From cd5f69dafe7d42b949234c373e1f449989454a11 Mon Sep 17 00:00:00 2001
From: Luke Bakken <luke@bakken.io>
Date: Fri, 2 Aug 2019 07:36:54 -0700
Subject: [PATCH] Factor out common code into lager_util:has_file_changed

---
 src/lager_file_backend.erl    |  8 ++------
 src/lager_rotator_default.erl | 25 +++++--------------------
 src/lager_util.erl            | 25 ++++++++++++++++++++++++-
 3 files changed, 31 insertions(+), 27 deletions(-)

diff --git a/src/lager_file_backend.erl b/src/lager_file_backend.erl
index 862e821..83a0b3c 100644
--- a/src/lager_file_backend.erl
+++ b/src/lager_file_backend.erl
@@ -289,12 +289,8 @@ write_should_check(#state{last_check=LastCheck0, check_interval=CheckInterval,
             % TODO this code is duplicated in the default rotator, but we need
             % to know if the file has changed "out from under lager" so we don't
             % write to an invalid FD
-            case file:read_file_info(Name, [raw]) of
-                {ok, #file_info{inode=Inode1, ctime=Ctime1}} ->
-                    Inode0 =/= Inode1 orelse Ctime0 =/= Ctime1;
-                _ ->
-                    true
-            end
+            {Result, _FInfo} = lager_util:has_file_changed(Name, Inode0, Ctime0),
+            Result
     end.
 
 do_write(#state{fd=FD, name=Name, flap=Flap} = State, Level, Msg) ->
diff --git a/src/lager_rotator_default.erl b/src/lager_rotator_default.erl
index 2d8a14f..f910c73 100644
--- a/src/lager_rotator_default.erl
+++ b/src/lager_rotator_default.erl
@@ -42,26 +42,11 @@ open_logfile(Name, Buffer) ->
 ensure_logfile(Name, undefined, _Inode, _Ctime, Buffer) ->
     open_logfile(Name, Buffer);
 ensure_logfile(Name, FD, Inode0, Ctime0, Buffer) ->
-    case file:read_file_info(Name, [raw]) of
-        {ok, FInfo} ->
-            {OsType, _} = os:type(),
-            Inode1 = FInfo#file_info.inode,
-            Ctime1 = FInfo#file_info.ctime,
-            case {OsType, Inode0 =:= Inode1, Ctime0 =:= Ctime1} of
-                % Note: on win32, Inode is always zero
-                % So check the file's ctime to see if it
-                % needs to be re-opened
-                {win32, _, false} ->
-                    reopen_logfile(Name, FD, Buffer);
-                {win32, _, true} ->
-                    {ok, {FD, Inode0, Ctime0, FInfo#file_info.size}};
-                {unix, true, _} ->
-                    {ok, {FD, Inode0, Ctime0, FInfo#file_info.size}};
-                {unix, false, _} ->
-                    reopen_logfile(Name, FD, Buffer)
-            end;
-        _ ->
-            reopen_logfile(Name, FD, Buffer)
+    case lager_util:has_file_changed(Name, Inode0, Ctime0) of
+        {true, _FInfo} ->
+            reopen_logfile(Name, FD, Buffer);
+        {_, FInfo} ->
+            {ok, {FD, Inode0, Ctime0, FInfo#file_info.size}}
     end.
 
 reopen_logfile(Name, FD0, Buffer) ->
diff --git a/src/lager_util.erl b/src/lager_util.erl
index 1c64c00..852b169 100644
--- a/src/lager_util.erl
+++ b/src/lager_util.erl
@@ -27,7 +27,8 @@
     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, expand_path/1, find_file/2, check_hwm/1, check_hwm/2,
-    make_internal_sink_name/1, otp_version/0, maybe_flush/2
+    make_internal_sink_name/1, otp_version/0, maybe_flush/2,
+    has_file_changed/3
 ]).
 
 -ifdef(TEST).
@@ -40,6 +41,8 @@
 
 -include("lager.hrl").
 
+-include_lib("kernel/include/file.hrl").
+
 levels() ->
     [debug, info, notice, warning, error, critical, alert, emergency, none].
 
@@ -592,6 +595,26 @@ maybe_flush(undefined, #lager_shaper{} = S) ->
 maybe_flush(Flag, #lager_shaper{} = S) when is_boolean(Flag) ->
     S#lager_shaper{flush_queue = Flag}.
 
+-spec has_file_changed(Name :: file:name_all(),
+                       Inode0 :: pos_integer(),
+                       Ctime0 :: file:date_time()) -> {boolean(), file:file_info()}.
+has_file_changed(Name, Inode0, Ctime0) ->
+    {OsType, _} = os:type(),
+    F = file:read_file_info(Name, [raw]),
+    case {OsType, F} of
+        {win32, {ok, #file_info{ctime=Ctime1}=FInfo}} ->
+            % Note: on win32, Inode is always zero
+            % So check the file's ctime to see if it
+            % needs to be re-opened
+            Changed = Ctime0 =/= Ctime1,
+            {Changed, FInfo};
+        {_, {ok, #file_info{inode=Inode1}=FInfo}} ->
+            Changed = Inode0 =/= Inode1,
+            {Changed, FInfo};
+        {_, _} ->
+            {true, undefined}
+    end.
+
 -ifdef(TEST).
 
 parse_test() ->