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Add CRC32 at the end of a transfer and demark the payload as a field #6

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merged 2 commits into from
Jun 8, 2023
Merged

Add CRC32 at the end of a transfer and demark the payload as a field #6

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fe96182
Add CRC32 at the end of a transfer and demark the payload as a field
emrainey Jun 7, 2023
85b4cb7
Adding separate sections for header/payload/footer
emrainey Jun 8, 2023
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58 changes: 37 additions & 21 deletions cyphal_udp.lua
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The version is only 4 bits. The following 4 bits are reserved.

Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@

-- Protocol constants
local CYPHAL_UDP_PORT = 9382 -- The port number used by Cyphal/UDP

local CYPHAL_UDP_HEADER_SIZE = 24 -- The sizeof the Cyphal/UDP Header
-- Custom protocol dissector
local cyphal_udp = Proto("cyphaludp", "Cyphal/UDP Protocol 1.0 beta")

Expand All @@ -23,7 +23,10 @@ frame_index_eot = ProtoField.uint32("cyphal_udp.frame_index_eot", "frame_index_e
frame_index = ProtoField.uint32("cyphal_udp.frame_index", "frame_index", base.DEC)
end_of_transfer = ProtoField.bool("cyphal_udp.end_of_transfer", "end_of_transfer", base.NONE)
user_data = ProtoField.uint16("cyphal_udp.user_data", "user_data", base.HEX)
crc16_ccitt_false = ProtoField.uint16("cyphal_udp.crc16_ccitt_false", "crc16_ccitt_false (BE)", base.HEX)
crc16_ccitt_false = ProtoField.uint16("cyphal_udp.crc16_ccitt_false", "CRC16-CCITT-FALSE (BE)", base.HEX)
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It's all upper-case now. Okay. Am I supposed to be impressed?

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All the reference online are in SHOUTY CASE. So I thought I'd SHOUT too.

serialized_payload = ProtoField.bytes("cyphal_udp.serialized_payload", "serialized_payload", base.SPACE)
serialized_payload_size = ProtoField.uint32("cyphal_udp.serialized_payload_size", "serialized_payload_size", base.DEC)
crc32 = ProtoField.uint32("cyphal_udp.crc32", "CRC32-C (LE)", base.HEX)

-- Protocol fields
cyphal_udp.fields = {
Expand All @@ -41,7 +44,10 @@ cyphal_udp.fields = {
frame_index,
end_of_transfer,
user_data,
crc16_ccitt_false
crc16_ccitt_false,
serialized_payload,
serialized_payload_size,
crc32
-- Add more fields as needed
}

Expand All @@ -51,22 +57,25 @@ ipv4_destination_address_field = Field.new("ip.dst")
-- Function to dissect the custom protocol
local function dissect_cyphal_udp(buffer, pinfo, tree)
-- Create a subtree for the custom protocol
local cyphal_udp_tree = tree:add(cyphal_udp, buffer(), "Cyphal/UDP Header")
local metadata_tree = tree:add(cyphal_udp, buffer(), "Cyphal/UDP Metadata")
local header_tree = tree:add(cyphal_udp, buffer(), "Cyphal/UDP Header")
local payload_tree = tree:add(cyphal_udp, buffer(), "Cyphal/UDP Payload")
local footer_tree = tree:add(cyphal_udp, buffer(), "Cyphal/UDP Footer")

if (ipv4_source_address_field()) then
local ip_src = ipv4_source_address_field().value
cyphal_udp_tree:add(ipv4_src, ip_src)
metadata_tree:add(ipv4_src, ip_src)
end
if (ipv4_destination_address_field()) then
local ip_dst = ipv4_destination_address_field().value
cyphal_udp_tree:add(ipv4_dst, ip_dst)
metadata_tree:add(ipv4_dst, ip_dst)
end

-- Add fields to the subtree
cyphal_udp_tree:add_le(version, buffer(0, 1))
cyphal_udp_tree:add_le(priority, buffer(1, 1))
cyphal_udp_tree:add_le(source_node_id, buffer(2, 2))
cyphal_udp_tree:add_le(destination_node_id, buffer(4, 2))
header_tree:add_le(version, buffer(0, 1))
header_tree:add_le(priority, buffer(1, 1))
header_tree:add_le(source_node_id, buffer(2, 2))
header_tree:add_le(destination_node_id, buffer(4, 2))
local ds = buffer(6, 2):le_uint()
local port_id = bit.band(ds, 0x7FFF)
local snm = bit.rshift(bit.band(ds, 0x8000), 15)
Expand All @@ -76,23 +85,30 @@ local function dissect_cyphal_udp(buffer, pinfo, tree)
port_id = port_id - 16384
rnr = true
end
cyphal_udp_tree:add_le(request_not_response, rnr)
cyphal_udp_tree:add_le(service_id, port_id)
header_tree:add_le(request_not_response, rnr)
header_tree:add_le(service_id, port_id)
else
cyphal_udp_tree:add_le(subject_id, port_id)
header_tree:add_le(subject_id, port_id)
end
cyphal_udp_tree:add_le(service_not_message, snm)
cyphal_udp_tree:add_le(data_specifier, buffer(6, 2))
cyphal_udp_tree:add_le(transfer_id, buffer(8, 8))
header_tree:add_le(service_not_message, snm)
header_tree:add_le(data_specifier, buffer(6, 2))
header_tree:add_le(transfer_id, buffer(8, 8))
-- process the number as BE
cyphal_udp_tree:add_le(frame_index_eot, buffer(16, 4))
header_tree:add_le(frame_index_eot, buffer(16, 4))
local fi = buffer(16, 4):le_uint()
local fidx = bit.band(fi, 0x7FFFFFFF)
local eot = bit.rshift(bit.band(fi, 0x80000000), 31)
cyphal_udp_tree:add_le(frame_index, fidx)
cyphal_udp_tree:add_le(end_of_transfer, eot)
cyphal_udp_tree:add_le(user_data, buffer(20, 2))
cyphal_udp_tree:add(crc16_ccitt_false, buffer(22, 2))
header_tree:add_le(frame_index, fidx)
header_tree:add_le(end_of_transfer, eot)
header_tree:add_le(user_data, buffer(20, 2))
header_tree:add(crc16_ccitt_false, buffer(22, 2))
local len = buffer:len()
local rem = len - CYPHAL_UDP_HEADER_SIZE - 4 -- the remaining bytes minus CRC32C
if rem > 0 then
payload_tree:add_le(serialized_payload_size, rem)
payload_tree:add_le(serialized_payload, buffer(24, rem))
end
footer_tree:add_le(crc32, buffer(len-4, 4))
-- Add more field dissectors as needed
end

Expand Down