Dynamic load updated APK for patching

Magisk Manager sometimes updates the code for patching the APK due to several changes.
When an old manager tries to patch an updated APK using its internal methods, it is
sometimes incomplete, or simply won't work at all.

This commit exposes an API that can be dynamically loaded from an old app to invoke the
updated patchAPK method from the downloaded new APK.

app/src/full/java/a/a.java

@@ -1,10 +1,13 @@
 package a;
 
 import com.topjohnwu.core.utils.BootSigner;
+import com.topjohnwu.magisk.utils.PatchAPK;
 
 import androidx.annotation.Keep;
 
 @Keep
 public class a extends BootSigner {
-    /* stub */
+    public static boolean patchAPK(String in, String out, String pkg) {
+        return PatchAPK.patch(in, out, pkg);
+    }
 }

app/src/full/java/com/topjohnwu/magisk/utils/DownloadApp.java

@@ -19,6 +19,8 @@ import java.io.BufferedOutputStream;
 import java.io.File;
 import java.io.FileOutputStream;
 
+import dalvik.system.DexClassLoader;
+
 public class DownloadApp {
 
     public static void upgrade(String name) {
@@ -72,10 +74,16 @@ public class DownloadApp {
                 progress.update();
                 patched = new File(apk.getParent(), "patched.apk");
                 try {
-                    JarMap jarMap = PatchAPK.patch(apk.getPath(), app.getPackageName());
+                    // Try using the new APK to patch itself
-                    SignAPK.sign(jarMap, new BufferedOutputStream(new FileOutputStream(patched)));
+                    ClassLoader loader = new DexClassLoader(apk.getPath(),
+                            apk.getParent(), null, ClassLoader.getSystemClassLoader());
+                    loader.loadClass("a.a")
+                            .getMethod("patchAPK", String.class, String.class, String.class)
+                            .invoke(null, apk.getPath(), patched.getPath(), app.getPackageName());
                 } catch (Exception e) {
-                    return;
+                    e.printStackTrace();
+                    // Fallback to use the current implementation
+                    PatchAPK.patch(apk.getPath(), patched.getPath(), app.getPackageName());
                 }
             }
             APKInstall.install(app, patched);

app/src/full/java/com/topjohnwu/magisk/utils/PatchAPK.java

@@ -102,14 +102,8 @@ public class PatchAPK {
         File repack = new File(app.getFilesDir(), "patched.apk");
         String pkg = genPackageName("com.", BuildConfig.APPLICATION_ID.length());
 
-        try {
+        if (!patch(app.getPackageCodePath(), repack.getPath(), pkg))
-            JarMap apk;
-            if ((apk = patch(app.getPackageCodePath(), pkg)) == null)
-                return false;
-            SignAPK.sign(apk, new BufferedOutputStream(new FileOutputStream(repack)));
-        } catch (Exception e) {
             return false;
-        }
 
         // Install the application
         repack.setReadable(true, false);
@@ -123,23 +117,24 @@ public class PatchAPK {
         return true;
     }
 
-    public static JarMap patch(String apk, String pkg) {
+    public static boolean patch(String in, String out, String pkg) {
         try {
-            JarMap jar = new JarMap(apk);
+            JarMap jar = new JarMap(in);
             JarEntry je = jar.getJarEntry(Const.ANDROID_MANIFEST);
             byte xml[] = jar.getRawData(je);
 
             if (!findAndPatch(xml, BuildConfig.APPLICATION_ID, pkg) ||
                     !findAndPatch(xml, R.string.app_name, R.string.re_app_name))
-                return null;
+                return false;
 
             // Write in changes
             jar.getOutputStream(je).write(xml);
-            return jar;
+            SignAPK.sign(jar, new BufferedOutputStream(new FileOutputStream(out)));
         } catch (Exception e) {
             e.printStackTrace();
-            return null;
+            return false;
         }
+        return true;
     }
 
     public static void hideManager() {