i have a websocket server written in php using ratchet websocket, and the clients are written in javascript creating websocket connection to connect to the php websocket server.

Client and server are communicating via json string, i found that when the json message size is greater than 64kB, the ratchet server would throw an 'underflow exception'

'UnderflowException' with message 'Frame must be coalesced before applying mask'

php server code

use Ratchet\Server\IoServer;
use Ratchet\Http\HttpServer;
use Ratchet\WebSocket\WsServer;
use MyApp\Socket;

$server = IoServer::factory(
    new HttpServer(
        new WsServer(
            new Socket()
        )
    ),
    8080
);

$server->run();

javascript client

var socket  = new WebSocket('ws://123.123.123.123:8080');

let reader = new FileReader();
reader.onload = function() 
{
    sendPackageImageFile(reader.result);
};

reader.onerror = function() 
{
    console.log('reader.error');
};  

reader.readAsDataURL('some-file');


function sendPackageImageFile(imageFileData)
{
    var message = {};
    message.sender = 'someUser';
    message.action = 'send-package-image';
    message.packer = 'packer';
    message.data = 'some data';
    message.file = imageFileData;
    const js = JSON.stringify(message);
    socket.send(js);
}