NodeMCU crashes when attempting to call net.socket:connect() - sockets

Question

I am attempting to send a broadcast packet to a certain port, but it seems that the code gives some weird errors for which I can't find a fix.
I've tried using net.socket:connect() and then calling the "send()" method, which didn't work, then I said that I should use the net.socket:on('connection') and send there, since I suppose net.socket:connect() isn't synchronous. But that gave a weird error too...
For this code:
function sendBroadcastPacket()
bip = wifi.sta.getbroadcast()
srv = net.createConnection(net.UDP,0)
print('Trying to connect on: ', bip)
srv:connect('9001', bip)
srv:send("Broadcast packet from: "..NODE_ID, function(sent)
print("Broadcasted packet! "..sent)
end)
end
I receive the following error:
PANIC: unprotected error in call to Lua API (init.lua:24: attempt to
call method 'connect' (a nil value))
Line 24 is the srv:connect line.
After that I tried listening for the connection event first, to see if it worked that way:
function sendBroadcastPacket()
bip = wifi.sta.getbroadcast()
srv = net.createConnection(net.UDP,0)
print('Trying to connect on: ', bip)
srv:on('connection', function(sck, c)
sck:send("Broadcast packet from: "..NODE_ID, function(sent)
print("Broadcasted packet! "..sent)
end)
end)
srv:connect('9001', bip)
end
I receive the following error:
PANIC: unprotected error in call to Lua API (init.lua:24: invalid
callback name)
Line 24 is the srv:on('connection') line.
What seems to be happening here? There aren't many google results, since a lot of other people use the Arduino-IDE version(btw, is that still nodemcu or do you need a different firmware for the ESP8266?).
I am getting a broadcast IP, and it connects to the AP. I didn't post here the wifi connection part because it works, I've used it to test mqtt and http connections which worked.
The build I'm using, Lua 5.1.4 on SDK 2.1.0(116b762), has the net module included.

Answer 1

Your attempts all failed because you don't seem to consider that UDP is a connection-less protocol. Hence, there's no connect() or on('connection'... for UDP.
The first attempt failed because send() needs to be called on a socket and not on the connection. The second failed because the connection callback name is only available for TCP, not for UDP.
Try something like this:
function sendBroadcastPacket()
local port = 9001
local bip = wifi.sta.getbroadcast()
print(string.format("Broadcasting to %s:%d", bip, port))
net.createUDPSocket():send(port, bip, "foo bar")
end
Documentation: https://nodemcu.readthedocs.io/en/latest/en/modules/net/#netudpsocket-module