NullPointerException: "Deflater has been closed" emanating from FilterServletOutputStream

[basil]

After upgrading to latest bits, I started seeing the following log spam when running Jenkins locally:

java.lang.NullPointerException: Deflater has been closed
	at java.base/java.util.zip.Deflater.ensureOpen(Deflater.java:902)
	at java.base/java.util.zip.Deflater.deflate(Deflater.java:564)
	at java.base/java.util.zip.Deflater.deflate(Deflater.java:464)
	at java.base/java.util.zip.GZIPOutputStream.finish(GZIPOutputStream.java:163)
	at java.base/java.util.zip.DeflaterOutputStream.close(DeflaterOutputStream.java:244)
	at org.kohsuke.stapler.compression.FilterServletOutputStream.close(FilterServletOutputStream.java:45)
	at org.kohsuke.stapler.compression.CompressionServletResponse.close(CompressionServletResponse.java:73)
	at org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:60)
	at Jenkins Main ClassLoader//org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:202)
	at Jenkins Main ClassLoader//org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1635)
	at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:86)
	at Jenkins Main ClassLoader//org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:202)
	at Jenkins Main ClassLoader//org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1635)
	at org.kohsuke.stapler.DiagnosticThreadNameFilter.doFilter(DiagnosticThreadNameFilter.java:31)
	at Jenkins Main ClassLoader//org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:202)
	at Jenkins Main ClassLoader//org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1635)
	at jenkins.security.SuspiciousRequestFilter.doFilter(SuspiciousRequestFilter.java:38)
	at Jenkins Main ClassLoader//org.eclipse.jetty.servlet.FilterHolder.doFilter(FilterHolder.java:202)
	at Jenkins Main ClassLoader//org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1635)
	at Jenkins Main ClassLoader//org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:527)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:131)
	at Jenkins Main ClassLoader//org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:569)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:122)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:223)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1580)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:221)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1384)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:176)
	at Jenkins Main ClassLoader//org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:484)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1553)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:174)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1306)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:129)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:122)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.Server.handle(Server.java:563)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.HttpChannel$RequestDispatchable.dispatch(HttpChannel.java:1598)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.HttpChannel.dispatch(HttpChannel.java:753)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:501)
	at Jenkins Main ClassLoader//org.eclipse.jetty.server.HttpChannel.run(HttpChannel.java:461)
	at Jenkins Main ClassLoader//org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.runTask(AdaptiveExecutionStrategy.java:421)
	at Jenkins Main ClassLoader//org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.consumeTask(AdaptiveExecutionStrategy.java:390)
	at Jenkins Main ClassLoader//org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.tryProduce(AdaptiveExecutionStrategy.java:277)
	at Jenkins Main ClassLoader//org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.produce(AdaptiveExecutionStrategy.java:193)
	at Jenkins Main ClassLoader//org.eclipse.jetty.http2.HTTP2Connection.produce(HTTP2Connection.java:208)
	at Jenkins Main ClassLoader//org.eclipse.jetty.http2.HTTP2Connection.onFillable(HTTP2Connection.java:155)
	at Jenkins Main ClassLoader//org.eclipse.jetty.http2.HTTP2Connection$FillableCallback.succeeded(HTTP2Connection.java:450)
	at Jenkins Main ClassLoader//org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:100)
	at Jenkins Main ClassLoader//org.eclipse.jetty.io.ssl.SslConnection$DecryptedEndPoint.onFillable(SslConnection.java:558)
	at Jenkins Main ClassLoader//org.eclipse.jetty.io.ssl.SslConnection.onFillable(SslConnection.java:379)
	at Jenkins Main ClassLoader//org.eclipse.jetty.io.ssl.SslConnection$2.succeeded(SslConnection.java:146)
	at Jenkins Main ClassLoader//org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:100)
	at Jenkins Main ClassLoader//org.eclipse.jetty.io.SelectableChannelEndPoint$1.run(SelectableChannelEndPoint.java:53)
	at Jenkins Main ClassLoader//org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.runTask(AdaptiveExecutionStrategy.java:421)
	at Jenkins Main ClassLoader//org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.consumeTask(AdaptiveExecutionStrategy.java:390)
	at Jenkins Main ClassLoader//org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.tryProduce(AdaptiveExecutionStrategy.java:277)
	at Jenkins Main ClassLoader//org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.run(AdaptiveExecutionStrategy.java:199)
	at Jenkins Main ClassLoader//org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:411)
	at Jenkins Main ClassLoader//org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:969)
	at Jenkins Main ClassLoader//org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.doRunJob(QueuedThreadPool.java:1194)
	at Jenkins Main ClassLoader//org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:1149)
	at java.base/java.lang.Thread.run(Thread.java:1583)

The cause is explained pretty well in omnifaces/omnifaces#768 (comment). In recent Java versions, GZIPOutputStream can't handle being closed twice. I fixed this by making FilterServletOutputStream behave like the Java Platform's FilterOutputStream—only attempt the close a single time, flushing first for good measure.

Testing done

Clicking around in the UI and running Pipeline jobs, I was able to see this stack trace within a few minutes of using the UI on trunk bits. I haven't seen the log spam after running with this change for 20 minutes or so.