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add two variants

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holger krekel
2020-02-19 14:20:07 +01:00
parent d1a26e66a7
commit 13e361aabc
1 changed files with 27 additions and 3 deletions
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draft/group-sync.rst
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@@ -28,9 +28,10 @@ For reference, please see https://github.com/deltachat/deltachat-core-rust/blob/
- If an incoming member-add/member-delete messages has a member list - If an incoming member-add/member-delete messages has a member list
which is, apart from the added/removed member, not consistent which is, apart from the added/removed member, not consistent
with our own view, send a "Chat-Group-Member-Correction" message out, with our own view, broadcast a "Chat-Group-Member-Correction" message to
attaching the original added/removed mime-message for all mismatching contacts. all members, attaching the original added/removed mime-message for all mismatching
If we have no relevant add/del information, don't send a correction message out. contacts. If we have no relevant add/del information, don't send a
correction message out.
- Upong receiving added/removed attachments we don't do the - Upong receiving added/removed attachments we don't do the
check_consistency+correction message dance. check_consistency+correction message dance.
@@ -53,10 +54,33 @@ Notes:
- somewhat backward compatible: older clients will probably ignore - somewhat backward compatible: older clients will probably ignore
messages which are signed by someone who is not the outer From-address. messages which are signed by someone who is not the outer From-address.
- the correction-protocol also helps with dropped messages. If a member
did not see a member-added/removed message, the next member add/removed
message in the group will likely heal group consistency for this member.
- we can quite easily extend the mechanism to also provide the group-avatar or - we can quite easily extend the mechanism to also provide the group-avatar or
other meta-information. other meta-information.
Discussions of variants
++++++++++++++++++++++++
- instead of acting on MemberAdded/Removed message we could send
corrections for any received message that addresses inconsistent group members but
a) this would delay group-membership healing
b) could lead to a lot of members sending corrections
- instead of broadcasting correction messages we could only send it to
the sender of the inconsistent member-added/removed message.
A receiver of such a correction message would then need to forward
the message to the members it thinks also have an inconsistent view.
This sounds complicated and error-prone. Concretely, if Alice
receives Bob's "Member-added: Doris" message, then Alice
broadcasting the correction message with "Member-added: Carol"
would reach all four members, healing group consistency in one step.
If Bob meanwhile receives Alice's "Member-Added: Carol" message,
Bob would broadcast a correction message to all four members as well.
(Imagine a situation where Alice/Bob added Carol/Doris
while both being in an offline or bad-connection situation).
solution2: repeat member-added/removed messages solution2: repeat member-added/removed messages