Transient failure: ClassFormatError: Truncated class file

[mbovel]

Is this a flaky CI issue?

Failed run: https://github.com/scala/scala3/actions/runs/8909891046/job/24468041106

Test 'tests/run/i5350.scala' failed with output:                                
java.lang.ClassFormatError: Truncated class file
	at java.base/java.lang.ClassLoader.defineClass1(Native Method)
	at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1017)
	at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)
	at java.base/java.net.URLClassLoader.defineClass(URLClassLoader.java:524)
	at java.base/java.net.URLClassLoader$1.run(URLClassLoader.java:427)
	at java.base/java.net.URLClassLoader$1.run(URLClassLoader.java:421)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:712)
	at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:420)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:592)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:525)
	at dotty.tools.vulpix.ChildJVMMain.runMain(ChildJVMMain.java:29)
	at dotty.tools.vulpix.ChildJVMMain.main(ChildJVMMain.java:47)
Exception in thread "main" java.lang.ClassFormatError: Truncated class file
	at java.base/java.lang.ClassLoader.defineClass1(Native Method)
	at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1017)
	at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)
	at java.base/java.net.URLClassLoader.defineClass(URLClassLoader.java:524)
	at java.base/java.net.URLClassLoader$1.run(URLClassLoader.java:427)
	at java.base/java.net.URLClassLoader$1.run(URLClassLoader.java:421)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:712)
	at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:420)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:592)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:525)
	at dotty.tools.vulpix.ChildJVMMain.runMain(ChildJVMMain.java:29)
	at dotty.tools.vulpix.ChildJVMMain.main(ChildJVMMain.java:47)

cc @hamzaremmal

[sadaaithal]

@mbovel

we hit a similar problem on one of our internal apps, along with this piece of stacktrace:

Suppressed: java.io.IOException: CRC error while extracting entry from JAR file
	at sun.misc.URLClassPath$JarLoader$2.getBytes(URLClassPath.java:1023)
	at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
	... 14 more

We were scratching our head when we decided to ask around (incl. chatgpt)
One of the responses was about "corrupted, or inconsistent" jar that contained the class under question.
Sure enough - the class we were trying to load (lets call it foo.bar.Sample) was part of a jar (lets call it abc.jar) and it was rightly on the classpath.

decompiler showed foo.bar.Sample entry was there..
However jar -tvf abc.jar showed there were 2 of those - each with different CRC
We think the classloader uses jarEntry of one but is comparing with the CRC of the other.

abc.jar is an uberjar and ideally a jar should have one copy of the class per package.
we think there's an issue somewhere in our gradle scripts that builds this jar.
investigations are underway, but maybe it helps you in your issue.

good day!

[mbovel]

@sadaaithal thanks for your comment. This instance of the error happens on our CI only from time to time, it might be due concurrent access to the same class file which would corrupt it.

[mbovel]

Got it again today: https://github.com/scala/scala3/actions/runs/13242917509/job/36962276025 for #22574.

[sadaaithal]

@mbovel from https://github.com/scala/scala3/actions/runs/13242917509/job/36962276025 I see the exception is

 java.lang.ClassFormatError: Truncated class file
	at java.base/java.lang.ClassLoader.defineClass1(Native Method)
	at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1017)
	at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)
	at java.base/java.net.URLClassLoader.defineClass(URLClassLoader.java:524)
	at java.base/java.net.URLClassLoader$1.run(URLClassLoader.java:427)
	at java.base/java.net.URLClassLoader$1.run(URLClassLoader.java:421)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:712)
	at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:420)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:592)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:525)
	at dotty.tools.vulpix.ChildJVMMain.runMain(ChildJVMMain.java:29)
	at dotty.tools.vulpix.ChildJVMMain.main(ChildJVMMain.java:47)

I see the source for ChildJVMMain here https://github.com/michelou/scala3/blob/main/compiler/test/dotty/tools/vulpix/ChildJVMMain.java

I can't see how the we can trigger a concurrent classload of the "Test" class.

It would help if you could point me in the right direction ..
tx!