ejabberd two functions with same name - erlang

Question

iam new in erlang and OTP i have two questions :
iam trying to read some erlang code from ejabberd source, it's very complex and iam surprised with two start/0 functions and two start/1 functions too in ejabberd_logger.erl so
1-what's this ? which function code will be executed when calling start/1?
2-should i read and understand all ejabberd source code to modify and customize it like i want ? i see that it's a huge code but is this a must for good handling ?
-module(ejabberd_logger).
-compile({no_auto_import, [get/0]}).
%% API
-export([start/0, get/0, set/1, get_log_path/0, flush/0]).
-export([convert_loglevel/1, loglevels/0]).
-ifndef(LAGER).
-export([progress_filter/2]).
-endif.
%% Deprecated functions
-export([restart/0, reopen_log/0, rotate_log/0]).
-deprecated([{restart, 0},
{reopen_log, 0},
{rotate_log, 0}]).
-type loglevel() :: none | emergency | alert | critical |
error | warning | notice | info | debug.
-define(is_loglevel(L),
((L == none) or (L == emergency) or (L == alert)
or (L == critical) or (L == error) or (L == warning)
or (L == notice) or (L == info) or (L == debug))).
-export_type([loglevel/0]).
%%%===================================================================
%%% API
%%%===================================================================
-spec get_log_path() -> string().
get_log_path() ->
case ejabberd_config:env_binary_to_list(ejabberd, log_path) of
{ok, Path} ->
Path;
undefined ->
case os:getenv("EJABBERD_LOG_PATH") of
false ->
"ejabberd.log";
Path ->
Path
end
end.
-spec loglevels() -> [loglevel(), ...].
loglevels() ->
[none, emergency, alert, critical, error, warning, notice, info, debug].
-spec convert_loglevel(0..5) -> loglevel().
convert_loglevel(0) -> none;
convert_loglevel(1) -> critical;
convert_loglevel(2) -> error;
convert_loglevel(3) -> warning;
convert_loglevel(4) -> info;
convert_loglevel(5) -> debug.
quiet_mode() ->
case application:get_env(ejabberd, quiet) of
{ok, true} -> true;
_ -> false
end.
-spec get_integer_env(atom(), T) -> T.
get_integer_env(Name, Default) ->
case application:get_env(ejabberd, Name) of
{ok, I} when is_integer(I), I>=0 ->
I;
{ok, infinity} ->
infinity;
undefined ->
Default;
{ok, Junk} ->
error_logger:error_msg("wrong value for ~ts: ~p; "
"using ~p as a fallback~n",
[Name, Junk, Default]),
Default
end.
-ifdef(LAGER).
-spec get_string_env(atom(), T) -> T.
get_string_env(Name, Default) ->
case application:get_env(ejabberd, Name) of
{ok, L} when is_list(L) ->
L;
undefined ->
Default;
{ok, Junk} ->
error_logger:error_msg("wrong value for ~ts: ~p; "
"using ~p as a fallback~n",
[Name, Junk, Default]),
Default
end.
-spec start() -> ok.
start() ->
start(info).
start(Level) ->
StartedApps = application:which_applications(5000),
case lists:keyfind(logger, 1, StartedApps) of
%% Elixir logger is started. We assume everything is in place
%% to use lager to Elixir logger bridge.
{logger, _, _} ->
error_logger:info_msg("Ignoring ejabberd logger options, using Elixir Logger.", []),
%% Do not start lager, we rely on Elixir Logger
do_start_for_logger(Level);
_ ->
do_start(Level)
end.
do_start_for_logger(Level) ->
application:load(sasl),
application:set_env(sasl, sasl_error_logger, false),
application:load(lager),
application:set_env(lager, error_logger_redirect, false),
application:set_env(lager, error_logger_whitelist, ['Elixir.Logger.ErrorHandler']),
application:set_env(lager, crash_log, false),
application:set_env(lager, handlers, [{elixir_logger_backend, [{level, Level}]}]),
ejabberd:start_app(lager),
ok.
