Crash log rotation & documentation on rotation

README.org

@@ -53,7 +53,10 @@
   {lager,
     {handlers, [
       {lager_console_backend, info},
-      {lager_file_backend, [{"error.log", error}, {"console.log", info}]}
+      {lager_file_backend, [
+        {"error.log", error, 10485760, "", 5},
+        {"console.log", info, 10485760, "", 5}
+      ]}
     ]}
   }.
 #+END_EXAMPLE
@@ -72,6 +75,9 @@
   information. The location of the crash log can be specified by the crash_log
   application variable. If undefined it is not written at all.
 
+  Messages in the crash log are subject to a maximum message size which can be
+  specified via the crash_log_msg_size application variable.
+
 * Runtime loglevel changes
   You can change the log level of any lager backend at runtime by doing the
   following:

src/lager.app.src

@@ -23,7 +23,13 @@
             %% Whether to write a crash log, and where. Undefined means no crash logger.
             {crash_log, "log/crash.log"},
             %% Maximum size in bytes of events in the crash log - defaults to 65536
-            {crash_log_size, 65536},
+            {crash_log_msg_size, 65536},
+            %% Maximum size of the crash log in bytes, before its rotated, set
+            %% to 0 to disable rotation - default is 0
+            {crash_log_size, 10485760},
+            %% Number of rotated crash logs to keep, 0 means keep only the
+            %% current one - default is 0
+            {crash_log_count, 5},
             %% Whether to redirect error_logger messages into lager - defaults to true
             {error_logger_redirect, true}
         ]}

src/lager_crash_log.erl

@@ -16,9 +16,15 @@
 
 %% @doc Lager crash log writer. This module implements a gen_server which writes
 %% error_logger error messages out to a file in their original format. The
-%% location to which it logs is configured by the environment var `crash_log'.
+%% location to which it logs is configured by the application var `crash_log'.
 %% Omitting this variable disables crash logging. Crash logs are printed safely
 %% using trunc_io via code mostly lifted from riak_err.
+%%
+%% 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'.
 
 -module(lager_crash_log).
 
@@ -30,29 +36,34 @@
 -export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2,
         code_change/3]).
 
--export([start_link/2, start/2]).
+-export([start_link/5, start/5]).
 
 -record(state, {
         name,
         fd,
         inode,
         fmtmaxbytes,
+        size,
+        count,
         flap=false
     }).
 
 %% @private
-start_link(Filename, MaxBytes) ->
-    gen_server:start_link({local, ?MODULE}, ?MODULE, [Filename, MaxBytes], []).
+start_link(Filename, MaxBytes, Size, _Date, Count) ->
+    gen_server:start_link({local, ?MODULE}, ?MODULE, [Filename, MaxBytes,
+            Size, Count], []).
 
 %% @private
-start(Filename, MaxBytes) ->
-    gen_server:start({local, ?MODULE}, ?MODULE, [Filename, MaxBytes], []).
+start(Filename, MaxBytes, Size, _Date, Count) ->
+    gen_server:start({local, ?MODULE}, ?MODULE, [Filename, MaxBytes, Size,
+            Count], []).
 
 %% @private
-init([Filename, MaxBytes]) ->
+init([Filename, MaxBytes, Size, Count]) ->
     case lager_util:open_logfile(Filename, false) of
         {ok, {FD, Inode, _}} ->
-            {ok, #state{name=Filename, fd=FD, inode=Inode, fmtmaxbytes=MaxBytes}};
+            {ok, #state{name=Filename, fd=FD, inode=Inode,
+                    fmtmaxbytes=MaxBytes, size=Size, count=Count}};
         Error ->
             Error
     end.
@@ -62,7 +73,8 @@ handle_call(_Call, _From, State) ->
     {reply, ok, State}.
 
 %% @private
-handle_cast({log, Event}, #state{name=Name, fd=FD, inode=Inode, flap=Flap, fmtmaxbytes=FmtMaxBytes} = State) ->
+handle_cast({log, Event}, #state{name=Name, fd=FD, inode=Inode, flap=Flap,
+        fmtmaxbytes=FmtMaxBytes, size=RotSize, count=Count} = State) ->
     %% borrowed from riak_err
     {ReportStr, Pid, MsgStr, _ErrorP} = case Event of
         {error, _GL, {Pid1, Fmt, Args}} ->
@@ -78,6 +90,9 @@ handle_cast({log, Event}, #state{name=Name, fd=FD, inode=Inode, flap=Flap, fmtma
             {noreply, State};
         true ->
             case lager_util:ensure_logfile(Name, FD, Inode, false) of
+                {ok, {_, _, Size}} when RotSize /= 0, Size > RotSize ->
+                    lager_util:rotate_logfile(Name, Count),
+                    handle_cast({log, Event}, State);
                 {ok, {NewFD, NewInode, _Size}} ->
                     {Date, TS} = lager_util:format_time(lager_stdlib:maybe_utc(erlang:localtime())),
                     Time = [Date, " ", TS," =", ReportStr, "====\n"],

src/lager_file_backend.erl

@@ -17,8 +17,13 @@
 %% @doc File backend for lager, with multiple file support.
 %% Multiple files are supported, each with the path and the loglevel being
 %% configurable. The configuration paramter for this backend is a list of
-%% 2-tuples of the form `{FileName, Level}'. This backend supports external log
-%% rotation and will re-open handles to files if the inode changes.
+%% 5-tuples of the form
+%% `{FileName, Level, RotationSize, RotationDate, RotationCount}'.
+%% This backend supports external and internal log
+%% 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.
 
 -module(lager_file_backend).
 

src/lager_sup.erl

@@ -41,11 +41,21 @@ init([]) ->
     %% check if the crash log is enabled
     Crash = case application:get_env(lager, crash_log) of
         {ok, File} ->
-            MaxBytes = case application:get_env(lager, crash_log_size) of
-                {ok, Val} -> Val;
+            MaxBytes = case application:get_env(lager, crash_log_msg_size) of
+                {ok, Val} when is_integer(Val) -> Val;
                 _ -> 65536
             end,
-            [{lager_crash_log, {lager_crash_log, start_link, [File, MaxBytes]},
+            RotationSize = case application:get_env(lager, crash_log_size) of
+                {ok, Val1} when is_integer(Val1) -> Val1;
+                _ -> 0
+            end,
+            RotationCount = case application:get_env(lager, crash_log_count) of
+                {ok, Val2} when is_integer(Val2) -> Val2;
+                _ -> 0
+            end,
+
+            [{lager_crash_log, {lager_crash_log, start_link, [File, MaxBytes,
+                        RotationSize, "", RotationCount]},
                     permanent, 5000, worker, [lager_crash_log]}];
         _ ->
             []