handle cases of malformed bencode data

src/main/java/com/mykola2312/retracker/bencode/BTree.java

@@ -4,8 +4,8 @@ import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 
 import com.mykola2312.retracker.bencode.error.BDecodeError;
+import com.mykola2312.retracker.bencode.error.BDecodeMalformed;
 import com.mykola2312.retracker.bencode.error.BDecodeParseError;
-import com.mykola2312.retracker.bencode.error.BDecodeUnknown;
 
 public class BTree {
 	private BValue root = null;
@@ -40,22 +40,31 @@ public class BTree {
 		
 		public BValue decode() throws BDecodeError {
 			BType type;
+			if (data.length < 2) {
+				/* no bencode data can be less than 2 bytes: for integer must be 'i0e' atleast,
+				 * strings must be at least '0:' and lists and dicts can be empty
+				 */
+				throw new BDecodeMalformed(data, offset, "data is shorter than 2 bytes");
+			}
 			
 			// consume and determine type
 			switch (data[offset]) {
 			case BE_INTEGER: type = BType.INTEGER; break;
 			case BE_LIST: type = BType.LIST; break;
 			case BE_DICT: type = BType.DICT; break;
-			default: throw new BDecodeUnknown(data, offset, data[offset]);
+			default: type = BType.STRING;
 			}
 			offset++;
 			
 			if (type.equals(BType.INTEGER)) {
 				// advance until we hit end marker
 				int end = offset;
-				while (data[end] != BDecoder.BE_END) {
+				while (end < data.length && data[end] != BDecoder.BE_END) {
 					end++;
 				}
+				if (end == data.length) {
+					throw new BDecodeMalformed(data, offset, "no integer terminator");
+				}
 				// convert bytes to string and string to integer
 				byte[] bytes = Arrays.copyOfRange(data, offset, end);
 				return new BInteger(parseLong(bytes));

src/main/java/com/mykola2312/retracker/bencode/error/BDecodeMalformed.java

@@ -0,0 +1,13 @@
+package com.mykola2312.retracker.bencode.error;
+
+/* this exception should be thrown in cases buffer overrun,
+ * missing terminators and other nasty stuff. but it also
+ * could signal that there is parsing logic error
+ */
+public class BDecodeMalformed extends BDecodeError {
+	private static final long serialVersionUID = -8134440302174728903L;
+
+	public BDecodeMalformed(byte[] data, int offset, String reason) {
+		super(data, offset, reason);
+	}
+}

src/test/java/com/mykola2312/retracker/bencode/BTreeTest.java

@@ -3,10 +3,12 @@ package com.mykola2312.retracker.bencode;
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import org.junit.jupiter.api.Test;
 
 import com.mykola2312.retracker.bencode.error.BDecodeError;
+import com.mykola2312.retracker.bencode.error.BDecodeMalformed;
 
 public class BTreeTest {
 	@Test
@@ -24,4 +26,14 @@ public class BTreeTest {
 			System.out.println("testParseInt: " + root.toString());
 		});
 	}
+	
+	@Test
+	public void testParseIntOverrun() throws BDecodeError {
+		final byte[] data = "i696969".getBytes();
+		
+		BTree tree = new BTree();
+		assertThrows(BDecodeMalformed.class, () -> {
+			tree.decode(data);
+		});
+	}
 }