I’m attempting to write a LAN edge driver where the device broadcasts a message over UDP whenever its state changes. However, I’m struggling to even get the UDP socket to receive messages when running on the hub. When I run basically the same code locally, it seems to work as I would expect.
Here is my listener code.
local udp = socket.udp()
assert(udp:setoption('broadcast', true)) -- Is this needed just for listening?
assert(udp:settimeout(2))
assert(udp:setsockname('*', 0)) -- Would love to specify port but I can't
local _, p = udp:getsockname() -- Instead, for now, grab the port that was assigned for testing purposes
log.debug('Listening on port ' .. p .. '...')
while true do
local data, ip, port = udp:receivefrom()
log.debug('Received from ' .. tostring(ip) .. ':' .. tostring(port) .. ' ' .. tostring(data))
end
When running on the hub, I only receive a message if I send a UDP message to the hub’s IP address and the generated port. If I send it to the broadcast IP (255.255.255.255) on the generated port, the message doesn’t show up. But, if I run locally on my machine, I get messages sent to either that machine IP or the broadcast IP.
It seems that when running on the hub, broadcast messages are ignored. Is this expected? Am I doing this all wrong?
Bonus question: Is there no way around passing 0 as the port number? Alternatively, is it possible to listen for UDP messages on all ports (this is a reach, I know).