plugin XEP-0115: Implement "Stream Feature":

Server features are now checked to find capabilities data and use it for disco caching.
This is §6.3 of the XEP.

libervia/backend/plugins/plugin_xep_0115.py

@@ -415,8 +415,47 @@ class XEP_0115_handler(XMPPHandler):
     def client(self) -> SatXMPPEntity:
         return self.parent  # type: ignore[return-value]
 
+    def _caps_node_cb(self, disco_infos, ver):
+        """Callback for caps node query."""
+        G.host.memory.disco.hashes[ver] = disco_infos
+        log.debug(f"Cached disco info for caps hash {ver}")
+
+    def _caps_node_eb(self, failure_, server_jid, ver):
+        """Errback for caps node query."""
+        log.warning(
+            f"Failed to query caps node for {server_jid} (ver={ver}): {failure_}"
+        )
+
     def connectionInitialized(self) -> None:
         assert self.xmlstream is not None
+        # Check if server advertised caps in stream features (XEP-0115 §6.3)
+        # xmlstream.features is a dict mapping (ns, name) to element
+        caps_key = (NS_ENTITY_CAPABILITY, "c")
+        if caps_key in self.xmlstream.features:
+            c_elt = self.xmlstream.features[caps_key]
+            ver = c_elt.getAttribute("ver")
+            node = c_elt.getAttribute("node")
+            if ver:
+                server_jid = self.client.server_jid
+                G.host.memory.update_entity_data(
+                    self.client, server_jid, C.ENTITY_CAP_HASH, ver
+                )
+
+                # If we already have the disco info, we're done
+                if ver in G.host.memory.disco.hashes:
+                    log.debug(
+                        f"Cached server caps from stream feature: {server_jid} ver={ver}"
+                    )
+                else:
+                    # Query the caps node to get disco info (XEP-0115 §6.2)
+                    caps_node = f"{node}#{ver}" if node else ver
+                    log.debug(
+                        f"Querying caps node {caps_node} for server {server_jid}"
+                    )
+                    d = self.client.disco.requestInfo(server_jid, nodeIdentifier=caps_node)
+                    d.addCallback(self._caps_node_cb, ver)
+                    d.addErrback(self._caps_node_eb, server_jid, ver)
+
         self.xmlstream.addObserver(
             CAPABILITY_UPDATE, self.plugin_parent._update, client=self.client
         )