Whitelist builtin Java exceptions, rather than display any

[Xyene]

[Xyene]

Overkill solution:

For Java 8, use ZipFile to list the contents of /usr/lib/jvm/java-8-openjdk-amd64/jre/lib/rt.jar and filter anything ending with Exception|Error. Only a handful of builtin throwables don't follow this pattern (ThreadDeath is the only one I could quickly find).

For Java 9+ which moved classes to the JRT "filesystem", use something like the code below:

Main.java

import java.util.*;
import java.nio.file.*;
import java.net.*;

public class Main {
    private static void listFiles(Path dir) throws Exception {
        try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
            for (Path entry : stream) {
                if (Files.isDirectory(entry)) {
                    listFiles(entry);
                } else {
                    String demangledName = demangleClassName(entry);
                    if (demangledName.endsWith("Exception") || demangledName.endsWith("Error")) {
                        System.out.println(demangledName);
                    }
                }
            }
        }
    }

    private static String demangleClassName(Path filePath) {
        String fileName = filePath.toString();
        String withoutExtension = fileName.substring(0, fileName.lastIndexOf('.'));
        String withoutLeadingPackages = withoutExtension.replaceFirst("^/packages/.*?/.*?/", "");
        String demangledName = withoutLeadingPackages.replace('$', '.').replace('/', '.');
        return demangledName;
    }

    public static void main(String[] args) throws java.lang.Exception {
        FileSystem fs = FileSystems.getFileSystem(URI.create("jrt:/"));
        Path rootPath = fs.getPath("/");
        listFiles(rootPath);
    }
}

Maybe this should just live as a cronjob...? Not sure.

[kiritofeng]

Should we try dynamically loading the classes and checking if they extend java.lang.Exception? 😛

[Xyene]

If we're doing that then we should definitely do it as a cronjob, otherwise doing it on startup would take too long.

[kiritofeng]

I'm in favour of doing it as a cronjob via Github Actions since this list will only change when Java updates, which is relatively infrequent (and not really worth the overhead on startup).

[Xyene]

If by cronjob then we ought to do only the Java 9+ thing, since exceptions are unlikely to be removed, but may be added.

[Xyene]

And I guess to make this more likely, we should only whitelist java.* exceptions.