OffHostApduService is a convenience {@link 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.
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 {@link 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
{@link CardEmulation#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 {@link CardEmulation#CATEGORY_PAYMENT} and {@link CardEmulation#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 {@link CardEmulation#CATEGORY_OTHER} category.
Service AID registration
To tell the platform which AIDs
reside off-host and are managed by this service, a {@link #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 {@link android.R.styleable#OffHostApduService <offhost-apdu-service>} is required
to contain a
{@link android.R.styleable#OffHostApduService_description <android:description>}
attribute that contains a user-friendly description of the service that may be shown in UI.
The {@link android.R.styleable#OffHostApduService <offhost-apdu-service>} must
contain one or more {@link android.R.styleable#AidGroup <aid-group>} tags.
Each {@link android.R.styleable#AidGroup <aid-group>} must contain one or
more {@link android.R.styleable#AidFilter <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
{@link PackageManager#FEATURE_NFC_HOST_CARD_EMULATION} to be present
on the device. | 