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CardEmulation / src / com.example.android.cardemulation /

CardService.java

       
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        /*
       
       
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        * Copyright (C) 2013 The Android Open Source Project
       
       
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        *
       
       
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        * Licensed under the Apache License, Version 2.0 (the "License");
       
       
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        * you may not use this file except in compliance with the License.
       
       
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        * You may obtain a copy of the License at
       
       
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        *
       
       
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        *      http://www.apache.org/licenses/LICENSE-2.0
       
       
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        *
       
       
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        * Unless required by applicable law or agreed to in writing, software
       
       
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        * distributed under the License is distributed on an "AS IS" BASIS,
       
       
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        * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
       
       
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        * See the License for the specific language governing permissions and
       
       
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        * limitations under the License.
       
       
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        */
       
       
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        package com.example.android.cardemulation;
       
       
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        import android.nfc.cardemulation.HostApduService;
       
       
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        import android.os.Bundle;
       
       
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        import com.example.android.common.logger.Log;
       
       
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        import java.util.Arrays;
       
       
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        /**
       
       
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        * This is a sample APDU Service which demonstrates how to interface with the card emulation support
       
       
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        * added in Android 4.4, KitKat.
       
       
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        *
       
       
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        * <p>This sample replies to any requests sent with the string "Hello World". In real-world
       
       
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        * situations, you would need to modify this code to implement your desired communication
       
       
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        * protocol.
       
       
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        *
       
       
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        * <p>This sample will be invoked for any terminals selecting AIDs of 0xF11111111, 0xF22222222, or
       
       
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        * 0xF33333333. See src/main/res/xml/aid_list.xml for more details.
       
       
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        *
       
       
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        * <p class="note">Note: This is a low-level interface. Unlike the NdefMessage many developers
       
       
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        * are familiar with for implementing Android Beam in apps, card emulation only provides a
       
       
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        * byte-array based communication channel. It is left to developers to implement higher level
       
       
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        * protocol support as needed.
       
       
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        */
       
       
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        public class CardService extends HostApduService {
       
       
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        private static final String TAG = "CardService";
       
       
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        // AID for our loyalty card service.
       
       
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        private static final String SAMPLE_LOYALTY_CARD_AID = "F222222222";
       
       
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        // ISO-DEP command HEADER for selecting an AID.
       
       
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        // Format: [Class | Instruction | Parameter 1 | Parameter 2]
       
       
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        private static final String SELECT_APDU_HEADER = "00A40400";
       
       
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        // "OK" status word sent in response to SELECT AID command (0x9000)
       
       
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        private static final byte[] SELECT_OK_SW = HexStringToByteArray("9000");
       
       
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        // "UNKNOWN" status word sent in response to invalid APDU command (0x0000)
       
       
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        private static final byte[] UNKNOWN_CMD_SW = HexStringToByteArray("0000");
       
       
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        private static final byte[] SELECT_APDU = BuildSelectApdu(SAMPLE_LOYALTY_CARD_AID);
       
       
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        /**
       
       
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        * Called if the connection to the NFC card is lost, in order to let the application know the
       
       
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        * cause for the disconnection (either a lost link, or another AID being selected by the
       
       
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        * reader).
       
       
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        *
       
       
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        * @param reason Either DEACTIVATION_LINK_LOSS or DEACTIVATION_DESELECTED
       
       
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        */
       
       
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        @Override
       
       
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        public void onDeactivated(int reason) { }
       
       
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        /**
       
       
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        * This method will be called when a command APDU has been received from a remote device. A
       
       
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        * response APDU can be provided directly by returning a byte-array in this method. In general
       
       
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        * response APDUs must be sent as quickly as possible, given the fact that the user is likely
       
       
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        * holding his device over an NFC reader when this method is called.
       
       
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        *
       
       
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        * <p class="note">If there are multiple services that have registered for the same AIDs in
       
       
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        * their meta-data entry, you will only get called if the user has explicitly selected your
       
       
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        * service, either as a default or just for the next tap.
       
       
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        *
       
       
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        * <p class="note">This method is running on the main thread of your application. If you
       
       
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        * cannot return a response APDU immediately, return null and use the {@link
       
       
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        * #sendResponseApdu(byte[])} method later.
       
       
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        *
       
       
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        * @param commandApdu The APDU that received from the remote device
       
       
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        * @param extras A bundle containing extra data. May be null.
       
       
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        * @return a byte-array containing the response APDU, or null if no response APDU can be sent
       
       
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        * at this point.
       
