fix: don't use FileChannel on ZipFs to avoid creation of temp files (#950)

jadx-plugins/jadx-dex-input/src/main/java/jadx/plugins/input/dex/DexFileLoader.java

@@ -1,8 +1,7 @@
 package jadx.plugins.input.dex;
 
 import java.io.IOException;
-import java.nio.ByteBuffer;
-import java.nio.channels.FileChannel;
+import java.io.InputStream;
 import java.nio.file.FileSystem;
 import java.nio.file.FileSystems;
 import java.nio.file.FileVisitResult;
@@ -12,7 +11,6 @@ import java.nio.file.SimpleFileVisitor;
 import java.nio.file.StandardOpenOption;
 import java.nio.file.attribute.BasicFileAttributes;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
@@ -35,11 +33,15 @@ public class DexFileLoader {
 	}
 
 	private static List<DexReader> loadDexFromPath(Path path, int depth) {
-		try (FileChannel fileChannel = FileChannel.open(path, StandardOpenOption.READ)) {
-			if (isDex(fileChannel)) {
-				return Collections.singletonList(new DexReader(path, fileChannel));
+		try (InputStream inputStream = Files.newInputStream(path, StandardOpenOption.READ)) {
+			byte[] magic = new byte[DexConsts.MAX_MAGIC_SIZE];
+			if (inputStream.read(magic) != magic.length) {
+				return Collections.emptyList();
 			}
-			if (depth == 0 && isZip(fileChannel)) {
+			if (isStartWithBytes(magic, DexConsts.DEX_FILE_MAGIC)) {
+				return Collections.singletonList(new DexReader(path));
+			}
+			if (depth == 0 && isStartWithBytes(magic, DexConsts.ZIP_FILE_MAGIC)) {
 				return collectDexFromZip(path, depth);
 			}
 		} catch (Exception e) {
@@ -64,22 +66,16 @@ public class DexFileLoader {
 		return result;
 	}
 
-	private static boolean isDex(FileChannel fileChannel) {
-		return isStartWithBytes(fileChannel, DexConsts.DEX_FILE_MAGIC);
-	}
-
-	private static boolean isZip(FileChannel fileChannel) {
-		return isStartWithBytes(fileChannel, DexConsts.ZIP_FILE_MAGIC);
-	}
-
-	private static boolean isStartWithBytes(FileChannel fileChannel, byte[] startBytes) {
-		try {
-			fileChannel.position(0);
-			ByteBuffer buf = ByteBuffer.allocate(startBytes.length);
-			fileChannel.read(buf);
-			return Arrays.equals(startBytes, buf.array());
-		} catch (Exception e) {
+	private static boolean isStartWithBytes(byte[] fileMagic, byte[] expectedBytes) {
+		int len = expectedBytes.length;
+		if (fileMagic.length < len) {
 			return false;
 		}
+		for (int i = 0; i < len; i++) {
+			if (fileMagic[i] != expectedBytes[i]) {
+				return false;
+			}
+		}
+		return true;
 	}
 }

jadx-plugins/jadx-dex-input/src/main/java/jadx/plugins/input/dex/DexReader.java

@@ -3,8 +3,8 @@ package jadx.plugins.input.dex;
 import java.io.Closeable;
 import java.io.IOException;
 import java.nio.ByteBuffer;
-import java.nio.channels.FileChannel;
 import java.nio.file.FileSystem;
+import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.function.Consumer;
 
@@ -17,32 +17,15 @@ import jadx.plugins.input.dex.sections.annotations.AnnotationsParser;
 public class DexReader implements Closeable {
 
 	private final Path path;
-	private final FileChannel fileChannel;
 	private final ByteBuffer buf;
 	private final DexHeader header;
 
-	public DexReader(Path path, FileChannel fileChannel) throws IOException {
+	public DexReader(Path path) throws IOException {
 		this.path = path;
-		this.fileChannel = fileChannel;
-		this.buf = loadIntoByteBuffer(fileChannel);
+		this.buf = ByteBuffer.wrap(Files.readAllBytes(path));
 		this.header = new DexHeader(new SectionReader(this, 0));
 	}
 
-	private static ByteBuffer loadIntoByteBuffer(FileChannel fileChannel) throws IOException {
-		long size = fileChannel.size();
-		if (size > Integer.MAX_VALUE) {
-			throw new IOException("File too big");
-		}
-		int readSize = (int) size;
-		ByteBuffer buf = ByteBuffer.allocate(readSize);
-		fileChannel.position(0);
-		int read = fileChannel.read(buf);
-		if (read != readSize) {
-			throw new IOException("Failed to read whole file into buffer. Read: " + read + ", expected: " + readSize);
-		}
-		return buf;
-	}
-
 	public String getDexVersion() {
 		return this.header.getVersion();
 	}
@@ -86,7 +69,6 @@ public class DexReader implements Closeable {
 
 	@Override
 	public void close() throws IOException {
-		this.fileChannel.close();
 	}
 
 	@Override

jadx-plugins/jadx-dex-input/src/main/java/jadx/plugins/input/dex/sections/DexConsts.java

@@ -6,6 +6,8 @@ public class DexConsts {
 
 	public static final byte[] ZIP_FILE_MAGIC = { 0x50, 0x4B, 0x03, 0x04 };
 
+	public static final int MAX_MAGIC_SIZE = 4;
+
 	public static final int ENDIAN_CONSTANT = 0x12345678;
 
 	public static final int NO_INDEX = -1;