public async Task <IActionResult> Post(
[FromForm] PostEmailRequest args,
CancellationToken cancellationToken)
{
cancellationToken.ThrowIfCancellationRequested();
var applicationId = User.GetApplicationId();
// the token will be used by both the processing engine and the
// client to track this request from start to finish
var token = EmailQueueToken.Create(applicationId);
_logger.LogInformation("Sending email using token {0}", token);
if (ModelState.IsValid)
{
// create an object that we then store as a BLOB (emails run
// the risk of being too large to fit in the queue, so BLOB
// storage is the best option)
var message = BuildMessage(args);
message.ApplicationId = applicationId;
await _blobStore.AddAsync(token, message, cancellationToken);
// now we can let the back-end processor know that there's a
// new message that it has to process
await _sender.SendAsync(token, cancellationToken);
// log that we queued the message for processing
await _logWriter.TryLogProcessAttemptAsync(token, 0, ProcessingStatus.Pending, token.TimeStamp, token.TimeStamp, null, cancellationToken);
// all done - let the client know that we've accepted their
// request, and what the tracking token is
Response.StatusCode = (int)HttpStatusCode.Accepted;
return(Json(new
{
Token = token.EncodeString()
}));
}
else
{
return(BadRequest(ModelState));
}
}
public async Task ProcessMessage(TMessage message, CancellationToken cancellationToken)
{
cancellationToken.ThrowIfCancellationRequested();
_logger.LogTrace("Processing message {0} on try {1}", message.Token, message.DequeueCount);
// start timing the process for logging purposes
var start = DateTime.UtcNow;
var sw = new Stopwatch();
sw.Start();
// load the args from the blob store; it's unlikely that they won't be found,
// but to be safe we'll check for null (the args are in the blob store because
// there's a chance that they'll exceed the 64KB limit on queue messages due
// to including data and HTML)
var args = await _blobStore.GetAsync(message.Token, cancellationToken);
if (args != null)
{
try
{
// do the actual sending and return information about the email that
// was sent so that we can log it; any failures will result in an
// exception that will be caught and handled in the catch block
var result = await TrySendEmailAsync(args);
result.DequeueCount = message.DequeueCount;
// after successful processing, the most important thing to do is
// to immediately remove this message from the queue; this will prevent
// retrieves if any of the subsequent calls fail (avoiding duplicate
// messages is more important than correct logging)
await _receiver.CompleteAsync(message, cancellationToken);
await _blobStore.RemoveAsync(message.Token, cancellationToken);
// stop timing the process
sw.Stop();
// now we can audit the event
await _logWriter.TryLogProcessAttemptAsync(message.Token, message.DequeueCount, ProcessingStatus.Succeeded, start, start.Add(sw.Elapsed), null, cancellationToken);
await _logWriter.TryLogSentMessageAsync(message.Token, result, cancellationToken);
_logger.LogInformation("Successfully sent email for message {0} on try {1}", message.Token, message.DequeueCount);
}
catch (Exception ex)
{
sw.Stop();
if (message.DequeueCount >= MaxDequeue)
{
// failed, and reached the maximum retry count; move the message to
// the poison queue and move the blob data to the bin of failure
await _receiver.MoveToPoisonQueueAsync(message, cancellationToken);
await _blobStore.MoveToPoisonStoreAsync(message.Token, cancellationToken);
await _logWriter.TryLogProcessAttemptAsync(message.Token, message.DequeueCount, ProcessingStatus.FailedAbandoned, start, start.Add(sw.Elapsed), ex.GetBaseException().Message, cancellationToken);
_logger.LogError("Failed to send email for message {0} after {1} tries, giving up\n{2}", message.Token, message.DequeueCount, ex);
}
else
{
// failed, but we'll let it retry to see if that fixes it
await _logWriter.TryLogProcessAttemptAsync(message.Token, message.DequeueCount, ProcessingStatus.FailedRequeued, start, start.Add(sw.Elapsed), ex.GetBaseException().Message, cancellationToken);
_logger.LogWarning("Failed to send email for message {0} after {1} tries\n{2}", message.Token, message.DequeueCount, ex);
}
}
}
else
{
// if we couldn't find a matching blob, then raise an error and remove
// the message from the queue
_logger.LogError("Could not find message params for {0}", message.Token);
await _receiver.CompleteAsync(message, cancellationToken);
}
}
