Reading REMOTE_IP on UDP socket crashes xsbug (and possibly the whole program)

[JanVanBraeckel]

Build environment: Windows
Target device: NodeMCU ESP8266

Description
Creating a UDP socket and reading the "REMOTE_IP" of an incoming connection crashes xsbug. It possibly also crashes the whole program, but since the debugger crashes I can't strep through to check it.

Console output:

Exception (28):
epc1=0x40252b4b epc2=0x00000000 epc3=0x00000000 excvaddr=0x00000004 depc=0x00000000
NMAKE : fatal error U1077: '%MODDABLE%\build\bin\win\release\serial2xsbug.EXE' : return code '0xc0000005'
Stop.

main.js:

import { Socket } from "socket";

new Socket({
  port: 8266,
  kind: "UDP",
}).callback = function () {
  trace(this.get("REMOTE_IP"));
};

manifest.json:

{
  "include": [
    "$(MODDABLE)/examples/manifest_base.json",
    "$(MODDABLE)/examples/manifest_net.json"
  ],
  "modules": {
    "*": [
      "./main",
      "$(MODULES)/network/http/*",
    ],
  },
  "preload": [
    "http",
  ],
}

Python test script:

import socket

def main():
  remote_address = ('%addr%', 8266)
  message = 'test'
  sock2 = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
  sock2.sendto(message.encode(), remote_address)
  sock2.settimeout(10)
  

if __name__ == '__main__':
  main()

Steps to Reproduce

1. Set up a program with a UDP socket where the callback tries to read the "REMOTE_IP"
2. Try to open the socket via an external program, for example a python script
3. See error

Expected behavior
I can read the REMOTE_IP and store it in a variable so I can include it in the Socket.write() method

[phoddie]

The way to retrieve the IP address of the remote is different for TCP and UDP sockets.

For a TCP socket, the remote IP address never changes during the lifetime of the connection It is available with this.get("REMOTE_IP").

For a UDP sockets, the remote IP address may be different for each packet received. Therefore, remote IP address is passed as an argument to the callback. The callback arguments for a UDP packet are:

callback(message, value, address, port)

The remote IP address is in address and the sending port is in port. You can see an example of this used in the mDNS implementation.

That said, calling this.get("REMOTE"_IP") on a TCP socket shouldn't crash. I'll fix that to return undefined in that case. It also looks like the documentation for Socket doesn't document most of this, so I'll update that as well.

[JanVanBraeckel]

Oh I see!

I indeed failed to check if there were any extra arguments passed to the callback, since the documentation didn't mention any difference for the callback of a UDP socket.

I was searching and found this little snippet, so I thought I had found what I needed:

moddable/modules/network/socket/lwip/modSocket.c

Line 442 in 5639abb

if (0 == c_strcmp(name, "REMOTE_IP")) {

Thank you so much for the quick response, I love the work you are all doing on this project and hope to be able to contribute in the near future ☺