Caught an exception on ClientToProxyConnection

[p0po]

we use littleproxy as http gateway in our website and set MaximumRequestBufferSize 4 * 1024 * 1024 bytes,it works well.

                    @Override
                    public int getMaximumRequestBufferSizeInBytes() {
                        return 4 * 1024 * 1024;
                    }

my server will log exception if a request bigger than 4 * 1024 * 1024:

[LittleProxy-0-ClientToProxyWorker-6] ERROR 
org.littleshoot.proxy.impl.ClientToProxyConnection -
 (AWAITING_INITIAL) [id: 0x61f4380b, L:/127.0.0.1:1802 - R:/127.0.0.1:37259]: 
Caught an exception on ClientToProxyConnection
io.netty.handler.codec.TooLongFrameException: HTTP content length exceeded 4194304 bytes.

and it will return bad request tips(http code:500) to the user, it will make the user confused.
how can i set specific tips response my user,such as:your request is too big?

I find these code in class org.littleshoot.proxy.impl.DefaultHttpProxyServer：

ChannelInitializer<Channel> initializer = new ChannelInitializer<Channel>() {
            protected void initChannel(Channel ch) throws Exception {
                new ClientToProxyConnection(
                        DefaultHttpProxyServer.this,
                        sslEngineSource,
                        authenticateSslClients,
                        ch.pipeline(),
                        globalTrafficShapingHandler);
            };
        };

in class io.netty.handler.codec.http.HttpObjectAggregator

if (content.readableBytes() > maxContentLength - chunk.content().readableBytes()) {
                // release current message to prevent leaks
                currentMessage.release();
                currentMessage = null;

                throw new TooLongFrameException(
                        "HTTP content length exceeded " + maxContentLength +
                        " bytes.");
            }

in class org.littleshoot.proxy.impl.ClientToProxyConnection

@Override
    protected void exceptionCaught(Throwable cause) {
        try {
            if (cause instanceof IOException) {
                // IOExceptions are expected errors, for example when a browser is killed and aborts a connection.
                // rather than flood the logs with stack traces for these expected exceptions, we log the message at the
                // INFO level and the stack trace at the DEBUG level.
                LOG.info("An IOException occurred on ClientToProxyConnection: " + cause.getMessage());
                LOG.debug("An IOException occurred on ClientToProxyConnection", cause);
            } else if (cause instanceof RejectedExecutionException) {
                LOG.info("An executor rejected a read or write operation on the ClientToProxyConnection (this is normal if the proxy is shutting down). Message: " + cause.getMessage());
                LOG.debug("A RejectedExecutionException occurred on ClientToProxyConnection", cause);
            } else {
                LOG.error("Caught an exception on ClientToProxyConnection", cause);
            }
        } finally {
            // always disconnect the client when an exception occurs on the channel
            disconnect();
        }
    }