examples/tv-casting-app/APIs.md

# Matter Casting APIs

Matter Casting consists of three parts:

-   **The mobile app**: For most content providers, this would be your
    consumer-facing mobile app. By making your mobile app a Matter "Casting
    Client", you enable the user to discover casting targets, cast content, and
    control casting sessions. The
    [example Matter tv-casting-app](https://github.com/project-chip/connectedhomeip/tree/master/examples/tv-casting-app)
    for Android / iOS and Linux builds on top of the Matter SDK to demonstrate
    how a TV Casting mobile app works.
-   **The TV content app**: For most content providers, this would be your
    consumer-facing app on a Smart TV. By enhancing your TV app to act as a
    Matter "Content app", you enable Matter Casting Clients to cast content. The
    [example Matter content-app](https://github.com/project-chip/connectedhomeip/tree/master/examples/tv-app/android/App/content-app)
    for Android builds on top of the Matter SDK to demonstrate how a TV Content
    app works.
-   **The TV platform app**: The TV platform app implements the Casting Video  
    Player device type and provides common capabilities around media playback on
    the TV such as play/pause, keypad navigation, input and output control,
    content search, and an implementation of an app platform as described in the
    media chapter of the device library specification. This is generally
    implemented by the TV manufacturer. The
    [example Matter tv-app](https://github.com/project-chip/connectedhomeip/tree/master/examples/tv-app)
    for Android builds on top of the Matter SDK to demonstrate how a TV platform
    app works.

This document describes how enable your Android and iOS apps to act as a Matter
"Casting Client". This documentation is also designed to work with the example
[example Matter tv-casting-app](https://github.com/project-chip/connectedhomeip/tree/master/examples/tv-casting-app)
samples so you can see the experience end to end.

## Introduction

A Casting Client (e.g. a mobile phone app) is expected to be a Matter
Commissionable Node and a `CastingPlayer` (i.e. a TV) is expected to be a Matter
Commissioner. In the context of the Matter Video Player architecture, a
`CastingPlayer` would map to Casting "Video" Player. The `CastingPlayer` is
expected to be hosting one or more `Endpoints` (some of which can represent
Content Apps in the Matter Video Player architecture) that support one or more
Matter Media `Clusters`.

The steps to start a casting session are:

1. [Initialize](#initialize-the-casting-client) the `CastingClient` using the
   Matter SDK.
1. [Discover](#discover-casting-players) `CastingPlayer` devices using Matter
   Commissioner discovery.
1. [Connect](#connect-to-a-casting-player) to the `CastingPlayer` to discover
   available endpoints. By connecting, the `CastingClient` will send a User
   Directed Commissioning (UDC) request to the `CastingPlayer` device in order
   to make a Matter commissioning request. The `CastingPlayer` will then obtain
   the appropriate user consent to allow a connection from this `CastingClient`
   and obtain the setup code needed to commission the `CastingClient`. The setup
   code will typically come from a corresponding TV content app or be input by
   the user.
1. [Select](#select-an-endpoint-on-the-casting-player) an available `Endpoint`
   hosted by the `CastingPlayer`.

Next, you're ready to:

1. [Issue commands](#issuing-commands) to the `Endpoint`.
1. [Read](#read-operations) endpoint attributes like playback state.
1. [Subscribe](#subscriptions) to playback events.

In order to illustrate these steps, refer to the figure below
![workflow of casting video player](./diagram/workflow_of_casting_video_player.png)

## Build and Setup

The Casting Client is expected to consume the Matter TV Casting library built
for its respective platform which implements the APIs described in this
document. Refer to the tv-casting-app READMEs for [Linux](linux/README.md),
Android and [iOS](darwin/TvCasting/README.md) to understand how to build and
consume each platform's specific libraries. The libraries MUST be built with the
client's specific values for `CHIP_DEVICE_CONFIG_DEVICE_VENDOR_ID` and
`CHIP_DEVICE_CONFIG_DEVICE_PRODUCT_ID` updated in the
[CHIPProjectAppConfig.h](tv-casting-common/include/CHIPProjectAppConfig.h) file.
Other values like the `CHIP_DEVICE_CONFIG_DEVICE_NAME` may be updated as well to
correspond to the client being built.

### Initialize the Casting Client

_{Complete Initialization examples: [Linux](linux/simple-app.cpp) |
[Android](android/App/app/src/main/java/com/matter/casting/InitializationExample.java)
| [iOS](darwin/TvCasting/TvCasting/MCInitializationExample.swift)}_

A Casting Client must first initialize the Matter SDK and define the following
`DataProvider` objects for the the Matter Casting library to use throughout the
client's lifecycle:

1.  **Rotating Device Identifier** - "This unique per-device identifier SHALL
    consist of a randomly-generated 128-bit or longer octet string." Refer to
    the Matter specification for more details. Instantiate a `DataProvider`
    object as described below to provide this identifier.

    On Linux, define a `RotatingDeviceIdUniqueIdProvider` to provide the Casting
    Client's `RotatingDeviceIdUniqueId`, by implementing a
    `matter:casting::support::MutableByteSpanDataProvider`:

    ```c
    class RotatingDeviceIdUniqueIdProvider : public MutableByteSpanDataProvider {
    private:
        chip::MutableByteSpan rotatingDeviceIdUniqueIdSpan;
        uint8_t rotatingDeviceIdUniqueId[chip::DeviceLayer::ConfigurationManager::kRotatingDeviceIDUniqueIDLength];

    public:
        RotatingDeviceIdUniqueIdProvider() {
            // generate a random Unique ID for this example app for demonstration
            for (size_t i = 0; i < sizeof(rotatingDeviceIdUniqueId); i++) {
                rotatingDeviceIdUniqueId[i] = chip::Crypto::GetRandU8();
            }
            rotatingDeviceIdUniqueIdSpan = chip::MutableByteSpan(rotatingDeviceIdUniqueId);
        }

        chip::MutableByteSpan * Get() { return &rotatingDeviceIdUniqueIdSpan; }
    };
    ```

    On Android, define a `rotatingDeviceIdUniqueIdProvider` to provide the
    Casting Client's `RotatingDeviceIdUniqueId`, by implementing a
    `com.matter.casting.support.DataSource`:

    ```java
    private static final DataProvider<byte[]> rotatingDeviceIdUniqueIdProvider =
      new DataProvider<byte[]>() {
        private static final String ROTATING_DEVICE_ID_UNIQUE_ID =
            "EXAMPLE_IDENTIFIER"; // dummy value for demonstration only

        @Override
        public byte[] get() {
          return ROTATING_DEVICE_ID_UNIQUE_ID.getBytes();
        }
      };
    ```

    On iOS, define the
    `func castingAppDidReceiveRequestForRotatingDeviceIdUniqueId` in a class,
    `MCAppParametersDataSource`, that implements the `MCDataSource`:

    ```swift
    class MCAppParametersDataSource : NSObject, MCDataSource
    {
        func castingAppDidReceiveRequestForRotatingDeviceIdUniqueId(_ sender: Any) -> Data {
            // dummy value, with at least 16 bytes (ConfigurationManager::kMinRotatingDeviceIDUniqueIDLength), for demonstration only
            return "0123456789ABCDEF".data(using: .utf8)!
        }
        ...
    }
    ```

2.  **Commissioning Data** - This object contains the passcode, discriminator,
    etc. which identify the app and are provided to the `CastingPlayer` during
    the commissioning process. "A Passcode SHALL be included as a 27-bit
    unsigned integer, which serves as proof of possession during commissioning."
    "A Discriminator SHALL be included as a 12-bit unsigned integer, which SHALL
    match the value which a device advertises during commissioning." Refer to
    the Matter specification's "Onboarding Payload" section for more details on
    commissioning data.

