Integer overflow in receiving code

[bsergean]

(quoting the email exchange with a reporter)

There is an integer overflow on the receiving frame size

IXWebSocket/ixwebsocket/IXWebSocketTransport.cpp

Line 545 in 0e9cf86

if (_rxbuf.size() < ws.header_size + ws.N)

that can be used to sneak past the guard clause _rxbuf.size() < ws.header_size + ws.N check.

Should be a simple fix - either by adding a reasonable limit to the ws.N value or checking for overflow before doing the addition. According to the websocket spec "the most significant bit MUST be 0" so that is a safe and simple check to do.