On 27/02/2025 19:56, Banana Kanana wrote:
Hi,
We are using Apache Tomcat 9.0 and frequently see logs related to
CloseNowException in one of our applications. This exception occurs on
multiple operating systems, including OpenSUSE, Ubuntu, and Windows, and in
different parts of our codebase.
From reading the Javadoc, our understanding is that this exception signals
that a connection should be closed. We are unsure about the best way to
handle it in our application.
• Should we rethrow it so that Tomcat can handle it properly?
That isn't necessary but it may help Tomcat end the request/response faster.
• What would be the implications if we just catch and log the exception
without rethrowing it? Could this interfere with Tomcat’s expected behavior
in any way?
It shouldn't. Tomcat should mark the request/response as having an error
so the request/response should be closed once control returns to Tomcat
whether the applications re-throws the exception or not.
My recommendation when an application sees this error would be:
- log it (if the application wants to)
- stop processing the current request/response as quickly as possible
- clean-up any resources used by the current request/response
- rethrow the exception (may enable Tomcat to skip some processing)
How much impact rethrowing has is going to depend on circumstances. I
think it will only help but you might want to test that.
Mark
We observe multiple variations of stack traces, but here is one example,
truncated to omit internal details. Please note that the log entry is
generated by our class, not by Tomcat:
2025-02-27 00:04:44.740 ERROR [ErrorFilter] [https-jsse-nio-443-exec-3604]
[] [] Request by anonymous failed for GET https://www.nnn.nnnn
org.apache.coyote.CloseNowException: Connection [1775817], Stream [27],
This stream is in state [CLOSED_RST_RX] and is not writable at
org.apache.coyote.http2.Stream.doStreamCancel(Stream.java:293) at
org.apache.coyote.http2.Http2UpgradeHandler.reserveWindowSize(Http2UpgradeHandler.java:941)
at
org.apache.coyote.http2.Stream$StreamOutputBuffer.flush(Stream.java:1050)
at
org.apache.coyote.http2.Stream$StreamOutputBuffer.doWrite(Stream.java:965)
at
org.apache.coyote.http2.Http2OutputBuffer.doWrite(Http2OutputBuffer.java:57)
at org.apache.coyote.Response.doWrite(Response.java:608) at
org.apache.catalina.connector.OutputBuffer.realWriteBytes(OutputBuffer.java:333)
at
org.apache.catalina.connector.OutputBuffer.appendByteArray(OutputBuffer.java:750)
at org.apache.catalina.connector.OutputBuffer.append(OutputBuffer.java:671)
at
org.apache.catalina.connector.OutputBuffer.writeBytes(OutputBuffer.java:380)
at org.apache.catalina.connector.OutputBuffer.write(OutputBuffer.java:358)
at
org.apache.catalina.connector.CoyoteOutputStream.write(CoyoteOutputStream.java:103)
at
org.apache.catalina.connector.CoyoteOutputStream.write(CoyoteOutputStream.java:95)
For additional context:
Tomcat versions: multiple versions. The provided stack traces is from
9.0.87 but we see this in 9.0.98 as well
• Operating systems affected: OpenSUSE, Ubuntu, Windows
• HTTP/2 enabled: Yes, in the environments where this exception occurs
We have reviewed the following resources without finding a clear answer:
• Tomcat’s official documentation
• Previous discussions in the user mailing list archives
• Related posts on Stack Overflow
We would appreciate guidance on the best approach to handling
CloseNowException in our application to ensure compatibility with Tomcat.
Thanks in advance for your help.
Daniel
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