    On Linux, define a function `InitCommissionableDataProvider` to initialize
    initialize a `LinuxCommissionableDataProvider` that can provide the required
    values to the `CastingApp`.

    ```c
    CHIP_ERROR InitCommissionableDataProvider(LinuxCommissionableDataProvider & provider, LinuxDeviceOptions & options) {
        chip::Optional<uint32_t> setupPasscode;

        if (options.payload.setUpPINCode != 0) {
            setupPasscode.SetValue(options.payload.setUpPINCode);
        } else if (!options.spake2pVerifier.HasValue()) {
            // default to TestOnlyCommissionableDataProvider for demonstration
            uint32_t defaultTestPasscode = 0;
            chip::DeviceLayer::TestOnlyCommissionableDataProvider TestOnlyCommissionableDataProvider;
            VerifyOrDie(TestOnlyCommissionableDataProvider.GetSetupPasscode(defaultTestPasscode) == CHIP_NO_ERROR);
            setupPasscode.SetValue(defaultTestPasscode);
            options.payload.setUpPINCode = defaultTestPasscode;
        }
        uint32_t spake2pIterationCount = chip::Crypto::kSpake2p_Min_PBKDF_Iterations;
        if (options.spake2pIterations != 0) {
            spake2pIterationCount = options.spake2pIterations;
        }
        return provider.Init(options.spake2pVerifier, options.spake2pSalt, spake2pIterationCount, setupPasscode,
                         options.payload.discriminator.GetLongValue());
    }
    ```

    On Android, define a `commissioningDataProvider` that can provide the
    required values to the `CastingApp`.

    ```java
    private static final DataProvider<CommissionableData> commissionableDataProvider =
      new DataProvider<CommissionableData>() {
        @Override
        public CommissionableData get() {
          // dummy values for demonstration only
          return new CommissionableData(20202021, 3874);
        }
      };
    ```

    On iOS, add a `func commissioningDataProvider` to the
    `MCAppParametersDataSource` class defined above, that can provide the
    required values to the `MCCastingApp`.

    ```swift
    func castingAppDidReceiveRequestForCommissionableData(_ sender: Any) -> MCCommissionableData {
        // dummy values for demonstration only
        return MCCommissionableData(
            passcode: 20202021,
            discriminator: 3874,
            spake2pIterationCount: 1000,
            spake2pVerifier: nil,
            spake2pSalt: nil)
    }
    ```

3.  **Device Attestation Credentials** - This object contains the
    `DeviceAttestationCertificate`, `ProductAttestationIntermediateCertificate`,
    etc. and implements a way to sign messages when called upon by the Matter TV
    Casting Library as part of the Matter Device Attestation process during
    commissioning.

    On Linux, implement a define a `dacProvider` to provide the Casting Client's
    Device Attestation Credentials, by implementing a
    `chip::Credentials::DeviceAttestationCredentialsProvider`. For this example,
    we will use the `chip::Credentials::Examples::ExampleDACProvider`

    On Android, define a `dacProvider` to provide the Casting Client's Device
    Attestation Credentials, by implementing a
    `com.matter.casting.support.DACProvider`:

    ```java
    private static final DACProvider dacProvider = new DACProviderStub();
    private final static DataProvider<DeviceAttestationCredentials> dacProvider = new DataProvider<DeviceAttestationCredentials>() {
        private static final String kDevelopmentDAC_Cert_FFF1_8001 = "MIIB5z...<snipped>...CXE1M=";     // dummy values for demonstration only
        private static final String kDevelopmentDAC_PrivateKey_FFF1_8001 = "qrYAror...<snipped>...StE+/8=";
        private static final String KPAI_FFF1_8000_Cert_Array = "MIIByzC...<snipped>...pwP4kQ==";

        @Override
        public DeviceAttestationCredentials get() {
            DeviceAttestationCredentials deviceAttestationCredentials = new DeviceAttestationCredentials() {
            @Override
            public byte[] SignWithDeviceAttestationKey(byte[] message) {
                try {
    	        byte[] privateKeyBytes = Base64.decode(kDevelopmentDAC_PrivateKey_FFF1_8001, Base64.DEFAULT);
    	        AlgorithmParameters algorithmParameters = AlgorithmParameters.getInstance("EC");
    	        algorithmParameters.init(new ECGenParameterSpec("secp256r1"));
    	        ECParameterSpec parameterSpec = algorithmParameters.getParameterSpec(ECParameterSpec.class);
    	        ECPrivateKeySpec ecPrivateKeySpec = new ECPrivateKeySpec(new BigInteger(1, privateKeyBytes), parameterSpec);

    	        KeyFactory keyFactory = KeyFactory.getInstance("EC");
    	        PrivateKey privateKey = keyFactory.generatePrivate(ecPrivateKeySpec);

    	        Signature signature = Signature.getInstance("SHA256withECDSA");
    	        signature.initSign(privateKey);
    	        signature.update(message);

    	        return signature.sign();
                } catch (Exception e) {
    	        return null;
                }
            }
            };

            deviceAttestationCredentials.setDeviceAttestationCert(
            Base64.decode(kDevelopmentDAC_Cert_FFF1_8001, Base64.DEFAULT));
            deviceAttestationCredentials.setProductAttestationIntermediateCert(
            Base64.decode(KPAI_FFF1_8000_Cert_Array, Base64.DEFAULT));
            return deviceAttestationCredentials;
        }
    };
    ```

    On iOS, add functions
    `castingAppDidReceiveRequestForDeviceAttestationCredentials` and
    `didReceiveRequestToSignCertificateRequest` to the
    `MCAppParametersDataSource` class defined above, that can return
    `MCDeviceAttestationCredentials` and sign messages for the Casting Client,
    respectively.

