Finish implementing time based log rotation

README.org

@@ -54,8 +54,8 @@
     {handlers, [
       {lager_console_backend, info},
       {lager_file_backend, [
-        {"error.log", error, 10485760, "", 5},
-        {"console.log", info, 10485760, "", 5}
+        {"error.log", error, 10485760, "$D0", 5},
+        {"console.log", info, 10485760, "$D0", 5}
       ]}
     ]}
   }.
@@ -97,3 +97,56 @@
   log messages, when no backend is consuming debug messages, are effectively
   free. A simple benchmark of doing 1 million debug log messages while the
   minimum threshold was above that takes less than half a second.
+
+* Internal log rotation
+  Lager can rotate its own logs or have it done via an external process. To
+  use internal rotation, use the last 3 values in the file backend's
+  configuration tuple. For example
+
+#+BEGIN_EXAMPLE
+  {"error.log", error, 10485760, "$D0", 5}
+#+END_EXAMPLE
+
+  This tells lager to log error and above messages to "error.log" and to
+  rotate the file at midnight or when it reaches 10mb, whichever comes first
+  and to keep 5 rotated logs, in addition to the current one. Setting the
+  count to 0 does not disable rotation, it instead rotates the file and keeps
+  no previous versions around. To disable rotation set the size to 0 and the
+  date to "".
+
+  The "$D0" syntax is taken from the syntax newsyslog uses in newsyslog.conf.
+  The relevant extract follows:
+
+#+BEGIN_EXAMPLE
+  Day, week and month time format: The lead-in character
+  for day, week and month specification is a `$'-sign.
+  The particular format of day, week and month
+  specification is: [Dhh], [Ww[Dhh]] and [Mdd[Dhh]],
+  respectively.  Optional time fields default to
+  midnight.  The ranges for day and hour specifications
+  are:
+
+    hh      hours, range 0 ... 23
+    w       day of week, range 0 ... 6, 0 = Sunday
+    dd      day of month, range 1 ... 31, or the
+            letter L or l to specify the last day of
+            the month.
+
+  Some examples:
+    $D0     rotate every night at midnight
+    $D23    rotate every day at 23:00 hr
+    $W0D23  rotate every week on Sunday at 23:00 hr
+    $W5D16  rotate every week on Friday at 16:00 hr
+    $M1D0   rotate on the first day of every month at
+            midnight (i.e., the start of the day)
+    $M5D6   rotate on every 5th day of the month at
+            6:00 hr
+#+END_EXAMPLE
+
+  To configure the crash log rotation, the following application variables are
+  used:
+  - crash_log_size
+  - crash_log_date
+  - crash_log_count
+
+  See the .app.src file for further details.

src/lager.app.src

@@ -27,6 +27,9 @@
             %% Maximum size of the crash log in bytes, before its rotated, set
             %% to 0 to disable rotation - default is 0
             {crash_log_size, 10485760},
+            %% What time to rotate the crash log - default is no time
+            %% rotation. See the README for a description of this format.
+            {crash_log_date, "$D0"},
             %% Number of rotated crash logs to keep, 0 means keep only the
             %% current one - default is 0
             {crash_log_count, 5},

src/lager_crash_log.erl

@@ -22,9 +22,10 @@
 %%
 %% The `crash_log_msg_size' application var is used to specify the maximum
 %% size of any message to be logged. `crash_log_size' is used to specify the
-%% maximum size of the crash log before it will be rotated (0 will disable)
-%% and to control the number of rotated files to be retained, use
-%% `crash_log_count'.
+%% maximum size of the crash log before it will be rotated (0 will disable).
+%% Time based rotation is configurable via `crash_log_date', the syntax is
+%% documented in the README. To control the number of rotated files to be
+%% retained, use `crash_log_count'.
 
 -module(lager_crash_log).
 
@@ -44,26 +45,28 @@
         inode,
         fmtmaxbytes,
         size,
+        date,
         count,
         flap=false
     }).
 
 %% @private
-start_link(Filename, MaxBytes, Size, _Date, Count) ->
+start_link(Filename, MaxBytes, Size, Date, Count) ->
     gen_server:start_link({local, ?MODULE}, ?MODULE, [Filename, MaxBytes,
-            Size, Count], []).
+            Size, Date, Count], []).
 
 %% @private
-start(Filename, MaxBytes, Size, _Date, Count) ->
+start(Filename, MaxBytes, Size, Date, Count) ->
     gen_server:start({local, ?MODULE}, ?MODULE, [Filename, MaxBytes, Size,
-            Count], []).
+            Date, Count], []).
 
 %% @private
-init([Filename, MaxBytes, Size, Count]) ->
+init([Filename, MaxBytes, Size, Date, Count]) ->
     case lager_util:open_logfile(Filename, false) of
         {ok, {FD, Inode, _}} ->
+            schedule_rotation(Date),
             {ok, #state{name=Filename, fd=FD, inode=Inode,
-                    fmtmaxbytes=MaxBytes, size=Size, count=Count}};
+                    fmtmaxbytes=MaxBytes, size=Size, count=Count, date=Date}};
         Error ->
             Error
     end.
@@ -120,6 +123,10 @@ handle_cast(_Request, State) ->
     {noreply, State}.
 
 %% @private
+handle_info(rotate, #state{name=Name, count=Count, date=Date} = State) ->
+    lager_util:rotate_logfile(Name, Count),
+    schedule_rotation(Date),
+    {noreply, State};
 handle_info(_Info, State) ->
     {noreply, State}.
 
