Hi @tss

The problem I think here is that you are attempting to getPayload() even though the isBlank() is true for the Payload.

The whole point of the isBlank is to indicate an empty payload - and therefore you would not be expected to extract a blank Payload.

If you refer to the examples that come with the RFA API you will note that when processing any responses or any payload / Data instances there is a check like:

if(respMsg.getHintMask() & RespMsg::PayloadFlag && respMsg.getPayload().isBlank())
{
   cout<<endl<<"Warning: RDMConsumerClient::processRDMMarketDataResp() received Response message with empty payload"<<endl;
   return;
}

OR

if ( ! data.isBlank() )
{
//decode data
}

If you do wish to understand why you occasionally get an empty payload, the best approach, for now, would be to improve the log output to indicate the instrument name and the exact time when the isBlank() check returns true, so if/when this happens again we can raise a ticket with the Elektron Content team so they can hopefully explain why a blank message is being received for that instrument at that point in time.

In theory, it is possible to get a blank field list. I have modified the provider to publish this update.

<updateMsg domainType="RSSL_DMT_MARKET_PRICE" streamId="3" containerType="RSSL_DT_FIELD_LIST" flags="0x0" updateType="0 (RDM_UPD_EVENT_TYPE_UNSPECIFIED)" dataSize="0">
    <dataBody>
    </dataBody>
</updateMsg>

Then, I added the code in the consumer to print the data type of data when the data is blank.

if (data.isBlank()) {
            printf("### Data is blank: 0x%x, %d\n", data.getDataType(), data.getDataType());            
        }

The consumer prints this message when decoding the update message with no payload.

2020 Jul  3 13:42:22.096 ST GMT+07:00 1AE4 33C4   611 TRACE <- Received MMT_MARKET_PRICE Update.
### Data is blank: 0x84, 132

However, the server shouldn't send the kind of update to the application.

To verify the problem, you need to print the raw hex data of the response message.

The code looks like:

void Decoder::printHexString(const unsigned char* data, int len) {
    char hexmap[] = { '0', '1', '2', '3', '4', '5', '6', '7',
                           '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
    std::string s(len * 2, ' ');
    for (int i = 0; i < len; ++i) {
        s[2 * i] = hexmap[(data[i] & 0xF0) >> 4];
        s[2 * i + 1] = hexmap[data[i] & 0x0F];
    }
    printf("\n%s\n", s.c_str());

}

Then, call the printHexString method with the encoded buffer inside the response message.

    _pDecoder->printHexString(respMsg.getEncodedBuffer().c_buf(), respMsg.getEncodedBuffer().capacity());

With this information, we can verify the data retrieved by the application.