    ```swift
    // dummy DAC values for demonstration only
    let kDevelopmentDAC_Cert_FFF1_8001: Data = Data(base64Encoded: "MIIB..<snipped>..CXE1M=")!;
    let kDevelopmentDAC_PrivateKey_FFF1_8001: Data = Data(base64Encoded: "qrYA<snipped>tE+/8=")!;
    let kDevelopmentDAC_PublicKey_FFF1_8001: Data = Data(base64Encoded: "BEY6<snipped>I=")!;
    let KPAI_FFF1_8000_Cert_Array: Data = Data(base64Encoded: "MIIB<snipped>4kQ==")!;
    let kCertificationDeclaration: Data = Data(base64Encoded: "MII<snipped>fA==")!;

    func castingAppDidReceiveRequestForDeviceAttestationCredentials(_ sender: Any) -> MCDeviceAttestationCredentials {
        return MCDeviceAttestationCredentials(
            certificationDeclaration: kCertificationDeclaration,
            firmwareInformation: Data(),
            deviceAttestationCert: kDevelopmentDAC_Cert_FFF1_8001,
            productAttestationIntermediateCert: KPAI_FFF1_8000_Cert_Array)
    }

    func castingApp(_ sender: Any, didReceiveRequestToSignCertificateRequest csrData: Data, outRawSignature: AutoreleasingUnsafeMutablePointer<NSData>) -> MatterError {
        Log.info("castingApp didReceiveRequestToSignCertificateRequest")

        // get the private SecKey
        var privateKeyData = Data()
        privateKeyData.append(kDevelopmentDAC_PublicKey_FFF1_8001);
        privateKeyData.append(kDevelopmentDAC_PrivateKey_FFF1_8001);
        let privateSecKey: SecKey = SecKeyCreateWithData(privateKeyData as NSData,
                                    [
                                        kSecAttrKeyType: kSecAttrKeyTypeECSECPrimeRandom,
                                        kSecAttrKeyClass: kSecAttrKeyClassPrivate,
                                        kSecAttrKeySizeInBits: 256
                                    ] as NSDictionary, nil)!

        // sign csrData to get asn1SignatureData
        var error: Unmanaged<CFError>?
        let asn1SignatureData: CFData? = SecKeyCreateSignature(privateSecKey, .ecdsaSignatureMessageX962SHA256, csrData as CFData, &error)
        if(error != nil)
        {
            Log.error("Failed to sign message. Error: \(String(describing: error))")
            return MATTER_ERROR_INVALID_ARGUMENT
        }
        else if (asn1SignatureData == nil)
        {
            Log.error("Failed to sign message. asn1SignatureData is nil")
            return MATTER_ERROR_INVALID_ARGUMENT
        }

        // convert ASN.1 DER signature to SEC1 raw format
        return MCCryptoUtils.ecdsaAsn1SignatureToRaw(withFeLengthBytes: 32,
                                                    asn1Signature: asn1SignatureData!,
                                                         outRawSignature: &outRawSignature.pointee)
    }
    ```

Once you have created the `DataProvider` objects above, you are ready to
initialize the Casting App as described below. Note: When you initialize the
Casting client, make sure your code initializes it only once, before it starts a
Matter casting session.

On Linux, create an `AppParameters` object using the
`RotatingDeviceIdUniqueIdProvider`, `LinuxCommissionableDataProvider`,
`CommonCaseDeviceServerInitParamsProvider`, `ExampleDACProvider` and
`DefaultDACVerifier`, and call `CastingApp::GetInstance()->Initialize` with it.
Then, call `Start` on the `CastingApp`.

```c
LinuxCommissionableDataProvider gCommissionableDataProvider;
int main(int argc, char * argv[]) {
    // Create AppParameters that need to be passed to CastingApp.Initialize()
    AppParameters appParameters;
    RotatingDeviceIdUniqueIdProvider rotatingDeviceIdUniqueIdProvider;
    CommonCaseDeviceServerInitParamsProvider serverInitParamsProvider;
    CHIP_ERROR err = CHIP_NO_ERROR;
    err            = InitCommissionableDataProvider(gCommissionableDataProvider, LinuxDeviceOptions::GetInstance());
    VerifyOrReturnValue(
        err == CHIP_NO_ERROR, 0,
        ChipLogError(AppServer, "Initialization of CommissionableDataProvider failed %" CHIP_ERROR_FORMAT, err.Format()));
    err = appParameters.Create(&rotatingDeviceIdUniqueIdProvider, &gCommissionableDataProvider,
                               chip::Credentials::Examples::GetExampleDACProvider(),
                               GetDefaultDACVerifier(chip::Credentials::GetTestAttestationTrustStore()), &serverInitParamsProvider);
    VerifyOrReturnValue(err == CHIP_NO_ERROR, 0,
                        ChipLogError(AppServer, "Creation of AppParameters failed %" CHIP_ERROR_FORMAT, err.Format()));

    // Initialize the CastingApp
    err = CastingApp::GetInstance()->Initialize(appParameters);
    VerifyOrReturnValue(err == CHIP_NO_ERROR, 0,
                        ChipLogError(AppServer, "Initialization of CastingApp failed %" CHIP_ERROR_FORMAT, err.Format()));

    // Initialize Linux KeyValueStoreMgr
    chip::DeviceLayer::PersistedStorage::KeyValueStoreMgrImpl().Init(CHIP_CONFIG_KVS_PATH);

    // Start the CastingApp
    err = CastingApp::GetInstance()->Start();
    VerifyOrReturnValue(err == CHIP_NO_ERROR, 0,
                        ChipLogError(AppServer, "CastingApp::Start failed %" CHIP_ERROR_FORMAT, err.Format()));
    ...
}
```

On Android, create an `AppParameters` object using the
`rotatingDeviceIdUniqueIdProvider`, `commissioningDataProvider`, `dacProvider`
and `DataProvider<ConfigurationManager>`, and call
`CastingApp.getInstance().initialize` with it. Then, call `start` on the
`CastingApp`

```java
public static MatterError initAndStart(Context applicationContext) {
    // Create an AppParameters object to pass in global casting parameters to the SDK
    final AppParameters appParameters =
        new AppParameters(
            applicationContext,
            new DataProvider<ConfigurationManager>() {
              @Override
              public ConfigurationManager get() {
                return new PreferencesConfigurationManager(
                    applicationContext, "chip.platform.ConfigurationManager");
              }
            },
            rotatingDeviceIdUniqueIdProvider,
            commissionableDataProvider,
            dacProvider);

    // Initialize the SDK using the appParameters and check if it returns successfully
    MatterError err = CastingApp.getInstance().initialize(appParameters);
    if (err.hasError()) {
      Log.e(TAG, "Failed to initialize Matter CastingApp");
      return err;
    }

    // Start the CastingApp
    err = CastingApp.getInstance().start();
    if (err.hasError()) {
      Log.e(TAG, "Failed to start Matter CastingApp");
      return err;
    }
    return err;
}
```

On iOS, call `MCCastingApp.initialize` with an object of the
`MCAppParametersDataSource`.

```swift
func initialize() -> MatterError {
    if let castingApp = MCCastingApp.getSharedInstance() {
        return castingApp.initialize(with: MCAppParametersDataSource())
    } else {
        return MATTER_ERROR_INCORRECT_STATE
    }
}
```

