Properly handle bundled server.jar

common/src/main/java/net/neoforged/gradle/common/runtime/tasks/GenerateExtraJar.java

@@ -14,10 +14,14 @@
 import org.gradle.api.tasks.PathSensitive;
 import org.gradle.api.tasks.PathSensitivity;
 import org.gradle.api.tasks.TaskAction;
+import org.jetbrains.annotations.Nullable;
 
 import java.io.BufferedOutputStream;
 import java.io.File;
 import java.io.FileOutputStream;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.Set;
 import java.util.jar.Attributes;
@@ -103,7 +107,24 @@ private static void addSourceDistEntries(Set<String> distFiles,
         }
     }
 
-    private static Set<String> getFileIndex(ZipFile zipFile) {
+    private Set<String> getFileIndex(ZipFile zipFile) throws IOException {
+        // Support "nested" ZIP-Files as in recent server jars
+        var embeddedVersionPath = readEmbeddedVersionPath(zipFile);
+        if (embeddedVersionPath != null) {
+            // Extract the embedded zip and instead index that
+            var versionJarEntry = zipFile.getEntry(embeddedVersionPath);
+            if (versionJarEntry == null) {
+                throw new IOException("version list in jar file " + zipFile + " refers to missing entry " + embeddedVersionPath);
+            }
+            var unbundledFile = new File(getTemporaryDir(), "unpacked.jar");
+            try (var in = zipFile.getInputStream(versionJarEntry)) {
+                Files.copy(in, unbundledFile.toPath());
+            }
+            try (ZipFile zf = new ZipFile(unbundledFile)) {
+                return getFileIndex(zf);
+            }
+        }
+
         var result = new HashSet<String>(zipFile.size());
 
         var entries = zipFile.entries();
@@ -134,6 +155,40 @@ private static boolean isSignatureFile(String name) {
                );
     }
 
+    /**
+     * Server jars support embedding the actual jar file using an indirection via a version listing at
+     * META-INF/versions.list
+     * This method will try to read that list and return the path to the actual jar embedded in the bundle jar.
+     */
+    @Nullable
+    private static String readEmbeddedVersionPath(ZipFile zipFile) throws IOException {
+        var entry = zipFile.getEntry("META-INF/versions.list");
+        if (entry == null) {
+            return null;
+        }
+
+        var entries = new ArrayList<String>();
+        try (var in = zipFile.getInputStream(entry)) {
+            for (var line : new String(in.readAllBytes()).split("\n")) {
+                if (line.isBlank()) {
+                    continue;
+                }
+                String[] pts = line.split("\t");
+                if (pts.length != 3)
+                    throw new IOException("Invalid file list line: " + line + " in " + zipFile);
+                entries.add(pts[2]);
+            }
+        }
+
+        if (entries.isEmpty()) {
+            return null;
+        } else if (entries.size() == 1) {
+            return "META-INF/versions/" + entries.get(0);
+        } else {
+            throw new IOException("Version file list contains more than one entry in " + zipFile);
+        }
+    }
+
     @InputFile
     @PathSensitive(PathSensitivity.NONE)
     public abstract RegularFileProperty getOriginalJar();