What does an update directory message containing an empty map entry mean?

Catherine Wong

In RFAJ_RDMUsageGuide.pdf,
“If the client specifies a service name in a directory request, it receives the
directory response for just the requested service. If the requested service
name is not available to RFA, RFA responds with a refresh message that contains
an empty map entry in the payload.” If the application receives an update
directory message containing an empty map entry in the payload what does this
mean?

pimchaya.wongrukun01

The update message means
there is change on a service which the application does not request for; RFA
has removed the changed info of non-requested service from the map so the map
is empty. Hence, the application can ignore this update message.

Please see details
below:

Even you application sets
the service name e.g. SERVICE_A into a directory request:

Msg Type: MsgType.REQUEST   
Msg Model Type: DIRECTORY   
Indication Flags: REFRESH   
Hint Flags: HAS_ATTRIB_INFO   
AttribInfo     
     ServiceName: SERVICE_A     
     Filter: 3 (INFO | STATE)   
Payload: None

RFA still requests
directory for all services. This is current expected behavior of RFA:

Msg Type: MsgType.REQUEST
Msg Model Type: DIRECTORY
Indication Flags: REFRESH
Hint Flags: HAS_ATTRIB_INFO
AttribInfo   
     Filter: 63 (INFO | STATE | GROUP | LOAD | DATA | LINK)
Payload: None

Hence, RFA receives response
messages (refresh and update) including all services info e.g. info of
SERVICE_A and SERVICE_B:

Since the application
requests only a specific service (SERVICE_A), RFA removes non-requested service
info(SERVICE_B) from the message and pass the message to the application. So
the application receives only info from the service that it has requested:

pimchaya.wongrukun01

When there is update on
SERVICE_B e.g. SERVICE_B goes down, RFA receives an update message with 1 entry
map; SERVICE_B(service id 4844) map entry containing down state:

The application does not request SERVICE_B
directory; it requests SERVICE_A directory so RFA removes SERVICE_B map entry. The
only 1 map entry has been removed; the update message contains an empty map
entry. Then, RFA pass the message to the application:

That’s why the
application receives an update message containing an empty map entry in the
payload.