Running epubcheck on an epub with a large opf file (13k+ lines) results in a StackOverflowError

[myork]

When running epubcheck on an epub with a large opf file (13k+ lines, 841k) it throws the following StackOverflowError. Unfortunately I can't share the epub since it isn't public content.

epubcheck-4.2.6$ java -jar epubcheck.jar foobar.epub 
Validating using EPUB version 3.2 rules.
java.lang.StackOverflowError
	at java.base/java.util.LinkedList.unlinkFirst(LinkedList.java:178)
	at java.base/java.util.LinkedList.poll(LinkedList.java:679)
	at com.adobe.epubcheck.opf.XRefChecker.checkReadingOrder(XRefChecker.java:538)
	at com.adobe.epubcheck.opf.XRefChecker.checkReadingOrder(XRefChecker.java:599)
	at com.adobe.epubcheck.opf.XRefChecker.checkReadingOrder(XRefChecker.java:599)

I've seen that the recommended fix is to increase xss, but is there a way to change epubcheck to not require as much stack size?

This particular opf file has 6000+ <itemref> elements in the <spine>, and if I'm reading correctly it looks like these are evaluated using a recursive algorithm.

Question: Would changing the above to use iteration instead of recursion potentially decrease the required stack size?

[bduga]

We are having a similar issue, which is blocking some content ingestion. Looking at the code, the iterative version seems to be about one line shorter - I don't understand why this is using recursion at all. Java is not good at tail recursion optimizations. @rdeltour is this something we can look at in 5.0? The fix seems reasonably straightforward, do you want a PR?

[Edit]: Oh, the reporter is us :) Hi Matt!

[bduga]

FWIW, I think the recursion can be replaced with for (URLReference ref : references) {...}. I think that should work with a Queue.

[rdeltour]

hi @myork and @bduga. Thanks for the report!
It seems this is the issue raised in PR #1356 by @kalaspuffar.

I'll look into it for v5.0.0, but need to merge the ongoing work first, as this code has been refactored and merging it early will create conflicts.

Unfortunately I can't share the epub since it isn't public content.

Would you be able to send the EPUB privately? I can possibly sign an NDA if needed.