NIFI-7825: Support native library loading via absolute path

[turcsanyip]

Use an AspectJ aspect and agent to intercept the load native library calls
at runtime, copy the native library file to temp folder and proceed with
the newly created file in order to provide classloader isolation.

https://issues.apache.org/jira/browse/NIFI-7825

Thank you for submitting a contribution to Apache NiFi.

Please provide a short description of the PR here:

Description of PR

Enables X functionality; fixes bug NIFI-YYYY.

In order to streamline the review of the contribution we ask you
to ensure the following steps have been taken:

For all changes:

• Is there a JIRA ticket associated with this PR? Is it referenced
  in the commit message?

• Does your PR title start with NIFI-XXXX where XXXX is the JIRA number you are trying to resolve? Pay particular attention to the hyphen "-" character.

• Has your PR been rebased against the latest commit within the target branch (typically main)?

• Is your initial contribution a single, squashed commit? Additional commits in response to PR reviewer feedback should be made on this branch and pushed to allow change tracking. Do not squash or use --force when pushing to allow for clean monitoring of changes.

For code changes:

• Have you ensured that the full suite of tests is executed via mvn -Pcontrib-check clean install at the root nifi folder?
• Have you written or updated unit tests to verify your changes?
• Have you verified that the full build is successful on JDK 8?
• Have you verified that the full build is successful on JDK 11?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE file, including the main LICENSE file under nifi-assembly?
• If applicable, have you updated the NOTICE file, including the main NOTICE file found under nifi-assembly?
• If adding new Properties, have you added .displayName in addition to .name (programmatic access) for each of the new properties?

For documentation related changes:

• Have you ensured that format looks appropriate for the output in which it is rendered?

Note:

Please ensure that once the PR is submitted, you check GitHub Actions CI for build issues and submit an update to your PR as soon as possible.

[bbende]

Do we have any concerns about aspectjweaver being directly in the lib directory which puts in on the classpath of every single NAR? Wondering if it should be separated like lib/aspectj/ which would not be added to NiFi's normal classpath, but I don't know enough to say if it still works correctly then.

[turcsanyip]

The agent does not require aspectjweaver.jar on the classpath so lib/aspectj directory could work.
If there are concerns about having this jar on the system classpath, I can try out that solution too.

[bbende]

I think if we can do the lib/aspectj approach then that is the best option, anything we can do to avoid introducing additional dependencies to the system classpath is good.

[turcsanyip]

I double checked it and unfortunately the aspect class in nifi-nar-utils.jar depends on aspectjrt.jar.
As nifi-nar-utils.jar is located in the lib folder and loaded by the system classloader, aspectjrt.jar must be on the system classpath too.
And I did not want to separate the 2 AspectJ jars so I put aspectjweaver.jar to the lib folder.

Options:

1. leave it as it is now (both aspectjrt.jar and aspectjweaver.jar in the lib folder)
2. leave aspectjrt.jar in lib and move aspectjweaver.jar to lib/aspectj
3. find another place for the aspect class and move its aspectjrt.jar dependency there, move aspectjweaver.jar to lib/aspectj

Option 2 seems to me a bit weird structure and one of the AspectJ jars is still on the system classpath.
Option 3 could work but I would keep the native library loading stuff (AbstractNativeLibHandlingClassLoader and LoadNativeLibAspect) in the same module.

So I would still vote for option 1.
These jars have no effect if they are not referenced in our code / the agent is not turned on.

[bbende]

Well it does have an effect... If the jars are in lib then they are on the classpath of every NAR, so if someone makes a custom NAR that bundles a different version of aspectj, then there will be two versions on the classpath, and there is nothing the NAR can do to avoid the one in lib.

I would actually vote for option 3... create a new module like nifi-nar-aspect-utils or whatever we want to call it, and put the dependency there along with LoadNativeLibAspect, then lib/aspectj can contain nifi-nar-aspect-utils jar and the aspectj jars. Would that work?

[turcsanyip]

It has been revealed that aspectjrt does not needed at runtime, only aspectjweaver (which is loaded directly by the agent, not from classpath).
So I removed aspectjrt.ajr from lib and moved aspectjweaver.jar to lib/aspectj subdirectory.
In this way, there are no AspectJ libraries on the system classpath by default (when the agent is turned off).

When the agent is turned on, it is being loaded by the system classloader (even if aspectjweaver.jar is not on the system classpath). So there might be collision between different versions in this case. I believe it is acceptable because only the "agent turned on" case affected.

[bbende]

Latest changes look good, thanks! Will merge