do_start(Level) ->
application:load(sasl),
application:set_env(sasl, sasl_error_logger, false),
application:load(lager),
ConsoleLog = get_log_path(),
Dir = filename:dirname(ConsoleLog),
ErrorLog = filename:join([Dir, "error.log"]),
CrashLog = filename:join([Dir, "crash.log"]),
LogRotateDate = get_string_env(log_rotate_date, ""),
LogRotateSize = case get_integer_env(log_rotate_size, 10*1024*1024) of
infinity -> 0;
V -> V
end,
LogRotateCount = get_integer_env(log_rotate_count, 1),
LogRateLimit = get_integer_env(log_rate_limit, 100),
ConsoleLevel0 = case quiet_mode() of
true -> critical;
_ -> Level
end,
ConsoleLevel = case get_lager_version() >= "3.6.0" of
true -> [{level, ConsoleLevel0}];
false -> ConsoleLevel0
end,
application:set_env(lager, error_logger_hwm, LogRateLimit),
application:set_env(
lager, handlers,
[{lager_console_backend, ConsoleLevel},
{lager_file_backend, [{file, ConsoleLog}, {level, Level}, {date, LogRotateDate},
{count, LogRotateCount}, {size, LogRotateSize}]},
{lager_file_backend, [{file, ErrorLog}, {level, error}, {date, LogRotateDate},
{count, LogRotateCount}, {size, LogRotateSize}]}]),
application:set_env(lager, crash_log, CrashLog),
application:set_env(lager, crash_log_date, LogRotateDate),
application:set_env(lager, crash_log_size, LogRotateSize),
application:set_env(lager, crash_log_count, LogRotateCount),
ejabberd:start_app(lager),
lists:foreach(fun(Handler) ->
lager:set_loghwm(Handler, LogRateLimit)
end, gen_event:which_handlers(lager_event)).
-spec restart() -> ok.
restart() ->
Level = ejabberd_option:loglevel(),
application:stop(lager),
start(Level).
-spec reopen_log() -> ok.
reopen_log() ->
ok.
-spec rotate_log() -> ok.
rotate_log() ->
catch lager_crash_log ! rotate,
lists:foreach(
fun({lager_file_backend, File}) ->
whereis(lager_event) ! {rotate, File};
(_) ->
ok
end, gen_event:which_handlers(lager_event)).
-spec get() -> loglevel().
get() ->
Handlers = get_lager_handlers(),
lists:foldl(fun(lager_console_backend, _Acc) ->
lager:get_loglevel(lager_console_backend);
(elixir_logger_backend, _Acc) ->
lager:get_loglevel(elixir_logger_backend);
(_, Acc) ->
Acc
end,
none, Handlers).
-spec set(0..5 | loglevel()) -> ok.
set(N) when is_integer(N), N>=0, N=<5 ->
set(convert_loglevel(N));
set(Level) when ?is_loglevel(Level) ->
case get() of
Level ->
ok;
_ ->
ConsoleLog = get_log_path(),
QuietMode = quiet_mode(),
lists:foreach(
fun({lager_file_backend, File} = H) when File == ConsoleLog ->
lager:set_loglevel(H, Level);
(lager_console_backend = H) when not QuietMode ->
lager:set_loglevel(H, Level);
(elixir_logger_backend = H) ->
lager:set_loglevel(H, Level);
(_) ->
ok
end, get_lager_handlers())
end,
case Level of
debug -> xmpp:set_config([{debug, true}]);
_ -> xmpp:set_config([{debug, false}])
end.
get_lager_handlers() ->
case catch gen_event:which_handlers(lager_event) of
{'EXIT',noproc} ->
[];
Result ->
Result
end.
-spec get_lager_version() -> string().
get_lager_version() ->
Apps = application:loaded_applications(),
case lists:keyfind(lager, 1, Apps) of
{_, _, Vsn} -> Vsn;
false -> "0.0.0"
end.
-spec flush() -> ok.
flush() ->
application:stop(lager),
application:stop(sasl).
-else.
-include_lib("kernel/include/logger.hrl").
