How to check if field exists or is null in a solace map?

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1

I am using Solace c client api (CCSMP), to subscribe to a Solace topic where messages contain a map. A value for the same key in a map can be a string or null. Is there a way to check if a value for a key is null? If I try to retrieve a value for a key and it’s null, Solace API logs “Field Type Null could not be converted to string”.

Sample code:


solClient_rxMsgCallback_returnCode_t
messageReceivedCallback(solClient_opaqueSession_pt opaqueSession_p, solClient_opaqueMsg_pt msg_p, void *user_p)
{
    solClient_returnCode_t rc = SOLCLIENT_OK;

    solClient_opaqueContainer_pt map_p;
    if ((rc = solClient_msg_getBinaryAttachmentMap(msg_p, &map_p))!= SOLCLIENT_OK)
    {
        //log error
        return  SOLCLIENT_CALLBACK_OK;
    }

    char buffer[128];

    //if(map_p has field "some_field" and it its value is not null) <-- how to do this?
    //{
        solClient_container_getString(map_p, buffer, 128, "some_field");
    //}
}

Thanks,
Vlad

2

Hello Vlad,

You can use solClient_container_getField to retrieve the field and type, then your code would look like this:


solClient_rxMsgCallback_returnCode_t
messageReceivedCallback(solClient_opaqueSession_pt opaqueSession_p, solClient_opaqueMsg_pt msg_p, void *user_p)
{
    solClient_returnCode_t rc = SOLCLIENT_OK;

    solClient_opaqueContainer_pt map_p;
    if ((rc = solClient_msg_getBinaryAttachmentMap(msg_p, &map_p))!= SOLCLIENT_OK)
    {
        //log error
        return  SOLCLIENT_CALLBACK_OK;
    }

    char buffer[128];
    solClient_field_t  mapEntry;

    //if(map_p has field "some_field" and it its value is not null) <-- how to do this?
    //{
        solClient_container_getField(map_p, &mapEntry, sizeof(mapEntry), "some_field");
    switch (mapEntry.type)
        {
        case SOLCLIENT_NULL:
        // handle null field
        break;
        case SOLCLIENT_STRING:
        strncpy (mapEntry.value.string, buffer, sizeof(buffer));
        break;
        default:
        // handle unexpected field
        break;
        }
    //}
    return SOLCLIENT_CALLBACK_OK;
}

I’ve left out the error checking necessary on ‘getField’ and strncpy but you get the idea.

Note also that where solClient_container_getString does a copy-out into your buffer, solClient_container_getField returns a pointer to the string (when it’s a string) and you must perform the copy-out operation yourself (i.e strncpy). That pointer returned may not be valid outside the scope of the callback and should not be saved or used later.

Ragnar

3

Thanks, that works well!