sd_entries.lua

-- File : sd_entries.lua
-- Who  : x-Felix-x
-- Based on: https://github.com/jamores/eth-ws-someip/blob/master/sd_entries.lua
-- What : SD subdissector in charge of parsing Entries within at EntriesArray
--
local p_sd_ents = Proto("sd_entries", "sd_entry")

local f_e_type      = ProtoField.uint8("sd.e.type", "Type", base.HEX)
local f_e_o1_i      = ProtoField.uint8("sd.e.opt1_i", "Index 1st options", base.HEX)
local f_e_o2_i      = ProtoField.uint8("sd.e.opt2_i", "Index 2nd options", base.HEX)
local f_e_o1_n      = ProtoField.uint8("sd.e.opt1_n", "# opt 1", base.HEX, nil, 0xf0)
local f_e_o2_n      = ProtoField.uint8("sd.e.opt2_n", "# opt 2", base.HEX, nil, 0x0f)
local f_e_srv_id    = ProtoField.uint16("sd.e.srv_id", "Service ID", base.HEX)
local f_e_inst_id   = ProtoField.uint16("sd.e.inst_id", "Instance ID", base.HEX)
local f_e_v_major   = ProtoField.uint8("sd.e.v_major", "MajorVersion", base.HEX)
local f_e_ttl       = ProtoField.uint24("sd.e.ttl", "TTL", base.DEC)
local f_e_v_minor   = ProtoField.uint32("sd.e.v_minor", "MinorVersion", base.HEX)
local f_e_cnt       = ProtoField.uint8("sd.e.cnt", "Counter", base.DEC)
local f_e_egrp_id   = ProtoField.uint8("sd.e.egrp_id", "EventGroup_ID", base.HEX)

local e_types = {
    [0] = "FIND_SERVICE",   -- 0x00
    [1] = "OFFER_SERVICE",  -- 0x01
    [6] = "SUBSCRIBE",      -- 0x06
    [7] = "SUBSCRIBE_ACK"   -- 0x07
}

p_sd_ents.fields = {f_e_type, f_e_o1_i, f_e_o2_i, f_e_o1_n, f_e_o2_n, f_e_srv_id, f_e_inst_id, f_e_v_major, f_e_ttl, f_e_v_minor, f_e_cnt, f_e_egrp_id}

function p_sd_ents.dissector(buf, pinfo, root)
    local offset = 0

    -- length of EntriesArray
    local e_len = buf(offset, 4):uint()
    offset = offset + 4

    -- parse entries  (NOTE : some extra variables to easen understanding)
    local e_len_parsed = 0
    while e_len_parsed < e_len do
        local i_parse = parse_entries(root, buf(offset, (e_len-e_len_parsed)))
        e_len_parsed = e_len_parsed + i_parse
        offset = offset + i_parse
    end
end

function is_entry_service(type_u8)
    -- TODO : remove this magic numbers
    if ((type_u8 == 0x00) or (type_u8 == 0x01)) then
        return true
    else
        return false
    end
end

function parse_entries(subtree, buf)
    local offset = 0

    local e_subtree = subtree:add(p_sd_ents)
    --Type
    local type_tree = e_subtree:add(f_e_type, buf(offset, 1))
    local type_u8 = buf(offset, 1):uint()
    if e_types[type_u8] ~= nil then
        type_tree:append_text(" (" .. e_types[type_u8] .. ")") 

        -- also update "root" with entry type
        e_subtree:append_text(" : " .. e_types[type_u8])
    else
        type_tree:append_text(" (type unknown)") 
    end
    offset = offset + 1

    -- Index 1st options
    e_subtree:add(f_e_o1_i, buf(offset, 1))
    offset = offset + 1
    -- Index 2nd options
    e_subtree:add(f_e_o2_i, buf(offset, 1))
    offset = offset + 1

    -- Num of opt 1 (NOTE : no increase in offset position, 4bit field)
    e_subtree:add(f_e_o1_n, buf(offset, 1))
    -- Num of opt 2
    e_subtree:add(f_e_o2_n, buf(offset, 1))
    offset = offset + 1

    -- ServiceID
    e_subtree:add(f_e_srv_id, buf(offset, 2))
    offset = offset + 2
    -- InstanceID
    e_subtree:add(f_e_inst_id, buf(offset, 2))
    offset = offset + 2

    -- Major version
    e_subtree:add(f_e_v_major, buf(offset, 1))
    offset = offset + 1 
    -- TTL
    e_subtree:add(f_e_ttl, buf(offset, 3))
    offset = offset + 3 

    -- SERVICE / EVENTGROUP entries
    if is_entry_service(type_u8) then
        -- SERVICE
        -- Minor Version
        e_subtree:add(f_e_v_minor, buf(offset, 4))
        offset = offset + 4
    else
        -- EVENTGROUP
        -- Counter
        offset = offset +1 -- skip reserved
        e_subtree:add(f_e_cnt, buf(offset, 1))
        offset = offset + 1

        -- EventGroup ID
        e_subtree:add(f_e_egrp_id, buf(offset, 2))
        offset = offset + 2
    end

    return offset
end