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/*
* Copyright (C) 2013 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.example.android.cardemulation;
import android.nfc.cardemulation.HostApduService;
import android.os.Bundle;
import com.example.android.common.logger.Log;
import java.util.Arrays;
/**
* This is a sample APDU Service which demonstrates how to interface with the card emulation support
* added in Android 4.4, KitKat.
*
* <p>This sample replies to any requests sent with the string "Hello World". In real-world
* situations, you would need to modify this code to implement your desired communication
* protocol.
*
* <p>This sample will be invoked for any terminals selecting AIDs of 0xF11111111, 0xF22222222, or
* 0xF33333333. See src/main/res/xml/aid_list.xml for more details.
*
* <p class="note">Note: This is a low-level interface. Unlike the NdefMessage many developers
* are familiar with for implementing Android Beam in apps, card emulation only provides a
* byte-array based communication channel. It is left to developers to implement higher level
* protocol support as needed.
*/
public class CardService extends HostApduService {
private static final String TAG = "CardService";
// AID for our loyalty card service.
private static final String SAMPLE_LOYALTY_CARD_AID = "F222222222";
// ISO-DEP command HEADER for selecting an AID.
// Format: [Class | Instruction | Parameter 1 | Parameter 2]
private static final String SELECT_APDU_HEADER = "00A40400";
// "OK" status word sent in response to SELECT AID command (0x9000)
private static final byte[] SELECT_OK_SW = HexStringToByteArray("9000");
// "UNKNOWN" status word sent in response to invalid APDU command (0x0000)
private static final byte[] UNKNOWN_CMD_SW = HexStringToByteArray("0000");
private static final byte[] SELECT_APDU = BuildSelectApdu(SAMPLE_LOYALTY_CARD_AID);
/**
* Called if the connection to the NFC card is lost, in order to let the application know the
* cause for the disconnection (either a lost link, or another AID being selected by the
* reader).
*
* @param reason Either DEACTIVATION_LINK_LOSS or DEACTIVATION_DESELECTED
*/
@Override
public void onDeactivated(int reason) { }
/**
* This method will be called when a command APDU has been received from a remote device. A
* response APDU can be provided directly by returning a byte-array in this method. In general
* response APDUs must be sent as quickly as possible, given the fact that the user is likely
* holding their device over an NFC reader when this method is called.
*
* <p class="note">If there are multiple services that have registered for the same AIDs in
* their meta-data entry, you will only get called if the user has explicitly selected your
* service, either as a default or just for the next tap.
*
* <p class="note">This method is running on the main thread of your application. If you
* cannot return a response APDU immediately, return null and use the {@link
* #sendResponseApdu(byte[])} method later.
*
* @param commandApdu The APDU that received from the remote device
* @param extras A bundle containing extra data. May be null.
* @return a byte-array containing the response APDU, or null if no response APDU can be sent
* at this point.
*/
// BEGIN_INCLUDE(processCommandApdu)
@Override
public byte[] processCommandApdu(byte[] commandApdu, Bundle extras) {
Log.i(TAG, "Received APDU: " + ByteArrayToHexString(commandApdu));
// If the APDU matches the SELECT AID command for this service,
// send the loyalty card account number, followed by a SELECT_OK status trailer (0x9000).
if (Arrays.equals(SELECT_APDU, commandApdu)) {
String account = AccountStorage.GetAccount(this);
byte[] accountBytes = account.getBytes();
Log.i(TAG, "Sending account number: " + account);
return ConcatArrays(accountBytes, SELECT_OK_SW);
} else {
return UNKNOWN_CMD_SW;
}
}
// END_INCLUDE(processCommandApdu)
/**
* Build APDU for SELECT AID command. This command indicates which service a reader is
* interested in communicating with. See ISO 7816-4.
*
* @param aid Application ID (AID) to select
* @return APDU for SELECT AID command
*/
public static byte[] BuildSelectApdu(String aid) {
// Format: [CLASS | INSTRUCTION | PARAMETER 1 | PARAMETER 2 | LENGTH | DATA]
return HexStringToByteArray(SELECT_APDU_HEADER + String.format("%02X",
aid.length() / 2) + aid);
}
/**
* Utility method to convert a byte array to a hexadecimal string.
*
* @param bytes Bytes to convert
* @return String, containing hexadecimal representation.
*/
public static String ByteArrayToHexString(byte[] bytes) {
final char[] hexArray = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
char[] hexChars = new char[bytes.length * 2]; // Each byte has two hex characters (nibbles)
int v;
for (int j = 0; j < bytes.length; j++) {
v = bytes[j] & 0xFF; // Cast bytes[j] to int, treating as unsigned value
hexChars[j * 2] = hexArray[v >>> 4]; // Select hex character from upper nibble
hexChars[j * 2 + 1] = hexArray[v & 0x0F]; // Select hex character from lower nibble
}
return new String(hexChars);
}
/**
* Utility method to convert a hexadecimal string to a byte string.
*
* <p>Behavior with input strings containing non-hexadecimal characters is undefined.
*
* @param s String containing hexadecimal characters to convert
* @return Byte array generated from input
* @throws java.lang.IllegalArgumentException if input length is incorrect
*/
public static byte[] HexStringToByteArray(String s) throws IllegalArgumentException {
int len = s.length();
if (len % 2 == 1) {
throw new IllegalArgumentException("Hex string must have even number of characters");
}
byte[] data = new byte[len / 2]; // Allocate 1 byte per 2 hex characters
for (int i = 0; i < len; i += 2) {
// Convert each character into a integer (base-16), then bit-shift into place
data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
+ Character.digit(s.charAt(i+1), 16));
}
return data;
}
/**
* Utility method to concatenate two byte arrays.
* @param first First array
* @param rest Any remaining arrays
* @return Concatenated copy of input arrays
*/
public static byte[] ConcatArrays(byte[] first, byte[]... rest) {
int totalLength = first.length;
for (byte[] array : rest) {
totalLength += array.length;
}
byte[] result = Arrays.copyOf(first, totalLength);
int offset = first.length;
for (byte[] array : rest) {
System.arraycopy(array, 0, result, offset, array.length);
offset += array.length;
}
return result;
}
}
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