implement log_dir option handling

src/lager_crash_log.erl

@@ -66,7 +66,8 @@ start(Filename, MaxBytes, Size, Date, Count) ->
             Date, Count], []).
 
 %% @private
-init([Filename, MaxBytes, Size, Date, Count]) ->
+init([RelFilename, MaxBytes, Size, Date, Count]) ->
+    Filename = lager_util:expand_path(RelFilename),
     case lager_util:open_logfile(Filename, false) of
         {ok, {FD, Inode, _}} ->
             schedule_rotation(Date),

src/lager_file_backend.erl

@@ -102,8 +102,9 @@ init(LogFileConfig) when is_list(LogFileConfig) ->
             {error, {fatal, bad_config}};
         Config ->
             %% probabably a better way to do this, but whatever
-            [Name, Level, Date, Size, Count, SyncInterval, SyncSize, SyncOn, CheckInterval, Formatter, FormatterConfig] =
+            [RelName, Level, Date, Size, Count, SyncInterval, SyncSize, SyncOn, CheckInterval, Formatter, FormatterConfig] =
               [proplists:get_value(Key, Config) || Key <- [file, level, date, size, count, sync_interval, sync_size, sync_on, check_interval, formatter, formatter_config]],
+            Name = lager_util:expand_path(RelName),
             schedule_rotation(Name, Date),
             State0 = #state{name=Name, level=Level, size=Size, date=Date, count=Count, formatter=Formatter,
                 formatter_config=FormatterConfig, sync_on=SyncOn, sync_interval=SyncInterval, sync_size=SyncSize,

src/lager_util.erl

@@ -22,7 +22,7 @@
         open_logfile/2, ensure_logfile/4, rotate_logfile/2, format_time/0, format_time/1,
         localtime_ms/0, localtime_ms/1, maybe_utc/1, parse_rotation_date_spec/1,
         calculate_next_rotation/1, validate_trace/1, check_traces/4, is_loggable/3,
-        trace_filter/1, trace_filter/2]).
+        trace_filter/1, trace_filter/2, expand_path/1]).
 
 -ifdef(TEST).
 -include_lib("eunit/include/eunit.hrl").
@@ -467,6 +467,15 @@ i2l(I)              -> integer_to_list(I).
 i3l(I) when I < 100 -> [$0 | i2l(I)];
 i3l(I)              -> integer_to_list(I).
 
+%% When log_root option is provided, get the real path to a file
+expand_path(RelPath) ->
+    case application:get_env(lager, log_root) of
+        {ok, LogRoot} when is_list(LogRoot) -> % Join relative path
+            filename:join(LogRoot, RelPath);
+        undefined -> % No log_root given, keep relative path
+            RelPath
+    end.
+
 -ifdef(TEST).
 
 parse_test() ->
@@ -707,4 +716,21 @@ mask_to_levels_test() ->
     ?assertEqual([debug, notice, error], mask_to_levels(?DEBUG bor ?NOTICE bor ?ERROR)),
     ok.
 
+expand_path_test() ->
+    OldRootVal = application:get_env(lager, log_root),
+
+    ok = application:unset_env(lager, log_root),
+    ?assertEqual("/foo/bar", expand_path("/foo/bar")),
+    ?assertEqual("foo/bar", expand_path("foo/bar")),
+
+    ok = application:set_env(lager, log_root, "log/dir"),
+    ?assertEqual("/foo/bar", expand_path("/foo/bar")), % Absolute path should not be changed
+    ?assertEqual("log/dir/foo/bar", expand_path("foo/bar")),
+
+    case OldRootVal of
+        undefined -> application:unset_env(lager, log_root);
+        {ok, Root} -> application:set_env(lager, log_root, Root)
+    end,
+    ok.
+
 -endif.