jetty 12: ee10: DefaultServlet: Binary data gets double-encoded via UTF-8 Writer, incomplete transmission

[kohlschuetter]

Jetty version(s)
jetty 12.0.x alpha3, HEAD

Java version/vendor (use: java -version)
openjdk version "18.0.1" 2022-04-19
OpenJDK Runtime Environment Temurin-18.0.1+10 (build 18.0.1+10)
OpenJDK 64-Bit Server VM Temurin-18.0.1+10 (build 18.0.1+10, mixed mode)

OS type/version
macOS 13.1

Description
ee10 DefaultServlet's ServletCoreResponse currently checks "ServletContextResponse#isStreaming()" to determine whether the (potentially binary) data has to be encoded via an existing Writer or can be sent directly as a byte stream.

Unfortunately, isStreaming() returns false when no data has been sent, i.e., even when isWriting() would be false, too.
This causes all sorts of exceptions thrown (sadly only logged at DEBUG level) with messages like java.io.IOException: written 25746 > 12014 content-length, for example:

[qtp1698156408-59] DEBUG org.eclipse.jetty.io.AbstractConnection - onClose HttpConnection@7e454f14::SocketChannelEndPoint@668ef72e[{l=null,r=null,CLOSED,fill=-,flush=-,to=11/30000}{io=0/0,kio=-1,kro=-1}]->[HttpConnection@7e454f14[p=HttpParser{s=END,0 of -1},g=HttpGenerator@358f72b8{s=COMMITTED}]=>HttpChannelState@24a9d4a0{processing=null, processed=true, writeState=NOT_LAST, completed=true, writeCallback=Blocker@5e76dc2c{java.io.IOException: written 25746 > 12014 content-length}, request=GET@630beed http://localhost:8123/blog/assets/img/favicons/favicon.ico HTTP/1.1}]
java.io.IOException: written 25746 > 12014 content-length
	at org.eclipse.jetty.server.internal.HttpChannelState$ChannelResponse.write(HttpChannelState.java:1067)
	at org.eclipse.jetty.ee10.servlet.HttpOutput.channelWrite(HttpOutput.java:213)
	at org.eclipse.jetty.ee10.servlet.HttpOutput.channelWrite(HttpOutput.java:198)
	at org.eclipse.jetty.ee10.servlet.HttpOutput.flush(HttpOutput.java:679)
	at org.eclipse.jetty.ee10.servlet.writer.HttpWriter.flush(HttpWriter.java:55)
	at org.eclipse.jetty.ee10.servlet.writer.ResponseWriter.flush(ResponseWriter.java:142)
	at java.base/java.io.PrintWriter.checkError(PrintWriter.java:465)
	at org.eclipse.jetty.ee10.servlet.writer.ResponseWriter.checkError(ResponseWriter.java:93)
	at org.eclipse.jetty.util.IO.copy(IO.java:215)
	at org.eclipse.jetty.util.IO.copy(IO.java:135)
	at org.eclipse.jetty.ee10.servlet.DefaultServlet$ServletCoreResponse.write(DefaultServlet.java:830)
	at org.eclipse.jetty.server.ResourceService$ContentWriterIteratingCallback.process(ResourceService.java:887)
	at org.eclipse.jetty.util.IteratingCallback.processing(IteratingCallback.java:243)
	at org.eclipse.jetty.util.IteratingCallback.iterate(IteratingCallback.java:224)
	at org.eclipse.jetty.server.ResourceService.writeHttpContent(ResourceService.java:648)
	at org.eclipse.jetty.server.ResourceService.sendData(ResourceService.java:601)
	at org.eclipse.jetty.server.ResourceService.doGet(ResourceService.java:197)
	at org.eclipse.jetty.ee10.servlet.DefaultServlet.doGet(DefaultServlet.java:420)
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:527)
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:614)
	at org.eclipse.jetty.ee10.servlet.ServletHolder.handle(ServletHolder.java:738)
	at org.eclipse.jetty.ee10.servlet.ServletHandler$ChainEnd.doFilter(ServletHandler.java:1585)
	at org.eclipse.jetty.ee10.servlet.ServletHandler$MappedServlet.handle(ServletHandler.java:1518)
	at org.eclipse.jetty.ee10.servlet.ServletChannel.lambda$handle$0(ServletChannel.java:425)
	at org.eclipse.jetty.ee10.servlet.ServletChannel.dispatch(ServletChannel.java:655)
	at org.eclipse.jetty.ee10.servlet.ServletChannel.handle(ServletChannel.java:420)
	at org.eclipse.jetty.ee10.servlet.ServletHandler.process(ServletHandler.java:442)
	at org.eclipse.jetty.ee10.servlet.security.SecurityHandler.process(SecurityHandler.java:563)
	at org.eclipse.jetty.ee10.servlet.SessionHandler.process(SessionHandler.java:756)
	at org.eclipse.jetty.server.handler.ContextHandler.process(ContextHandler.java:696)
	at org.eclipse.jetty.server.handler.ContextHandlerCollection.process(ContextHandlerCollection.java:166)
	at org.eclipse.jetty.server.Handler$Wrapper.process(Handler.java:541)
	at org.eclipse.jetty.server.internal.HttpChannelState$HandlerInvoker.run(HttpChannelState.java:551)
	at org.eclipse.jetty.server.internal.HttpConnection.onFillable(HttpConnection.java:457)
	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:322)
	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:100)
	at org.eclipse.jetty.io.SelectableChannelEndPoint$1.run(SelectableChannelEndPoint.java:53)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.runTask(AdaptiveExecutionStrategy.java:473)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.consumeTask(AdaptiveExecutionStrategy.java:436)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.tryProduce(AdaptiveExecutionStrategy.java:288)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.lambda$new$0(AdaptiveExecutionStrategy.java:136)
	at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:411)
	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 issue can be averted by replacing checks for isStreaming() by !isWriting().

How to reproduce?
In an embedded jetty, try to open a binary file (e.g., favicon.ico) that is served from a resource URL.