node_udp_receiver.js

import dgram from 'dgram';

const PCAP_HEADER_PREFIX = Buffer.from("d4c3b2a1020004000000000000000000", "hex");

let ret = { offset: 0 };
const socket = dgram.createSocket({ type: 'udp4', reuseAddr: true });
socket.bind(1234);

socket.on('message', (msg, rinfo) => {
  if ((msg.length === 24) &&
      (msg.slice(0, PCAP_HEADER_PREFIX.length).equals(PCAP_HEADER_PREFIX))
  ) {
    console.log("Ignoring PCAP header (start of PCAP)");
    return;
  }

  if (msg.length < 16) {
    console.log("Ignoring bad PCAP record");
    return;
  }

  // skip the PCAP record, go to the IP header
  const data = msg.slice(16);
  ret = decoders.IPV4(data, ret.offset);
  console.log('ip', ret)

  ret = decoders.UDP(data, ret.offset);
  console.log('udp', ret)

  if (ret.info.protocol === PROTOCOL.UDP) {
    console.log("TODO handle UDP");
  }
});