Add a `<store>` hint to OMEMO messages.

updates #497

spec/omemo.js

@@ -194,6 +194,7 @@
                             `</header>`+
                             `<payload>${sent_stanza.nodeTree.querySelector('payload').textContent}</payload>`+
                         `</encrypted>`+
+                        `<store xmlns='urn:xmpp:hints'/>`+
                     `</message>`);
 
                 // Test reception of an encrypted message
@@ -327,15 +328,6 @@
         }));
 
 
-        it("will add processing hints to sent out encrypted <message> stanzas",
-            mock.initConverseWithPromises(
-                null, ['rosterGroupsFetched'], {},
-                function (done, _converse) {
-            // TODO
-            done();
-        }));
-
-
         it("updates device lists based on PEP messages",
             mock.initConverseWithPromises(
                 null, ['rosterGroupsFetched'], {},

src/converse-omemo.js

@@ -410,8 +410,12 @@
                             .map(device => this.encryptKey(obj.key_and_tag, device));
 
                         return Promise.all(promises)
-                            .then((dicts) => this.addKeysToMessageStanza(stanza, dicts, obj.iv))
-                            .then((stanza) => stanza.c('payload').t(obj.payload))
+                            .then(dicts => this.addKeysToMessageStanza(stanza, dicts, obj.iv))
+                            .then(stanza => {
+                                stanza.c('payload').t(obj.payload).up().up();
+                                stanza.c('store', {'xmlns': Strophe.NS.HINTS});
+                                return stanza;
+                            });
                     });
                 },