private async Task ExecuteAsync(HttpContext context, ConnectionDelegate connectionDelegate, HttpConnectionDispatcherOptions options, ConnectionLogScope logScope)
{
// set a tag to allow Application Performance Management tools to differentiate long running requests for reporting purposes
context.Features.Get <IHttpActivityFeature>()?.Activity.AddTag("http.long_running", "true");
var supportedTransports = options.Transports;
// Server sent events transport
// GET /{path}
// Accept: text/event-stream
var headers = context.Request.GetTypedHeaders();
if (headers.Accept?.Contains(new Net.Http.Headers.MediaTypeHeaderValue("text/event-stream")) == true)
{
// Connection must already exist
var connection = await GetConnectionAsync(context);
if (connection == null)
{
// No such connection, GetConnection already set the response status code
return;
}
if (!await EnsureConnectionStateAsync(connection, context, HttpTransportType.ServerSentEvents, supportedTransports, logScope, options))
{
// Bad connection state. It's already set the response status code.
return;
}
Log.EstablishedConnection(_logger);
// ServerSentEvents is a text protocol only
connection.SupportedFormats = TransferFormat.Text;
// We only need to provide the Input channel since writing to the application is handled through /send.
var sse = new ServerSentEventsServerTransport(connection.Application.Input, connection.ConnectionId, connection, _loggerFactory);
await DoPersistentConnection(connectionDelegate, sse, context, connection);
}
else if (context.WebSockets.IsWebSocketRequest)
{
// Connection can be established lazily
var connection = await GetOrCreateConnectionAsync(context, options);
if (connection == null)
{
// No such connection, GetOrCreateConnection already set the response status code
return;
}
if (!await EnsureConnectionStateAsync(connection, context, HttpTransportType.WebSockets, supportedTransports, logScope, options))
{
// Bad connection state. It's already set the response status code.
return;
}
Log.EstablishedConnection(_logger);
// Allow the reads to be canceled
connection.Cancellation = new CancellationTokenSource();
var ws = new WebSocketsServerTransport(options.WebSockets, connection.Application, connection, _loggerFactory);
await DoPersistentConnection(connectionDelegate, ws, context, connection);
}
else
{
// GET /{path} maps to long polling
// Connection must already exist
var connection = await GetConnectionAsync(context);
if (connection == null)
{
// No such connection, GetConnection already set the response status code
return;
}
if (!await EnsureConnectionStateAsync(connection, context, HttpTransportType.LongPolling, supportedTransports, logScope, options))
{
// Bad connection state. It's already set the response status code.
return;
}
if (!await connection.CancelPreviousPoll(context))
{
// Connection closed. It's already set the response status code.
return;
}
// Create a new Tcs every poll to keep track of the poll finishing, so we can properly wait on previous polls
var currentRequestTcs = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
if (!connection.TryActivateLongPollingConnection(
connectionDelegate, context, options.LongPolling.PollTimeout,
currentRequestTcs.Task, _loggerFactory, _logger))
{
return;
}
var resultTask = await Task.WhenAny(connection.ApplicationTask !, connection.TransportTask !);
try
{
// If the application ended before the transport task then we potentially need to end the connection
if (resultTask == connection.ApplicationTask)
{
// Complete the transport (notifying it of the application error if there is one)
connection.Transport.Output.Complete(connection.ApplicationTask.Exception);
// Wait for the transport to run
// Ignore exceptions, it has been logged if there is one and the application has finished
// So there is no one to give the exception to
await connection.TransportTask !.NoThrow();
// If the status code is a 204 it means the connection is done
if (context.Response.StatusCode == StatusCodes.Status204NoContent)
{
// Cancel current request to release any waiting poll and let dispose acquire the lock
currentRequestTcs.TrySetCanceled();
// We should be able to safely dispose because there's no more data being written
// We don't need to wait for close here since we've already waited for both sides
await _manager.DisposeAndRemoveAsync(connection, closeGracefully : false);
}
else
{
// Only allow repoll if we aren't removing the connection.
connection.MarkInactive();
}
}
else if (resultTask.IsFaulted || resultTask.IsCanceled)
{
// Cancel current request to release any waiting poll and let dispose acquire the lock
currentRequestTcs.TrySetCanceled();
// We should be able to safely dispose because there's no more data being written
// We don't need to wait for close here since we've already waited for both sides
await _manager.DisposeAndRemoveAsync(connection, closeGracefully : false);
}
else
{
// Only allow repoll if we aren't removing the connection.
connection.MarkInactive();
}
}
finally
{
// Artificial task queue
// This will cause incoming polls to wait until the previous poll has finished updating internal state info
currentRequestTcs.TrySetResult();
}
}
}