DynamoDB/AWS SDK error handling doesn't work properly

[yerke]

Describe the bug

We are calling DynamoDB like follows:

_, err = d.database.PutItem(
			ctx,
			&dynamodb.PutItemInput{
				Item:                item,
				TableName:           aws.String(decisionEventsTableName),
				ConditionExpression: aws.String("attribute_not_exists(#Token)"), // prevents overwrite
				ExpressionAttributeNames: map[string]string{
					"#Token": "Token", // Token is a keyword in aws
				},
			})

Then we are trying to handle exception

	if err != nil {
		var ccf *types.ConditionalCheckFailedException
		if errors.As(err, &ccf) { some_stuff_here() }
		return err
	}

This way of handling exception in aws-sdk-go-v2 is suggested in migration guide: https://aws.github.io/aws-sdk-go-v2/docs/handling-errors/#api-error-responses

Expected Behavior

I expect that if DynamoDB returns ConditionalCheckFailedException, errors.As call as written above to return true.

Current Behavior

The problem is that it doesn't work. I can see that that err contains *smithy.OperationError: operation error DynamoDB: PutItem, https response error StatusCode: 400, RequestID: UVDSN7JDGHJFC7AGUH3UNQQ4IFVV4KQNSO5AEMVJF66Q9ASUAAJG, ConditionalCheckFailedException: The conditional request failed, but errors.As(err, &ccf) does not return true.

Reproduction Steps

Please see code above

Possible Solution

I had to use a workaround as suggested in https://github.com/aws/aws-sdk-go-v2/issues/1386.

Additional Information/Context

It looks similar to https://github.com/aws/aws-sdk-go-v2/issues/1386.

I have a support case open with Case ID 10424576731.

AWS Go SDK V2 Module Versions Used

	github.com/aws/aws-sdk-go-v2 v1.16.7
	github.com/aws/aws-sdk-go-v2/config v1.15.0
	github.com/aws/aws-sdk-go-v2/credentials v1.12.4
	github.com/aws/aws-sdk-go-v2/feature/dynamodb/attributevalue v1.9.2
	github.com/aws/aws-sdk-go-v2/feature/dynamodb/expression v1.4.1
	github.com/aws/aws-sdk-go-v2/service/dynamodb v1.15.5

Compiler and Version used

go1.17.6

Operating System and version

Linux, CentOS 7

[RanVaknin]

Hi, Thanks for opening the ticket.
I'll try to repro and see what I can find.

[RanVaknin]

Hi @yerke ,

As I mentioned on the separate thread you referenced. This is not a known error with the DynamoDB API.

I am not able to reproduce your issue. Since your code is missing a lot of things like what your item looks like, the client initialization and more.. It's hard for me to get a concrete idea of what might be the problem on your end.

Here is my complete code

package main

import (
	"context"
	"errors"
	"fmt"
	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/feature/dynamodb/attributevalue"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb/types"
)

type Office struct {
	Season  int
	Episode int
	Foo     string
}

func main() {
	cfg, err := config.LoadDefaultConfig(
		context.Background(),
		config.WithRegion("us-east-1"),
	)
	if err != nil {
		panic(fmt.Sprintf("Error configuring AWS: %s", err))
	}

	db := dynamodb.NewFromConfig(cfg)

	item, err := attributevalue.MarshalMap(&Office{
		Season:  11,
		Episode: 11,
		Foo:     "bar",
	})
	if err != nil {
		fmt.Println(err)
	}

	putItemInput := dynamodb.PutItemInput{
		TableName:           aws.String("TEST_TABLE"),
		Item:                item,
		ConditionExpression: aws.String("attribute_not_exists(#Foo)"),
		ExpressionAttributeNames: map[string]string{
			"#Foo": "Foo",
		},
	}

	putItemOutput, err := db.PutItem(context.Background(), &putItemInput)
	if err != nil {
		var ccf *types.ConditionalCheckFailedException
		if errors.As(err, &ccf) {
			fmt.Println("this is a smithy generated error")
		}
		return
	}

	fmt.Printf("%v\n", putItemOutput)
}

The first time the code ran it created the record in DDB, after I changed the value of Foo and executed the file again the output was as expected:

This is a smithy generated error

Let me know if this helps.
Thanks

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[yerke]

@RanVaknin I will try to make a smaller repro for you.

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[DennisPing]

Commenting for any future readers. What tripped me up was "double pointer" thing as @RanVaknin showed.

// Doing an update. If Key doesn't exist, just add a new item. Return nothing.

_, err = d.Client.UpdateItem(ctx, &dynamodb.UpdateItemInput{
	Key: map[string]types.AttributeValue{
		"userId": &types.AttributeValueMemberN{Value: strconv.Itoa(userId)},
	},
	TableName:                 aws.String("myTableName"),
	ExpressionAttributeNames:  expr.Names(),
	ExpressionAttributeValues: expr.Values(),
	UpdateExpression:          expr.Update(),
	ReturnValues:              types.ReturnValueNone,
})
if err != nil {
	var opErr *smithy.OperationError
	if errors.As(err, &opErr) {
		switch opErr.Unwrap().(type) {
		case *types.ProvisionedThroughputExceededException:
			// handle update rate too high
		case *types.RequestLimitExceeded:
			// handle ran out of money
		default:
			// handle some other operational error
		}
	}
	return fmt.Errorf("unexpected error: %w", err)
}
return nil

[ilovejs]

no, above example would not work for ConditionalCheckFailedException casting.
also, switch opErr.Unwrap().(type) is not so good piece of code..
what if err.Error(), it print without any err detail e.g. fields,
detail was truncated. as far as i can tell it ends with :

@RanVaknin