From 45a830f6c7248ef627e64306df994c058d29f002 Mon Sep 17 00:00:00 2001
From: Takuro Ashie <ashie@clear-code.com>
Date: Thu, 9 Jun 2022 21:59:25 +0900
Subject: [PATCH] Reopen log file when rotation is detected

In the previous vesions, there was no way to detect log rotation event when
log file was rotated by external tool (logrotate)

It causes that DaemonLogger continues to write logs to rotated file even even
when it's already renamed or removed, it's not expected behavior.

This commit fixes by reopening log file when inode is changed.

Signed-off-by: Takuro Ashie <ashie@clear-code.com>
---
 lib/serverengine/daemon_logger.rb | 37 +++++++++++++++++++++++++++++++
 spec/daemon_logger_spec.rb        | 25 +++++++++++++++++++++
 2 files changed, 62 insertions(+)

diff --git a/lib/serverengine/daemon_logger.rb b/lib/serverengine/daemon_logger.rb
index 007aaa3..a63f603 100644
--- a/lib/serverengine/daemon_logger.rb
+++ b/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
diff --git a/spec/daemon_logger_spec.rb b/spec/daemon_logger_spec.rb
index 9d52ca5..0bb19f6 100644
--- a/spec/daemon_logger_spec.rb
+++ b/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