Java WebSocket message limit

Question

I'm trying to create communication between simple Java App (using java.net.http.WebSocket class) and remote google-chrome run using google-chrome --remote-debugging-port=9222 --user-data-dir=.

Sending and receiving small messages works as expected, but there is an issue in case of bigger messages, 16kb.

Here is part of java source:

var uri = new URI("ws://127.0.0.1:9222/devtools/page/C0D7B4DBC53FB39F7A4BE51DA79E96BB");

/// create websocket client
WebSocket ws = HttpClient
    .newHttpClient()
    .newWebSocketBuilder()
    .connectTimeout(Duration.ofSeconds(30))
    .buildAsync(uri, simpleListener)
    .join();

// session Id attached to chrome tab
String sessionId = "...";

// send message
String message = "{\"id\":1,\"method\":\"Runtime.evaluate\",\"params\":{\"expression\":\"document.body.style.backgroundColor = 'blue';\",\"returnByValue\":true,\"awaitPromise\":true,\"userGesture\":true},\"sessionId\":\"" + sessionId + "\"}";

// this works
ws.send(message, true);

// generate big string contains over 18k chars for testing purpose
String bigMessage = "{\"id\":2,\"method\":\"Runtime.evaluate\",\"params\":{\"expression\":\"[" + ("1,".repeat(9000)) + "1]\",\"returnByValue\":true,\"awaitPromise\":true,\"userGesture\":true},\"sessionId\":\"" + sessionId + "\"}";

// this doesn't work
ws.send(bigMessage, true);

Here is stack:

java.net.SocketException: Connection reset
    at java.base/sun.nio.ch.SocketChannelImpl.throwConnectionReset(SocketChannelImpl.java:345)
    at java.base/sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:376)
    at java.net.http/jdk.internal.net.http.SocketTube.readAvailable(SocketTube.java:1153)
    at java.net.http/jdk.internal.net.http.SocketTube$InternalReadPublisher$InternalReadSubscription.read(SocketTube.java:821)
    at java.net.http/jdk.internal.net.http.SocketTube$SocketFlowTask.run(SocketTube.java:175)
    at java.net.http/jdk.internal.net.http.common.SequentialScheduler$SchedulableTask.run(SequentialScheduler.java:198)
...

I've tried basically the same by using puppeteer (nodejs library) and it works as expected.

I can't find any resource online about this issue. Is there anything I'm missing in my example?

---

Here is url to simple example: https://github.com/zeljic/websocket-devtools-protocol

Answer 1

Based on what I've seen so far, my best guess would be that Chrome Dev Tools do not process fragmented Text messages on that exposed webSocketDebuggerUrl endpoint. Whether Chrome Dev Tools can be configured to do so or not, is another question. I must note, however, that RFC 6455 (The WebSocket Protocol) mandates it:

Clients and servers MUST support receiving both fragmented and unfragmented messages.

There's one workaround I can see here. Keep in mind that this is unsupported and may change in the future unexpectedly. When running your client, specify the following system property on the command line -Djdk.httpclient.websocket.intermediateBufferSize=1048576 (or pick any other suitable size). As long as you keep sending your messages with true passed as boolean last argument to the send* methods, java.net.http.WebSocket will send messages unfragment, in a single WebSocket frame.