1 /* 2 * Copyright (C) 2013 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 package com.example.android.cardreader; 17 18 import android.nfc.NfcAdapter; 19 import android.nfc.Tag; 20 import android.nfc.tech.IsoDep; 21 22 import com.example.android.common.logger.Log; 23 24 import java.io.IOException; 25 import java.lang.ref.WeakReference; 26 import java.util.Arrays; 27 28 /** 29 * Callback class, invoked when an NFC card is scanned while the device is running in reader mode. 30 * 31 * Reader mode can be invoked by calling NfcAdapter 32 */ 33 public class LoyaltyCardReader implements NfcAdapter.ReaderCallback { 34 private static final String TAG = "LoyaltyCardReader"; 35 // AID for our loyalty card service. 36 private static final String SAMPLE_LOYALTY_CARD_AID = "F222222222"; 37 // ISO-DEP command HEADER for selecting an AID. 38 // Format: [Class | Instruction | Parameter 1 | Parameter 2] 39 private static final String SELECT_APDU_HEADER = "00A40400"; 40 // "OK" status word sent in response to SELECT AID command (0x9000) 41 private static final byte[] SELECT_OK_SW = {(byte) 0x90, (byte) 0x00}; 42 43 // Weak reference to prevent retain loop. mAccountCallback is responsible for exiting 44 // foreground mode before it becomes invalid (e.g. during onPause() or onStop()). 45 private WeakReference<AccountCallback> mAccountCallback; 46 47 public interface Acco untCallback { 48 public void onAccountReceived(String account); 49 } 50 51 public LoyaltyCardReader(AccountCallback accountCallback) { 52 mAccountCallback = new WeakReference<AccountCallback>(accountCallback); 53 } 54 55 /** 56 * Callback when a new tag is discovered by the system. 57 * 58 * <p>Communication with the card should take place here. 59 * 60 * @param tag Discovered tag 61 */ 62 @Override 63 public void onTagDiscovered(Tag tag) { 64 Log.i(TAG, "New tag discovered"); 65 // Android's Host-based Card Emulation (HCE) feature implements the ISO-DEP (ISO 14443-4) 66 // protocol. 67 // 68 // In order to communicate with a device using HCE, the discovered tag should be processed 69 // using the IsoDep class. 70 IsoDep isoDep = IsoDep.get(tag); 71 if (isoDep != null) { 72 try { 73 // Connect to the remote NFC device 74 isoDep.connect(); 75 // Build SELECT AID command for our loyalty card service. 76 // This command tells the remote device which service we wish to communicate with. 77 Log.i(TAG, "Requesting remote AID: " + SAMPLE_LOYALTY_CARD_AID); 78 byte[] command = BuildSelectApdu(SAMPLE_LOYALTY_CARD_AID); 79 // Send command to remote device 80 Log.i(TAG, "Sending: " + ByteArrayToHexString(command)); 81 byte[] result = isoDep.transceive(command); 82 // If AID is successfully selected, 0x9000 is returned as the status word (last 2 83 // bytes of the result) by convention. Everything before the status word is 84 // optional payload, which is used here to hold the account number. 85 int resultLength = result.length; 86 byte[] statusWord = {result[resultLength-2], result[resultLength-1]}; 87 byte[] payload = Arrays.copyOf(result, resultLength-2); 88 if (Arrays.equals(SELECT_OK_SW, statusWord)) { 89 // The remote NFC device will immediately respond with its stored account number 90 String accountNumber = new String(payload, "UTF-8"); 91 Log.i(TAG, "Received: " + accountNumber); 92 // Inform CardReaderFragment of received account number 93 mAccountCallback.get().onAccountReceived(accountNumber); 94 } 95 } catch (IOException e) { 96 Log.e(TAG, "Error communicating with card: " + e.toString()); 97 } 98 } 99 } 100 101 /** 102 * Build APDU for SELECT AID command. This command indicates which service a reader is 103 * interested in communicating with. See ISO 7816-4. 104 * 105 * @param aid Application ID (AID) to select 106 * @return APDU for SELECT AID command 107 */ 108 public static byte[] BuildSelectApdu(String aid) { 109 // Format: [CLASS | INSTRUCTION | PARAMETER 1 | PARAMETER 2 | LENGTH | DATA] 110 return HexStringToByteArray(SELECT_APDU_HEADER + String.format("%02X", aid.length() / 2) + aid); 111 } 112 113 /** 114 * Utility class to convert a byte array to a hexadecimal string. 115 * 116 * @param bytes Bytes to convert 117 * @return String, containing hexadecimal representation. 118 */ 119 public static String ByteArrayToHexString(byte[] bytes) { 120 final char[] hexArray = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'}; 121 char[] hexChars = new char[bytes.length * 2]; 122 int v; 123 for ( int j = 0; j < bytes.length; j++ ) { 124 v = bytes[j] & 0xFF; 125 hexChars[j * 2] = hexArray[v >>> 4]; 126 hexChars[j * 2 + 1] = hexArray[v & 0x0F]; 127 } 128 return new String(hexChars); 129 } 130 131 /** 132 * Utility class to convert a hexadecimal string to a byte string. 133 * 134 * <p>Behavior with input strings containing non-hexadecimal characters is undefined. 135 * 136 * @param s String containing hexadecimal characters to convert 137 * @return Byte array generated from input 138 */ 139 public static byte[] HexStringToByteArray(String s) { 140 int len = s.length(); 141 byte[] data = new byte[len / 2]; 142 for (int i = 0; i < len; i += 2) { 143 data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) 144 + Character.digit(s.charAt(i+1), 16)); 145 } 146 return data; 147 } 148 149 }