1.datagram的UDP插件

npm i cordova-plugin-datagram4

https://www.npmjs.com/package/cordova-plugin-datagram4

var datagram = cordova.require("cordova-plugin-datagram4.datagram");
var socket = datagram.createSocket("udp4");
var myPort = 3000;
var targetPort = 3001;
var targetIp = "target device ip";

socket.bind(listenPort, function(data) {
  alert("bind \n" + JSON.parse(data));
});

socket.on("message", function(data, info) {
  console.log(data + " / " + JSON.stringify(info));
});

var button = document.getElementById("button");
button.addEventListener(button, "click", function() {
  var message = "HelloWorld";
  if (message.length > 20480) {
    alert("Too large!");
    return;
  }
  socket.send(message, targetIp, targetPort, function() {
    alert("done");
  });
});

很遗憾，这个插件不支持16进制收发

2.谷歌API

因UDP通信已被谷歌废弃，需要NPM：

npm i cordova-plugin-chrome-apps-sockets-udp

function convertStringToArrayBuffer(str) {//将字符串转化成buffer用于串口数据发送
	var buf = new ArrayBuffer(str.length);// (str.length+1)增加一位来放回车符
	var bufView = new Uint8Array(buf);
	for (var i = 0; i < str.length; i++) {
		bufView[i] = str.charCodeAt(i);
	}
	// bufView[str.length] = 13;//最后一位为回车符的ascii码
	return buf;
};
function convertArrayBufferToString(buf) {//将串口接收到的buffer数据转化成字符串
	var bufView = new Uint8Array(buf);
	var encodedString = String.fromCharCode.apply(null, bufView);
	// document.write(iconv.decode(encodedString, 'gbk'));
	// return iconv.decode(encodedString, 'gbk');
	return encodedString;
}


// 被谷歌浏览器废弃的UDP-API

var socketId;
// Handle the "onReceive" event.
var onReceive = function (info) {
	// if (info.socketId !== socketId)
	//   return;
	$('body').append('11411.data: ' + convertArrayBufferToString(info.data) + '<br>')
};

// Create the Socket
chrome.sockets.udp.create({ name: "why" }, function (socketInfo) {
	socketId = socketInfo.socketId;
	// Setup event handler and bind socket.
	chrome.sockets.udp.onReceive.addListener(onReceive);
	chrome.sockets.udp.bind(socketId, "0.0.0.0", 11411, function (result) {
		if (result < 0) {
			console.log("Error binding socket..................");
			return;
		}
		chrome.sockets.udp.send(socketId, convertStringToArrayBuffer('send data'),
			'192.168.1.108', 1337, function (sendInfo) {
				console.log("sent " + sendInfo.bytesSent);
			});

	});
});

注意：模拟器里占用的端口号是随机的，只有部署安装版才正常（踩过的坑！）

convertStringToArrayBuffer(str)
convertArrayBufferToString(buf)

发现这个曾经在node.js使用的16进制Buffer互转方法在capacitor里不好用！！！

在网上找了好久才找到新方法：

function buf2hex(buffer, space) { // buffer is an ArrayBuffer
	return Array.prototype.map.call(new Uint8Array(buffer), x => ('00' + x.toString(16)).slice(-2)).join(space);
}

function hex2buf(key, space) {
	key = '0x' + key.replace(new RegExp(space, 'g'), ',0x');
	return new Uint8Array(key.split(",")).buffer;
}

var socketId;
var onReceive = function (info) {
	$('body').prepend('IP:' + info.remoteAddress + ' Port:' + info.remotePort + '<br>' + buf2hex(info.data, ' ') + '<br>')
};

// Create the Socket
chrome.sockets.udp.create({ }, function (socketInfo) {
	socketId = socketInfo.socketId;
	// Setup event handler and bind socket.
	chrome.sockets.udp.onReceive.addListener(onReceive);
	chrome.sockets.udp.bind(socketId, "0.0.0.0", 11411, function (result) {
		if (result < 0) {
			console.log("Error binding socket..................");
			return;
		}
		chrome.sockets.udp.send(socketId, hex2buf('FE 0F 00 00 00 08 01 FF F1 D1', ' '),
			'192.168.1.108', 60000, function (sendInfo) {
				console.log("sent " + sendInfo.bytesSent);
			});

	});
});

这里的需求时将 FE 0F 00 00 00 08 01 FF F1 D1 字符串发送和收到此类型的16进制，发送时需要分割加0x转Buffer发送。

hex2buf(key, space)

也就是转为 new Uint8Array([ 0xFE, 0x0F, 0x00, 0x00, 0x00, 0x08, 0x01, 0xFF, 0xF1, 0xD1 ]).buffer

buf2hex(buffer, space)

接收时又需要分割成字符串。

最后发现，发送时只需Buffer.from()

chrome.sockets.udp.send(socketId, Buffer.from("3C-7C-3F-12-F8-FE".replace(/-+|\s+/g, ""), "hex"),
    '192.168.1.10', 10101, function (sendInfo) {
    console.log("sent " + sendInfo.bytesSent);
});