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Sending binary messages between client and server using uWS
var socket = new WebSocket("ws://localhost:3000");
socket.binaryType = "arraybuffer";
socket.onopen = function(){
var arrayBufferMessage = stringToArrayBuffer("Test message from client");
socket.onmessage = function(e){
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));
#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)) {;
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johnroper100 commented May 16, 2018

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

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WesThorburn commented May 17, 2018

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.

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