Sending binary messages between client and server using uWS

client.js

var socket = new WebSocket("ws://localhost:3000");
socket.binaryType = "arraybuffer";

socket.onopen = function(){
  var arrayBufferMessage = stringToArrayBuffer("Test message from client");
  socket.send(arrayBufferMessage);
};

socket.onmessage = function(e){
  console.log(arrayBufferToString(e.data));
}

function stringToArrayBuffer(string){
  var buffer = new ArrayBuffer(string.length);
  var bufferView = new Uint8Array(buffer);
  for(var i = 0; i < string.length; i++){
    bufferView[i] = string.charCodeAt(i);
  }
  return bufferView;
}

function arrayBufferToString(arrayBuffer){
  return String.fromCharCode.apply(null, new Uint8Array(arrayBuffer));
}

server.cpp

#include <uWS/uWS.h>
#include <string>
#include <iostream>

int main(){
	uWS::Hub h;

	h.onMessage([](uWS::WebSocket<uWS::SERVER> *ws, char *message, size_t length, uWS::OpCode opCode) {
		std::string receivedMessage(message, length);
		std::cout << receivedMessage << std::endl;
		ws->send("Reponse from server", uWS::OpCode::BINARY);
	});

	if (h.listen(3000)) {
		h.run();
	}
}

does this work if I just want to send a string with text, maybe with json?

If you're just wanting to send straight text, skip the whole stringToArrayBuffer() step on the client side and don't set a socket.binaryType. On the server side, you won't need uWS::OpCode::BINARY.

I would advise not sending JSON via websockets, JSON contains a lot of bloat and you'll end up consuming far more resources than necessary.