public async Task <string> EventSource()
{
// use the event stream content type, as per specification
HttpContext.Response.ContentType = "text/event-stream";
// get the last event id out of the header
string lastEventIdString = HttpContext.Request.Headers["Last-Event-ID"].FirstOrDefault();
int temp;
int? lastEventId = null;
if (lastEventIdString != null && int.TryParse(lastEventIdString, out temp))
{
lastEventId = temp;
}
string remoteIp = HttpContext.Connection.RemoteIpAddress.ToString();
// open the current request stream for writing.
// Use UTF-8 encoding, and do not close the stream when disposing.
using (var clientStream = new StreamWriter(HttpContext.Response.Body, Encoding.UTF8, 1024, true)
{
AutoFlush = true
}) {
// subscribe to the heartbeat event. Elsewhere, a timer will push updates to this event periodically.
using (EventSubscription <EventSourceUpdate> subscription = eventsService.SubscribeTo <EventSourceUpdate>("heartbeat")) {
try {
logger.LogInformation($"Opened event source stream to address: {remoteIp}");
await clientStream.WriteLineAsync($":connected {DateTimeOffset.Now.ToString("o")}");
// If a last event id is given, pump out any intermediate events here.
if (lastEventId != null)
{
// We're not doing anything that stores events in this heartbeat demo,
// so do nothing here.
}
// start pumping out events as they are pushed to the subscription queue
while (true)
{
// asynchronously wait for an event to fire before continuing this loop.
// this is implemented with a semaphore slim using the async wait, so it
// should play nice with the async framework.
EventSourceUpdate update = await subscription.WaitForData();
// push the update down the request stream to the client
if (update != null)
{
string updateString = update.ToString();
await clientStream.WriteAsync(updateString);
}
if (HttpContext.RequestAborted.IsCancellationRequested == true)
{
break;
}
}
}
catch (Exception e) {
// catch client closing the connection
logger.LogInformation($"Closed event source stream from {remoteIp}. Message: {e.Message}");
}
}
}
return(":closed");
}