NanoWSD.java

public Response handleWebSocket(final IHTTPSession session) {
        Map<String, String> headers = session.getHeaders();
        if (isWebsocketRequested(session)) {
            if (!NanoWSD.HEADER_WEBSOCKET_VERSION_VALUE.
                    equalsIgnoreCase(headers.get(NanoWSD.HEADER_WEBSOCKET_VERSION))) {
                return Response.
                        newFixedLengthResponse(Status.BAD_REQUEST, NanoHTTPD.MIME_PLAINTEXT,
                        "Invalid Websocket-Version " + headers.get(NanoWSD.HEADER_WEBSOCKET_VERSION));
            }

            if (!headers.containsKey(NanoWSD.HEADER_WEBSOCKET_KEY)) {
                return Response.
                        newFixedLengthResponse
                                (Status.BAD_REQUEST, NanoHTTPD.MIME_PLAINTEXT, "Missing Websocket-Key");
            }

            WebSocket webSocket = openWebSocket(session);
            Response handshakeResponse = webSocket.getHandshakeResponse();
            try {
                handshakeResponse.
                        addHeader(NanoWSD.HEADER_WEBSOCKET_ACCEPT,
                                makeAcceptKey(headers.get(NanoWSD.HEADER_WEBSOCKET_KEY)));
            } catch (NoSuchAlgorithmException e) {
                return Response.newFixedLengthResponse(Status.INTERNAL_ERROR, NanoHTTPD.MIME_PLAINTEXT,
                        "The SHA-1 Algorithm required for websockets is not available on the server.");
            }

            if (headers.containsKey(NanoWSD.HEADER_WEBSOCKET_PROTOCOL)) {
                handshakeResponse.
                        addHeader(NanoWSD.HEADER_WEBSOCKET_PROTOCOL,
                                headers.get(NanoWSD.HEADER_WEBSOCKET_PROTOCOL).split(",")[0]);
            }

            return handshakeResponse;
        } else {
            return null;
        }
    }