After initialization, on iOS, call `start` and `stop` on the `MCCastingApp`
shared instance when the App sends the
`UIApplication.didBecomeActiveNotification` and
`UIApplication.willResignActiveNotification`

```objectivec
struct TvCastingApp: App {
    let Log = Logger(subsystem: "com.matter.casting", category: "TvCastingApp")
    @State
    var firstAppActivation: Bool = true

    var body: some Scene {
        WindowGroup {
            ContentView()
                .onAppear(perform: {
                    let err: Error? = MCInitializationExample().initialize()
                    if err != nil
                    {
                        self.Log.error("MCCastingApp initialization failed \(err)")
                        return
                    }
                })
                .onReceive(NotificationCenter.default.publisher(for: UIApplication.didBecomeActiveNotification)) { _ in
                    self.Log.info("TvCastingApp: UIApplication.didBecomeActiveNotification")
                    if let castingApp = MCCastingApp.getSharedInstance()
                    {
                        castingApp.start(completionBlock: { (err : Error?) -> () in
                            if err != nil
                            {
                                self.Log.error("MCCastingApp start failed \(err)")
                            }
                        })
                    }
                }
                .onReceive(NotificationCenter.default.publisher(for: UIApplication.willResignActiveNotification)) { _ in
                    self.Log.info("TvCastingApp: UIApplication.willResignActiveNotification")
                    if let castingApp = MCCastingApp.getSharedInstance()
                    {
                        castingApp.stop(completionBlock: { (err : Error?) -> () in
                            if err != nil
                            {
                                self.Log.error("MCCastingApp stop failed \(err)")
                            }
                        })
                    }
                }
            }   // WindowGroup
    }   // body
}   // App
```

Note about on-device cache: The Casting App maintains an on-device cache
containing information about the Casting Players it has connected with so far.
This cached information allows the Casting App to connect with Casting Players
(that it had previously connected with) faster and using fewer resources, by
potentially skipping the longer commissioning process and instead, simply
re-establishing the CASE session. This cache can be cleared by calling the
`ClearCache` API on the `CastingApp`, say when the user signs out of the app.
See API and its documentation for [Linux](tv-casting-common/core/CastingApp.h),
[Android](android/App/app/src/main/jni/com/matter/casting/core/CastingApp.java)
and [iOS](darwin/MatterTvCastingBridge/MatterTvCastingBridge/MCCastingApp.h).

### Discover Casting Players

_{Complete Discovery examples: [Linux](linux/simple-app-helper.cpp) |
[Android](android/App/app/src/main/java/com/matter/casting/DiscoveryExampleFragment.java)
| [iOS](darwin/TvCasting/TvCasting/MCDiscoveryExampleViewModel.swift)}_

The Casting Client discovers `CastingPlayers` using Matter Commissioner
discovery over DNS-SD by listening for `CastingPlayer` events as they are
discovered, updated, or lost from the network.

On Linux, define a `DiscoveryDelegateImpl` that implements the
`matter::casting::core::DiscoveryDelegate`.

```c
class DiscoveryDelegateImpl : public DiscoveryDelegate {
private:
    int commissionersCount = 0;

public:
    void HandleOnAdded(matter::casting::memory::Strong<CastingPlayer> player) override {
        if (commissionersCount == 0) {
            ChipLogProgress(AppServer, "Select discovered CastingPlayer to request commissioning");
            ChipLogProgress(AppServer, "Example: cast request 0");
        }
        ++commissionersCount;
        ChipLogProgress(AppServer, "Discovered CastingPlayer #%d", commissionersCount);
        player->LogDetail();
    }

    void HandleOnUpdated(matter::casting::memory::Strong<CastingPlayer> player) override {
        ChipLogProgress(AppServer, "Updated CastingPlayer with ID: %s", player->GetId());
    }
};
```

On Android, implement the `CastingPlayerDiscovery.CastingPlayerChangeListener`.

```java
private static final CastingPlayerDiscovery.CastingPlayerChangeListener castingPlayerChangeListener =
    new CastingPlayerDiscovery.CastingPlayerChangeListener() {
        private final String TAG = CastingPlayerDiscovery.CastingPlayerChangeListener.class.getSimpleName();

        @Override
        public void onAdded(CastingPlayer castingPlayer) {
            Log.i(TAG, "onAdded() Discovered CastingPlayer deviceId: " + castingPlayer.getDeviceId());
            // Display CastingPlayer info on the screen
            new Handler(Looper.getMainLooper()).post(() -> {
                arrayAdapter.add(castingPlayer);
            });
        }

        @Override
        public void onChanged(CastingPlayer castingPlayer) {
            Log.i(TAG, "onChanged() Discovered changes to CastingPlayer with deviceId: " + castingPlayer.getDeviceId());
            // Update the CastingPlayer on the screen
            new Handler(Looper.getMainLooper()).post(() -> {
                final Optional<CastingPlayer> playerInList = castingPlayerList.stream().filter(node -> castingPlayer.equals(node)).findFirst();
                if (playerInList.isPresent()) {
                    Log.d(TAG, "onChanged() Updating existing CastingPlayer entry " + playerInList.get().getDeviceId() + " in castingPlayerList list");
                    arrayAdapter.remove(playerInList.get());
                }
                arrayAdapter.add(castingPlayer);
            });
        }

        @Override
        public void onRemoved(CastingPlayer castingPlayer) {
            Log.i(TAG, "onRemoved() Removed CastingPlayer with deviceId: " + castingPlayer.getDeviceId());
            // Remove CastingPlayer from the screen
            new Handler(Looper.getMainLooper()).post(() -> {
                final Optional<CastingPlayer> playerInList = castingPlayerList.stream().filter(node -> castingPlayer.equals(node)).findFirst();
                if (playerInList.isPresent()) {
                    Log.d(TAG, "onRemoved() Removing existing CastingPlayer entry " + playerInList.get().getDeviceId() + " in castingPlayerList list");
                    arrayAdapter.remove(playerInList.get());
                }
            });
        }
};
```

On iOS, implement a `func addDiscoveredCastingPlayers`,
`func removeDiscoveredCastingPlayers` and `func updateDiscoveredCastingPlayers`
which listen to notifications as Casting Players are added, removed, or updated.

```swift
@objc
func didAddDiscoveredCastingPlayers(notification: Notification)
{
    Log.info("didAddDiscoveredCastingPlayers() called")
    guard let userInfo = notification.userInfo,
        let castingPlayer     = userInfo["castingPlayer"] as? MCCastingPlayer else {
        self.Log.error("didAddDiscoveredCastingPlayers called with no MCCastingPlayer")
        return
    }

    self.Log.info("didAddDiscoveredCastingPlayers notified of a MCCastingPlayer with ID: \(castingPlayer.identifier())")
    DispatchQueue.main.async
    {
        self.displayedCastingPlayers.append(castingPlayer)
    }
}

@objc
func didRemoveDiscoveredCastingPlayers(notification: Notification)
{
    Log.info("didRemoveDiscoveredCastingPlayers() called")
    guard let userInfo = notification.userInfo,
        let castingPlayer     = userInfo["castingPlayer"] as? MCCastingPlayer else {
        self.Log.error("didRemoveDiscoveredCastingPlayers called with no MCCastingPlayer")
        return
    }

    self.Log.info("didRemoveDiscoveredCastingPlayers notified of a MCCastingPlayer with ID: \(castingPlayer.identifier())")
    DispatchQueue.main.async
    {
        self.displayedCastingPlayers.removeAll(where: {$0 == castingPlayer})
    }
}

@objc
func didUpdateDiscoveredCastingPlayers(notification: Notification)
{
    Log.info("didUpdateDiscoveredCastingPlayers() called")
    guard let userInfo = notification.userInfo,
        let castingPlayer     = userInfo["castingPlayer"] as? MCCastingPlayer else {
        self.Log.error("didUpdateDiscoveredCastingPlayers called with no MCCastingPlayer")
        return
    }

    self.Log.info("didUpdateDiscoveredCastingPlayers notified of a MCCastingPlayer with ID: \(castingPlayer.identifier())")
    if let index = displayedCastingPlayers.firstIndex(where: { castingPlayer.identifier() == $0.identifier() })
    {
        DispatchQueue.main.async
        {
            self.displayedCastingPlayers[index] = castingPlayer
        }
    }
}
```

Finally, register these listeners and start discovery.

