[Standards] Business rules of Last Message Correction

Dave Cridland dave at cridland.net
Wed Jun 13 22:46:58 UTC 2018

On 11 June 2018 at 09:47, Klaus Herberth <klaus at jsxc.org> wrote:

> Hi everyone,
> I plan to implement XEP-0308 Last Message Correction [1] and I'm asking
> myself how I should handle corrections of older messages. The XEP just
> says: "While it is possible to use this protocol to correct messages
> older than the most recent received from a full JID, such use is out of
> scope for this document and support for this SHOULD NOT be assumed without
> further negotiation.", but what should I do with such a message? Drop it?
> Show it as new message?
I'm surprised nobody said the obvious:

You can correct messages older than the most recent received.

The specification simply says you cannot assume *other* implementations
will do so, and since the specification declares this "out of scope", this
is the dreaded "undefined behaviour". So don't send a correction; or if you
do, at least be aware that another implementation might drop it, show it as
a new message, or - perhaps - correct the older message.

(A survey of existing practise would be interesting here, mind, and if we
want a mechanism to negotiate, just add another feature in...)

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