[jboss-jira] [JBoss JIRA] (JASSIST-270) Error loading class only available to bootstrap loader with jboss7+ and javassist 3.22

[Patson Luk (JIRA)]

Patson Luk created JASSIST-270:
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             Summary: Error loading class only available to bootstrap loader with jboss7+ and javassist 3.22
                 Key: JASSIST-270
                 URL: https://issues.jboss.org/browse/JASSIST-270
             Project: Javassist
          Issue Type: Bug
    Affects Versions: 3.22.0-GA
         Environment: oracle JDK 1.8.0_40
jboss 7, wildfly 8, wildfly 9, wildfly 10
            Reporter: Patson Luk
            Assignee: Shigeru Chiba


h3. Description
After upgrading our agent from javassist 3.21 to 3.22, we started observing class loading problem during injection of code

{{CannotCompileException: [source error] no such class: test.TestClass}}

h3. Setup
# Our agent inject a piece of code with reference to class `test.TestClass`
# `test.TestClass` is provided by adding Boot-Class-Path entry in MANIFEST.MF, for example : Boot-Class-Path: ./  (with relative path, which we put the class binary `test.TestClass.class` within "test" folder relative to the agent JAR)
# When obtaining the classpool, we always call `ClassPool.appendSystemPath()` such that `test.TestClass` available to bootstrap classloader will be loaded properly in all situations
# Start Jboss 7 or any wildfly with `javaagent` that triggers the code injection, we will then observe the exception mentioned. Such a problem does not exist in version 3.21

h3. Cause
With some drill down into the source code, it appears that this [change|https://github.com/jboss-javassist/javassist/commit/778c463e5aa1795591e56916c6c1c3205317fc3e#diff-bfaa8fd6d3084d2b4a978ea2254ccb1cR243] in 3.22 combined with how jboss loads classes with its module class loader trigger the problem

The steps are:
# JBoss tries to load a class that triggers transformation, the javasist classpool used to load the class has a reference to the "module classloader" provided by JBoss + our  `ClassPool.appendSystemPath()` call, which in 3.22, appends a LoaderClassPath of the thread's Context classloader, which is also a jboss module classloader (Module "org.jboss.as.standalone:main")
# The injected code references class `test.TestClass`
# `ClassPool.find` tries to use all the `ClassPath` to load `test.TestClass`, which they are both JBoss's "module classloader". Unfortunately, neither of those loaders can load the `test.TestClass` which is available to bootstrap loader
# Throws the CannotCompileException exception as the referenced class in injected code cannot be loaded

Take note that this worked in 3.21 as `appendSystemPath` appends the `ClassClassPath` intead of a `LoaderClassPath` with the context class loader.

As a workaround, instead of calling `appendSystemPath`, i called `classPool.appendClassPath(new ClassClassPath(Object.class));` and it no longer complains about class loading problem


Sorry about the long post. I honestly do not know whether this should be considered as a bug as all. As the name `appendSystemPath` somehow suggests to me that a class available to bootstrap classloader should be taken care of (is it considered part of the "system path"?), but i might be totally mistaken...

Many thanks for your attention!







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