We are using Jersey Server-Sent Events (SSE) to allow remote components
of our application to listen to events raised by our Jersey/Tomcat
server. This works great.
However, it is crucial that our server have an accurate list of
currently-connected listeners (our remote components). To this end, we
send a tiny message to each caller (via eventOutput.write) once every
five seconds. If our remote component is shut down while SSE-connected,
or if the remote computer is powered off while SSE-connected,
eventOutput.write throws the ClientAbortException/SocketException
exception shown below. That's perfect: we catch the exception, mark that
caller as no longer connected, and move on.
Now, for the problem. As I mentioned, eventOutput. write throws an
exception in cases where our remote component software is not running,
or where the computer it runs on has been powered down. However, there
are two cases where calling eventOutput.write to a disconnected computer
does NOT throw an exception: 1) if the Ethernet cable of the remote
computer is simply pulled while the caller is SSE-connected, and 2) if
the network adapter in the remote computer is turned off (i.e., by an
administrative action) while the caller is SSE-connected. In these two
cases, we can call eventOutput.write to the remote computer every five
seconds for hours and no exception is thrown. This makes it impossible
to detect that the remote computer is no longer connected.
I see that EventOutput (and ChunkedOutput) has very few methods and
properties, but I wonder if there is any way to configure or use it that
will cause an exception to be thrown when writing to a remote computer
that has been disconnected by having its Ethernet cable pulled or
network adapter turned off.
And here is the (good/useful) exception we get in cases where
eventOutput.write DOES throw the exception we want:
org.apache.catalina.connector.ClientAbortException: null
at
org.apache.catalina.connector.OutputBuffer.doFlush(OutputBuffer.java:371) ~[catalina.jar:7.0.53]
at
org.apache.catalina.connector.OutputBuffer.flush(OutputBuffer.java:333)
~[catalina.jar:7.0.53]
at
org.apache.catalina.connector.CoyoteOutputStream.flush(CoyoteOutputStream.java:101)
~[catalina.jar:7.0.53]
at
org.glassfish.jersey.servlet.internal.ResponseWriter$NonCloseableOutputStreamWrapper.flush(ResponseWriter.java:303)
~[jaxrs-ri-2.13.jar:2.13.]
at
org.glassfish.jersey.message.internal.CommittingOutputStream.flush(CommittingOutputStream.java:292)
~[jaxrs-ri-2.13.jar:2.13.]
at
org.glassfish.jersey.server.ChunkedOutput$1.call(ChunkedOutput.java:240)
~[jaxrs-ri-2.13.jar:2.13.]
at
org.glassfish.jersey.server.ChunkedOutput$1.call(ChunkedOutput.java:190)
~[jaxrs-ri-2.13.jar:2.13.]
at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
~[jaxrs-ri-2.13.jar:2.13.]
at org.glassfish.jersey.internal.Errors.process(Errors.java:242)
~[jaxrs-ri-2.13.jar:2.13.]
at
org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:347)
~[jaxrs-ri-2.13.jar:2.13.]
at
org.glassfish.jersey.server.ChunkedOutput.flushQueue(ChunkedOutput.java:190)
~[jaxrs-ri-2.13.jar:2.13.]
at
org.glassfish.jersey.server.ChunkedOutput.write(ChunkedOutput.java:180)
~[jaxrs-ri-2.13.jar:2.13.]
at
com.appserver.webservice.AgentSsePollingManager$ConnectionChecker.run(AgentSsePollingManager.java:174)
~[AgentSsePollingManager$ConnectionChecker.class:na]
at
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
[na:1.7.0_71]
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:304)
[na:1.7.0_71]
at
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178)
[na:1.7.0_71]
at
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
[na:1.7.0_71]
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
[na:1.7.0_71]
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
[na:1.7.0_71]
at java.lang.Thread.run(Thread.java:745) [na:1.7.0_71]
Caused by: java.net.SocketException: Broken pipe
at java.net.SocketOutputStream.socketWrite0(Native Method)
~[na:1.7.0_71]
at
java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:113)
~[na:1.7.0_71]
at java.net.SocketOutputStream.write(SocketOutputStream.java:159)
~[na:1.7.0_71]
at
org.apache.coyote.http11.InternalOutputBuffer.realWriteBytes(InternalOutputBuffer.java:215)
~[tomcat-coyote.jar:7.0.53]
at
org.apache.tomcat.util.buf.ByteChunk.flushBuffer(ByteChunk.java:480)
~[tomcat-coyote.jar:7.0.53]
at
org.apache.coyote.http11.InternalOutputBuffer.flush(InternalOutputBuffer.java:119)
~[tomcat-coyote.jar:7.0.53]
at
org.apache.coyote.http11.AbstractHttp11Processor.action(AbstractHttp11Processor.java:799)
~[tomcat-coyote.jar:7.0.53]
at org.apache.coyote.Response.action(Response.java:174)
~[tomcat-coyote.jar:7.0.53]
at
org.apache.catalina.connector.OutputBuffer.doFlush(OutputBuffer.java:366) ~[catalina.jar:7.0.53]
... 19 common frames omitted