[Standards] Inbox and Other Stories

Ненахов Андрей andrew.nenakhov at redsolution.ru
Mon Jun 3 14:26:36 UTC 2019

Ok, it took me some time to get to this. I think some preamble is
necessary, with explanation of our motives. *Those who're just interested
in stanza format can skip to big TL;DR header below. *

The whole idea, and even utter necessity of such mechanics came to us when
we were preparing to make an XMPP client that is capable to work on iOS. As
you all know, basic XMPP works well enough when there is a persistent
connection with server. This persistent connection can be more or less
maintained on most modern OSs, even on Android (though it is more and more
difficult, later versions of Android really fight against any persistent
processes). But with iOS, there is no way other than to work fully offline,
relying on push notifications to wake up.

Not only that, on iOS, an app has less than 30 seconds before it is shut
down, or brought into foreground by user. Thus, an iOS app has to quickly
connect, fetch all the necessary data, present, if necessary, all
notifications to a user, and prepare to go offline.

The most direct approach to catch up what was missed is with offline
messages. It works more or less OK (more on that later) if a user is active
on a single device, but starts to fail utterly if user is trying to use
several devices simultaneously. Second approach is to fetch all messages
from an archive, between now and the latest message received from the
server. This *can* work more or less OK, if periods of disconnection are
relatively brief. (btw this is the method employed in current builds for
Xabber for iOS). However, there are scenarios when such approach will
clearly fail. Most of them revolve around device being offline for a
significant amount of time and a user being active on another device,
sending and receiving multiple messages in one conversation, 'burying'
incoming unread message from another conversation deeper than query to
message archive.

To effectively tackle this problem we came up with an approach, essentially
orthogonal to what was tried with XMPP before: *instead of an attempt to
re-establish a stream, catching up on what was missed, we're trying to
receive a slice of a current account state*.

This, naturally, leads to ideas about 'inbox' that are very alike to Dave's
proposal. True, with regular messages it is enough for us to build a list
of recent conversations and some delivered/read marker IDs. However, we do
not agree that unread message counter is not needed: if a client is doing a
cold sync, it'll only have the most recent message in a conversation, and
won't know how many are there until it loads the whole history up to that
point. As telegram channels show, there are often many thousands of unread
messages in some channels, and it is not a good idea to make clients load
all those messages only to present user a 4-digit number.

There are two more cases that we think should be accounted for: VoIP calls
and Message Editing/Deleting/Retracting.

First, in VoIP. We've stumbled in this just recently, when it became clear
that if a user is called via XEP-0353, and a message with session
initiation ends up in an archive, it can be quickly followed by subsequent
messages, even from a same contact, which will inevitably 'bury' call in
some unfetched unread messages and recipient device would never know that
there was a call (or that there is still a call in progress!)

Second, Message Editing (as we call it for now cause we didn't yet come up
with a proper name, thought we have a pretty nicely working
implementation). If you have 7 unread messages, 3 or them can very well be
edits to your previously received messages, and you'll never know that.

One more thing to consider: we don't think this will work well as a roster
extension. Users generally want to be able to access chat history even with
those who are already deleted from their rosters, and maybe even want to
have separate chat threads with single contact. Great example for this and
most obvious use is separating chats with e2e and without them into
separate chats, like Telegram or WhatsApp do. So, instead of roster we came
up with entity we call 'conversation', and last message, unread counter,
message edits and VoIP calls are property of that entity.

To make this work, a server intercepts all passing stanzas, and creates a
slice of current user account's state, based on messages, chat markers,
voip session messages, retract/edit messages.
Reconnecting client tells server the timestamp of the last message received
from the server (in our implementation all stanzas received from the server
are timestamped by the server, and clients rely on server time to be
correct for the needs of synchronization and message ordering), and server
responds with a list of conversations that was updated since that time.

Client initiates synchronization with sync request:

<iq type='get' id=’id2'>
    <query xmlns='http://xabber.com/protocol/synchronization'

Server responds with list of conversations updated since '1556111424456379':

<iq type=’result’ to=’andrey.gagarin at redsolution.com/Xabber-web’ from=’
redsolution.com’ id=’id1’>
    <synchronization xmlns=’http://xabber.com/protocol/synchronization’
        <conversation jid=’andrew.nenakhov at redsolution.com’
thread=’1asd123sd’ stamp=’1556111424456980’>
            <retract version='3'>
            <unread count=’4’ after=’andrew_id_211’ />
            <displayed id=’andrey_id_210’ />
            <delivered id=’andrey_id_215’ />
                <propose xmlns='urn:xmpp:jingle-message:0'
                <description xmlns='urn:xmpp:jingle:apps:rtp:1'
                <message from=’andrew.nenakhov at redsolution.com/Xabber-web’
to=’andrey.gagarin at redsolution.com/Xabber-web’ id=’andrew_id_214’>
                    <stanza-id id=’id342’ by=’
andrew.nenakhov at redsolution.com’ />
        <set xmlns='http://jabber.org/protocol/rsm'>
             <first index='0'>1556111424456980</first>

thread - name of a thread, or, 'conversation'. Same conversation should
have same thread, and default is nil, like, general converstion with a
displayed - AKA 'read' by remote chat partner
deliverred - received by remote partner's client
unread ... after - refers to an ID of a message of a last message read by
call - if there is an active call in progress, we pass all the propose
stanza, so client can immediately pick up the phone.
retract - versions of edits in this convesation

In case of a cold start (like, first connection with new client), client
just asks for a synchoronization without timestamp, and receives full list
of conversations in return.

