Don’t treat presence updates as MUC joins

If the user sends a directed presence to an unjoined MUC without a <x/>
element, send a presence error back instead of attempting to join it
again, as this is almost never what the user wants.

Fixes #3415.

src/bridge/bridge.cpp

@@ -170,8 +170,7 @@ IrcClient* Bridge::find_irc_client(const std::string& hostname) const
 bool Bridge::join_irc_channel(const Iid& iid, std::string nickname,
                               const std::string& password,
                               const std::string& resource,
-                              HistoryLimit history_limit,
+                              HistoryLimit history_limit)
-                              const bool force_join)
 {
   const auto& hostname = iid.get_server();
 #ifdef USE_DATABASE
@@ -189,8 +188,8 @@ bool Bridge::join_irc_channel(const Iid& iid, std::string nickname,
     {
       irc->send_join_command(iid.get_local(), password);
       return true;
-    } else if (!res_in_chan || force_join) {
+    } else {
-      // See https://github.com/xsf/xeps/pull/499 for the force_join argument
+      // See https://github.com/xsf/xeps/pull/499
       this->generate_channel_join_for_resource(iid, resource);
     }
   return false;

src/bridge/bridge.hpp

@@ -72,14 +72,12 @@ public:
    **/
 
   /**
-   * Try to join an irc_channel, does nothing and return true if the channel
+   * Try to join an irc_channel.
-   * was already joined.
    */
   bool join_irc_channel(const Iid& iid, std::string nickname,
                         const std::string& password,
                         const std::string& resource,
-                        HistoryLimit history_limit,
+                        HistoryLimit history_limit);
-                        const bool force_join);
 
   void send_channel_message(const Iid& iid, const std::string& body, std::string id);
   void send_private_message(const Iid& iid, const std::string& body, const std::string& type="PRIVMSG");

src/xmpp/biboumi_component.cpp

@@ -158,8 +158,24 @@ void BiboumiComponent::handle_presence(const Stanza& stanza)
         {
           const std::string own_nick = bridge->get_own_nick(iid);
           const XmlNode* x = stanza.get_child("x", MUC_NS);
-          const XmlNode* password = x ? x->get_child("password", MUC_NS): nullptr;
+          const IrcClient* irc = bridge->find_irc_client(iid.get_server());
-          const XmlNode* history = x ? x->get_child("history", MUC_NS): nullptr;
+          if (irc)
+            {
+              const auto chan = irc->find_channel(iid.get_local());
+              if (chan->joined)
+                bridge->send_irc_nick_change(iid, to.resource, from.resource);
+              else if (!x)
+                { // send an error if we are not joined yet, instead of treating it as a join
+                  this->send_stanza_error("presence", from_str, to_str, id,
+                                          "modify", "not-acceptable",
+                                          "You are not joined to this MUC.");
+                }
+            }
+          // if there is no <x/>, this is a presence status update, we don’t care about those
+          if (x)
+            {
+              const XmlNode* password = x->get_child("password", MUC_NS);
+              const XmlNode* history = x->get_child("history", MUC_NS);
               HistoryLimit history_limit;
               if (history)
                 {
@@ -184,13 +200,7 @@ void BiboumiComponent::handle_presence(const Stanza& stanza)
                     history_limit.stanzas = 0;
                 }
               bridge->join_irc_channel(iid, to.resource, password ? password->get_inner(): "",
-                                   from.resource, history_limit, x != nullptr);
+                                       from.resource, history_limit);
-          const IrcClient* irc = bridge->find_irc_client(iid.get_server());
-          if (irc)
-            {
-              const auto chan = irc->find_channel(iid.get_local());
-              if (chan->joined)
-                bridge->send_irc_nick_change(iid, to.resource, from.resource);
             }
         }
       else if (type == "unavailable")