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Comment: Troubleshooting unexpected Response state problems - Improve text about issues with libraries

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If you encounter problems that manifest themselves as accessing a request or response that is an inconsistent state, the main suspect is your own web application (or a library that it uses) keeping a reference to Request or Response objects outside of their life cycle. Examples: BZ 61289, BZ 58457.

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  1. Make sure that your Tomcat is configured to discard facades to its internal objects when request processing completes. This makes it easier to spot illegal access when it happens, instead of waiting until side effects of such access become visible. Essentially, it protects Tomcat internals from misbehaving web applications.

    This feature is always on when you are running Tomcat with a Java Security Manager being enabled. Starting with Tomcat 10.0 this feature is enabled by default. It is disabled by default in earlier versions of Tomcat. The way this feature is configured differs between versions: it is controlled by an attribute on Connector element or by a system property.

    If you are running Tomcat 9.0 or earlier, do both of the following:

    - Set the following system property in Tomcat configuration:
    org.apache.catalina.connector.RECYCLE_FACADES=true

    - Add the following attribute to all Connector elements:
    discardFacades="true"

    The Connector attribute was added in Tomcat 10.0.0-M1, 9.0.31, 8.5.51 and 7.0.100. The system property is an older way to configure this feature. In case of a doubt, or if you are switching back and forth between versions while troubleshooting the issue, it is safer to configure both of them.

    This feature is also mentioned on the Security Considerations page in Tomcat documentation. You can also search the archives of the Tomcat users' mailing lists for previous discussions mentioning the RECYCLE_FACADES flag.
    Read about Java ImageIO issue.

Accessing response objects after their lifetime can lead to security issues in your application, such as sending responses to wrong clients, mixing up responses. If you can reproduce the issue and the above diagnostic does not show your own bug, but a bug in Apache Tomcat, if the problem manifests as a security issue, see how to report it.

There are some known examples of broken libraries / APIs:

  1. Read about Java ImageIO issue — an issue with javax.imageio.ImageIO API. It may have already been fixed as it is an old issue, but there are no clear records of it.
  2. Read about an issue in PD4ML, a library that is used to generate PDF files, — fixed in their version 3.8.0, earlier versions may be affected.

Troubleshooting "Too many open file descriptors"

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