Flazlo.Sse 1.0.1

SSE Blazor Utility for .NET 8

This library provides streamlined utilities for working with Server-Sent Events (SSE) in both ASP.NET Core backends and Blazor WebAssembly frontends. It enables structured JSON-based communication over text/event-stream, with minimal boilerplate.

Quick Start

Define a structured SSE endpoint:

[HttpGet("/stream")]
public async Task StreamStructured(CancellationToken cancellationToken)
{
    async IAsyncEnumerable<SseMessage> GetStream([EnumeratorCancellation] CancellationToken token)
    {
        int counter = 0;
        while (!token.IsCancellationRequested)
        {
            yield return new SseMessage
            {
                Data = JsonSerializer.Serialize(new { Name = "Mike", Age = counter++ }),
                Event = "heartbeat",
                Id = counter.ToString()
            };

            await Task.Delay(1000, token);
        }
    }

    await HttpContext.StreamAsync(GetStream(cancellationToken), eventName: "heartbeat");
}

Consuming SSE Events (Blazor WebAssembly)

@using SseBlazor
@using System.Text.Json
@inject HttpClient Http

<PageTitle>Counter</PageTitle>

@foreach (var item in messages)
{
    <b>@((MarkupString)string.Format("Name: {0} Age: {1} <br/> EventType: {2} Id: {3}", item.Name, item.Age, item.SSE.Event, item.SSE.Id))</b>
    <br />
}

@code {
    private List<Person> messages = [];
    private SseClient<SseMessage>? _sse;
    private CancellationTokenSource _cts = new();

    protected override async Task OnInitializedAsync()
    {
        _sse = new SseClient<SseMessage>(Http, "/stream");

        await foreach (var evt in _sse.StreamAsync(_cts.Token))
        {
            var message = JsonSerializer.Deserialize<Person>(evt.Data);
            message.SSE = evt;
            messages.Add(message);

            await InvokeAsync(StateHasChanged);
        }
    }

    public void Dispose()
    {
        _cts.Cancel();
        _cts.Dispose();
    }

    public class Person
    {
        public string Name { get; set; }
        public int Age { get; set; }
        public SseMessage SSE { get; set; }
    }
}