Copy permission and ownership at shift

Fix #80

Author: nobu

lib/logger/log_device.rb

@@ -226,9 +226,23 @@ def shift_log_period(period_end)
     end
 
     def shift_log_file(shifted)
+      stat = @dev.stat
       @dev.close rescue nil
       File.rename(@filename, shifted)
       @dev = create_logfile(@filename)
+      mode, uid, gid = stat.mode, stat.uid, stat.gid
+      begin
+        @dev.chmod(mode) if mode
+        mode = nil
+        @dev.chown(uid, gid)
+      rescue Errno::EPERM
+        if mode
+          # failed to chmod, probably nothing can do more.
+        elsif uid
+          uid = nil
+          retry # to change gid only
+        end
+      end
       return true
     end
   end

test/logger/test_logdevice.rb

@@ -205,6 +205,23 @@ def test_reopen_file_by_file
     end
   end
 
+  def test_perm_after_shift
+    mode = 0o611
+    File.open(@filename, "w") {|f| f.chmod mode}
+    logfile = @filename
+    logfile0 = logfile + '.0'
+    logdev = d(@filename, shift_age: 1, shift_size: 0)
+    logdev.write('hello')
+    logdev.write('hello')
+    logdev.close
+
+    assert_equal File.stat(logfile0).mode, File.stat(logfile).mode
+  ensure
+    if logfile0
+      File.unlink(logfile0) rescue nil
+    end
+  end
+
   def test_shifting_size_with_reopen
     tmpfile = Tempfile.new([File.basename(__FILE__, '.*'), '_1.log'])
     logfile = tmpfile.path