/* * Copyright (C) 2016 The Android Open Source Project * * 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.google.android.exoplayer2.extractor.mkv; import com.google.android.exoplayer2.C; import com.google.android.exoplayer2.extractor.ExtractorInput; import java.io.EOFException; import java.io.IOException; /** * Reads EBML variable-length integers (varints) from an {@link ExtractorInput}. */ /* package */ final class VarintReader { private static final int STATE_BEGIN_READING = 0; private static final int STATE_READ_CONTENTS = 1; /** * The first byte of a variable-length integer (varint) will have one of these bit masks * indicating the total length in bytes. * * <p>{@code 0x80} is a one-byte integer, {@code 0x40} is two bytes, and so on up to eight bytes. */ private static final long[] VARINT_LENGTH_MASKS = new long[] { 0x80L, 0x40L, 0x20L, 0x10L, 0x08L, 0x04L, 0x02L, 0x01L }; private final byte[] scratch; private int state; private int length; public VarintReader() { scratch = new byte[8]; } /** * Resets the reader to start reading a new variable-length integer. */ public void reset() { state = STATE_BEGIN_READING; length = 0; } /** * Reads an EBML variable-length integer (varint) from an {@link ExtractorInput} such that * reading can be resumed later if an error occurs having read only some of it. * <p> * If an value is successfully read, then the reader will automatically reset itself ready to * read another value. * <p> * If an {@link IOException} or {@link InterruptedException} is throw, the read can be resumed * later by calling this method again, passing an {@link ExtractorInput} providing data starting * where the previous one left off. * * @param input The {@link ExtractorInput} from which the integer should be read. * @param allowEndOfInput True if encountering the end of the input having read no data is * allowed, and should result in {@link C#RESULT_END_OF_INPUT} being returned. False if it * should be considered an error, causing an {@link EOFException} to be thrown. * @param removeLengthMask Removes the variable-length integer length mask from the value. * @param maximumAllowedLength Maximum allowed length of the variable integer to be read. * @return The read value, or {@link C#RESULT_END_OF_INPUT} if {@code allowEndOfStream} is true * and the end of the input was encountered, or {@link C#RESULT_MAX_LENGTH_EXCEEDED} if the * length of the varint exceeded maximumAllowedLength. * @throws IOException If an error occurs reading from the input. * @throws InterruptedException If the thread is interrupted. */ public long readUnsignedVarint(ExtractorInput input, boolean allowEndOfInput, boolean removeLengthMask, int maximumAllowedLength) throws IOException, InterruptedException { if (state == STATE_BEGIN_READING) { // Read the first byte to establish the length. if (!input.readFully(scratch, 0, 1, allowEndOfInput)) { return C.RESULT_END_OF_INPUT; } int firstByte = scratch[0] & 0xFF; length = parseUnsignedVarintLength(firstByte); if (length == C.LENGTH_UNSET) { throw new IllegalStateException("No valid varint length mask found"); } state = STATE_READ_CONTENTS; } if (length > maximumAllowedLength) { state = STATE_BEGIN_READING; return C.RESULT_MAX_LENGTH_EXCEEDED; } if (length != 1) { // Read the remaining bytes. input.readFully(scratch, 1, length - 1); } state = STATE_BEGIN_READING; return assembleVarint(scratch, length, removeLengthMask); } /** * Returns the number of bytes occupied by the most recently parsed varint. */ public int getLastLength() { return length; } /** * Parses and the length of the varint given the first byte. * * @param firstByte First byte of the varint. * @return Length of the varint beginning with the given byte if it was valid, * {@link C#LENGTH_UNSET} otherwise. */ public static int parseUnsignedVarintLength(int firstByte) { int varIntLength = C.LENGTH_UNSET; for (int i = 0; i < VARINT_LENGTH_MASKS.length; i++) { if ((VARINT_LENGTH_MASKS[i] & firstByte) != 0) { varIntLength = i + 1; break; } } return varIntLength; } /** * Assemble a varint from the given byte array. * * @param varintBytes Bytes that make up the varint. * @param varintLength Length of the varint to assemble. * @param removeLengthMask Removes the variable-length integer length mask from the value. * @return Parsed and assembled varint. */ public static long assembleVarint(byte[] varintBytes, int varintLength, boolean removeLengthMask) { long varint = varintBytes[0] & 0xFFL; if (removeLengthMask) { varint &= ~VARINT_LENGTH_MASKS[varintLength - 1]; } for (int i = 1; i < varintLength; i++) { varint = (varint << 8) | (varintBytes[i] & 0xFFL); } return varint; } }