How can i access error individual attributes in golang-CodePudding

!! i Am new to go !!

I Am using the datasync API to start a task execution , that works with no issues. I Am struggling with the returned error struct, i want to acces individual elements but i can't seem to be a ble to do so.

for exemple in the following error i want to be able to access the content of Message_

2022/03/19 09:33:48 Sync called : 
InvalidRequestException: Unable to queue the task execution for task task-xxxxxxxxxxxx. The task already has another task execution exec-030b4a31dc2e33641 currently running or queued with identical Include and Exclude filter patterns. Please provide unique Include and Exclude filter patterns for the new task execution and try again.
{
  RespMetadata: {
    StatusCode: 400,
    RequestID: "xxxxxxxxxxxxxxxxxxxxx"
  },
  ErrorCode: "DedupeFailed",
  Message_: "Unable to queue the task execution for task task-xxxxxxxxxx. The task already has another task execution exec-xxxxxxxxxx currently running or queued with identical Include and Exclude filter patterns. Please provide unique Include and Exclude filter patterns for the new task execution and try again."
}

Here is my working exemple :

    // Create datasync service client
    svc := datasync.New(sess)

    params := &datasync.StartTaskExecutionInput{
        TaskArn : aws.String("arn:aws:datasync:*******************************"),
    }

    // start task execution
    resp, err := svc.StartTaskExecution(params)

    //err = req.Send()

    if err == nil { // resp is now filled
        fmt.Println(resp)  // this outputs this { TaskExecutionArn: "arn:aws:datasync:xxxxxxxx:task/task-03ecb7728e984e36a/execution/exec-xxxxxxxxxx" }

    } else {
        fmt.Println(err)
        //fmt.Println(err.Message()) THIS DOES NOT WORK
        //fmt.Println(err.Message_)  THIS ALSO DOES NOT WORK
    }

If I do this fmt.Println(err.Message()) or this fmt.Println(err.Message_) I get this error err.Message undefined (type error has no field or method Message) err.Message_ undefined (type error has no field or method Message_)

Where did I go wrong ?

CodePudding user response：

Errors in the AWS SDK for Go are often of the interface awserr.Error (Code on Github).

If you just want to have the message, you can do this:

resp, err := svc.StartTaskExecution(params)

if err != nil {
    if awsErr, ok := err.(awserr.Error); ok {
        fmt.Println(awsErr.Message())
    } else {
        fmt.Println(err.Error())
    }
}

First, there is a check if there is actually an error:

if err != nil {...}

Then, we try to cast the error to it's specific "type" awserr.Error:

err.(awserr.Error)

The return value of cast is the specific error awsErr and a bool to indicate if the cast worked or not (ok).

awsErr, ok := err.(awserr.Error)

The rest of the code is basically just checking, if ok == true and if that is the case you can access the errors fields like Message:

if awsErr, ok := err.(awserr.Error); ok {
    fmt.Println(awsErr.Message())
}

Otherwise, you just print the standard Go error message:

if awsErr, ok := err.(awserr.Error); ok {
    ...
} else {
    fmt.Println(err.Error())
}