@@ -131,6 +138,11 @@ terminate(_Reason, _State) ->
 code_change(_OldVsn, State, _Extra) ->
     {ok, State}.
 
+schedule_rotation(undefined) ->
+    make_ref();
+schedule_rotation(Date) ->
+    erlang:send_after(lager_util:calculate_next_rotation(Date) * 1000, self(), rotate).
+
 %% ===== Begin code lifted from riak_err =====
 
 -spec limited_fmt(string(), list(), integer()) -> iolist().

src/lager_file_backend.erl

@@ -23,7 +23,8 @@
 %% rotation and will re-open handles to files if the inode changes. It will
 %% also rotate the files itself if the size of the file exceeds the
 %% `RotationSize' and keep `RotationCount' rotated files. `RotationDate' is
-%% currently ignored.
+%% an alternate rotation trigger, based on time. See the README for
+%% documentation.
 
 -module(lager_file_backend).
 
@@ -57,6 +58,7 @@
 -spec init([{string(), lager:log_level()},...]) -> {ok, #state{}}.
 init(LogFiles) ->
     Files = [begin
+                schedule_rotation(Name, Date),
                 case lager_util:open_logfile(Name, true) of
                     {ok, {FD, Inode, _}} ->
                         #file{name=Name, level=lager_util:level_to_num(Level), fd=FD,
@@ -109,6 +111,17 @@ handle_event(_Event, State) ->
     {ok, State}.
 
 %% @private
+handle_info({rotate, File}, #state{files=Files} = State) ->
+    case lists:keyfind(File, #file.name, Files) of
+        false ->
+            %% no such file exists
+            ?INT_LOG(warning, "Asked to rotate non-existant file ~p", [File]),
+            {ok, State};
+        #file{name=Name, date=Date, count=Count} ->
+            lager_util:rotate_logfile(Name, Count),
+            schedule_rotation(Name, Date),
+            {ok, State}
+    end;
 handle_info(_Info, State) ->
     {ok, State}.
 
@@ -167,27 +180,43 @@ validate_logfiles([{Name, Level, Size, Date, Count}|T]) ->
                 true ->
                     case (is_integer(Count) andalso Count >= 0) of
                         true ->
-                            [{Name, Level, Size, Date,
-                                    Count}|validate_logfiles(T)];
+                            case lager_util:parse_rotation_date_spec(Date) of
+                                {ok, Spec} ->
+                                    [{Name, Level, Size, Spec,
+                                            Count}|validate_logfiles(T)];
+                                {error, _} when Date == "" ->
+                                    %% blank ones are fine.
+                                    [{Name, Level, Size, undefined,
+                                            Count}|validate_logfiles(T)];
+                                {error, _} ->
+                                    ?INT_LOG(error, "Invalid rotation date of ~p for ~s.",
+                                        [Date, Name]),
+                                    validate_logfiles(T)
+                            end;
                         _ ->
                             ?INT_LOG(error, "Invalid rotation count of ~p for ~s.",
-                                [Name, Count]),
+                                [Count, Name]),
                             validate_logfiles(T)
                     end;
                 _ ->
                     ?INT_LOG(error, "Invalid rotation size of ~p for ~s.",
-                        [Name, Size]),
+                        [Size, Name]),
                     validate_logfiles(T)
             end;
         _ ->
             ?INT_LOG(error, "Invalid log level of ~p for ~s.",
-                [Name, Level]),
+                [Level, Name]),
             validate_logfiles(T)
     end;
 validate_logfiles([H|T]) ->
     ?INT_LOG(error, "Invalid logfile config ~p.", [H]),
     validate_logfiles(T).
 
+schedule_rotation(_, undefined) ->
+    make_ref();
+schedule_rotation(Name, Date) ->
+    erlang:send_after(lager_util:calculate_next_rotation(Date) * 1000, self(), {rotate, Name}).
+
 -ifdef(TEST).
 
 get_loglevel_test() ->

src/lager_sup.erl

@@ -53,9 +53,21 @@ init([]) ->
                 {ok, Val2} when is_integer(Val2) -> Val2;
                 _ -> 0
             end,
+            RotationDate = case application:get_env(lager, crash_log_date) of
+                {ok, Val3} ->
+                    case lager_util:parse_rotation_date_spec(Val3) of
+                        {ok, Spec} -> Spec;
+                        {error, _} when Val3 == "" -> undefined; %% blank is ok
+                        {error, _} ->
+                            error_logger:error_msg("Invalid date spec for "
+                                "crash log ~p~n", [Val3]),
+                            undefined
+                    end;
+                _ -> undefined
+            end,
 
             [{lager_crash_log, {lager_crash_log, start_link, [File, MaxBytes,
-                        RotationSize, "", RotationCount]},
+                        RotationSize, RotationDate, RotationCount]},
                     permanent, 5000, worker, [lager_crash_log]}];
         _ ->
             []

src/lager_util.erl

@@ -318,6 +318,8 @@ rotation_calculation_test() ->
     ?assertMatch({{2000, 2, 3}, {16, 0, 0}}, calculate_next_rotation([{day, 4}, {hour, 16}], {{2000, 1, 29}, {17, 34, 43}})),
 
     ?assertMatch({{2000, 1, 7}, {16, 0, 0}}, calculate_next_rotation([{day, 5}, {hour, 16}], {{2000, 1, 3}, {17, 34, 43}})),
+    
+    ?assertMatch({{2000, 1, 3}, {16, 0, 0}}, calculate_next_rotation([{day, 1}, {hour, 16}], {{1999, 12, 28}, {17, 34, 43}})),
     ok.
 
 -endif.