package dynamodb import ( "bytes" "hash/crc32" "io" "io/ioutil" "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" ) func init() { initClient = func(c *client.Client) { if c.Config.Retryer == nil { // Only override the retryer with a custom one if the config // does not already contain a retryer setCustomRetryer(c) } c.Handlers.Build.PushBack(disableCompression) c.Handlers.Unmarshal.PushFront(validateCRC32) } } func setCustomRetryer(c *client.Client) { maxRetries := aws.IntValue(c.Config.MaxRetries) if c.Config.MaxRetries == nil || maxRetries == aws.UseServiceDefaultRetries { maxRetries = 10 } c.Retryer = client.DefaultRetryer{ NumMaxRetries: maxRetries, MinRetryDelay: 50 * time.Millisecond, } } 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) } }