       
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        */
       
       
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        @Override
       
       
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        public byte[] processCommandApdu(byte[] commandApdu, Bundle extras) {
       
       
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        Log.i(TAG, "Received APDU: " + ByteArrayToHexString(commandApdu));
       
       
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        // If the APDU matches the SELECT AID command for this service,
       
       
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        // send the loyalty card account number, followed by a SELECT_OK status trailer (0x9000).
       
       
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        if (Arrays.equals(SELECT_APDU, commandApdu)) {
       
       
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        String account = AccountStorage.GetAccount(this);
       
       
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        byte[] accountBytes = account.getBytes();
       
       
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        Log.i(TAG, "Sending account number: " + account);
       
       
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        return ConcatArrays(accountBytes, SELECT_OK_SW);
       
       
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        } else {
       
       
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        return UNKNOWN_CMD_SW;
       
       
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        }
       
       
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        }
       
       
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        /**
       
       
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        * Build APDU for SELECT AID command. This command indicates which service a reader is
       
       
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        * interested in communicating with. See ISO 7816-4.
       
       
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        *
       
       
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        * @param aid Application ID (AID) to select
       
       
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        * @return APDU for SELECT AID command
       
       
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        */
       
       
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        public static byte[] BuildSelectApdu(String aid) {
       
       
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        // Format: [CLASS | INSTRUCTION | PARAMETER 1 | PARAMETER 2 | LENGTH | DATA]
       
       
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        return HexStringToByteArray(SELECT_APDU_HEADER + String.format("%02X",
       
       
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        aid.length() / 2) + aid);
       
       
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        }
       
       
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        /**
       
       
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        * Utility method to convert a byte array to a hexadecimal string.
       
       
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        *
       
       
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        * @param bytes Bytes to convert
       
       
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        * @return String, containing hexadecimal representation.
       
       
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        */
       
       
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        public static String ByteArrayToHexString(byte[] bytes) {
       
       
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        final char[] hexArray = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
       
       
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        char[] hexChars = new char[bytes.length * 2]; // Each byte has two hex characters (nibbles)
       
       
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        int v;
       
       
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        for (int j = 0; j < bytes.length; j++) {
       
       
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        v = bytes[j] & 0xFF; // Cast bytes[j] to int, treating as unsigned value
       
       
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        hexChars[j * 2] = hexArray[v >>> 4]; // Select hex character from upper nibble
       
       
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        hexChars[j * 2 + 1] = hexArray[v & 0x0F]; // Select hex character from lower nibble
       
       
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        }
       
       
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        return new String(hexChars);
       
       
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        }
       
       
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        /**
       
       
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        * Utility method to convert a hexadecimal string to a byte string.
       
       
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        *
       
       
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        * <p>Behavior with input strings containing non-hexadecimal characters is undefined.
       
       
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        *
       
       
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        * @param s String containing hexadecimal characters to convert
       
       
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        * @return Byte array generated from input
       
       
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        * @throws java.lang.IllegalArgumentException if input length is incorrect
       
       
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        */
       
       
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        public static byte[] HexStringToByteArray(String s) throws IllegalArgumentException {
       
       
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        int len = s.length();
       
       
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        if (len % 2 == 1) {
       
       
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        throw new IllegalArgumentException("Hex string must have even number of characters");
       
       
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        }
       
       
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        byte[] data = new byte[len / 2]; // Allocate 1 byte per 2 hex characters
       
       
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        for (int i = 0; i < len; i += 2) {
       
       
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        // Convert each character into a integer (base-16), then bit-shift into place
       
       
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        data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
       
       
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        + Character.digit(s.charAt(i+1), 16));
       
       
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        }
       
       
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        return data;
       
       
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        }
       
       
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        /**
       
       
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        * Utility method to concatenate two byte arrays.
       
       
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        * @param first First array
       
       
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        * @param rest Any remaining arrays
       
       
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        * @return Concatenated copy of input arrays
       
       
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        */
       
       
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        public static byte[] ConcatArrays(byte[] first, byte[]... rest) {
       
       
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        int totalLength = first.length;
       
       
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        for (byte[] array : rest) {
       
       
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        totalLength += array.length;
       
       
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        }
       
       
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        byte[] result = Arrays.copyOf(first, totalLength);
       
       
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        int offset = first.length;
       
       
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        for (byte[] array : rest) {
       
       
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        System.arraycopy(array, 0, result, offset, array.length);
       
       
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        offset += array.length;
       
       
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        }
       
       
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        return result;
       
       
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        }
       
       
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        }