1 /* 2 * Copyright 2021 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.android.server.nearby.common.bluetooth.fastpair; 18 19 import static com.google.common.io.BaseEncoding.base16; 20 21 import com.google.common.primitives.Bytes; 22 import com.google.errorprone.annotations.FormatMethod; 23 import com.google.errorprone.annotations.FormatString; 24 25 import java.util.ArrayList; 26 import java.util.Arrays; 27 import java.util.List; 28 29 /** 30 * A length, type, value (LTV) data block. 31 */ 32 public class Ltv { 33 34 private static final int SIZE_OF_LEN_TYPE = 2; 35 36 final byte mType; 37 final byte[] mValue; 38 39 /** 40 * Thrown if there's an error during {@link #parse}. 41 */ 42 public static class ParseException extends Exception { 43 44 @FormatMethod ParseException(@ormatString String format, Object... objects)45 private ParseException(@FormatString String format, Object... objects) { 46 super(String.format(format, objects)); 47 } 48 } 49 50 /** 51 * Constructor. 52 */ Ltv(byte type, byte... value)53 public Ltv(byte type, byte... value) { 54 this.mType = type; 55 this.mValue = value; 56 } 57 58 /** 59 * Parses a list of LTV blocks out of the input byte block. 60 */ parse(byte[] bytes)61 static List<Ltv> parse(byte[] bytes) throws ParseException { 62 List<Ltv> ltvs = new ArrayList<>(); 63 // The "+ 2" is for the length and type bytes. 64 for (int valueLength, i = 0; i < bytes.length; i += SIZE_OF_LEN_TYPE + valueLength) { 65 // - 1 since the length in the packet includes the type byte. 66 valueLength = bytes[i] - 1; 67 if (valueLength < 0 || bytes.length < i + SIZE_OF_LEN_TYPE + valueLength) { 68 throw new ParseException( 69 "Wrong length=%d at index=%d in LTVs=%s", bytes[i], i, 70 base16().encode(bytes)); 71 } 72 ltvs.add(new Ltv(bytes[i + 1], Arrays.copyOfRange(bytes, i + SIZE_OF_LEN_TYPE, 73 i + SIZE_OF_LEN_TYPE + valueLength))); 74 } 75 return ltvs; 76 } 77 78 /** 79 * Returns an LTV block, where length is mValue.length + 1 (for the type byte). 80 */ getBytes()81 public byte[] getBytes() { 82 return Bytes.concat(new byte[]{(byte) (mValue.length + 1), mType}, mValue); 83 } 84 } 85