// APIErrorCode type of error status.
type APIErrorCode int

//go:generate stringer -type=APIErrorCode -trimprefix=Err $GOFILE

// Error codes, non exhaustive list - http://docs.aws.amazon.com/AmazonS3/latest/API/ErrorResponses.html
const (
	ErrNone APIErrorCode = iota
	ErrAccessDenied
	ErrBadDigest
	ErrEntityTooSmall
	ErrEntityTooLarge
	ErrPolicyTooLarge
	ErrIncompleteBody
	ErrInternalError
	ErrInvalidAccessKeyID

	return req, err
}

// preSignV4 presign the request, in accordance with
// http://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-query-string-auth.html.
func preSignV4(req *http.Request, accessKeyID, secretAccessKey string, expires int64) error {
	// Presign is not needed for anonymous credentials.
	if accessKeyID == "" || secretAccessKey == "" {