Bugfix: irc_text:truncate/3 goes out of bounds with a non-empty Ellipsis.

Author: hyperimpose

src/lib/irc_text.erl

@@ -25,7 +25,7 @@ truncate(Text, Limit) -> truncate(Text, Limit, <<>>).
 
 truncate(Text, Limit, Ellipsis) ->
     E = unicode:characters_to_binary([Ellipsis]),
-    truncate(Text, Limit + byte_size(E), E, 0, []).
+    truncate(Text, Limit - byte_size(E), E, 0, []).
 
 truncate(Text, Limit, Ellipsis, Size, Acc) ->
     case string:next_grapheme(Text) of

test/irc_text_tests.erl

@@ -0,0 +1,34 @@
+%%--------------------------------------------------------------------
+%% Copyright (C) 2023 hyperimpose.org
+%%
+%% This file is part of irc.
+%%
+%% This program is free software: you can redistribute it and/or modify
+%% it under the terms of the GNU Affero General Public License as published
+%% by the Free Software Foundation, version 3.
+%%
+%% This program is distributed in the hope that it will be useful,
+%% but WITHOUT ANY WARRANTY; without even the implied warranty of
+%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+%% GNU Affero General Public License for more details.
+%%
+%% You should have received a copy of the GNU Affero General Public License
+%% along with this program.  If not, see <https://www.gnu.org/licenses/>.
+%%--------------------------------------------------------------------
+
+-module(irc_text_tests).
+
+-include_lib("eunit/include/eunit.hrl").
+
+
+%%% truncate/2, truncate/3
+
+truncate_bounds_test_() ->
+    L = fun (X) -> byte_size(unicode:characters_to_binary(X)) end,
+
+    [%% Without Ellipsis
+     ?_assert(11 >= L(irc_text:truncate("Hello, World!", 11))),
+     ?_assert(26 >= L(irc_text:truncate("Γειά σου, Κόσμε!", 26))),
+     %% With Ellipsis
+     ?_assert(11 >= L(irc_text:truncate("Hello, World!", 11, <<"...">>))),
+     ?_assert(26 >= L(irc_text:truncate("Γειά σου, Κόσμε!", 26, <<"...">>)))].