Detect log rotation and release renamed files

.github/workflows/linux.yml

@@ -9,8 +9,12 @@ jobs:
       fail-fast: false
       matrix:
         ruby: [ '3.0', '2.7', '2.6', '2.5' ]
-        os:
-          - ubuntu-latest
+        os: [ 'ubuntu-latest' ]
+        test-optional: [ true ]
+        include:
+          - ruby: '2.7'
+            os: ubuntu-latest
+            test-optional: false
     name: Ruby ${{ matrix.ruby }} unit testing on ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v2
@@ -22,5 +26,5 @@ jobs:
         CI: true
       run: |
         gem install bundler rake
-        bundle install --jobs 4 --retry 3
+        bundle install --jobs 4 --retry 3 ${{ matrix.test-optional && '--with inotify' || '' }}
         bundle exec rake spec

Gemfile

@@ -1,2 +1,5 @@
 source 'https://rubygems.org/'
 gemspec
+group :inotify, optional: true do
+  gem 'rb-inotify'
+end

lib/serverengine/daemon_logger.rb

@@ -16,6 +16,7 @@
 #    limitations under the License.
 #
 require 'logger'
+require 'serverengine/utils'
 
 module ServerEngine
 
@@ -36,6 +37,13 @@ def initialize(logdev, config={})
 
       super(nil)
 
+      if ServerEngine::linux?
+        begin
+          require 'rb-inotify'
+        rescue LoadError
+        end
+      end
+
       self.level = config[:log_level] || 'debug'
       self.logdev = logdev
     end
@@ -58,6 +66,7 @@ def logdev=(logdev)
         old_file_dev.close if old_file_dev
         @logdev = @file_dev
       end
+      enable_watching_logdev(logdev) if defined?(INotify)
       logdev
     end
 
@@ -76,9 +85,56 @@ def add(severity, message = nil, progname = nil, &block)
       end
       progname ||= @progname
       self << format_message(SEVERITY_FORMATS_[severity+1], Time.now, progname, message)
+      poll_pending_inotify if defined?(INotify)
       true
     end
 
+    def poll_pending_inotify
+      return unless ServerEngine::linux?
+      return unless @inotify
+
+      if IO.select([@inotify.to_io], [], [], 0)
+        @inotify.process
+      end
+    end
+
+    def enable_watching_logdev(logdev)
+      return unless ServerEngine::linux?
+
+      target = nil
+      if logdev.respond_to?(:filename)
+        target = logdev.filename
+      elsif logdev.respond_to?(:path)
+        target = logdev.path
+      elsif logdev.is_a?(String)
+        target = logdev
+      else
+        # ignore StringIO for some test cases
+        return
+      end
+      if target
+        @inotify.close if @inotify
+        @inotify = INotify::Notifier.new
+        def @inotify.readpartial(size)
+          @handle.read_nonblock(size)
+        rescue Errno::EBADF, Errno::EAGAIN, EWOULDBLOCK
+          nil
+        end
+        @inotify.watch(target, :move_self) do |event|
+          if @logdev.respond_to?(:filename)
+            @logdev.close
+            @logdev.reopen(@logdev.filename)
+          elsif @logdev.respond_to?(:path)
+            @logdev.close
+            @logdev.reopen(@logdev.path)
+          else
+            close
+            reopen
+          end
+        end
+      end
+    end
+
     module Severity
       include Logger::Severity
       TRACE = -1

lib/serverengine/utils.rb

@@ -18,12 +18,17 @@
 module ServerEngine
 
   IS_WINDOWS = /mswin|mingw/ === RUBY_PLATFORM
+  IS_LINUX = /linux/ === RUBY_PLATFORM
   private_constant :IS_WINDOWS
 
   def self.windows?
     IS_WINDOWS
   end
 
+  def self.linux?
+    IS_LINUX
+  end
+
   module ClassMethods
     def dump_uncaught_error(e)
       STDERR.write "Unexpected error #{e}\n"

spec/daemon_logger_spec.rb

@@ -172,4 +172,47 @@
     $stderr = STDERR
     stderr.should_not =~ /(log shifting failed|log writing failed|log rotation inter-process lock failed)/
   end
+
+  def lsof(path)
+    IO.popen("lsof | grep #{path}") do |io|
+      io.read
+    end
+  end
+
+  it 'reopen log when path is renamed' do
+    pending "not supported except Linux with inotify" unless ServerEngine.linux? and defined?(INotify)
+
+    log = DaemonLogger.new("tmp/rotate.log", level: 'info')
+    File.rename("tmp/rotate.log", "tmp/rotate.log.1")
+    log.info '1' * 15
+    FileUtils.touch("tmp/rotate.log")
+    lsof("rotate.log").should_not include("rotate.log.1")
+  end
+
+  it 'reopen log when path is renamed by external process' do
+    pending "not supported except Linux with inotify" unless ServerEngine.linux? and defined?(INotify)
+
+    log = DaemonLogger.new("tmp/rotate.log", level: 'info')
+    pid1 = Process.fork do
+      File.rename("tmp/rotate.log", "tmp/rotate.log.1")
+      FileUtils.touch("tmp/rotate.log")
+    end
+    Process.waitpid pid1
+    log.info '1' * 15
+    lsof("rotate.log").should_not include("rotate.log.1")
+  end
+
+  it 'reopen logger when file is renamed' do
+    pending "not supported except Linux with inotify" unless ServerEngine.linux? and defined?(INotify)
+
+    log = DaemonLogger.new("tmp/dummy.log", level: 'info')
+    log.logdev = File.open("tmp/rotate.log", "w")
+    pid1 = Process.fork do
+      File.rename("tmp/rotate.log", "tmp/rotate.log.1")
+      FileUtils.touch("tmp/rotate.log")
+    end
+    Process.waitpid pid1
+    log.info '1' * 15
+    lsof("rotate.log").should_not include("rotate.log.1")
+  end
 end