On Linux, register an instance of the `DiscoveryDelegateImpl` with
`matter::casting::core::CastingPlayerDiscovery` by calling `SetDelegate` on its
singleton instance. Then, call `StartDiscovery` by optionally specifying the
`kTargetPlayerDeviceType` to filter results by.

```c
const uint64_t kTargetPlayerDeviceType = 35; // 35 represents device type of Matter Video Player
...
...
DiscoveryDelegateImpl delegate;
CastingPlayerDiscovery::GetInstance()->SetDelegate(&delegate);
VerifyOrReturnValue(err == CHIP_NO_ERROR, 0,
                    ChipLogError(AppServer, "CastingPlayerDiscovery::SetDelegate failed %" CHIP_ERROR_FORMAT, err.Format()));

err = CastingPlayerDiscovery::GetInstance()->StartDiscovery(kTargetPlayerDeviceType);
VerifyOrReturnValue(err == CHIP_NO_ERROR, 0,
                    ChipLogError(AppServer, "CastingPlayerDiscovery::StartDiscovery failed %" CHIP_ERROR_FORMAT, err.Format()));
chip::DeviceLayer::PlatformMgr().RunEventLoop();
...
```

On Android, add the implemented `castingPlayerChangeListener` as a listener to
the singleton instance of `MatterCastingPlayerDiscovery` to listen to changes in
the discovered Casting Players and call `startDiscovery`.

```java
MatterError err = MatterCastingPlayerDiscovery.getInstance().addCastingPlayerChangeListener(castingPlayerChangeListener);
if (err.hasError()) {
    Log.e(TAG, "startDiscovery() addCastingPlayerChangeListener() called, err Add: " + err);
    return false;
}

// Start discovery
Log.i(TAG, "startDiscovery() calling CastingPlayerDiscovery.startDiscovery()");
err = MatterCastingPlayerDiscovery.getInstance().startDiscovery(DISCOVERY_TARGET_DEVICE_TYPE);
if (err.hasError()) {
    Log.e(TAG, "Error in startDiscovery(): " + err);
    return false;
}
```

On iOS, register the listeners by calling `addObserver` on the
`NotificationCenter` with the appropriate selector, and then call start on the
`sharedInstance` of `MCCastingPlayerDiscovery`.

```swift
func startDiscovery() {
    NotificationCenter.default.addObserver(self, selector: #selector(self.didAddDiscoveredCastingPlayers), name: NSNotification.Name.didAddCastingPlayers, object: nil)
    NotificationCenter.default.addObserver(self, selector: #selector(self.didRemoveDiscoveredCastingPlayers), name: NSNotification.Name.didRemoveCastingPlayers, object: nil)
    NotificationCenter.default.addObserver(self, selector: #selector(self.didUpdateDiscoveredCastingPlayers), name: NSNotification.Name.didUpdateCastingPlayers, object: nil)

    MCCastingPlayerDiscovery.sharedInstance().start()
    ...
}
```

Note: You will need to connect with a Casting Player as described below to see
the list of Endpoints that they support. Refer to the
[Connection](#connect-to-a-casting-player) section for details on how to
discover available endpoints supported by a Casting Player.

### Connect to a Casting Player

_{Complete Connection examples: [Linux](linux/simple-app-helper.cpp) |
[iOS](darwin/TvCasting/TvCasting/MCConnectionExampleViewModel.swift)}_

Each `CastingPlayer` object created during
[Discovery](#discover-casting-players) contains information such as
`deviceName`, `vendorId`, `productId`, etc. which can help the user pick the
right `CastingPlayer`. A Casting Client can attempt to connect to the
`selectedCastingPlayer` using Matter User Directed Commissioning (UDC). The
Matter TV Casting library locally caches information required to reconnect to a
`CastingPlayer`, once the Casting client has been commissioned by it. After
that, the Casting client is able to skip the full UDC process by establishing
CASE with the `CastingPlayer` directly. Once connected, the `CastingPlayer`
object will contain the list of available Endpoints on that `CastingPlayer`.
Optionally, the following arguments may also be passed in. The optional
`commissioningWindowTimeoutSec` indicates how long to keep the commissioning
window open, if commissioning is required. And `DesiredEndpointFilter` specifies
the attributes, such as Vendor ID and Product ID of the `Endpoint`, the Casting
client desires to interact with after connecting. This forces the Matter TV
Casting library to go through the full UDC process in search of the desired
Endpoint, in cases where it is not available in the Casting client's cache.

On Linux, the Casting Client can connect to a `CastingPlayer` by successfully
calling `VerifyOrEstablishConnection` on it.

```c
// VendorId of the Endpoint on the CastingPlayer that the CastingApp desires to interact with after connection
const uint16_t kDesiredEndpointVendorId = 65521;

void ConnectionHandler(CHIP_ERROR err, matter::casting::core::CastingPlayer * castingPlayer)
{
    if(err == CHIP_NO_ERROR)
    {
        ChipLogProgress(AppServer, "ConnectionHandler: Successfully connected to CastingPlayer(ID: %s)", castingPlayer->GetId());
        ...
    }
}

...
// targetCastingPlayer is a discovered CastingPlayer
matter::casting::core::EndpointFilter desiredEndpointFilter;
desiredEndpointFilter.vendorId = kDesiredEndpointVendorId;
targetCastingPlayer->VerifyOrEstablishConnection(ConnectionHandler,
                                                    matter::casting::core::kCommissioningWindowTimeoutSec,
                                                    desiredEndpointFilter);
...
```

On Android, the Casting Client may call `verifyOrEstablishConnection` on the
`CastingPlayer` object it wants to connect to.

```java
private static final long MIN_CONNECTION_TIMEOUT_SEC = 3 * 60;

EndpointFilter desiredEndpointFilter = new EndpointFilter();
desiredEndpointFilter.vendorId = DESIRED_ENDPOINT_VENDOR_ID;

MatterError err = targetCastingPlayer.verifyOrEstablishConnection(
                      MIN_CONNECTION_TIMEOUT_SEC,
                      desiredEndpointFilter,
                      new MatterCallback<Void>() {
                        @Override
                        public void handle(Void v) {
                          Log.i(
                              TAG,
                              "Connected to CastingPlayer with deviceId: "
                                  + targetCastingPlayer.getDeviceId());
                          getActivity()
                              .runOnUiThread(
                                  () -> {
                                    connectionFragmentStatusTextView.setText(
                                        "Connected to Casting Player with device name: "
                                            + targetCastingPlayer.getDeviceName()
                                            + "\n\n");
                                    connectionFragmentNextButton.setEnabled(true);
                                  });
                        }
                      },
                      new MatterCallback<MatterError>() {
                        @Override
                        public void handle(MatterError err) {
                          Log.e(TAG, "CastingPLayer connection failed: " + err);
                          getActivity()
                              .runOnUiThread(
                                  () -> {
                                    connectionFragmentStatusTextView.setText(
                                        "Casting Player connection failed due to: " + err + "\n\n");
                                  });
                        }
                      });

if (err.hasError())
{
    getActivity()
        .runOnUiThread(
            () -> {
                connectionFragmentStatusTextView.setText(
                    "Casting Player connection failed due to: " + err + "\n\n");
            });
}
```

