ADR-006: SignalR for Real-time Communication

Status

Accepted - December 2024

Context

The chat functionality requires real-time, bidirectional communication between clients and servers with support for multiple transport protocols and horizontal scaling.

Decision

Use ASP.NET Core SignalR for real-time communication in the chat service.

Rationale

• Transport Flexibility: WebSockets, Server-Sent Events, Long Polling fallback
• Scaling Support: Azure SignalR Service for horizontal scaling
• Type Safety: Strongly-typed hub methods and clients
• Integration: Native ASP.NET Core integration
• Authentication: Works with existing authentication system

Implementation

public sealed class ChatStreamHub : Hub
{
    public IAsyncEnumerable<ClientMessageFragment> Stream(
        Guid id,
        StreamContext streamContext,
        IChatStreaming streaming,
        CancellationToken token
    )
    {
        return StreamAsync();

        async IAsyncEnumerable<ClientMessageFragment> StreamAsync()
        {
            await foreach (
                var message in streaming.GetMessageStream(
                    id,
                    streamContext.LastMessageId,
                    streamContext.LastFragmentId,
                    token
                )
            )
            {
                yield return message;
            }
        }
    }
}

Consequences

Positive

• Real-time user experience
• Automatic transport fallback
• Easy horizontal scaling with Azure SignalR
• Built-in connection management

Negative

• Stateful connections require careful scaling
• Additional complexity in client applications
• WebSocket compatibility considerations

Related Decisions

• ADR-003: .NET Aspire for Cloud-Native Development