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OffHostApduService

public abstract class OffHostApduService
extends Service

java.lang.Object
   ↳ android.content.Context
     ↳ android.content.ContextWrapper
       ↳ android.app.Service
         ↳ android.nfc.cardemulation.OffHostApduService


OffHostApduService is a convenience Service class that can be extended to describe one or more NFC applications that are residing off-host, for example on an embedded secure element or a UICC.

Developer Guide

For a general introduction into the topic of card emulation, please read the NFC card emulation developer guide.

NFC Protocols

Off-host applications represented by this class are based on the NFC-Forum ISO-DEP protocol (based on ISO/IEC 14443-4) and support processing command Application Protocol Data Units (APDUs) as defined in the ISO/IEC 7816-4 specification.

Service selection

When a remote NFC device wants to talk to your off-host NFC application, it sends a so-called "SELECT AID" APDU as defined in the ISO/IEC 7816-4 specification. The AID is an application identifier defined in ISO/IEC 7816-4.

The registration procedure for AIDs is defined in the ISO/IEC 7816-5 specification. If you don't want to register an AID, you are free to use AIDs in the proprietary range: bits 8-5 of the first byte must each be set to '1'. For example, "0xF00102030405" is a proprietary AID. If you do use proprietary AIDs, it is recommended to choose an AID of at least 6 bytes, to reduce the risk of collisions with other applications that might be using proprietary AIDs as well.

AID groups

In some cases, an off-host environment may need to register multiple AIDs to implement a certain application, and it needs to be sure that it is the default handler for all of these AIDs (as opposed to some AIDs in the group going to another service).

An AID group is a list of AIDs that should be considered as belonging together by the OS. For all AIDs in an AID group, the OS will guarantee one of the following:

  • All AIDs in the group are routed to the off-host execution environment
  • No AIDs in the group are routed to the off-host execution environment
In other words, there is no in-between state, where some AIDs in the group can be routed to this off-host execution environment, and some to another or a host-based HostApduService.

AID groups and categories

Each AID group can be associated with a category. This allows the Android OS to classify services, and it allows the user to set defaults at the category level instead of the AID level.

You can use isDefaultServiceForCategory(android.content.ComponentName, String) to determine if your off-host service is the default handler for a category.

In this version of the platform, the only known categories are CATEGORY_PAYMENT and CATEGORY_OTHER. AID groups without a category, or with a category that is not recognized by the current platform version, will automatically be grouped into the CATEGORY_OTHER category.

Service AID registration

To tell the platform which AIDs reside off-host and are managed by this service, a SERVICE_META_DATA entry must be included in the declaration of the service. An example of a OffHostApduService manifest declaration is shown below:

 <service android:name=".MyOffHostApduService" android:exported="true" android:permission="android.permission.BIND_NFC_SERVICE">
     <intent-filter>
         <action android:name="android.nfc.cardemulation.action.OFF_HOST_APDU_SERVICE"/>
     </intent-filter>
     <meta-data android:name="android.nfc.cardemulation.off_host_apdu_ervice" android:resource="@xml/apduservice"/>
 </service>
This meta-data tag points to an apduservice.xml file. An example of this file with a single AID group declaration is shown below:
 <offhost-apdu-service xmlns:android="http://schemas.android.com/apk/res/android"
           android:description="@string/servicedesc">
       <aid-group android:description="@string/subscription" android:category="other">
           <aid-filter android:name="F0010203040506"/>
           <aid-filter android:name="F0394148148100"/>
       </aid-group>
 </offhost-apdu-service>
 

The <offhost-apdu-service> is required to contain a <android:description> attribute that contains a user-friendly description of the service that may be shown in UI.

The <offhost-apdu-service> must contain one or more <aid-group> tags. Each <aid-group> must contain one or more <aid-filter> tags, each of which contains a single AID. The AID must be specified in hexadecimal format, and contain an even number of characters.

This registration will allow the service to be included as an option for being the default handler for categories. The Android OS will take care of correctly routing the AIDs to the off-host execution environment, based on which service the user has selected to be the handler for a certain category.

The service may define additional actions outside of the Android namespace that provide further interaction with the off-host execution environment.

Use of this class requires the FEATURE_NFC_HOST_CARD_EMULATION to be present on the device.

Summary

Constants

String SERVICE_INTERFACE

The Intent action that must be declared as handled by the service.

String SERVICE_META_DATA

The name of the meta-data element that contains more information about this service.

Inherited constants

From class android.app.Service
From class android.content.Context
From interface android.content.ComponentCallbacks2

Public constructors

OffHostApduService()

Public methods

abstract IBinder onBind(Intent intent)

The Android platform itself will not bind to this service, but merely uses its declaration to keep track of what AIDs the service is interested in.

Inherited methods

From class android.app.Service
From class android.content.ContextWrapper
From class android.content.Context
From class java.lang.Object
From interface android.content.ComponentCallbacks2
From interface android.content.ComponentCallbacks

Constants

SERVICE_INTERFACE

Added in API level 19
String SERVICE_INTERFACE

The Intent action that must be declared as handled by the service.

Constant Value: "android.nfc.cardemulation.action.OFF_HOST_APDU_SERVICE"

SERVICE_META_DATA

Added in API level 19
String SERVICE_META_DATA

The name of the meta-data element that contains more information about this service.

Constant Value: "android.nfc.cardemulation.off_host_apdu_service"

Public constructors

OffHostApduService

Added in API level 19
OffHostApduService ()

Public methods

onBind

Added in API level 19
IBinder onBind (Intent intent)

The Android platform itself will not bind to this service, but merely uses its declaration to keep track of what AIDs the service is interested in. This information is then used to present the user with a list of applications that can handle an AID, as well as correctly route those AIDs either to the host (in case the user preferred a HostApduService), or to an off-host execution environment (in case the user preferred a OffHostApduService. Implementers may define additional actions outside of the Android namespace that allow further interactions with the off-host execution environment. Such implementations would need to override this method.

Parameters
intent Intent: The Intent that was used to bind to this service, as given to Context.bindService. Note that any extras that were included with the Intent at that point will not be seen here.
Returns
IBinder Return an IBinder through which clients can call on to the service.
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