Host Card Emulation is the technology in Android Devices, that let the device act as a host in the NFC communication. This technology can be used, e.g. to simulate the passive smart cards or NFC tags. This package allows the react-native application to use the adventages of this technology.

For now, the only out-of-the-box solution provided by this package is:

• NFC Type 4 tag emulation (Text and URI record types supported)

anyways, the module's architecture is ready to engage also the new, other usages.

Architectural overview

Core part of the library (on the native side) is a Service which implements HostApduService Android interface. The key difference between usual Android services and HostApduService is the initializer entity. HostApduService is initiated by OS - when phone taps the NFC reader. Thus, the Service (and - in the big picture - the entire library) has been prepared to the case, when the React Activity is in the background or even not available at the time in time of card data transfer.

Because of this special behavior of HostApduService, we have chosen the "declarativeness over interactivity" approach in the architecture design. To make the transactions stable and reliable, library stores the state on the Native side (in Android, the data are stored in SharedPreferences). The application can specify the available data in advance, to store it to native memory right away and pass it efficiently to the Service, if needed. Also, the Service can pass the data to a storage without considering the presence of JS thread. React app can grab the saved data later on.

Of course, all of this synchronization operations are handled in the React part of the library, so the end user can control the entire HCE session with convenient abstraction - the HCEService class. The library also provides the convenient wrapper that binds the HCEService with React application lifecycle using the "Contexts" feature of React.js.

Important notes

• Currenlty supported only on the Android platform, as there is no official support for HCE in Apple platform.
• Required minimum SDK version is API 21
• Be careful when using this library for transmission of any sensitive data. This library does not provide any built-it cryptographic layer, the data are transmitted in plain form. Ensure that You know, what You are doing and take care about any needed ensafements on Your own.

Installation

npm install react-native-hce --save

or

yarn add react-native-hce

...up to Your preferences and project configuration. Autolinking will take care about the rest.

Post-installation steps

After the installation, following changes must be made inside the <projectRoot>/android:

aid_list.xml

Create new file aid_list.xml in <projectRoot>/android/app/src/main/res/xml directory. Create the directory, if it does not exist yet.

• Put the following content to the file:

<host-apdu-service xmlns:android="http://schemas.android.com/apk/res/android"
                   android:description="@string/app_name"
                   android:requireDeviceUnlock="false">
  <aid-group android:category="other"
             android:description="@string/app_name">
    <!-- Create a separate <aid-filer /> node for each NFC application ID, that You intent to emulate/host. -->
    <!-- For the NFC Type 4 tag emulation, let's put "D2760000850101" -->
    <aid-filter android:name="D2760000850101" />
  </aid-group>
</host-apdu-service>

AndroidManifest.xml

Open the app's manifest (<projectRoot>/android/app/src/main/AndroidManifest.xml):

• Add permission to use NFC in the application, and add the declaration of usage the HCE feature:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
  package="com.example.reactnativehce">

    <uses-permission android:name="android.permission.INTERNET" />

    <!-- add the following two nodes: -->
    <uses-permission android:name="android.permission.NFC" />
    <uses-feature android:name="android.hardware.nfc.hce" android:required="true" />
    ...

</manifest>

• HCE emulation on the Android platform works as a service. react-native-hce module communicating with this service, so that's why we need to place the reference in AndroidManifest.

<application
      android:name=".MainApplication"
      android:label="@string/app_name"
      android:icon="@mipmap/ic_launcher"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:allowBackup="false"
      android:theme="@style/AppTheme">

    <!-- ... -->

    <!-- Add the following block: -->
    <service
        android:name="com.reactnativehce.services.CardService"
        android:exported="true"
        android:enabled="false"
        android:permission="android.permission.BIND_NFC_SERVICE" >
        <intent-filter>
          <action android:name="android.nfc.cardemulation.action.HOST_APDU_SERVICE" />
          <category android:name="android.intent.category.DEFAULT"/>
        </intent-filter>

        <meta-data
          android:name="android.nfc.cardemulation.host_apdu_service"
          android:resource="@xml/aid_list" />
    </service>
    <!-- ... -->
</application>

That's it.

Usage

API documentation

You can find the generated documentation on the project's website.

Example application

You can try out the example react-native app, which presents the usage of this package in practice. The instructions regarding starting up the example application are provided in Contribution guide.

NFC Type 4 tag emulation feature

Inspired by underwindfall's NFC Type 4 tag communication handling used in NFCAndroid.

Note! If You want to use this feature, make sure that You added the proper aid to Your aid_list.xml. Otherwise, the app will not handle any signal of NFC reader related with NFC Tags v4.

This is how to enable the NFC Tag emulation:

import { HCESession, NFCTagType4NDEFContentType, NFCTagType4 } from 'react-native-hce';

let session;

const startSession = async () => {
  const tag = new NFCTagType4({
    type: NFCTagType4NDEFContentType.Text,
    content: "Hello world",
    writable: false
  });

  session = await HCESession.getInstance();
  session.setApplication(tag);
  await session.setEnabled(true);
}

startSession();

stops this way:

const stopSession = async () => {
  await session.setEnabled(false);
}

stopSimulation();

It is possible to listen for events during the emulation:

const listen = async () => {
  const removeListener = session.on(HCESession.Events.HCE_STATE_READ, () => {
    ToastAndroid.show("The tag has been read! Thank You.", ToastAndroid.LONG);
  });

  // to remove the listener:
  removeListener();
}

listen();

Example application shows also the usage of writable tag feature.

Other features

This project is opened for Your ideas. You can contribute to the library and add the other functionalities, if You eager.

Troubleshooting

• Ensure, that there is no AID conflict with other HCE-enabled apps. Try to disable all HCE-enabled apps except the Your one. You can do this in Android Settings. See more details...
• If You experience the issues when trying to start up the example application, ensure, that You follow the steps described in contribution guide.

Development roadmap

• support for more types of NDEF Messages
• support for writable NFC Tags
• support for development of custom applications

Contributing

This project has been bootstrapped with Bob.

See the contributing guide to learn how to contribute to the repository and the development workflow.

License

MIT