[Bug 37413] New: Clarify message edits (edit-timestamp and supersedes)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=37413

           Summary: Clarify message edits (edit-timestamp and supersedes)
           Product: Telepathy
           Version: git master
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: tp-spec
        AssignedTo: telepathy-bugs at lists.freedesktop.org
        ReportedBy: david.laban at collabora.co.uk
         QAContact: telepathy-bugs at lists.freedesktop.org


We need an additional "edit-timestamp" message header to make it clear that the
timestamp on a message with supersedes set is that of the original message
(this is required for efficiently locating the original message in e.g. the
logger). Messing about with the semantics of received-timestamp is also not
acceptable.

We should also clarify the chain of superseding messages, and what is
considered an error or not.

The following case should be valid:
message a;
message b with supersedes = a;
message c with supersedes = a;

The following should also be valid, and handled gracefully by clients in case
the CM can't retrieve it (it's not in the interests of the sender to re-send
the message x telling you how he fucked up if you lost it: he mostly wants you
to know what he *meant to say*):
message x gets lost
message y with supersedes = x;
message z with supersedes = x;

I would quite like to ban the following case (we handle every case in the
logger, but most people will only think to handle one case or another, and it
would make the code a lot simpler if we just specified that one is valid and
the other isn't).
message a;
message b with supersedes = a;
message c with supersedes = b;

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