Hi Simon,
Ok to add a new packet type for v2 PUBLISH-1 and leave 0x0C for v1.2 PUBLISH. If I have correctly understood, this option may limit the variants of PUBLISH-1 to only 2. This option increases the overhead of PUBLISH-1 by 1 byte and I think we should avoid this. . We may limit the usage of PUBLISH-1 only to the Active and Asleep states, so only after a session has been established (eventually lasting for a very long time). In any case for security
reasons we need to identify the sender and provide it with a token to authorize the data published as QoS-1.
Bye
Davide
From: Simon Johnson <
thesii@gmail.com>
Sent: Monday, January 9, 2023 4:03 PM
To: Andy Stanford-Clark <
ANDYSC@uk.ibm.com>
Cc: Davide Lenzarini <
davide.lenzarini@u-blox.com>; Ian Craggs <
icraggs@gmail.com>;
tara.walker@microsoft.com;
mqtt-sn@lists.oasis-open.org Subject: Re: Packet Type Field Change
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I fear we may have our hand forced actually; the ENCAPSULATED message type sits at 0xFE right at the end of the reserved range in 1.2 which precludes the use of bits 0-1 for any nefarious purposes such as this so the available solutions
to this as I see it are as follows:
Create a NEW packet type for version 2 which is a new PUBLISH_MINUS_1 specific packet format such that version 1.2 PUBLISH -1's received by a gateway will decode successfully in the old format and can be differentiated
Modify the meaning of flags (byte 3) field bit 3 (presently reserved in the current PUBLISH spec) where 0 means "old style PUBLISH" and 1 means "new style -1 PUBLISH" - this mean old style packets will still decode ok since they are forced to send 0 here, and
there is no extra byte required - this is important since many old client impls still exist and we will want to be able to accept valid 1.2 traffic on new gateways
Use one of those reserved bits above to mean "protocol" version byte follows, which when set to 1 will decode the a protocol byte inserted at Byte 4
Ignore and accept the broken change
Other suggestions....
Now we have the packet versions broken out for QoS -1 & 0 in the document anyway, this seems less impactful - but as Andy said, we need to ensure we're good going forward.
S
On Mon, 9 Jan 2023 at 09:26, Andy Stanford-Clark <
ANDYSC@uk.ibm.com > wrote:
Well spotted, Si