adding config for maximum decoded string length to display in a comment

Author: nklapste

src/main/java/jadx/plugins/stringdecoder/B64DeobfuscateOptions.java

@@ -5,16 +5,25 @@
 public class B64DeobfuscateOptions extends BasePluginOptionsBuilder {
 
 	private boolean enable;
+	private int maxCommentLength;
 
 	@Override
 	public void registerOptions() {
 		boolOption(JadxStringDecoderPlugin.PLUGIN_ID + ".enable")
 				.description("Enable Base64 string detection and decoding")
 				.defaultValue(true)
 				.setter(v -> enable = v);
+		intOption(JadxStringDecoderPlugin.PLUGIN_ID + ".maxCommentLength")
+				.description("Maximum decoded string length in comment (0 for unlimited)")
+				.defaultValue(100)
+				.setter(v -> maxCommentLength = v);
 	}
 
 	public boolean isEnable() {
 		return enable;
 	}
+
+	public int getMaxCommentLength() {
+		return maxCommentLength;
+	}
 }

src/main/java/jadx/plugins/stringdecoder/B64DeobfuscatePass.java

@@ -17,6 +17,12 @@
 
 public class B64DeobfuscatePass implements JadxDecompilePass {
 
+	private final int maxCommentLength;
+
+	public B64DeobfuscatePass(int maxCommentLength) {
+		this.maxCommentLength = maxCommentLength;
+	}
+
 	@Override
 	public JadxPassInfo getInfo() {
 		return new OrderedJadxPassInfo(
@@ -53,8 +59,8 @@ public void visit(MethodNode mth) {
 		}
 	}
 
-	private static void processConstString(ConstStringNode insn) {
-		String decoded = B64Detector.detect(insn.getString());
+	private void processConstString(ConstStringNode insn) {
+		String decoded = B64Detector.detect(insn.getString(), maxCommentLength);
 		if (decoded != null) {
 			insn.addAttr(AType.CODE_COMMENTS, new CodeComment("b64: " + decoded, CommentStyle.LINE));
 		}

src/main/java/jadx/plugins/stringdecoder/B64Detector.java

@@ -14,13 +14,15 @@ public final class B64Detector {
 	private static final Pattern BASE64_URL_SAFE = Pattern.compile("^[A-Za-z0-9_-]+=*$");
 	private static final int MIN_LENGTH = 8;
 	private static final double MIN_PRINTABLE_RATIO = 0.75;
-	static final int MAX_COMMENT_LENGTH = 100;
 
 	private B64Detector() {
 	}
 
-	/** Returns the decoded+truncated string if {@code str} looks like Base64, otherwise null. */
-	public static String detect(String str) {
+	/**
+	 * Returns the decoded string if {@code str} looks like Base64, otherwise null.
+	 * The result is truncated to {@code maxLength} chars (0 = unlimited).
+	 */
+	public static String detect(String str, int maxLength) {
 		if (str.length() < MIN_LENGTH) {
 			return null;
 		}
@@ -31,7 +33,7 @@ public static String detect(String str) {
 		if (decoded == null) {
 			return null;
 		}
-		return truncate(decoded);
+		return truncate(decoded, maxLength);
 	}
 
 	private static String tryDecode(String str) {
@@ -69,10 +71,10 @@ private static boolean isPrintable(String str) {
 		return (double) printableCount / str.length() >= MIN_PRINTABLE_RATIO;
 	}
 
-	static String truncate(String str) {
+	static String truncate(String str, int maxLength) {
 		String safe = str.replace("\n", "\\n").replace("\r", "\\r");
-		if (safe.length() > MAX_COMMENT_LENGTH) {
-			return safe.substring(0, MAX_COMMENT_LENGTH) + "...";
+		if (maxLength > 0 && safe.length() > maxLength) {
+			return safe.substring(0, maxLength) + "...";
 		}
 		return safe;
 	}

src/main/java/jadx/plugins/stringdecoder/B64FieldInitPass.java

@@ -14,6 +14,12 @@
 
 public class B64FieldInitPass implements JadxDecompilePass {
 
+	private final int maxCommentLength;
+
+	public B64FieldInitPass(int maxCommentLength) {
+		this.maxCommentLength = maxCommentLength;
+	}
+
 	@Override
 	public JadxPassInfo getInfo() {
 		return new OrderedJadxPassInfo(
@@ -37,7 +43,7 @@ public boolean visit(ClassNode cls) {
 			if (!(initInsn instanceof ConstStringNode)) {
 				continue;
 			}
-			String decoded = B64Detector.detect(((ConstStringNode) initInsn).getString());
+			String decoded = B64Detector.detect(((ConstStringNode) initInsn).getString(), maxCommentLength);
 			if (decoded != null) {
 				field.addCodeComment("b64: " + decoded);
 			}

src/main/java/jadx/plugins/stringdecoder/JadxStringDecoderPlugin.java

@@ -24,8 +24,8 @@ public JadxPluginInfo getPluginInfo() {
 	public void init(JadxPluginContext context) {
 		context.registerOptions(options);
 		if (options.isEnable()) {
-			context.addPass(new B64DeobfuscatePass());
-			context.addPass(new B64FieldInitPass());
+			context.addPass(new B64DeobfuscatePass(options.getMaxCommentLength()));
+			context.addPass(new B64FieldInitPass(options.getMaxCommentLength()));
 		}
 	}
 }

src/test/java/jadx/plugins/stringdecoder/JadxStringDecoderPluginTest.java

@@ -8,6 +8,7 @@
 import java.io.File;
 import java.net.URISyntaxException;
 import java.net.URL;
+import java.util.Map;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -84,9 +85,32 @@ public void staticFieldB64Test() throws Exception {
 		assertThat(code).contains("b64: hello");
 	}
 
+	@Test
+	public void maxCommentLengthOptionTest() throws Exception {
+		// maxCommentLength=10 should truncate the 650-char decoded string to 10 chars + "..."
+		String code = decompileSmali("b64/long_b64.smali", Map.of("b64-deobfuscate.maxCommentLength", "10"));
+		System.out.println(code);
+		assertThat(code).contains("b64: " + "A".repeat(10) + "...");
+		assertThat(code).doesNotContain("A".repeat(11));
+	}
+
+	@Test
+	public void unlimitedCommentLengthOptionTest() throws Exception {
+		// maxCommentLength=0 should produce a comment with all 650 decoded chars, no truncation
+		String code = decompileSmali("b64/long_b64.smali", Map.of("b64-deobfuscate.maxCommentLength", "0"));
+		System.out.println(code);
+		assertThat(code).contains("b64: " + "A".repeat(650));
+		assertThat(code).doesNotContain("...");
+	}
+
 	private String decompileSmali(String fileName) throws Exception {
+		return decompileSmali(fileName, Map.of());
+	}
+
+	private String decompileSmali(String fileName, Map<String, String> pluginOptions) throws Exception {
 		JadxArgs args = new JadxArgs();
 		args.getInputFiles().add(getSampleFile(fileName));
+		args.setPluginOptions(pluginOptions);
 		try (JadxDecompiler jadx = new JadxDecompiler(args)) {
 			jadx.load();
 			JavaClass cls = jadx.getClasses().get(0);