[OASIS Issue Tracker] (MQTT-501) Change type of Maximum Packet Size to Variable Byte Integer

[OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>]

    [ https://issues.oasis-open.org/browse/MQTT-501?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=67557#comment-67557 ] 

Ed Briggs commented on MQTT-501:
--------------------------------

There are several possible solutions here, each have been proposed in the past and we need to select one:

1. Define the maximum packet size as the maximum payload size (that is, the remaining length field would be used as the maximum packet size, and it would be left to the caller/ implementation to add in the size of the fixed header in performing the calculations regarding what the maximum should be set to.)

Pros:  easy to implement,  no need to specify a value larger than can be encoded in the variable length integer

Cons: caller must perform calculations which is inconvenient

2.  Define the maximum packet size as the full packet length (including the fixed header) and encode it as a fixed size integer capable of encoding the maximum remaining length field plus the fixed header size

Pros:  Easy to understand, the maximum value is equal to the full MQTT packet length, including all headers.

Cons:  additional overhead of 3 bytes when encoding small values. This only needs to be send during connection establishment.

My suggestion is NOT to use a magic number of INT or UINTMAX, to signal 'no size restriction' but to simply not send the maximum size property to signal this.

I suggest the editors decide on the least disruptive approach and add to current draft.

> Change type of Maximum Packet Size to Variable Byte Integer
> -----------------------------------------------------------
>
>                 Key: MQTT-501
>                 URL: https://issues.oasis-open.org/browse/MQTT-501
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Bug
>          Components: edits
>    Affects Versions: 5, CSD01
>            Reporter: Ken Borgendale
>            Assignee: Ed Briggs
>             Fix For: 5
>
>
> Please revise the type of Maximum Packet Size from Four Byte Integer
> to Variable Integer in 2.2.2.2, 3.1.2.11.5, and 3.2.2.3.5.
> Regards,
> Tatsuzo



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