On iOS, the Casting Client may call `verifyOrEstablishConnection` on the
`MCCastingPlayer` object it wants to connect to and handle any `NSErrors` that
may happen in the process.

```swift
// VendorId of the MCEndpoint on the MCCastingPlayer that the MCCastingApp desires to interact with after connection
let kDesiredEndpointVendorId: UInt16 = 65521;

@Published var connectionSuccess: Bool?;

@Published var connectionStatus: String?;

func connect(selectedCastingPlayer: MCCastingPlayer?) {
    let desiredEndpointFilter: MCEndpointFilter = MCEndpointFilter()
    desiredEndpointFilter.vendorId = kDesiredEndpointVendorId
    selectedCastingPlayer?.verifyOrEstablishConnection(completionBlock: { err in
        self.Log.error("MCConnectionExampleViewModel connect() completed with \(err)")
        if(err == nil)
        {
            self.connectionSuccess = true
            self.connectionStatus = "Connected!"
        }
        else
        {
            self.connectionSuccess = false
            self.connectionStatus = "Connection failed with \(String(describing: err))"
        }
    }, desiredEndpointFilter: desiredEndpointFilter)
}
```

### Select an Endpoint on the Casting Player

_{Complete Endpoint selection examples: [Linux](linux/simple-app-helper.cpp) |
[Android](android/App/app/src/main/java/com/matter/casting/ContentLauncherLaunchURLExampleFragment.java)
|
[iOS](darwin/TvCasting/TvCasting/MCContentLauncherLaunchURLExampleViewModel.swift)}_

On a successful connection with a `CastingPlayer`, a Casting Client may select
one of the Endpoints to interact with based on its attributes (e.g. Vendor ID,
Product ID, list of supported Clusters, etc).

On Linux, for example, it may select an Endpoint with a particular VendorID.

```c
// VendorId of the Endpoint on the CastingPlayer that the CastingApp desires to interact with after connection
const uint16_t kDesiredEndpointVendorId = 65521;

std::vector<matter::casting::memory::Strong<matter::casting::core::Endpoint>> endpoints = castingPlayer->GetEndpoints();
// Find the desired Endpoint and auto-trigger some Matter Casting demo interactions
auto it = std::find_if(endpoints.begin(), endpoints.end(),
                        [](const matter::casting::memory::Strong<matter::casting::core::Endpoint> & endpoint) {
                            return endpoint->GetVendorId() == 65521;
                        });
if (it != endpoints.end())
{
    // The desired endpoint is endpoints[index]
    unsigned index = (unsigned int) std::distance(endpoints.begin(), it);
    ...
}
```

On Android, it can select an `Endpoint` as shown below.

```java
private static final Integer SAMPLE_ENDPOINT_VID = 65521;

private Endpoint selectEndpoint()
{
    Endpoint endpoint = null;
    if(selectedCastingPlayer != null)
    {
        List<Endpoint> endpoints = selectedCastingPlayer.getEndpoints();
        if (endpoints == null)
        {
            Log.e(TAG, "No Endpoints found on CastingPlayer");
        }
        else
        {
            endpoint = endpoints
                    .stream()
                    .filter(e -> SAMPLE_ENDPOINT_VID.equals(e.getVendorId()))
                    .findFirst()
                    .get();
        }
    }
    return endpoint;
}
```

On iOS, it can select an `MCEndpoint` similarly and as shown below.

```swift
// VendorId of the MCEndpoint on the MCCastingPlayer that the MCCastingApp desires to interact with after connection
let sampleEndpointVid: Int = 65521
...
// select the MCEndpoint on the MCCastingPlayer to invoke the command on
if let endpoint: MCEndpoint = castingPlayer.endpoints().filter({ $0.vendorId().intValue == sampleEndpointVid}).first
{
...
}
```

## Interacting with a Casting Endpoint

Once the Casting Client has selected an `Endpoint`, it is ready to
[issue commands](#issuing-commands) to it, [read](#read-operations) current
playback state, and [subscribe](#subscriptions) to playback events.

On Linux refer to the following platform specific files:

1. For a list of clusters, commands and attributes supported by the Matter TV
   Casting library:
   [tv-casting-common/clusters/Clusters.h](tv-casting-common/clusters/Clusters.h)
2. For the IDs and request / response types to use with these APIs:
   [/zzz_generated/app-common/app-common/zap-generated/cluster-objects.h](/zzz_generated/app-common/app-common/zap-generated/cluster-objects.h)

On iOS refer to the following platform specific files:

1. For a list of clusters, commands and attributes supported by the Matter TV
   Casting library:
   [/darwin/MatterTvCastingBridge/MatterTvCastingBridge/zap-generated/MCClusterObjects.h](/darwin/MatterTvCastingBridge/MatterTvCastingBridge/zap-generated/MCClusterObjects.h)
2. For the IDs and request / response types to use with the commands:
   [/darwin/MatterTvCastingBridge/MatterTvCastingBridge/zap-generated/MCCommandObjects.h](/darwin/MatterTvCastingBridge/MatterTvCastingBridge/zap-generated/MCCommandObjects.h)
   and
   [/darwin/MatterTvCastingBridge/MatterTvCastingBridge/zap-generated/MCCommandPayloads.h](/darwin/MatterTvCastingBridge/MatterTvCastingBridge/zap-generated/MCCommandPayloads.h)
3. For attribute [read operations](#read-operations) and
   [subscriptions](#subscriptions):
   [/darwin/MatterTvCastingBridge/MatterTvCastingBridge/zap-generated/MCAttributeObjects.h](/darwin/MatterTvCastingBridge/MatterTvCastingBridge/zap-generated/MCAttributeObjects.h)

### Issuing Commands

_{Complete Command invocation examples: [Linux](linux/simple-app-helper.cpp) |
[iOS](darwin/TvCasting/TvCasting/MCContentLauncherLaunchURLExampleViewModel.swift)}_

The Casting Client can get a reference to an `Endpoint` on a `CastingPlayer`,
check if it supports the required cluster/command, and send commands to it. It
can then handle any command response / error the `CastingPlayer` sends back.

