Speedup jar package scanning

src/main/java/cpw/mods/cl/JarModuleFinder.java

@@ -23,6 +23,9 @@ public class JarModuleFinder implements ModuleFinder {
     JarModuleFinder(final SecureJar... jars) {
         record ref(SecureJar.ModuleDataProvider jar, ModuleReference ref) {}
         this.moduleReferenceMap = Arrays.stream(jars)
+                // Computing the module descriptor can be slow so do it in parallel!
+                // Jars are not thread safe internally but they are independent, so this is safe.
+                .parallel()
                 .map(jar->new ref(jar.moduleDataProvider(), new JarModuleReference(jar.moduleDataProvider())))
                 .collect(Collectors.toMap(r->r.jar.name(), r->r.ref, (r1, r2)->r1));
     }

src/main/java/cpw/mods/jarhandling/SecureJarRuntime.java

@@ -0,0 +1,12 @@
+package cpw.mods.jarhandling;
+
+import java.util.Set;
+
+public interface SecureJarRuntime {
+    /**
+     * Return the set of top-level folders in the JARs that should not be searched for class files.
+     */
+    default Set<String> ignoredRootPackages() {
+        return Set.of("META-INF");
+    }
+}

src/main/java/cpw/mods/jarhandling/impl/Jar.java

@@ -11,9 +11,12 @@
 import java.io.UncheckedIOException;
 import java.lang.module.ModuleDescriptor;
 import java.net.URI;
+import java.nio.file.FileVisitResult;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.nio.file.SimpleFileVisitor;
+import java.nio.file.attribute.BasicFileAttributes;
 import java.nio.file.spi.FileSystemProvider;
 import java.security.CodeSigner;
 import java.util.*;
@@ -214,16 +217,29 @@ public String name() {
     @Override
     public Set<String> getPackages() {
         if (this.packages == null) {
-            try (var walk = Files.walk(this.filesystem.getRoot())) {
-                this.packages = walk
-                    .filter(path->path.getNameCount()>0)
-                    .filter(path->!path.getName(0).toString().equals("META-INF"))
-                    .filter(path->path.getFileName().toString().endsWith(".class"))
-                    .filter(Files::isRegularFile)
-                    .map(Path::getParent)
-                    .map(path->path.toString().replace('/','.'))
-                    .filter(pkg->pkg.length()!=0)
-                    .collect(toSet());
+            Set<String> packages = new HashSet<>();
+            try {
+                Files.walkFileTree(this.filesystem.getRoot(), new SimpleFileVisitor<>() {
+                    @Override
+                    public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) {
+                        if (file.getFileName().toString().endsWith(".class") && attrs.isRegularFile()) {
+                            var pkg = file.getParent().toString().replace('/','.');
+                            if (pkg.length() != 0) {
+                                packages.add(pkg);
+                            }
+                        }
+                        return FileVisitResult.CONTINUE;
+                    }
+
+                    @Override
+                    public FileVisitResult preVisitDirectory(Path path, BasicFileAttributes attrs) {
+                        if (path.getNameCount() > 0 && SecureJarEnvironment.isIgnoredRootPackage(path.getName(0).toString())) {
+                            return FileVisitResult.SKIP_SUBTREE;
+                        }
+                        return FileVisitResult.CONTINUE;
+                    }
+                });
+                this.packages = packages;
             } catch (IOException e) {
                 throw new UncheckedIOException(e);
             }

src/main/java/cpw/mods/jarhandling/impl/SecureJarEnvironment.java

@@ -0,0 +1,30 @@
+package cpw.mods.jarhandling.impl;
+
+import cpw.mods.jarhandling.SecureJarRuntime;
+
+import java.util.ServiceLoader;
+import java.util.Set;
+
+class SecureJarEnvironment {
+    static final SecureJarRuntime runtime = findRuntime();
+    static final Set<String> ignoredRootPackages = findIgnoredRootPackages();
+
+    private static SecureJarRuntime findRuntime() {
+        return ServiceLoader.load(SecureJarRuntime.class).findFirst().orElse(new SecureJarRuntime() {});
+    }
+
+    private static Set<String> findIgnoredRootPackages() {
+        var packages = runtime.ignoredRootPackages();
+        // Validate root packages
+        for (var pkg : packages) {
+            if (pkg.contains(".") || pkg.contains("/")) {
+                throw new IllegalArgumentException("Invalid root package: " + pkg);
+            }
+        }
+        return packages;
+    }
+
+    public static boolean isIgnoredRootPackage(String pkg) {
+        return ignoredRootPackages.contains(pkg);
+    }
+}

src/main/java/module-info.java

@@ -14,4 +14,5 @@
     provides java.nio.file.spi.FileSystemProvider with UnionFileSystemProvider;
     uses cpw.mods.cl.ModularURLHandler.IURLProvider;
     provides ModularURLHandler.IURLProvider with UnionURLStreamHandler;
+    uses cpw.mods.jarhandling.SecureJarRuntime;
 }