-spec start() -> ok | {error, term()}.
start() ->
start(info).
start(Level) ->
EjabberdLog = get_log_path(),
Dir = filename:dirname(EjabberdLog),
ErrorLog = filename:join([Dir, "error.log"]),
LogRotateSize = get_integer_env(log_rotate_size, 10*1024*1024),
LogRotateCount = get_integer_env(log_rotate_count, 1),
Config = #{max_no_bytes => LogRotateSize,
max_no_files => LogRotateCount,
filesync_repeat_interval => no_repeat,
file_check => 1000,
sync_mode_qlen => 1000,
drop_mode_qlen => 1000,
flush_qlen => 5000},
FmtConfig = #{legacy_header => false,
time_designator => $ ,
max_size => 100*1024,
single_line => false},
FileFmtConfig = FmtConfig#{template => file_template()},
ConsoleFmtConfig = FmtConfig#{template => console_template()},
try
ok = logger:set_primary_config(level, Level),
DefaultHandlerId = get_default_handlerid(),
ok = logger:update_formatter_config(DefaultHandlerId, ConsoleFmtConfig),
case quiet_mode() of
true ->
ok = logger:set_handler_config(DefaultHandlerId, level, critical);
_ ->
ok
end,
case logger:add_primary_filter(progress_report,
{fun ?MODULE:progress_filter/2, stop}) of
ok -> ok;
{error, {already_exist, _}} -> ok
end,
case logger:add_handler(ejabberd_log, logger_std_h,
#{level => all,
config => Config#{file => EjabberdLog},
formatter => {logger_formatter, FileFmtConfig}}) of
ok -> ok;
{error, {already_exist, _}} -> ok
end,
case logger:add_handler(error_log, logger_std_h,
#{level => error,
config => Config#{file => ErrorLog},
formatter => {logger_formatter, FileFmtConfig}}) of
ok -> ok;
{error, {already_exist, _}} -> ok
end
catch _:{Tag, Err} when Tag == badmatch; Tag == case_clause ->
?LOG_CRITICAL("Failed to set logging: ~p", [Err]),
Err
end.
get_default_handlerid() ->
Ids = logger:get_handler_ids(),
case lists:member(default, Ids) of
true -> default;
false -> hd(Ids)
end.
-spec restart() -> ok.
restart() ->
ok.
progress_filter(#{level:=info,msg:={report,#{label:={_,progress}}}} = Event, _) ->
case get() of
debug ->
logger_filters:progress(Event#{level => debug}, log);
_ ->
stop
end;
progress_filter(Event, _) ->
Event.
console_template() ->
[time, " [", level, "] " | msg()].
file_template() ->
[time, " [", level, "] ", pid,
{mfa, ["#", mfa, {line, [":", line], []}], []}, " " | msg()].
msg() ->
[{logger_formatter, [[logger_formatter, title], ":", io_lib:nl()], []},
msg, io_lib:nl()].
-spec reopen_log() -> ok.
reopen_log() ->
ok.
-spec rotate_log() -> ok.
rotate_log() ->
ok.
-spec get() -> loglevel().
get() ->
#{level := Level} = logger:get_primary_config(),
Level.
-spec set(0..5 | loglevel()) -> ok.
set(N) when is_integer(N), N>=0, N=<5 ->
set(convert_loglevel(N));
set(Level) when ?is_loglevel(Level) ->
case get() of
Level -> ok;
PrevLevel ->
?LOG_NOTICE("Changing loglevel from '~s' to '~s'",
[PrevLevel, Level]),
logger:set_primary_config(level, Level),
case Level of
debug -> xmpp:set_config([{debug, true}]);
_ -> xmpp:set_config([{debug, false}])
end
end.
-spec flush() -> ok.
flush() ->
lists:foreach(
fun(#{id := HandlerId, module := logger_std_h}) ->
logger_std_h:filesync(HandlerId);
(#{id := HandlerId, module := logger_disk_log_h}) ->
logger_disk_log_h:filesync(HandlerId);
(_) ->
ok
end, logger:get_handler_config()).
-endif.

Answer 1

Here, the first version is protected by -ifdef(LAGER). and thus gets used if the macro LAGER is defined, and the second version comes after '-else.', and gets used if LAGER is not defined. (The first version uses the Lager library for logging, and the second version uses the newer built-in logger library.)