Aws-sdk-go: Nil de-reference panic from attempts to access nil Retryer provider of Request object

Created on 14 Oct 2019 · 4Comments · Source: aws/aws-sdk-go

Companion issue for https://github.com/aws/aws-dax-go/issues/18

Version of AWS SDK for Go?

v1.25.9

Version of Go (`go version`)?

go1.12.9 darwin/amd64

What issue did you see?

Nil-dereference panics from attempts to access nil retryer function r.MaxRetries() of request object here: https://github.com/aws/aws-sdk-go/blob/master/aws/request/request.go#L557
This a result of passing a nil retryer to NewDaxRequest in aws-dax-go as described in https://github.com/aws/aws-dax-go/issues/18.

Steps to reproduce

Use dax go client to read from a dynamo table and force a server error from Dynamo. For us, we set read capacity to 1 read unit and started getting throttled event errors from Dynamo.

A potential solution is to ensure all accesses of r.MaxRetries() only happen if aws.BoolValue(r.Retryable) is true:
https://github.com/aws/aws-sdk-go/blob/master/aws/request/request.go#L557

We also filed against the dax go project as a fix in both places would make dep management much easier for consumers of both libraries.

Source

CMLivingston

Most helpful comment

In order to reproduce it you have to do the following:

cfg := dax.
cfg.HostPorts = []string{endpoint}
cfg.Region = region
client := dax.New(cfg)
in := &dynamodb.GetItemInput{
    TableName: aws.String(table),
    Key:       key,
}
r, _ := client.GetItemRequest(in)
r.Send()

so the key point here is to use Request.Send method, which we actually don't use in our examples

VasilyFomin on 22 Oct 2019

👍2 ❤1

All 4 comments

Hi @CMLivingston, thanks for reaching out to us about this. Unfortunately I haven't been able to reproduce this using the sample code for aws/aws-dax-go modified to send GetItem requests instead of PutItem - I'm able to elicit ProvisionedThroughputExceededException errors without the client panicking on a nil dereference. Can you provide a code sample that exhibits this behavior so we can better understand how you're running into this?

diehlaws on 18 Oct 2019

In order to reproduce it you have to do the following:

cfg := dax.
cfg.HostPorts = []string{endpoint}
cfg.Region = region
client := dax.New(cfg)
in := &dynamodb.GetItemInput{
    TableName: aws.String(table),
    Key:       key,
}
r, _ := client.GetItemRequest(in)
r.Send()

so the key point here is to use Request.Send method, which we actually don't use in our examples

VasilyFomin on 22 Oct 2019

👍2 ❤1

Thanks for letting us know about this issue. I've merged in PR #2934 which patches the ability of the SDK to more cleanly handle a nil Retryer value. This change will be included in our next tagged release.