Handle nickname conflicts by sending the correct XMPP error presence

src/bridge/bridge.cpp

@@ -216,3 +216,8 @@ void Bridge::kick_muc_user(Iid&& iid, const std::string& target, const std::stri
 {
   this->xmpp->kick_user(iid.chan + "%" + iid.server, target, reason, author, this->user_jid);
 }
+
+void Bridge::send_nickname_conflict_error(const Iid& iid, const std::string& nickname)
+{
+  this->xmpp->send_nickname_conflict_error(iid.chan + "%" + iid.server, nickname, this->user_jid);
+}

src/bridge/bridge.hpp

@@ -89,6 +89,7 @@ public:
    */
   void send_nick_change(Iid&& iid, const std::string& old_nick, const std::string& new_nick, const bool self);
   void kick_muc_user(Iid&& iid, const std::string& target, const std::string& reason, const std::string& author);
+  void send_nickname_conflict_error(const Iid& iid, const std::string& nickname);
 
   /**
    * Misc

src/irc/irc_client.cpp

@@ -303,6 +303,19 @@ void IrcClient::on_erroneous_nickname(const IrcMessage& message)
   this->send_gateway_message(error_msg + ": " + message.arguments[1], message.prefix);
 }
 
+void IrcClient::on_nickname_conflict(const IrcMessage& message)
+{
+  const std::string nickname = message.arguments[1];
+  this->on_generic_error(message);
+  for (auto it = this->channels.begin(); it != this->channels.end(); ++it)
+  {
+    Iid iid;
+    iid.chan = it->first;
+    iid.server = this->hostname;
+    this->bridge->send_nickname_conflict_error(iid, nickname);
+  }
+}
+
 void IrcClient::on_generic_error(const IrcMessage& message)
 {
   const std::string error_msg = message.arguments.size() >= 3 ?

src/irc/irc_client.hpp

@@ -148,6 +148,11 @@ public:
    * We tried to set an invalid nickname
    */
   void on_erroneous_nickname(const IrcMessage& message);
+  /**
+   * When the IRC servers denies our nickname because of a conflict.  Send a
+   * presence conflict from all channels, because the name is server-wide.
+   */
+  void on_nickname_conflict(const IrcMessage& message);
   /**
    * Handles most errors from the server by just forwarding the message to the user.
    */
@@ -237,6 +242,7 @@ static const std::unordered_map<std::string, irc_callback_t> irc_callbacks = {
   {"TOPIC", &IrcClient::on_topic_received},
   {"366", &IrcClient::on_channel_completely_joined},
   {"432", &IrcClient::on_erroneous_nickname},
+  {"433", &IrcClient::on_nickname_conflict},
   {"461", &IrcClient::on_generic_error},
   {"001", &IrcClient::on_welcome_message},
   {"PART", &IrcClient::on_part},

src/xmpp/xmpp_component.cpp

@@ -20,6 +20,7 @@
 #define DISCO_ITEMS_NS   DISCO_NS"#items"
 #define DISCO_INFO_NS    DISCO_NS"#info"
 #define XHTMLIM_NS       "http://jabber.org/protocol/xhtml-im"
+#define STANZA_NS        "urn:ietf:params:xml:ns:xmpp-stanzas"
 
 XmppComponent::XmppComponent(const std::string& hostname, const std::string& secret):
   served_hostname(hostname),
@@ -195,8 +196,7 @@ void XmppComponent::handle_presence(const Stanza& stanza)
           const std::string own_nick = bridge->get_own_nick(iid);
           if (!own_nick.empty() && own_nick != to.resource)
             bridge->send_irc_nick_change(iid, to.resource);
-          else
+          bridge->join_irc_channel(iid, to.resource);
-            bridge->join_irc_channel(iid, to.resource);
         }
       else if (type == "unavailable")
         {
@@ -479,3 +479,28 @@ void XmppComponent::kick_user(const std::string& muc_name,
   presence.close();
   this->send_stanza(presence);
 }
+
+void XmppComponent::send_nickname_conflict_error(const std::string& muc_name,
+                                                 const std::string& nickname,
+                                                 const std::string& jid_to)
+{
+  Stanza presence("presence");
+  presence["from"] = muc_name + "@" + this->served_hostname + "/" + nickname;
+  presence["to"] = jid_to;
+  XmlNode x("x");
+  x["xmlns"] = MUC_NS;
+  x.close();
+  presence.add_child(std::move(x));
+  XmlNode error("error");
+  error["by"] = muc_name + "@" + this->served_hostname;
+  error["type"] = "cancel";
+  error["code"] = "409";
+  XmlNode conflict("conflict");
+  conflict["xmlns"] = STANZA_NS;
+  conflict.close();
+  error.add_child(std::move(conflict));
+  error.close();
+  presence.add_child(std::move(error));
+  presence.close();
+  this->send_stanza(presence);
+}

src/xmpp/xmpp_component.hpp

@@ -107,6 +107,12 @@ public:
                      const std::string& reason,
                      const std::string& author,
                      const std::string& jid_to);
+  /**
+   * Send a presence type=error with a conflict element
+   */
+  void send_nickname_conflict_error(const std::string& muc_name,
+                                    const std::string& nickname,
+                                    const std::string& jid_to);
   /**
    * Handle the various stanza types
    */