNSPECIFIED = 0; NONE = 1; LZMA = 2; }
message PacketMessage {
optional uint32 messageId = 1; /** [0 - 2^32] */
reserved 2;
BodyCompressType bodyCompressType = 3;
BodyType bodyType = 4;
bytes body = 5;
}
handshake.proto :
syntax = "proto3";
package pb_hs;
message Handshake { fixed32 protocolVersion = 1; string hostname = 2; string mac = 3; }
v2x.proto:
syntax = "proto3";
package pb_v2x;
import "V2X/Facility/Facility.proto";
import "V2X/Fluent/Fluent.proto";
message V2X { reserved 1 to 2, 5; oneof v2x { fac.Facility facility = 3; fl.Fluent fluent = 4; } }
I wrote some lua dissectors, and it works fine for one type of body field:
do
local protobuf_dissector = Dissector.get("protobuf")
local proto = Proto("tedix", "TEDIX Protocol")
proto.dissector = function(tvb, pinfo, tree)
local subtree = tree:add(proto, tvb())
if "pb_pm.PacketMessage" ~= nil then
pinfo.private["pb_msg_type"] = "message," .. "pb_pm.PacketMessage"
end
pcall(Dissector.call, protobuf_dissector, tvb, pinfo, subtree)
end
local ws_dissector_table = DissectorTable.get("ws.port")
ws_dissector_table:add(7246, proto)
end
do
local protobuf_field_table = DissectorTable.get("protobuf_field")
local message_type_dissector = Dissector.get("protobuf")
proto_messge_type_V2X = Proto("message_type_dissector", "V2X")
proto_messge_type_V2X.dissector = function(tvb, pinfo, subtree)
pinfo.cols.protocol = proto_messge_type_V2X.name
local subsubtree = subtree:add(proto_messge_type_V2X, tvb())
if "pb_v2x.V2X" ~= nil then
pinfo.private["pb_msg_type"] = "message," .. "pb_v2x.V2X"
end
pcall(Dissector.call, message_type_dissector, tvb, pinfo, subsubtree)
end
protobuf_field_table:add("pb_pm.PacketMessage.body", proto_messge_type_V2X)
end
The protocol consists of several nested proto structures. Moreover, it is implied that, depending on the BodyType field, there will be different filling of the body field. for example, there may be a message like V2X or Handshake.
How can I write a dissector for such a protocol?
How to get the value of the BodyType field inside the Lua dissector to call different dissectors of the body field?
