improve support for bytecode patching signed jars (#128613)

* improve support for bytecode patching signed jars

* Update docs/changelog/128613.yaml
---------

Co-authored-by: elasticsearchmachine <infra-root+elasticsearchmachine@elastic.co>
Co-authored-by: Johannes Freden Jansson <johannes.freden@elastic.co>

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/dependencies/patches/Utils.java

@@ -24,9 +24,11 @@ import java.util.Enumeration;
 import java.util.HexFormat;
 import java.util.Locale;
 import java.util.function.Function;
+import java.util.jar.Attributes;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
 import java.util.jar.JarOutputStream;
+import java.util.jar.Manifest;
 import java.util.stream.Collectors;
 
 import static org.objectweb.asm.ClassWriter.COMPUTE_FRAMES;
@@ -60,6 +62,10 @@ public class Utils {
         }
     }
 
+    public static void patchJar(File inputJar, File outputJar, Collection<PatcherInfo> patchers) {
+        patchJar(inputJar, outputJar, patchers, false);
+    }
+
     /**
      * Patches the classes in the input JAR file, using the collection of patchers. Each patcher specifies a target class (its jar entry
      * name) and the SHA256 digest on the class bytes.
@@ -69,8 +75,11 @@ public class Utils {
      * @param inputFile the JAR file to patch
      * @param outputFile the output (patched) JAR file
      * @param patchers list of patcher info (classes to patch (jar entry name + optional SHA256 digest) and ASM visitor to transform them)
+     * @param unsignJar whether to remove class signatures from the JAR Manifest; set this to true when patching a signed JAR,
+     *                  otherwise the patched classes will fail to load at runtime due to mismatched signatures.
+     *                  @see <a href="https://docs.oracle.com/javase/tutorial/deployment/jar/intro.html">Understanding Signing and Verification</a>
      */
-    public static void patchJar(File inputFile, File outputFile, Collection<PatcherInfo> patchers) {
+    public static void patchJar(File inputFile, File outputFile, Collection<PatcherInfo> patchers, boolean unsignJar) {
         var classPatchers = patchers.stream().collect(Collectors.toMap(PatcherInfo::jarEntryName, Function.identity()));
         var mismatchedClasses = new ArrayList<MismatchInfo>();
         try (JarFile jarFile = new JarFile(inputFile); JarOutputStream jos = new JarOutputStream(new FileOutputStream(outputFile))) {
@@ -101,9 +110,23 @@ public class Utils {
                         );
                     }
                 } else {
-                    // Read the entry's data and write it to the new JAR
                     try (InputStream is = jarFile.getInputStream(entry)) {
-                        is.transferTo(jos);
+                        if (unsignJar && entryName.equals("META-INF/MANIFEST.MF")) {
+                            var manifest = new Manifest(is);
+                            for (var manifestEntry : manifest.getEntries().entrySet()) {
+                                var nonSignatureAttributes = new Attributes();
+                                for (var attribute : manifestEntry.getValue().entrySet()) {
+                                    if (attribute.getKey().toString().endsWith("Digest") == false) {
+                                        nonSignatureAttributes.put(attribute.getKey(), attribute.getValue());
+                                    }
+                                }
+                                manifestEntry.setValue(nonSignatureAttributes);
+                            }
+                            manifest.write(jos);
+                        } else if (unsignJar == false || entryName.matches("META-INF/.*\\.SF") == false) {
+                            // Read the entry's data and write it to the new JAR
+                            is.transferTo(jos);
+                        }
                     }
                 }
                 jos.closeEntry();

docs/changelog/128613.yaml

@@ -0,0 +1,5 @@
+pr: 128613
+summary: Improve support for bytecode patching signed jars
+area: Infra/Core
+type: enhancement
+issues: []