ср, 29 мая 2019 г. в 19:28, Dave Cridland <dave at cridland.net>:

> On Wed, 29 May 2019 at 12:27, Ненахов Андрей <
> andrew.nenakhov at redsolution.ru> wrote:
>> We have this (not exactly this, but for the very same purpose) mostly
>> implemented and already working, would be happy to share the results with
>> everyone. Currently, it's implemented on a server, client support (in Web
>> version of Xabber) will arrive in a week or two. We also plan to release an
>> open-source server (ejabberd fork) that will support this.
>> Problem is, we definitely lack skills putting this as a 'XEP' formatted
>> thing with proper description, and, what's worse, current documentation is
>> mostly in Russian, but XMLs are in english and if someone would volunteer
>> help us putting it in a XEP-like way, I'll muster myself to translate
>> crucial bits into English.
> Right - I knew you had this but had forgotten. It'd be great to collate
> all these ideas and pick the best bits from them all.
> Just a high-level technical sketch would be really useful.
>> ср, 29 мая 2019 г. в 16:12, Dave Cridland <dave at cridland.net>:
>>> Having spent a while playing with - gasp! - non-XMPP based chat systems,
>>> I'm quite taken with the notion that some kind of Inbox might be rather
>>> useful to us.
>>> Currently, there is Erlang Solutions (ESL)'s Inbox, which is essentially
>>> a duplication of MAM with some chat state tracking. It's more than just
>>> that, of course, but the essential concept I see is that it's a different,
>>> but largely equivalent interface to MAM, with the concept of an unread
>>> counter added.
>>> Instagram, on the other hand, has no roster, as such, and its Inbox
>>> simply lists (recent) conversations, in much the same way as a client might
>>> display them. Each record contains the conversation's participants, and the
>>> most recent message. Things like presence subscription, in the Instagram
>>> model, are simply the open conversations.
>>> We do have a roster, of course, and we're putting more things into it -
>>> MIX channels, MUC Light in ESL's case, and so on.
>>> This makes me wonder if the right way to design an Inbox is actually to
>>> enhance our Roster with MAM and state awareness, and make it the
>>> conversation information hub for IM.
>>> Let's suppose that the nature of what is "unread" is equivalent across
>>> all clients of a particular user, to begin with.
>>> If a client requests the inbox "since" a particular point, it would then
>>> receive a series of records:
>>> First, a set of N records similar to a roster item, containing a jid,
>>> subscription state, the last archive-id received in the conversation, and
>>> the number of unacknowledged (by some definition) messages. Our roster also
>>> includes groups and a name; we could also include the type (MUC, MIX, or a
>>> user), the full message, etc - these are all optimisations.
>>> We do not, actually, need the numbers of unread messages - a client
>>> seeing that the last archive-id isn't in its cache knows the conversation
>>> has messages that are unread to it, at least. But if we can track message
>>> read state, that's useful for multi-device.
>>> Finally, an update message to indicate the current point, where things
>>> change. I would use an archive-id again here - even if the thing causing
>>> the update isn't an archived message at all. This allows a client to ask
>>> for the archive either since a particular message, or since an event.
>>> You'll note I'm not building this directly on PubSub in the XEP-0060 (or
>>> XEP-0163) sense - instead I'm proposing building this on the existing
>>> Roster and MAM.
>>> So:
>>> <iq type='get' id='some-id'>
>>>   <query xmlns='jabber:iq:roster' ver='last-archive-id'>
>>>     <inbox xmlns='urn:xmpp:inbox'><!-- Add enhanced inbox info -->
>>>       <messages/><!-- Include the entire last message? -->
>>>       <unread/><!-- Include unread count -->
>>>     </inbox>
>>>    </query>
>>> </iq>
>>> I'd dearly love to return updates using <message/>, MAM-style, actually.
>>> But let's say we stick with the roster design, the pushes look like:
>>> <iq from='romeo at montague.lit' id='b2gs90j5' to='romeo at montague.lit/home'
>>> type='set'>
>>>      <query xmlns='jabber:iq:roster' ver='ver42'>
>>>        <item jid='bill at shakespeare.lit' subscription='both'>
>>>           <unread count='4'/>
>>>           <stanza-id id='ver42' xmlns='...'/>
>>>           <message ...>
>>>                <body>Yeah, sure - whenever you like.</body>
>>>           </message>
>>>      </query>
>>>    </iq>
>>> Any message "counts" for updating the roster version, by dint of
>>> unifying the namespace of stanza-id (for archive) and roster version. So
>>> any new message arriving updates the current point of the roster as well,
>>> and any new change in the roster changes the archive pointer similarly.
>>> Updating the shared unread count could be by Carbonizing the
>>> read-receipts (or similar), and using the stanza-id from that, or by an
>>> explicit roster push. Either's good - I think the roster pushes are more
>>> explicit, which is helpful.
>>> I'm fully expecting some push-back here. Comments are, of course,
>>> welcome.
>>> Dave.
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>>> _______________________________________________
>> --
>> Andrew Nenakhov
>> CEO, Redsolution, Inc.
>> https://redsolution.com <http://www.redsolution.com>
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Andrew Nenakhov
CEO, Redsolution, Inc.
https://redsolution.com <http://www.redsolution.com>
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