/// <summary>
/// The <see cref="ProcessMessageStreamAsync(Stream)"/> method is overridden to
/// provide specific behavior for this base class.
/// </summary>
/// <remarks>
/// This method cannot be overridden.
/// </remarks>
/// <param name="stream">The stream with the request payload.</param>
/// <returns>The task object representing the asynchronous operation.</returns>
public override sealed async Task <Stream> ProcessMessageStreamAsync(Stream stream)
{
// read stream into memory
LogInfo("reading stream body");
string snsEventBody;
using (var reader = new StreamReader(stream)) {
snsEventBody = reader.ReadToEnd();
}
var stopwatch = Stopwatch.StartNew();
var metrics = new List <LambdaMetric>();
// process received sns record (there is only ever one)
try {
// sns event deserialization
LogInfo("deserializing SNS event");
try {
var snsEvent = LambdaSerializerSettings.LambdaSharpSerializer.Deserialize <SNSEvent>(snsEventBody);
_currentRecord = snsEvent.Records.First().Sns;
// message deserialization
LogInfo("deserializing message");
var message = Deserialize(CurrentRecord.Message);
// process message
LogInfo("processing message");
await ProcessMessageAsync(message);
// record successful processing metrics
stopwatch.Stop();
var now = DateTimeOffset.UtcNow;
metrics.Add(("MessageSuccess.Count", 1, LambdaMetricUnit.Count));
metrics.Add(("MessageSuccess.Latency", stopwatch.Elapsed.TotalMilliseconds, LambdaMetricUnit.Milliseconds));
metrics.Add(("MessageSuccess.Lifespan", (now - CurrentRecord.GetLifespanTimestamp()).TotalSeconds, LambdaMetricUnit.Seconds));
return("Ok".ToStream());
} catch (Exception e) {
LogError(e);
try {
// attempt to send failed message to the dead-letter queue
await RecordFailedMessageAsync(LambdaLogLevel.ERROR, FailedMessageOrigin.SNS, LambdaSerializer.Serialize(snsEventBody), e);
// record failed processing metrics
metrics.Add(("MessageDead.Count", 1, LambdaMetricUnit.Count));
} catch {
// NOTE (2020-04-22, bjorg): since the message could not be sent to the dead-letter queue,
// the next best action is to let Lambda retry it; unfortunately, there is no way
// of knowing how many attempts have occurred already.
// unable to forward message to dead-letter queue; report failure to lambda so it can retry
metrics.Add(("MessageFailed.Count", 1, LambdaMetricUnit.Count));
throw;
}
return($"ERROR: {e.Message}".ToStream());
}
} finally {
_currentRecord = null;
LogMetric(metrics);
}
}
