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package dynamodb
import (
"bytes"
"hash/crc32"
"io"
"io/ioutil"
"math"
"strconv"
"time"
"github.com/aws/aws-sdk-go/aws"
"github.com/aws/aws-sdk-go/aws/awserr"
"github.com/aws/aws-sdk-go/aws/client"
"github.com/aws/aws-sdk-go/aws/request"
)
type retryer struct {
client.DefaultRetryer
}
func (d retryer) RetryRules(r *request.Request) time.Duration {
delay := time.Duration(math.Pow(2, float64(r.RetryCount))) * 50
return delay * time.Millisecond
}
func init() {
initClient = func(c *client.Client) {
r := retryer{}
if c.Config.MaxRetries == nil || aws.IntValue(c.Config.MaxRetries) == aws.UseServiceDefaultRetries {
r.NumMaxRetries = 10
} else {
r.NumMaxRetries = *c.Config.MaxRetries
}
c.Retryer = r
c.Handlers.Build.PushBack(disableCompression)
c.Handlers.Unmarshal.PushFront(validateCRC32)
}
}
func drainBody(b io.ReadCloser, length int64) (out *bytes.Buffer, err error) {
if length < 0 {
length = 0
}
buf := bytes.NewBuffer(make([]byte, 0, length))
if _, err = buf.ReadFrom(b); err != nil {
return nil, err
}
if err = b.Close(); err != nil {
return nil, err
}
return buf, nil
}
func disableCompression(r *request.Request) {
r.HTTPRequest.Header.Set("Accept-Encoding", "identity")
}
func validateCRC32(r *request.Request) {
if r.Error != nil {
return // already have an error, no need to verify CRC
}
// Checksum validation is off, skip
if aws.BoolValue(r.Config.DisableComputeChecksums) {
return
}
// Try to get CRC from response
header := r.HTTPResponse.Header.Get("X-Amz-Crc32")
if header == "" {
return // No header, skip
}
expected, err := strconv.ParseUint(header, 10, 32)
if err != nil {
return // Could not determine CRC value, skip
}
buf, err := drainBody(r.HTTPResponse.Body, r.HTTPResponse.ContentLength)
if err != nil { // failed to read the response body, skip
return
}
// Reset body for subsequent reads
r.HTTPResponse.Body = ioutil.NopCloser(bytes.NewReader(buf.Bytes()))
// Compute the CRC checksum
crc := crc32.ChecksumIEEE(buf.Bytes())
if crc != uint32(expected) {
// CRC does not match, set a retryable error
r.Retryable = aws.Bool(true)
r.Error = awserr.New("CRC32CheckFailed", "CRC32 integrity check failed", nil)
}
}
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