On Linux, for example, given an `Endpoint`, it can send a `LaunchURL` command
(part of the Content Launcher cluster) by calling the `Invoke` API on a
`Command` of type
`matter::casting::core::Command<chip::app::Clusters::ContentLauncher::Commands::LaunchURL::Type>`

```c
void InvokeContentLauncherLaunchURL(matter::casting::memory::Strong<matter::casting::core::Endpoint> endpoint)
{
    // get contentLauncherCluster from the endpoint
    matter::casting::memory::Strong<matter::casting::clusters::content_launcher::ContentLauncherCluster> contentLauncherCluster =
        endpoint->GetCluster<matter::casting::clusters::content_launcher::ContentLauncherCluster>();
    VerifyOrReturn(contentLauncherCluster != nullptr);

    // get the launchURLCommand from the contentLauncherCluster
    matter::casting::core::Command<chip::app::Clusters::ContentLauncher::Commands::LaunchURL::Type> * launchURLCommand =
        static_cast<matter::casting::core::Command<chip::app::Clusters::ContentLauncher::Commands::LaunchURL::Type> *>(
            contentLauncherCluster->GetCommand(chip::app::Clusters::ContentLauncher::Commands::LaunchURL::Id));
    VerifyOrReturn(launchURLCommand != nullptr, ChipLogError(AppServer, "LaunchURL command not found on ContentLauncherCluster"));

    // create the LaunchURL request
    chip::app::Clusters::ContentLauncher::Commands::LaunchURL::Type request;
    request.contentURL    = chip::CharSpan::fromCharString(kContentURL);
    request.displayString = chip::Optional<chip::CharSpan>(chip::CharSpan::fromCharString(kContentDisplayStr));
    request.brandingInformation =
        chip::MakeOptional(chip::app::Clusters::ContentLauncher::Structs::BrandingInformationStruct::Type());

    // call Invoke on launchURLCommand while passing in success/failure callbacks
    launchURLCommand->Invoke(
        request, nullptr,
        [](void * context, const chip::app::Clusters::ContentLauncher::Commands::LaunchURL::Type::ResponseType & response) {
            ChipLogProgress(AppServer, "LaunchURL Success with response.data: %.*s", static_cast<int>(response.data.Value().size()),
                            response.data.Value().data());
        },
        [](void * context, CHIP_ERROR error) {
            ChipLogError(AppServer, "LaunchURL Failure with err %" CHIP_ERROR_FORMAT, error.Format());
        },
        chip::MakeOptional(kTimedInvokeCommandTimeoutMs));      // time out after kTimedInvokeCommandTimeoutMs
}
```

On iOS, given an `MCEndpoint` endpoint, it can send a `LaunchURL` command (part
of the Content Launcher cluster) by calling the `invoke` API on a
`MCContentLauncherClusterLaunchURLCommand`

```swift
// validate that the selected endpoint supports the ContentLauncher cluster
if(!endpoint.hasCluster(MCEndpointClusterTypeContentLauncher))
{
    self.Log.error("No ContentLauncher cluster supporting endpoint found")
    DispatchQueue.main.async
    {
        self.status = "No ContentLauncher cluster supporting endpoint found"
    }
    return
}

// get ContentLauncher cluster from the endpoint
let contentLaunchercluster: MCContentLauncherCluster = endpoint.cluster(for: MCEndpointClusterTypeContentLauncher) as! MCContentLauncherCluster

// get the launchURLCommand from the contentLauncherCluster
let launchURLCommand: MCContentLauncherClusterLaunchURLCommand? = contentLaunchercluster.launchURLCommand()
if(launchURLCommand == nil)
{
    self.Log.error("LaunchURL not supported on cluster")
    DispatchQueue.main.async
    {
        self.status = "LaunchURL not supported on cluster"
    }
    return
}

// create the LaunchURL request
let request: MCContentLauncherClusterLaunchURLParams = MCContentLauncherClusterLaunchURLParams()
request.contentURL = contentUrl
request.displayString = displayString

// call invoke on launchURLCommand while passing in a completion block
launchURLCommand!.invoke(request, context: nil, completion: { context, err, response in
    DispatchQueue.main.async
    {
        if(err == nil)
        {
            self.Log.info("LaunchURLCommand invoke completion success with \(String(describing: response))")
            self.status = "Success. Response data: \(String(describing: response?.data))"
        }
        else
        {
            self.Log.error("LaunchURLCommand invoke completion failure with \(String(describing: err))")
            self.status = "Failure: \(String(describing: err))"
        }
    }
},
timedInvokeTimeoutMs: 5000) // time out after 5000ms
```

### Read Operations

_{Complete Attribute Read examples: [Linux](linux/simple-app-helper.cpp) |
[iOS](darwin/TvCasting/TvCasting/MCApplicationBasicReadVendorIDExampleViewModel.swift)}_

The `CastingClient` may read an Attribute from the `Endpoint` on the
`CastingPlayer`. It should ensure that the desired cluster / attribute are
available for reading on the endpoint before trying to read it.

On Linux, for example, given an `endpoint`, it can read the `VendorID` (part of
the Application Basic cluster) by calling the `Read` API on an `Attribute` of
type
`matter::casting::core::Attribute<chip::app::Clusters::ApplicationBasic::Attributes::VendorID::TypeInfo>`

```c
void ReadApplicationBasicVendorID(matter::casting::memory::Strong<matter::casting::core::Endpoint> endpoint)
{
    // get applicationBasicCluster from the endpoint
    matter::casting::memory::Strong<matter::casting::clusters::application_basic::ApplicationBasicCluster> applicationBasicCluster =
        endpoint->GetCluster<matter::casting::clusters::application_basic::ApplicationBasicCluster>();
    VerifyOrReturn(applicationBasicCluster != nullptr);

    // get the vendorIDAttribute from the applicationBasicCluster
    matter::casting::core::Attribute<chip::app::Clusters::ApplicationBasic::Attributes::VendorID::TypeInfo> * vendorIDAttribute =
        static_cast<matter::casting::core::Attribute<chip::app::Clusters::ApplicationBasic::Attributes::VendorID::TypeInfo> *>(
            applicationBasicCluster->GetAttribute(chip::app::Clusters::ApplicationBasic::Attributes::VendorID::Id));
    VerifyOrReturn(vendorIDAttribute != nullptr,
                   ChipLogError(AppServer, "VendorID attribute not found on ApplicationBasicCluster"));

    // call Read on vendorIDAttribute while passing in success/failure callbacks
    vendorIDAttribute->Read(
        nullptr,
        [](void * context,
           chip::Optional<chip::app::Clusters::ApplicationBasic::Attributes::VendorID::TypeInfo::DecodableArgType> before,
           chip::app::Clusters::ApplicationBasic::Attributes::VendorID::TypeInfo::DecodableArgType after) {
            if (before.HasValue())
            {
                ChipLogProgress(AppServer, "Read VendorID value: %d [Before reading value: %d]", after, before.Value());
            }
            else
            {
                ChipLogProgress(AppServer, "Read VendorID value: %d", after);
            }
        },
        [](void * context, CHIP_ERROR error) {
            ChipLogError(AppServer, "VendorID Read failure with err %" CHIP_ERROR_FORMAT, error.Format());
        });
}
```

