Add properties to the will message

["Ken Borgendale" <kwb@us.ibm.com>]

One of the comments received during the MQTTv5.0 CSD01 public review was that there is no way to set properties on the will message. This is now the final issue for the MQTT TC to resolve before starting another public review. The TC has decided to allow properties to be set on will messages, but is split over how to do this. We are therefore asking for comments now. The time is short as we expect to resolve this issue on October 12. There are three options under consideration

Option A

• Add several to the CONNECT Packet which apply to the the will message: Publication Expiry Interval, Payload Format Indicator, and Content Type
• Add a new property definition for Will User Properties on the CONNECT Packet to allow User Properties on the will message

Pros: CONNECT payload is the same as v3.1.1
Cons: The two sets of User Properties on CONNECT (one for CONNECT user properties, one for will message user properties)

Option B

• Replace the current WILL Message field in the CONNECT Packet with a full PUBLISH Packet.
• Remove existing CONNECT Flags for Will QoS and Will Retain as well as Will Topic field
• Define the set of limitations on this publish packet (no Topic Alias or Subscription ID, packet ID must be 0).

Pros: Clean specification definition of Will Message as a form of PUBLISH packet 
Cons: Large change to specification and possible impact to current implementations

Option C

• Add new field Will Properties in CONNECT payload before Will Topic
• If Will Flag is set, the Will Properties is required (if there are no properties this is just adding one 0x00 byte)
• Define the exact list properties in the Will Properties

Pros: Only a minor change from v3.1.1 and existing v5.0 CONNECT payload
Cons: Adds a properties structure into the CONNECT payload

For details you can view: https://issues.oasis-open.org/browse/MQTT-498
If you have a preference, you can reply to this comment list.

Ken Borgendale  --  kwb@us.ibm.com