Notification Channels — Email, SMS, Push, SignalR, SSE & Custom

Every delivery channel implements INotificationChannel. The engine resolves all registered channels and routes delivery commands by name. See email-specific details and SMS, push, and real-time channels for provider configuration.

INotificationChannel

Every delivery channel implements this interface. The engine resolves all registered INotificationChannel services and routes by Name:

public interface INotificationChannel
{
    string Name { get; }
    Task SendAsync(NotificationDeliveryContext context,
        CancellationToken cancellationToken = default);
}

Channels not registered are silently skipped with a warning log (graceful degradation pattern).

Well-known channels

public static class NotificationChannels
{
    public const string InApp = "InApp";
    public const string SignalR = "SignalR";
    public const string Email = "Email";
    public const string Sms = "Sms";
    public const string WhatsApp = "WhatsApp";
    public const string Push = "Push";        // W3C Web Push
    public const string MobilePush = "MobilePush";
    public const string Sse = "Sse";
    public const string Zulip = "Zulip";
}

Channel registration

Channel	Registration	Provider resolution
InApp	Built-in (auto-registered)	N/A
Email	AddGranitNotificationsEmail()	Keyed Service: "Smtp", "Brevo", "AzureCommunicationServices", "Scaleway", "SendGrid"
SMS	AddGranitNotificationsSms()	Keyed Service: "Brevo", "AzureCommunicationServices", "AwsSns", "Twilio"
WhatsApp	AddGranitNotificationsWhatsApp()	Keyed Service: "Brevo", "Twilio"
Mobile Push	AddGranitNotificationsMobilePush()	Keyed Service: "GoogleFcm", "AzureNotificationHubs", "AwsSns"
SignalR	AddGranitNotificationsSignalR()	Direct (NotificationHub)
Web Push	AddGranitNotificationsPush()	VAPID (Lib.Net.Http.WebPush)
SSE	AddGranitNotificationsSse()	Native .NET 10 SSE
Zulip	AddGranitNotificationsZulip()	Zulip Bot API

Implementing a custom channel

public class TeamsNotificationChannel(IRecipientResolver resolver)
    : INotificationChannel
{
    public string Name => "Teams";

    public async Task SendAsync(
        NotificationDeliveryContext context,
        CancellationToken cancellationToken = default)
    {
        RecipientInfo? recipient = await resolver
            .ResolveAsync(context.RecipientUserId, cancellationToken)
            .ConfigureAwait(false);
        if (recipient is null) return;

        // Send via Microsoft Graph API...
    }
}

// Register
services.AddSingleton<INotificationChannel, TeamsNotificationChannel>();

IRecipientResolver

The application must implement this interface to resolve contact information from user identifiers. It is not provided by Granit — each application knows its own user model.

public interface IRecipientResolver
{
    Task<RecipientInfo?> ResolveAsync(
        string userId, CancellationToken cancellationToken = default);
}

public sealed record RecipientInfo
{
    public required string UserId { get; init; }
    public string? Email { get; init; }
    public string? PhoneNumber { get; init; }     // E.164 format
    public string? PreferredCulture { get; init; } // BCP 47
    public string? DisplayName { get; init; }
}