fix: better String constructor from byte and char arrays (#530) (PR #533)

jadx-core/src/main/java/jadx/core/dex/info/MethodInfo.java

@@ -33,6 +33,21 @@ public final class MethodInfo {
 		shortId = makeSignature(true);
 	}
 
+	private MethodInfo(ClassInfo declClass, String name, List<ArgType> args, ArgType retType) {
+		this.name = name;
+		alias = name;
+		aliasFromPreset = false;
+		this.declClass = declClass;
+
+		this.args = args;
+		this.retType = retType;
+		shortId = makeSignature(true);
+	}
+
+	public static MethodInfo externalMth(ClassInfo declClass, String name, List<ArgType> args, ArgType retType) {
+		return new MethodInfo(declClass, name, args, retType);
+	}
+
 	public static MethodInfo fromDex(DexNode dex, int mthIndex) {
 		MethodInfo mth = dex.root().getInfoStorage().getMethod(dex, mthIndex);
 		if (mth != null) {

jadx-core/src/main/java/jadx/core/dex/instructions/InvokeNode.java

@@ -36,7 +36,7 @@ public class InvokeNode extends InsnNode implements CallMthInterface {
 		}
 	}
 
-	private InvokeNode(MethodInfo mth, InvokeType invokeType, int argsCount) {
+	public InvokeNode(MethodInfo mth, InvokeType invokeType, int argsCount) {
 		super(InsnType.INVOKE, argsCount);
 		this.mth = mth;
 		this.type = invokeType;

jadx-core/src/main/java/jadx/core/dex/visitors/SimplifyVisitor.java

@@ -8,7 +8,9 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import jadx.core.Consts;
+import jadx.core.deobf.NameMapper;
 import jadx.core.dex.attributes.AFlag;
+import jadx.core.dex.info.ClassInfo;
 import jadx.core.dex.info.FieldInfo;
 import jadx.core.dex.info.MethodInfo;
 import jadx.core.dex.instructions.ArithNode;
@@ -19,6 +21,7 @@ import jadx.core.dex.instructions.IfNode;
 import jadx.core.dex.instructions.IndexInsnNode;
 import jadx.core.dex.instructions.InsnType;
 import jadx.core.dex.instructions.InvokeNode;
+import jadx.core.dex.instructions.InvokeType;
 import jadx.core.dex.instructions.args.ArgType;
 import jadx.core.dex.instructions.args.FieldArg;
 import jadx.core.dex.instructions.args.InsnArg;
@@ -29,6 +32,7 @@ import jadx.core.dex.instructions.mods.TernaryInsn;
 import jadx.core.dex.nodes.BlockNode;
 import jadx.core.dex.nodes.InsnNode;
 import jadx.core.dex.nodes.MethodNode;
+import jadx.core.dex.nodes.RootNode;
 import jadx.core.dex.regions.conditions.IfCondition;
 
 public class SimplifyVisitor extends AbstractVisitor {
@@ -95,12 +99,55 @@ public class SimplifyVisitor extends AbstractVisitor {
 				}
 				break;
 
+			case CONSTRUCTOR:
+				simplfyConstructor(mth.root(), (ConstructorInsn) insn);
+				break;
+
 			default:
 				break;
 		}
 		return null;
 	}
 
