HostApduService is a convenience
Service class that can be
extended to emulate an NFC card inside an Android
Cards emulated 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.
When a remote NFC device wants to talk to your service, 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.
In some cases, a service 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:
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
to determine if your service is the default handler for a category.
In this version of the platform, the only known categories
AID groups without a category, or with a category that is not recognized
by the current platform version, will automatically be
grouped into the
To tell the platform which AIDs groups
are requested by this service, a
entry must be included in the declaration of the service. An
example of a HostApduService manifest declaration is shown below:
<service android:name=".MyHostApduService" android:exported="true" android:permission="android.permission.BIND_NFC_SERVICE"> <intent-filter> <action android:name="android.nfc.cardemulation.action.HOST_APDU_SERVICE"/> </intent-filter> <meta-data android:name="android.nfc.cardemulation.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:
<host-apdu-service xmlns:android="http://schemas.android.com/apk/res/android" android:description="@string/servicedesc" android:requireDeviceUnlock="false"> <aid-group android:description="@string/aiddescription" android:category="other"> <aid-filter android:name="F0010203040506"/> <aid-filter android:name="F0394148148100"/> </aid-group> </host-apdu-service>
<host-apdu-service> is required
to contain a
attribute that contains a user-friendly description of the service that may be shown in UI.
attribute can be used to specify that the device must be unlocked before this service
can be invoked to handle APDUs.
contain one or more
<aid-group> must contain one or
<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.
Once the platform has resolved a "SELECT AID" command APDU to a specific
service component, the "SELECT AID" command APDU and all subsequent
command APDUs will be sent to that service through
processCommandApdu(byte, Bundle), until either:
Use of this class requires the
FEATURE_NFC_HOST_CARD_EMULATION to be present
on the device.
|String||SERVICE_META_DATA||The name of the meta-data element that contains more information about this service.|
Calling this method allows the service to tell the OS that it won't be able to complete this transaction - for example, because it requires data connectivity that is not present at that moment.
Return the communication channel to the service.
This method will be called in two possible scenarios:
This method will be called when a command APDU has been received from a remote device.
Sends a response APDU back to the remote device.
Indicates deactivation was due to a different AID being selected (which implicitly deselects the AID currently active on the logical channel).
Note that this next AID may still be resolved to this
service, in which case
will be called again.
Indicates deactivation was due to the NFC link
Intent action that must be declared as handled by the service.
The name of the meta-data element that contains more information about this service.
Calling this method allows the service to tell the OS that it won't be able to complete this transaction - for example, because it requires data connectivity that is not present at that moment. The OS may use this indication to give the user a list of alternative applications that can handle the last AID that was selected. If the user would select an application from the list, that action by itself will not cause the default to be changed; the selected application will be invoked for the next tap only. If there are no other applications that can handle this transaction, the OS will show an error dialog indicating your service could not complete the transaction.
Note that unlike other application components, calls on to the IBinder interface returned here may not happen on the main thread of the process. More information about the main thread can be found in Processes and Threads.
|intent||The Intent that was used to bind to this service,
as given to
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. Note that in general response APDUs must be sent as quickly as possible, given the fact that the user is likely holding his device over an NFC reader when this method is called.
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.
This method is running on the main thread of your application.
If you cannot return a response APDU immediately, return null
and use the
sendResponseApdu(byte) method later.
|commandApdu||The APDU that was received from the remote device|
|extras||A bundle containing extra data. May be null.|
Sends a response APDU back to the remote device.
Note: this method may be called from any thread and will not block.
|responseApdu||A byte-array containing the reponse APDU.|