Header image for Jetty demo page fails on hard refresh

[gregpoulos]

Jetty version(s)
Jetty 12

Java version/vendor
openjdk version "19.0.1" 2022-10-18

OS type/version
macOS Monterey 12.6.2

Description
When running the demos module that ships with Jetty 12, I am seeing some odd behavior upon accessing the demo home page at http://0.0.0.0:8080/.

When the page first loads, everything looks fine. But if I do a hard refresh (Cmd+Shift+R), the header image no longer appears and I get the following stacktrace in my terminal:

2022-12-21 15:32:43.501:WARN :oejs.Response:qtp640363654-29: writeError: status=500, message=java.io.IOException: written 0 < 493852 content-length, response=org.eclipse.jetty.server.internal.HttpChannelState$ErrorResponse@7db7a010
java.io.IOException: written 0 < 493852 content-length
	at org.eclipse.jetty.server.internal.HttpChannelState$ChannelResponse.write(HttpChannelState.java:1111)
	at org.eclipse.jetty.ee10.servlet.HttpOutput.channelWrite(HttpOutput.java:213)
	at org.eclipse.jetty.ee10.servlet.HttpOutput.complete(HttpOutput.java:443)
	at org.eclipse.jetty.ee10.servlet.ServletContextResponse.completeOutput(ServletContextResponse.java:152)
	at org.eclipse.jetty.ee10.servlet.ServletChannel.handle(ServletChannel.java:597)
	at org.eclipse.jetty.ee10.servlet.ServletHandler.process(ServletHandler.java:442)
	at org.eclipse.jetty.ee10.servlet.security.SecurityHandler.process(SecurityHandler.java:563)
	at org.eclipse.jetty.ee10.servlet.SessionHandler.process(SessionHandler.java:756)
	at org.eclipse.jetty.server.handler.ContextHandler.process(ContextHandler.java:696)
	at org.eclipse.jetty.server.handler.ContextHandlerCollection.process(ContextHandlerCollection.java:166)
	at org.eclipse.jetty.server.Handler$Collection.process(Handler.java:577)
	at org.eclipse.jetty.server.Handler$Wrapper.process(Handler.java:541)
	at org.eclipse.jetty.rewrite.handler.RewriteHandler.process(RewriteHandler.java:118)
	at org.eclipse.jetty.server.Handler$Wrapper.process(Handler.java:541)
	at org.eclipse.jetty.server.internal.HttpChannelState$HandlerInvoker.run(HttpChannelState.java:594)
	at org.eclipse.jetty.server.internal.HttpConnection.onFillable(HttpConnection.java:445)
	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:322)
	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:100)
	at org.eclipse.jetty.io.SelectableChannelEndPoint$1.run(SelectableChannelEndPoint.java:53)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:934)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:1078)
	at java.base/java.lang.Thread.run(Thread.java:1589)

The fact that the page loads correctly at first and only breaks upon refresh is what seems particularly weird to me here.

How to reproduce?
$ java -jar $JETTY_HOME/start.jar --add-modules=demos $ java -jar $JETTY_HOME/start.jar
Then navigate to http://0.0.0.0:8080/. The page loads correctly upon first load, but if I do a hard refresh (Cmd+Shift+R) the image no longer appears.

[gregw]

Sounds like a problem with an If-Not-Modified response. My guess is we are sending a 304 not modified, but also setting content-length. @lorban do you want to take this?

[lorban]

@gregw I managed to reproduce the problem. See #9079 for a reproducing test and a prototype fix which should be discussed with @lachlan-roberts. But at least it solves the problem for now so maybe we want to merge it right away and clean it later?

It's not surprising we did not catch this earlier because we need to serve a file of a certain size otherwise it's not mmap'ed and the slow path is taken.