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

vkhavulya

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

Ragnar

Hello Vlad,

You can use solClient_container_getFieldto 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

vkhavulya

Thanks, that works well!

Ragnar

Hello Vlad,

You can use solClient_container_getFieldto 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

vkhavulya

Thanks, that works well!