xmpp-parsers: Implement XEP-0490: Message Displayed Synchronization

This XEP is used to synchronize where each client has stopped reading a
conversation, so that we can e.g. stop displaying a notification when
the user has read this particular message on a different device.

parsers/src/lib.rs

@@ -290,3 +290,6 @@ pub mod stream_limits;
 
 /// XEP-0484: Fast Authentication Streamlining Tokens
 pub mod fast;
+
+/// XEP-0490: Message Displayed Synchronization
+pub mod message_displayed;

parsers/src/message_displayed.rs

@@ -0,0 +1,19 @@
+// Copyright (c) 2024 Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+use xso::{AsXml, FromXml};
+
+use crate::ns;
+use crate::stanza_id::StanzaId;
+
+/// Mention that a particular message has been displayed by at least one client.
+#[derive(FromXml, AsXml, PartialEq, Debug, Clone)]
+#[xml(namespace = ns::MDS, name = "displayed")]
+pub struct Displayed {
+    /// Reference to the message having been displayed.
+    #[xml(child)]
+    pub stanza_id: StanzaId,
+}

parsers/src/ns.rs

@@ -308,6 +308,9 @@ pub const STREAM_LIMITS: &str = "urn:xmpp:stream-limits:0";
 /// XEP-0484: Fast Authentication Streamlining Tokens
 pub const FAST: &str = "urn:xmpp:fast:0";
 
+/// XEP-0490: Message Displayed Synchronization
+pub const MDS: &str = "urn:xmpp:mds:displayed:0";
+
 /// Alias for the main namespace of the stream, that is "jabber:client" when
 /// the component feature isn’t enabled.
 #[cfg(not(feature = "component"))]