@Override
    public long getRequestContentLength() {
        return requestContentLength;
    }
Returns the number of bytes to be expected in the request, or -1 if the
number is unknown (e.g. when the request is still not serialized yet, or
when the request contains raw InputStream as the payload in which case
the SDK cannot infer the content-length in advance).
aws-java-sdk-core/src/main/java/com/amazonaws/event/request/ProgressSupport.java