Java tutorial
/** * Copyright (C) 2011-2012 Turn, Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.tps.ttorrent.bcodec; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import java.io.EOFException; import java.math.BigInteger; import java.nio.ByteBuffer; import java.util.ArrayList; import java.util.List; import java.util.HashMap; import java.util.Map; import org.apache.commons.io.input.AutoCloseInputStream; /** * B-encoding decoder. * * <p> * A b-encoded byte stream can represent byte arrays, numbers, lists and maps * (dictionaries). This class implements a decoder of such streams into * {@link BEValue}s. * </p> * * <p> * Inspired by Snark's implementation. * </p> * * @author mpetazzoni * @see <a href="http://en.wikipedia.org/wiki/Bencode">B-encoding specification</a> */ public class BDecoder { // The InputStream to BDecode. private final InputStream in; // The last indicator read. // Zero if unknown. // '0'..'9' indicates a byte[]. // 'i' indicates an Number. // 'l' indicates a List. // 'd' indicates a Map. // 'e' indicates end of Number, List or Map (only used internally). // -1 indicates end of stream. // Call getNextIndicator to get the current value (will never return zero). private int indicator = 0; /** * Initializes a new BDecoder. * * <p> * Nothing is read from the given <code>InputStream</code> yet. * </p> * * @param in The input stream to read from. */ public BDecoder(InputStream in) { this.in = in; } /** * Decode a B-encoded stream. * * <p> * Automatically instantiates a new BDecoder for the provided input stream * and decodes its root member. * </p> * * @param in The input stream to read from. */ public static BEValue bdecode(InputStream in) throws IOException { return new BDecoder(in).bdecode(); } /** * Decode a B-encoded byte buffer. * * <p> * Automatically instantiates a new BDecoder for the provided buffer and * decodes its root member. * </p> * * @param data The {@link ByteBuffer} to read from. */ public static BEValue bdecode(ByteBuffer data) throws IOException { return BDecoder.bdecode(new AutoCloseInputStream(new ByteArrayInputStream(data.array()))); } /** * Returns what the next b-encoded object will be on the stream or -1 * when the end of stream has been reached. * * <p> * Can return something unexpected (not '0' .. '9', 'i', 'l' or 'd') when * the stream isn't b-encoded. * </p> * * This might or might not read one extra byte from the stream. */ private int getNextIndicator() throws IOException { if (this.indicator == 0) { this.indicator = in.read(); } return this.indicator; } /** * Gets the next indicator and returns either null when the stream * has ended or b-decodes the rest of the stream and returns the * appropriate BEValue encoded object. */ public BEValue bdecode() throws IOException { if (this.getNextIndicator() == -1) return null; if (this.indicator >= '0' && this.indicator <= '9') return this.bdecodeBytes(); else if (this.indicator == 'i') return this.bdecodeNumber(); else if (this.indicator == 'l') return this.bdecodeList(); else if (this.indicator == 'd') return this.bdecodeMap(); else throw new InvalidBEncodingException("Unknown indicator '" + this.indicator + "'"); } /** * Returns the next b-encoded value on the stream and makes sure it is a * byte array. * * @throws InvalidBEncodingException If it is not a b-encoded byte array. */ public BEValue bdecodeBytes() throws IOException { int c = this.getNextIndicator(); int num = c - '0'; if (num < 0 || num > 9) throw new InvalidBEncodingException("Number expected, not '" + (char) c + "'"); this.indicator = 0; c = this.read(); int i = c - '0'; while (i >= 0 && i <= 9) { // This can overflow! num = num * 10 + i; c = this.read(); i = c - '0'; } if (c != ':') { throw new InvalidBEncodingException("Colon expected, not '" + (char) c + "'"); } return new BEValue(read(num)); } /** * Returns the next b-encoded value on the stream and makes sure it is a * number. * * @throws InvalidBEncodingException If it is not a number. */ public BEValue bdecodeNumber() throws IOException { int c = this.getNextIndicator(); if (c != 'i') { throw new InvalidBEncodingException("Expected 'i', not '" + (char) c + "'"); } this.indicator = 0; c = this.read(); if (c == '0') { c = this.read(); if (c == 'e') return new BEValue(BigInteger.ZERO); else throw new InvalidBEncodingException("'e' expected after zero," + " not '" + (char) c + "'"); } // We don't support more the 255 char big integers char[] chars = new char[256]; int off = 0; if (c == '-') { c = this.read(); if (c == '0') throw new InvalidBEncodingException("Negative zero not allowed"); chars[off] = (char) c; off++; } if (c < '1' || c > '9') throw new InvalidBEncodingException("Invalid Integer start '" + (char) c + "'"); chars[off] = (char) c; off++; c = this.read(); int i = c - '0'; while (i >= 0 && i <= 9) { chars[off] = (char) c; off++; c = read(); i = c - '0'; } if (c != 'e') throw new InvalidBEncodingException("Integer should end with 'e'"); String s = new String(chars, 0, off); return new BEValue(new BigInteger(s)); } /** * Returns the next b-encoded value on the stream and makes sure it is a * list. * * @throws InvalidBEncodingException If it is not a list. */ public BEValue bdecodeList() throws IOException { int c = this.getNextIndicator(); if (c != 'l') { throw new InvalidBEncodingException("Expected 'l', not '" + (char) c + "'"); } this.indicator = 0; List<BEValue> result = new ArrayList<BEValue>(); c = this.getNextIndicator(); while (c != 'e') { result.add(this.bdecode()); c = this.getNextIndicator(); } this.indicator = 0; return new BEValue(result); } /** * Returns the next b-encoded value on the stream and makes sure it is a * map (dictionary). * * @throws InvalidBEncodingException If it is not a map. */ public BEValue bdecodeMap() throws IOException { int c = this.getNextIndicator(); if (c != 'd') { throw new InvalidBEncodingException("Expected 'd', not '" + (char) c + "'"); } this.indicator = 0; Map<String, BEValue> result = new HashMap<String, BEValue>(); c = this.getNextIndicator(); while (c != 'e') { // Dictionary keys are always strings. String key = this.bdecode().getString(); BEValue value = this.bdecode(); result.put(key, value); c = this.getNextIndicator(); } this.indicator = 0; return new BEValue(result); } /** * Returns the next byte read from the InputStream (as int). * * @throws EOFException If InputStream.read() returned -1. */ private int read() throws IOException { int c = this.in.read(); if (c == -1) throw new EOFException(); return c; } /** * Returns a byte[] containing length valid bytes starting at offset zero. * * @throws EOFException If InputStream.read() returned -1 before all * requested bytes could be read. Note that the byte[] returned might be * bigger then requested but will only contain length valid bytes. The * returned byte[] will be reused when this method is called again. */ private byte[] read(int length) throws IOException { byte[] result = new byte[length]; int read = 0; while (read < length) { int i = this.in.read(result, read, length - read); if (i == -1) throw new EOFException(); read += i; } return result; } }