Reopen log file when rotation is detected

lib/serverengine/daemon_logger.rb

@@ -55,6 +55,9 @@ def logdev=(logdev)
         # update path string
         old_file_dev = @file_dev
         @file_dev = LogDevice.new(logdev, shift_age: @rotate_age, shift_size: @rotate_size)
+        # Enable to detect rotation done by external tools.
+        # Otherwise it continues writing logs to old file unexpectedly.
+        @file_dev.extend(RotationAware)
         old_file_dev.close if old_file_dev
         @logdev = @file_dev
       end
@@ -130,6 +133,40 @@ def close
       nil
     end
 
+    module RotationAware
+      def self.extended(obj)
+        obj.update_ino
+      end
+
+      def update_ino
+        (@ino_mutex ||= Mutex.new).synchronize do
+          @ino = File.stat(filename).ino rescue nil
+          @last_ino_time = Time.now
+        end
+      end
+
+      def reopen(log = nil)
+        super(log)
+        update_ino
+      end
+
+      def reopen!
+        super
+        update_ino
+      end
+
+      def write(message)
+        reopen_needed = false
+        @ino_mutex.synchronize do
+          if (Time.now - @last_ino_time).abs > 1
+            ino = File.stat(filename).ino rescue nil
+            reopen_needed = true if ino && ino != @ino
+          end
+        end
+        reopen! if reopen_needed
+        super(message)
+      end
+    end
   end
 
 end

spec/daemon_logger_spec.rb

@@ -1,4 +1,5 @@
 require 'stringio'
+require 'timecop'
 
 describe ServerEngine::DaemonLogger do
   before { FileUtils.rm_rf("tmp") }
@@ -172,4 +173,28 @@
     $stderr = STDERR
     stderr.should_not =~ /(log shifting failed|log writing failed|log rotation inter-process lock failed)/
   end
+
+  it 'reopen log when path is renamed' do
+    pending "rename isn't supported on windows" if ServerEngine.windows?
+
+    log = DaemonLogger.new("tmp/rotate.log", { level: 'info', log_rotate_age: 0  })
+
+    log.info '11111'
+    File.read("tmp/rotate.log").should include('11111')
+    File.rename("tmp/rotate.log", "tmp/rotate.log.1")
+
+    Timecop.travel(Time.now + 1)
+
+    log.info '22222'
+    contents = File.read("tmp/rotate.log.1")
+    contents.should include('11111')
+    contents.should include('22222')
+
+    FileUtils.touch("tmp/rotate.log")
+    Timecop.travel(Time.now + 1)
+
+    log.info '33333'
+    File.read("tmp/rotate.log").should include('33333')
+    File.read("tmp/rotate.log.1").should_not include('33333')
+  end
 end