In multi-device environments marking a chat as displayed on one device should mark that chat as displayed on all devices. Historically carbon copies (Message Carbons (XEP-0280) [1]) of the <displayed/> element of Displayed Markers (Displayed Markers (XEP-0333) [2]) have been used to achieve this effect. However this approach has a couple of downsides that this specification is trying eliminate:
This specification isolates the task of multi-device synchronization from providing information to the contact, while borrowing some of the semantics of Displayed Markers such as displayed refering to all messages up to this point.
Clients use items in a private PEP (Personal Eventing Protocol (XEP-0163) [3]) node called 'urn:xmpp:mds:displayed:0' to synchronize and persist the displayed state (See Best Practices for Persistent Storage of Private Data via Publish-Subscribe (XEP-0223) [4]). The item ID corresponds to the JID of the respective chat. For normal, 1:1 chats this SHOULD be the bare JID of the contact, for group chats this SHOULD be the bare JID of the room and for private messages in group chats the full JID of the participant.
The item contains a single <displayed/> element qualified by the 'xrn:xmpp:mds:displayed:0' namespace. The <displayed/> element MUST contain exactly one Unique and Stable Stanza IDs (XEP-0359) [5] <stanza-id/> element that corresponds to the stanza-id of the most recent, displayed message, in that particular chat.
Only messages received by the user (meaning sent by third parties such as a contact, a participant in a group chat, etc) SHOULD be flagged as 'displayed'. However since 'displayed' means all messages up to this point and the stanza-id of a message sent by the user indicates a valid point in the chat history, sent messages MAY be flagged as well.
Flagging a chat as displayed up to this point happens by publishing a PEP item with an id corresponding to the JID of the chat and a <displayed/> payload element into the 'urn:xmpp:mds:displayed:0' node.
For group chats the <stanza-id/> child of the <displayed/> element refers to the stanza-id injected by the room. For all other chats the stanza-id child refers to the stanza-id injected by the user’s server (the server hosting the user account).
The client MUST include appropriate publish-options in the publication, including, but not limited to, setting the access model to whitelist and the max-items to max.
<iq from='juliet@capulet.lit/balcony' type='set' id='flag-as-displayed-1'>
<pubsub xmlns='http://jabber.org/protocol/pubsub'>
<publish node='urn:xmpp:mds:displayed:0'>
<item id='romeo@montegue.lit'>
<displayed xmlns='urn:xmpp:mds:displayed:0'>
<stanza-id xmlns='urn:xmpp:sid:0'
by='juliet@capulet.lit'
id='0f710f2b-52ed-4d52-b928-784dad74a52b'/>
</display>
</item>
</publish>
<publish-options>
<x xmlns='jabber:x:data' type='submit'>
<field var='FORM_TYPE' type='hidden'>
<value>http://jabber.org/protocol/pubsub#publish-options</value>
</field>
<field var='pubsub#persist_items'>
<value>true</value>
</field>
<field var='pubsub#max_items'>
<value>max</value>
</field>
<field var='pubsub#send_last_published_item'>
<value>never</value>
</field>
<field var='pubsub#access_model'>
<value>whitelist</value>
</field>
</x>
</publish-options>
</pubsub>
</iq>
<iq to='juliet@capulet.lit/balcony' type='result' id='flag-as-displayed-1'/>
A client interested in synchronizing the displayed state with other clients SHOULD include the 'urn:xmpp:mds:displayed:0+notify' feature in its Entity Capabilities (XEP-0115) [7], as per Personal Eventing Protocol (XEP-0163) [3] rules.
Upon bind and initial presence a client retrieves all items in the 'urn:xmpp:mds:displayed:0' node to learn what changes to the displayed state have occured while the client was offline.
<iq from='juliet@capulet.lit/balcony' type='get' id='catchup-1'>
<pubsub xmlns='http://jabber.org/protocol/pubsub'>
<items node='urn:xmpp:mds:displayed:0'/>
</pubsub>
</iq>
<iq type='result'
to='juliet@capulet.lit/balcony'
id='catchup-1'>
<pubsub xmlns='http://jabber.org/protocol/pubsub'>
<items node='urn:xmpp:mds:displayed:0'>
<item id='romeo@montegue.lit'>
<displayed xmlns='urn:xmpp:mds:displayed:0'>
<stanza-id xmlns='urn:xmpp:sid:0'
id='0f710f2b-52ed-4d52-b928-784dad74a52b'
by='juliet@capulet.lit'/>
</displayed>
</item>
<item id='example@conference.shakespeare.lit'>
<displayed xmlns='urn:xmpp:mds:displayed:0'
<stanza-id xmlns='urn:xmpp:sid:0'
id='ca21deaf-812c-48f1-8f16-339a674f2864'
by='example@conference.shakespeare.lit'/>
</displayed>
</item>
</items>
</pubsub>
</iq>
A Displayed Markers (XEP-0333) [2] displayed marker refers to the message id set by the sender of the message whereas the displayed element defined in this specification refers to the stanza-id injected by the user’s server.
In the likely scenario that a client wishes to share the displayed state with their own devices and the sender of the message, a client SHOULD sent a Displayed Markers (XEP-0333) [2] displayed marker and ensure that the 'urn:xmpp:mds:displayed:0' node gets updated.
A Publish-Subscribe (XEP-0060) [8] item publication is a fairly verbose operation for something that is expected to happen rather frequently. Therfore this specification defines an optional way to combine the PEP node item update and the Displayed Marker in one simple message.
Server assisted displayed node updates are an optional feature a user’s server can provide. To signal support the server announces an Entity Capabilities (XEP-0115) [7] feature of 'urn:xmpp:mds:server-assist:0' on the account.
