Use XMPP Roster for BuddyList

This allows the same user to keep the buddy list across clients and
config resets. At the same time this allows for per lobby buddy lists
which is needed as the same nickname may refer to different people.

Use lower case comparison for buddy names. This is in line with the idea
of local part of jid should be seen as normalized nick and is used
server-side to compare user names.

The migration is kept simple. I.e. only attempted if the roster is
empty and the config indicates no migration was done before.

Fixes: #6824
Signed-off-by: Ralph Sennhauser <ralph.sennhauser@gmail.com>

source/lobby/scripting/JSInterface_Lobby.cpp

@@ -51,6 +51,21 @@ bool HasXmppClient()
 	return g_XmppClient;
 }
 
+/**
+ * Whether the given nickname is a buddy of the current user.
+ *
+ * @param nick The nickname to look up, compared case-insensitively
+ */
+static bool IsLobbyBuddy([[maybe_unused]] const std::string& nick)
+{
+#if CONFIG2_LOBBY
+	return g_XmppClient && g_XmppClient->IsBuddy(nick);
+#else
+	// Without the lobby there is no roster to look the nickname up in.
+	return false;
+#endif
+}
+
 void SetRankedGame(bool isRanked)
 {
 	g_rankedGame = isRanked;
@@ -190,6 +205,7 @@ void RegisterScriptFunctions(const Script::Request& rq)
 {
 	// Lobby functions
 	Script::Function::Register<&HasXmppClient>(rq, "HasXmppClient");
+	Script::Function::Register<&IsLobbyBuddy>(rq, "IsLobbyBuddy");
 	Script::Function::Register<&SetRankedGame>(rq, "SetRankedGame");
 #if CONFIG2_LOBBY // Allow the lobby to be disabled
 	Script::Function::Register<&StartXmppClient>(rq, "StartXmppClient");
@@ -229,6 +245,10 @@ void RegisterScriptFunctions(const Script::Request& rq)
 	REGISTER_XMPP(GetRole, "LobbyGetPlayerRole");
 	REGISTER_XMPP(GetRating, "LobbyGetPlayerRating");
 	REGISTER_XMPP(GetSubject, "LobbyGetRoomSubject");
+
+	// Roster
+	REGISTER_XMPP(AddBuddy, "LobbyAddBuddy");
+	REGISTER_XMPP(RemoveBuddy, "LobbyRemoveBuddy");
 #undef REGISTER_XMPP
 
 	Script::Function::Register<&EncryptPassword>(rq, "EncryptPassword");