panic when missing credentials

[amznpurple]

Confirm by changing [ ] to [x] below to ensure that it's a bug:

• I've gone though the API reference
• I've checked AWS Forums and StackOverflow for answers
• I've searched for previous similar issues and didn't find any solution

Describe the bug
A clear and concise description of what the bug is.

Panic with this code:

package main
import (
	"context"
	"fmt"
	"github.com/aws/aws-sdk-go-v2/service/s3"
)
const region = "ca-central-1"
func main() {
	fmt.Printf("hello s3\n")
	options := s3.Options{
		// The region to send requests to. (Required)
		Region: region,
	}
	client := s3.New(options)
	fmt.Printf("list buckets\n")
	output, err := client.ListBuckets(context.TODO(), &s3.ListBucketsInput{}) // XXX: panics here!
	if err != nil {
return
	}
	fmt.Printf("Bucket owner: %+v\n", output.Owner) // *DisplayName or *ID
	for _, bucket := range output.Buckets {
		fmt.Printf("Bucket: %+v\n", bucket.Name)
	}
}

Version of AWS SDK for Go?
Example: v1.29.22

• get SDK version by printing the output of aws.SDKVersion in your code after importing "github.com/aws/aws-sdk-go-v2/aws"

git master/main

Version of Go (go version)?
1.16

To Reproduce (observed behavior)
Steps to reproduce the behavior (please share code or minimal repo)

Run code.
It should not panic. It does.

Panic: runtime error: index out of range [1024] with length 1024
 
goroutine 1 [running]:
github.com/aws/smithy-go/io.(*RingBuffer).Read(0xc000486060, 0xc0000ae000, 0x200, 0x200, 0x4, 0xc000500780, 0x7f6a80365638)
	/home/purple/go/pkg/mod/github.com/aws/[email protected]/io/ringbuffer.go:63 +0xb6
bytes.(*Buffer).ReadFrom(0xc000486c90, 0x79b200, 0xc000486060, 0x7f6a80365638, 0xc000486c90, 0x1)
	/usr/lib/go-1.16/src/bytes/buffer.go:204 +0xbe
io.copyBuffer(0x79ae60, 0xc000486c90, 0x79b200, 0xc000486060, 0x0, 0x0, 0x0, 0x1, 0x1, 0x79af40)
	/usr/lib/go-1.16/src/io/io.go:409 +0x357
io.Copy(...)
	/usr/lib/go-1.16/src/io/io.go:382

Expected behavior
A clear and concise description of what you expected to happen.

Should not panic.

Additional context
Add any other context about the problem here.

When you pass in credentials, then it doesn't panic. But it's a bug that a user could ever cause a panic.

[skmcgrail]

Can reproduce the panic with the following code, a very subtle bug that can only happen on certain data sizes that are a multiple of 1024. This code reproduces the same bug but just with a smaller data size.

package main

import (
	"bytes"
	"fmt"
	smithyio "github.com/aws/smithy-go/io"
	"io"
	"io/ioutil"
	"math/rand"
)

func main() {
	var data [100]byte

	_, err := rand.Read(data[:])
	if err != nil {
		panic(err)
	}

	dataReader := bytes.NewReader(data[:])

	var stack [10]byte
	ringBuffer := smithyio.NewRingBuffer(stack[:])

	reader := io.TeeReader(dataReader, ringBuffer)

	_, err = ioutil.ReadAll(reader)
	if err != nil {
		panic(err)
	}

	var buffer bytes.Buffer

	_, err = io.Copy(&buffer, ringBuffer)
	if err != nil {
		panic(err)
	}

	fmt.Printf("%x\n", buffer.String())
}

[amznpurple]

/cc @purpleidea who discovered this bug.

[github-actions]

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