SignalR

Declarative ASP.NET Core SignalR client hub interfaces with compile-time proxy generation. Hub invokes, sends, server streams, and client callbacks map to R3 Observable<T> or IObservable<T>.

Packages

Package	Return types
Observables.SignalR.R3	R3 Observable<T>, Observable<Unit> for sends
Observables.SignalR.Reactive	IObservable<T>, IObservable<Unit>

Both include the Observables.SignalR runtime (HubService, SignalRObservable bridges) and the matching Roslyn analyzer. 0.1.0-preview4 and later are on nuget.org (same model as Events/RestAPI).

Also reference Microsoft.AspNetCore.SignalR.Client and R3 or System.Reactive in your app.

Define a hub

using Observables.SignalR;
using R3;
using Microsoft.AspNetCore.SignalR.Client;

[Hub]
public interface IChatHub
{
    [HubInvoke]
    Observable<int> GetUserCount();

    [HubSend("Send")]
    Observable<Unit> Send(string user, string message);

    [HubStream("Counter")]
    Observable<int> Counter(int count, int delayMs);

    [HubOn("ReceiveMessage")]
    Observable<ChatMessage> ReceiveMessage { get; }
}

var connection = new HubConnectionBuilder()
    .WithUrl("https://example.com/chathub")
    .Build();
await connection.StartAsync();

var hub = HubService.For<IChatHub>(connection);

using var sub = hub.ReceiveMessage.Subscribe(m => Console.WriteLine(m.Text));
await hub.Send("alice", "hello").FirstAsync();
int count = await hub.GetUserCount().FirstAsync();

Boundary attributes

Attribute	Member	SignalR client API
[HubInvoke]	Method	InvokeAsync<T> (cold, single value)
[HubSend]	Method	SendAsync → Observable<Unit>
[HubStream]	Method	StreamAsync<T> (multiple values)
[HubOn]	Property	On<T> (hot multicast per proxy property)

Method names default to the hub method name when the attribute name is omitted. Optional trailing CancellationToken is forwarded to invoke/stream calls.

System.Reactive

Use IObservable<T> return types and Observables.SignalR.Reactive; entry point remains HubService.For<T>(connection).

Diagnostics

See Diagnostics.

Design notes

Implementation details and generator output shape are documented in the Observables repo: docs/design/signalr.md.