Why does the browser fail to correctly process the 401 status code when developing a WebSocket server using Netty?

When developing a WebSocket server with Netty, the browser may not be able to properly process the 401 unauthorized status code returned by the server. When the server fails to verify the token, the browser does not respond. This article analyzes this problem and provides solutions.

Problem scenario:

The client uses JavaScript code to connect to the WebSocket server:

 var socket = new WebSocket("ws://127.0.0.1:18080/ws?token=xxxx");

After the server-side verification token fails, send a 401 response and close the connection:

 private void httpresponse401(ChannelHandlerContext ctx, FullHttpRequest request){
    FullHttpResponse response = new DefaultFullHttpResponse(request.protocolVersion(), HttpResponseStatus.UNAUTHORIZED);
    response.headers().set(HttpHeaderNames.CONTENT_LENGTH, 0);
    ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
    ReferenceCountUtil.release(request);
}

The browser does not display any error prompts.

Solution:

In order for the browser to correctly recognize the 401 error, it is necessary to improve the server-side and client code:

1. Improve HTTP response: Although WebSocket uses the ws/wss protocol, the handshake phase relies on the HTTP protocol. Make sure the 401 response is a complete HTTP response containing the necessary header information such as Content-Type and Content-Length . An empty response may cause the browser to fail to parse correctly.

2. Enhanced client error handling: Add onerror and onclose event listeners in client JavaScript code, catch connection errors and print detailed error information:

 socket.onerror = function(event) {
    console.error("WebSocket error:", event);
};

socket.onclose = function(event) {
    console.log("WebSocket closed:", event.code, event.reason);
};

3. Server-side improvement of HTTP response: Provides a more detailed 401 response, including error information:

 private void httpResponse401(ChannelHandlerContext ctx, FullHttpRequest request){
    FullHttpResponse response = new DefaultFullHttpResponse(request.protocolVersion(), HttpResponseStatus.UNAUTHORIZED);
    ByteBuf content = Unpooled.copiedBuffer("Authentication failed", CharsetUtil.UTF_8);
    response.content().writeBytes(content);
    response.headers().set(HttpHeaderNames.CONTENT_TYPE, "text/plain; charset=UTF-8");
    response.headers().set(HttpHeaderNames.CONTENT_LENGTH, content.readableBytes());
    ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
    ReferenceCountUtil.release(request);
}

With these improvements, the server sends a complete 401 response with error messages that the client can capture and process, thereby displaying clearer error message on the browser side. This helps debug and resolve WebSocket connection issues.

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