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