begin working on bencode decoding

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

@@ -0,0 +1,71 @@
+package com.mykola2312.retracker.bencode;
+
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
+
+import com.mykola2312.retracker.bencode.error.BDecodeError;
+import com.mykola2312.retracker.bencode.error.BDecodeParseError;
+import com.mykola2312.retracker.bencode.error.BDecodeUnknown;
+
+public class BTree {
+	private BValue root = null;
+	
+	public BValue getRoot() {
+		return root;
+	}
+	
+	class BDecoder {
+		private byte[] data;
+		private int offset = 0;
+		
+		public BDecoder(byte[] data, int offset) {
+			this.data = data;
+			this.offset = offset;
+		}
+		
+		private Long parseLong(byte[] bytes) throws BDecodeParseError {
+			String strInt = new String(bytes, StandardCharsets.UTF_8);
+			try {
+				return Long.parseLong(strInt);
+			} catch (NumberFormatException e) {
+				throw new BDecodeParseError(data, offset, e);
+			}
+		}
+		
+		private static final byte BE_INTEGER = (byte)'i';
+		private static final byte BE_LIST = (byte)'l';
+		private static final byte BE_DICT = (byte)'d';
+		private static final byte BE_STRING_SEP = (byte)':';
+		private static final byte BE_END = (byte)'e';
+		
+		public BValue decode() throws BDecodeError {
+			BType type;
+			
+			// 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]);
+			}
+			offset++;
+			
+			if (type.equals(BType.INTEGER)) {
+				// advance until we hit end marker
+				int end = offset;
+				while (data[end] != BDecoder.BE_END) {
+					end++;
+				}
+				// convert bytes to string and string to integer
+				byte[] bytes = Arrays.copyOfRange(data, offset, end);
+				return new BInteger(parseLong(bytes));
+			}
+			
+			return null;
+		}
+	}
+	
+	public void decode(byte[] data) throws BDecodeError {
+		this.root = new BDecoder(data, 0).decode();
+	}
+}

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

@@ -0,0 +1,20 @@
+package com.mykola2312.retracker.bencode.error;
+
+public class BDecodeError extends Exception {
+	private static final long serialVersionUID = 4282658520481186036L;
+	
+	public byte[] data;
+	public int offset;
+	
+	public BDecodeError(byte[] data, int offset, String error) {
+		super(error);
+		this.data = data;
+		this.offset = offset;
+	}
+	
+	public BDecodeError(byte[] data, int offset) {
+		super(String.format("Error parsing data at offset %d", offset));
+		this.data = data;
+		this.offset = offset;
+	}
+}

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

@@ -0,0 +1,10 @@
+package com.mykola2312.retracker.bencode.error;
+
+public class BDecodeParseError extends BDecodeError {
+	private static final long serialVersionUID = 8987586062482975916L;
+
+	public BDecodeParseError(byte[] data, int offset, Throwable cause) {
+		super(data, offset, String.format("Failed to parse into primitive type at offset %d", offset));
+		initCause(cause);
+	}
+}

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

@@ -0,0 +1,12 @@
+package com.mykola2312.retracker.bencode.error;
+
+public class BDecodeUnknown extends BDecodeError {
+	private static final long serialVersionUID = -7027240782119100714L;
+	
+	byte unknown;
+	
+	public BDecodeUnknown(byte[] data, int offset, byte unknown) {
+		super(data, offset, String.format("Unknown symbol 0x%x at offset %d", unknown));
+		this.unknown = unknown;
+	}
+}

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

@@ -0,0 +1,27 @@
+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 org.junit.jupiter.api.Test;
+
+import com.mykola2312.retracker.bencode.error.BDecodeError;
+
+public class BTreeTest {
+	@Test
+	public void testParseInt() throws BDecodeError {
+		final byte[] data = "i696969e".getBytes();
+		
+		BTree tree = new BTree();
+		assertDoesNotThrow(() -> {
+			tree.decode(data);
+			
+			BValue root = tree.getRoot();
+			assertNotNull(root);
+			assertEquals(root, new BInteger(696969));
+			
+			System.out.println("testParseInt: " + root.toString());
+		});
+	}
+}