UA-.NETStandard/Libraries/Opc.Ua.Client/Subscription/SubscriptionRecoveryPolicy.cs

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namespace Opc.Ua.Client
{
    /// <summary>
    /// Controls how the client reacts to server-emitted status change
    /// notifications and other recoverable subscription events.
    /// Declared as a <see cref="System.FlagsAttribute"/> so additional
    /// recovery behaviours can be combined as the surface evolves
    /// (e.g. dedicated handling for <c>Bad_Timeout</c> or republish
    /// failures); for now only the <c>Good_SubscriptionTransferred</c>
    /// case (OPC UA Part 4 §5.14.7 / §7.25.4) has a dedicated flag.
    /// <para>
    /// Per the specification the
    /// <c>Good_SubscriptionTransferred</c> notification is sent to
    /// the <i>old</i> Session when its Subscription was transferred
    /// away to another Session via the
    /// <c>TransferSubscriptions</c> Service. Some servers (e.g.
    /// Kepware after a server reinitialisation) have been observed
    /// to emit the notification against a Subscription that the
    /// client only just created on the new Session, which under the
    /// default behaviour leaves the Subscription dark with no
    /// further notifications dispatched.
    /// </para>
    /// </summary>
    [System.Flags]
    public enum SubscriptionRecoveryPolicy
    {
        /// <summary>
        /// Spec-strict, backwards-compatible behaviour: no
        /// recovery flags set. The relevant publish-state flag is
        /// still raised so the application can react, but the SDK
        /// does not attempt to recreate the Subscription on its
        /// own. In the <c>Good_SubscriptionTransferred</c> case the
        /// Subscription is treated as transferred away from this
        /// Session and stops processing notifications on the client
        /// side.
        /// </summary>
        ReportOnly = 0,

        /// <summary>
        /// If the client did not initiate a TransferSubscriptions
        /// request for this Subscription, treat a server-emitted
        /// <c>Good_SubscriptionTransferred</c> as the server having
        /// invalidated the Subscription on the current Session and
        /// recreate it in place using the existing options.
        /// Resolves the symptom of a "stuck" Subscription after
        /// server-initiated quirks but does not preserve the
        /// server-side retransmission queue or triggering
        /// relationships that were tied to the invalidated
        /// Subscription identifier.
        /// </summary>
        RecreateOnUnsolicitedTransfer = 1 << 0
    }
}