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Re: [hono-dev] Hono-Kura integration
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On Wed, 2018-06-27 at 15:18 +0000, De Alti, Cristiano wrote:
> Hi,
> I wonder if there is still room for an improvement in the MQTT topic format
> for telemetry and event.
>
Are we talking about the existing Kura adapter or the MQTT adapter?
> Kura would always authenticate to Hono, and does not use the Hono “gateway”
> concept.
> Having to use the “extended” topic form is unfortunate as it wastes two extra
> bytes (“t/”) compared to the Kura/Kapua “data messages”.
>
> Shrinking the topic to the minimum will benefit people connecting over a
> cellular link on a cheap (and limited) data plan, and being able to use
> “t/${topic-suffix}” would represent a significant cost saving.
>
> As this “compact” form is ambiguous and cannot be used, I wonder If one of the
> following alternatives (in order of preference) could be added to the current
> topic rules
>
> 1. t//$topic-suffix}. Two adjacent topic separators are explicitly allowed in
> section 4.7.1.1, Topic level separator, of the 3.1.1 spec, delimiting a zero-
> length topic level.
> It would indicate “this tenant-id and device-id”
> 2. t///$topic-suffix}. As above but with two zero-length topic levels
> indicating “this tenant-id” and “this device-id” respectively
> 3. t/_/$topic-suffix}. The “_” placeholder is used to indicate “this tenant-id
> and device-id”
> 4. t/_/_/$topic-suffix}. Same as above but using two levels to indicate “this
> tenant-id” and “this device-id” respectively
>
> As said above, 1 and 2 would be preferred but I’ve never tried to publish such
> topics, so I don’t know yet if they could be problematic for some client
> implementations.
> The last two forms, 3 and 4, are definitely less problematic.
> Maybe all four should be supported.
>
> Regards,
> Cristiano
>
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