Handle forced-join by just sending an invitation

fix #3116

src/bridge/bridge.cpp

@@ -839,8 +839,19 @@ void Bridge::send_xmpp_message(const std::string& from, const std::string& autho
 void Bridge::send_user_join(const std::string& hostname, const std::string& chan_name,
                             const IrcUser* user, const char user_mode, const bool self)
 {
-  for (const auto& resource: this->resources_in_chan[ChannelKey{chan_name, hostname}])
+  const auto resources = this->resources_in_chan[ChannelKey{chan_name, hostname}];
+  if (self && resources.empty())
+    { // This was a forced join: no client ever asked to join this room,
+      // but the server tells us we are in that room anyway.  XMPP can’t
+      // do that, so we invite all the resources to join that channel.
+      const Iid iid(chan_name, hostname, Iid::Type::Channel);
+      this->send_xmpp_invitation(iid, "");
+    }
+    else
+    {
+      for (const auto& resource: resources)
         this->send_user_join(hostname, chan_name, user, user_mode, self, resource);
+    }
 }
 
 void Bridge::send_user_join(const std::string& hostname, const std::string& chan_name,

src/xmpp/biboumi_component.cpp

@@ -855,6 +855,9 @@ void BiboumiComponent::send_invitation(const std::string& room_target,
   XmlNode x("x");
   x["xmlns"] = MUC_USER_NS;
   XmlNode invite("invite");
+  if (author_nick.empty())
+    invite["from"] = room_target + "@" + this->served_hostname;
+  else
     invite["from"] = room_target + "@" + this->served_hostname + "/" + author_nick;
   x.add_child(std::move(invite));
   message.add_child(std::move(x));