Server-sent event in ASP.NET Core 10

Program.cs

var app = builder.Build();

app.UseCors();

// SSE endpoint in ASP.NET Core 10
app.MapGet("/countries/stream", (CountryService service, CancellationToken ct) =>
{
    var stream = service.StreamCountries(ct);

    // Each Country will be sent as an SSE event named "country"
    // Content-Type: text/event-stream
    // Fits for unidirectional push, where Websockets is good for both
    // Replace data polling
    return TypedResults.ServerSentEvents(stream, eventType: "country");
});

app.Run();