<iq type='get' id='disco-1' to='juliet@capulet.lit' from='juliet@capulet.lit/balcony'> <query xmlns='http://jabber.org/protocol/disco#info'/> </iq>
<iq type='result' id='disco1' from='juliet@capulet.lit' to='juliet@capulet.lit/balcony'>
<query xmlns='http://jabber.org/protocol/disco#info'>
<feature var='urn:xmpp:mds:server-assist:0'/>
</query>
</iq>
To update the displayed item in the 'urn:xmpp:mds:displayed:0' PEP node more efficiently a client MAY send a message with the 'to' attribute set to the item id (which is equivalent to the JID of the contact) and with a <displayed/> element qualified by the 'urn:xmpp:mds:displayed:0' namespace. The server MUST strip the <displayed/> element from the message and continue to process it normally. The server MUST publish a PEP item on the 'urn:xmpp:mds:displayed:0' node where the item id is taken from the 'to' attribute and the payload is the <displayed/> element. A client MUST NOT include the <displayed/> element qualified by the 'urn:xmpp:mds:displayed:0' namespace if the message would otherwise be empty. A client that wishes to update the device synchronized displayed state but not inform the sender of the message via Displayed Markers SHOULD use the regular PubSub publication process.
<message to='juliet@capulet.lit' from='romeo@montegue.lit/orchard' id='the-msg-1'> <body>Hi. How are you?</body> <markable xmlns='urn:xmpp:chat-markers:0'/> <stanza-id xmlns='urn:xmpp:sid:0' by='juliet@capulet.lit' id='0423e3a9-d516-493d-bb06-bee0e51ab9fb'/> </message>
<message to='romeo@montegue.lit'>
<displayed xmlns='urn:xmpp:chat-markers:0' id='the-msg-1'/>
<displayed xmlns='urn:xmpp:mds:displayed:0'>
<stanza-id xmlns='urn:xmpp:sid:0' by='juliet@capulet.lit' id='0423e3a9-d516-493d-bb06-bee0e51ab9fb'/>
</displayed>
</message>
<message to='romeo@montegue.lit' from='juliet@capulet.let/balcony'> <displayed xmlns='urn:xmpp:chat-markers:0' id='the-msg-1'/> </message>
<message from='juliet@capulet.lit' to='juliet@capulet.lit/balcony' type='headline' id='new-displayed-pep-event'>
<event xmlns='http://jabber.org/protocol/pubsub#event'>
<items node='urn:xmpp:mds:displayed:0'>
<item id='romeo@montegue.lit'>
<displayed xmlns='urn:xmpp:mds:displayed:0'>
<stanza-id xmlns='urn:xmpp:sid:0' by='juliet@capulet.lit' id='0423e3a9-d516-493d-bb06-bee0e51ab9fb'/>
</displayed>
</item>
</items>
</event>
</message>
This specification comes with no accessibility considerations that go beyond what is required of any client (i.e. providing an accessible distinction between read and unread chats).
Implementing this specification gives the server the opportunity to perform activity tracking of a similiar scope than implementing Chat State Notifications (XEP-0085) [10] or Displayed Markers (XEP-0333) [2] would.
When using the server assist feature in conjunction with Displayed Markers (XEP-0333) [2] the Privacy Considerations of Display Markers apply.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA).
This specification introduces a distinct element to enable server assist instead of utilizing Displayed Markers (XEP-0333) [2] because Displayed Markers use the message id instead of stanza-ids. Translating between message id and stanza-id would require that the message (or parts of it) are archived on the server. Archiving should not be a requirement to offer server assist. (Especially since archived or not can depend on user settings.)
Server assist is not allowed in messages that would otherwise be empty. Overloading the semantic of sending a stanza to a third party entity solely to perform an action on the account that involves said third party is a dangerous example to set. (For example if server assit fails due to implementation errors a third party can be flooded with messages.) While stripping elements from stanzas is a common requirement on XMPP dropping entire stanzas without error is not.
This specification defines the following XML namespace:
REQUIRED for protocol specifications.
This document in other formats: XML PDF
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The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
1. XEP-0280: Message Carbons <https://xmpp.org/extensions/xep-0280.html>.
2. XEP-0333: Displayed Markers <https://xmpp.org/extensions/xep-0333.html>.
3. XEP-0163: Personal Eventing Protocol <https://xmpp.org/extensions/xep-0163.html>.
4. XEP-0223: Best Practices for Persistent Storage of Private Data via Publish-Subscribe <https://xmpp.org/extensions/xep-0223.html>.
5. XEP-0359: Unique and Stable Stanza IDs <https://xmpp.org/extensions/xep-0359.html>.
6. XEP-0313: Message Archive Management <https://xmpp.org/extensions/xep-0313.html>.
7. XEP-0115: Entity Capabilities <https://xmpp.org/extensions/xep-0115.html>.
8. XEP-0060: Publish-Subscribe <https://xmpp.org/extensions/xep-0060.html>.
9. XEP-0409: IM Routing-NG <https://xmpp.org/extensions/xep-0409.html>.
10. XEP-0085: Chat State Notifications <https://xmpp.org/extensions/xep-0085.html>.
Note: Older versions of this specification might be available at https://xmpp.org/extensions/attic/
Split Business Rules into Server and Client sections.
Add Accessibility, Privacy and Design Considerations
First draft.
@report{gultsch2024mds,
title = {Message Displayed Synchronization},
author = {Gultsch, Daniel},
type = {XEP},
number = {0490},
version = {1.0.0},
institution = {XMPP Standards Foundation},
url = {https://xmpp.org/extensions/xep-0490.html},
date = {2024-02-21/2024-11-06},
}END