How to access uploadSequenceToken variable from response(DescribeLogStreamResponse) object

[RachaelSMathew]

When I call describeLogStreams I am getting a nil value for the uploadSequenceToken.

So, I am trying to catch the CloudWatchErrorType.invalidNextToken error so that I can get the uploadSequenceToken value. To produce the CloudWatchErrorType.invalidNextToken error I need to access the uploadSequenceToken from the response or DescribeLogStreamResponse object.

[adam-fowler]

Hi @RachaelSMathew

There are a number of issues with your code above. First any error thrown in the whenComplete closure will not be caught by the catch block. You need to chain your EventLoopFutures to catch errors eg

logClient.describeLogStreams(describeLogStreamsRequest)
    .flatMap { response in
        logClient.putEventStreams(...)
    }
    .flatMapErrorThrowing { error in
        // deal with error
    }

Reading the SwiftNIO docs on EventLoopFuture may help.

Secondly you are trying to catch an error from the CloudWatch module related to the pagination tokens when calling a function in the CloudWatchLogs module. Are you wanting to catch CloudWatchLogs.invalidSequenceTokenException?

Once you have a CloudWatchLogs.invalidSequenceTokenException error you can access the expectedSequenceToken via

error.context.additionalFields["expectedSequenceToken"]

[adam-fowler]

Have you thought about using the new async/await APIs as they are easier to use.

let logs = try await logClient.describeLogStreams(describeLogStreamsRequest)
do {
    try await logClient.putEventStreams(...)
} catch let error as CloudWatchLogsErrorType where error == . expectedSequenceToken {
    print(error.context.additionalFields["expectedSequenceToken"])
}