+	private static void simplfyConstructor(RootNode root, ConstructorInsn insn) {
+		if (insn.getArgsCount() != 0
+				&& insn.getCallMth().getDeclClass().getType().equals(ArgType.STRING)) {
+			InsnArg arg = insn.getArg(0);
+			InsnNode node = arg.isInsnWrap()
+					? ((InsnWrapArg) arg).getWrapInsn()
+					: insn;
+		    if (node.getArgsCount() != 0) {
+		    	ArgType argType = node.getArg(0).getType();
+		    	if (node.getType() == InsnType.FILLED_NEW_ARRAY
+		    			&& (argType == ArgType.BYTE || argType == ArgType.CHAR)) {
+		    		int printable = 0;
+		    		byte[] arr = new byte[node.getArgsCount()];
+		    		for (int i = 0; i < arr.length; i++) {
+		    			arr[i] = (byte) ((LiteralArg) node.getArg(i)).getLiteral();
+		    			if (NameMapper.isPrintableChar(arr[i])) {
+		    				printable++;
+		    			}
+		    		}
+		    		if (printable >= arr.length - printable) {
+		    			InsnWrapArg wa = new InsnWrapArg(new ConstStringNode(new String(arr)));
+		    			if (insn.getArgsCount() == 1) {
+		    				insn.setArg(0, wa);
+		    			} else {
+		    				MethodInfo mi = MethodInfo.externalMth(
+		    						ClassInfo.fromType(root, ArgType.STRING),
+		    						"getBytes",
+		    						Collections.emptyList(),
+		    						ArgType.array(ArgType.BYTE));
+		    				InvokeNode in = new InvokeNode(mi, InvokeType.VIRTUAL, 1);
+		    				in.addArg(wa);
+		    				insn.setArg(0, new InsnWrapArg(in));
+		    			}
+		    		}
+		    	}
+		    }
+		}
+	}
+
 	private static InsnNode processCast(MethodNode mth, InsnNode insn) {
 		InsnArg castArg = insn.getArg(0);
 		ArgType argType = castArg.getType();

jadx-core/src/test/java/jadx/tests/integration/others/TestStringConstructor.java

+package jadx.tests.integration.others;
+
+import static jadx.tests.api.utils.JadxMatchers.containsOne;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import java.nio.charset.StandardCharsets;
+
+import org.junit.jupiter.api.Test;
+
+import jadx.core.dex.nodes.ClassNode;
+import jadx.tests.api.IntegrationTest;
+
+public class TestStringConstructor extends IntegrationTest {
+
+	public static class TestCls {
+		public String tag = new String(new byte[] {'a', 'b', 'c'});
+	}
+
+	@Test
+	public void test() {
+		ClassNode cls = getClassNode(TestCls.class);
+		String code = cls.getCode().toString();
+
+		assertThat(code, containsOne("abc"));
+	}
+
+	public static class TestCls2 {
+		public String tag = new String(new byte[] {'a', 'b', 'c'}, StandardCharsets.UTF_8);
+	}
+
+	@Test
+	public void test2() {
+		ClassNode cls = getClassNode(TestCls2.class);
+		String code = cls.getCode().toString();
+
+		assertThat(code, containsOne("new String(\"abc\".getBytes(), StandardCharsets.UTF_8)"));
+	}
+
+	public static class TestCls3 {
+		public String tag = new String(new byte[] {1, 2, 3, 'a', 'b', 'c'});
+	}
+
+	@Test
+	public void test3() {
+		ClassNode cls = getClassNode(TestCls3.class);
+		String code = cls.getCode().toString();
+
+		assertThat(code, containsOne("\\u0001\\u0002\\u0003abc"));
+	}
+
+	public static class TestCls4 {
+		public String tag = new String(new char[] {1, 2, 3, 'a', 'b', 'c'});
+	}
+
+	@Test
+	public void test4() {
+		ClassNode cls = getClassNode(TestCls4.class);
+		String code = cls.getCode().toString();
+
+		assertThat(code, containsOne("\\u0001\\u0002\\u0003abc"));
+	}
+
+	public static class TestCls5 {
+		public String tag = new String(new char[] {1, 2, 3, 'a', 'b'});
+	}
+
+	@Test
+	public void test5() {
+		ClassNode cls = getClassNode(TestCls5.class);
+		String code = cls.getCode().toString();
+
+		assertThat(code, containsOne("{1, 2, 3, 'a', 'b'}"));
+	}
+
+	public static class TestClsNegative {
+		public String tag = new String();
+	}
+
+	@Test
+	public void testNegative() {
+		ClassNode cls = getClassNode(TestClsNegative.class);
+		String code = cls.getCode().toString();
+
+		assertThat(code, containsOne("tag = new String();"));
+	}
+}