On iOS, given a `MCEndpoint`, the `VendorID` can be read similarly, by calling
the `read` API on the `MCApplicationBasicClusterVendorIDAttribute`

```swift
// validate that the selected endpoint supports the ApplicationBasic cluster
if(!endpoint.hasCluster(MCEndpointClusterTypeApplicationBasic))
{
    self.Log.error("No ApplicationBasic cluster supporting endpoint found")
    DispatchQueue.main.async
    {
        self.status = "No ApplicationBasic cluster supporting endpoint found"
    }
    return
}

// get ApplicationBasic cluster from the endpoint
let applicationBasiccluster: MCApplicationBasicCluster = endpoint.cluster(for: MCEndpointClusterTypeApplicationBasic) as! MCApplicationBasicCluster

// get the vendorIDAttribute from the applicationBasiccluster
let vendorIDAttribute: MCApplicationBasicClusterVendorIDAttribute? = applicationBasiccluster.vendorIDAttribute()
if(vendorIDAttribute == nil)
{
    self.Log.error("VendorID attribute not supported on cluster")
    DispatchQueue.main.async
    {
        self.status = "VendorID attribute not supported on cluster"
    }
    return
}

// call read on vendorIDAttribute and pass in a completion block
vendorIDAttribute!.read(nil) { context, before, after, err in
    DispatchQueue.main.async
    {
        if(err != nil)
        {
            self.Log.error("Error when reading VendorID value \(String(describing: err))")
            self.status = "Error when reading VendorID value \(String(describing: err))"
            return
        }

        if(before != nil)
        {
            self.Log.info("Read VendorID value: \(String(describing: after)) Before: \(String(describing: before))")
            self.status = "Read VendorID value: \(String(describing: after)) Before: \(String(describing: before))"
        }
        else
        {
            self.Log.info("Read VendorID value: \(String(describing: after))")
            self.status = "Read VendorID value: \(String(describing: after))"
        }
    }
}
```

### Subscriptions

_{Complete Attribute subscription examples: [Linux](linux/simple-app-helper.cpp)
|[iOS](darwin/TvCasting/TvCasting/MCMediaPlaybackSubscribeToCurrentStateExampleViewModel.swift)}_

A Casting Client may subscribe to an attribute on an `Endpoint` of the
`CastingPlayer` to get data reports when the attributes change.

On Linux, for example, given an `endpoint`, it can subscribe to the
`CurrentState` (part of the Media Playback Basic cluster) by calling the
`Subscribe` API on an `Attribute` of type
`matter::casting::core::Attribute<chip::app::Clusters::MediaPlayback::Attributes::CurrentState::TypeInfo>`

```c
void SubscribeToMediaPlaybackCurrentState(matter::casting::memory::Strong<matter::casting::core::Endpoint> endpoint)
{
    // get mediaPlaybackCluster from the endpoint
    matter::casting::memory::Strong<matter::casting::clusters::media_playback::MediaPlaybackCluster> mediaPlaybackCluster =
        endpoint->GetCluster<matter::casting::clusters::media_playback::MediaPlaybackCluster>();
    VerifyOrReturn(mediaPlaybackCluster != nullptr);

    // get the currentStateAttribute from the mediaPlaybackCluster
    matter::casting::core::Attribute<chip::app::Clusters::MediaPlayback::Attributes::CurrentState::TypeInfo> *
        currentStateAttribute =
            static_cast<matter::casting::core::Attribute<chip::app::Clusters::MediaPlayback::Attributes::CurrentState::TypeInfo> *>(
                mediaPlaybackCluster->GetAttribute(chip::app::Clusters::MediaPlayback::Attributes::CurrentState::Id));
    VerifyOrReturn(currentStateAttribute != nullptr,
                   ChipLogError(AppServer, "CurrentState attribute not found on MediaPlaybackCluster"));

    // call Subscribe on currentStateAttribute while passing in success/failure callbacks
    currentStateAttribute->Subscribe(
        nullptr,
        [](void * context,
           chip::Optional<chip::app::Clusters::MediaPlayback::Attributes::CurrentState::TypeInfo::DecodableArgType> before,
           chip::app::Clusters::MediaPlayback::Attributes::CurrentState::TypeInfo::DecodableArgType after) {
            if (before.HasValue())
            {
                ChipLogProgress(AppServer, "Read CurrentState value: %d [Before reading value: %d]", static_cast<int>(after),
                                static_cast<int>(before.Value()));
            }
            else
            {
                ChipLogProgress(AppServer, "Read CurrentState value: %d", static_cast<int>(after));
            }
        },
        [](void * context, CHIP_ERROR error) {
            ChipLogError(AppServer, "CurrentState Read failure with err %" CHIP_ERROR_FORMAT, error.Format());
        },
        kMinIntervalFloorSeconds, kMaxIntervalCeilingSeconds);
}
```

On iOS, given a `MCEndpoint`, `CurrentState` can be subscribed to by calling the
`subscribe` API on the it can subscribe to the `CurrentState` (part of the Media
Playback Basic cluster) by calling the `Subscribe` API on the
`MCMediaPlaybackClusterCurrentStateAttribute`

```swift
// validate that the selected endpoint supports the MediaPlayback cluster
if(!endpoint.hasCluster(MCEndpointClusterTypeMediaPlayback))
{
    self.Log.error("No MediaPlayback cluster supporting endpoint found")
    DispatchQueue.main.async
    {
        self.status = "No MediaPlayback cluster supporting endpoint found"
    }
    return
}

// get MediaPlayback cluster from the endpoint
let mediaPlaybackCluster: MCMediaPlaybackCluster = endpoint.cluster(for: MCEndpointClusterTypeMediaPlayback) as! MCMediaPlaybackCluster

// get the currentStateAttribute from the mediaPlaybackCluster
let currentStateAttribute: MCMediaPlaybackClusterCurrentStateAttribute? = mediaPlaybackCluster.currentStateAttribute()
if(currentStateAttribute == nil)
{
    self.Log.error("CurrentState attribute not supported on cluster")
    DispatchQueue.main.async
    {
        self.status = "CurrentState attribute not supported on cluster"
    }
    return
}

// call read on currentStateAttribute and pass in a completion block
currentStateAttribute!.read(nil) { context, before, after, err in

    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "HH:mm:ss"
    let currentTime = dateFormatter.string(from: Date())
    DispatchQueue.main.async
    {
        if(err != nil)
        {
            self.Log.error("Error when reading CurrentState value \(String(describing: err)) at \(currentTime)")
            self.status = "Error when reading CurrentState value \(String(describing: err)) at \(currentTime)"
            return
        }
        if(before != nil)
        {
            self.Log.info("Read CurrentState value: \(String(describing: after)) Before: \(String(describing: before)) at \(currentTime)")
            self.status = "Read CurrentState value: \(String(describing: after)) Before: \(String(describing: before)) at \(currentTime)"
        }
        else
        {
            self.Log.info("Read CurrentState value: \(String(describing: after)) at \(currentTime)")
            self.status = "Read CurrentState value: \(String(describing: after)) at \(currentTime)"
        }
    }
}
```

The Casting client can Shutdown all running Subscriptions by calling the
`ShutdownAllSubscriptions` API on the `CastingApp` on Linux/Android and
`MCCastingApp` on iOS. See API and its documentation for
[Linux](tv-casting-common/core/CastingApp.h),
[Android](android/App/app/src/main/jni/com/matter/casting/core/CastingApp.java)
and [iOS](darwin/MatterTvCastingBridge/MatterTvCastingBridge/MCCastingApp.h).