file.rb

require 'digest/md5'

module Listen
  class File
    def self.change(record, rel_path)
      path = Pathname.new(record.root) + rel_path
      lstat = path.lstat

      data = { mtime: lstat.mtime.to_f, mode: lstat.mode, size: lstat.size }

      record_data = record.file_data(rel_path)

      if record_data.empty?
        record.update_file(rel_path, data)
        return :added
      end

      if data[:mode] != record_data[:mode]
        record.update_file(rel_path, data)
        return :modified
      end

      if data[:mtime] != record_data[:mtime]
        record.update_file(rel_path, data)
        return :modified
      end
      
      if data[:size] != record_data[:size]
        record.update_file(rel_path, data)
        return :modified
      end
      
      return if /1|true/ =~ ENV['LISTEN_GEM_DISABLE_HASHING']
      return unless self.inaccurate_mac_time?(lstat)

      # Check if change happened within 1 second (maybe it's even
      # too much, e.g. 0.3-0.5 could be sufficient).
      #
      # With rb-fsevent, there's a (configurable) latency between
      # when file was changed and when the event was triggered.
      #
      # If a file is saved at ???14.998, by the time the event is
      # actually received by Listen, the time could already be e.g.
      # ???15.7.
      #
      # And since Darwin adapter uses directory scanning, the file
      # mtime may be the same (e.g. file was changed at ???14.001,
      # then at ???14.998, but the fstat time would be ???14.0 in
      # both cases).
      #
      # If change happend at ???14.999997, the mtime is 14.0, so for
      # an mtime=???14.0 we assume it could even be almost ???15.0
      #
      # So if Time.now.to_f is ???15.999998 and stat reports mtime
      # at ???14.0, then event was due to that file'd change when:
      #
      # ???15.999997 - ???14.999998 < 1.0s
      #
      # So the "2" is "1 + 1" (1s to cover rb-fsevent latency +
      # 1s maximum difference between real mtime and that recorded
      # in the file system)
      #
      return if data[:mtime].to_i + 2 <= Time.now.to_f

      md5 = Digest::MD5.file(path).digest
      record.update_file(rel_path, data.merge(md5: md5))
      :modified if record_data[:md5] && md5 != record_data[:md5]
    rescue SystemCallError
      record.unset_path(rel_path)
      :removed
    rescue
      Listen::Logger.debug "lstat failed for: #{rel_path} (#{$ERROR_INFO})"
      raise
    end

    def self.inaccurate_mac_time?(stat)
      # 'mac' means Modified/Accessed/Created

      # Since precision depends on mounted FS (e.g. you can have a FAT partiion
      # mounted on Linux), check for fields with a remainder to detect this

      [stat.mtime, stat.ctime, stat.atime].map(&:usec).all?(&:zero?)
    end
  end
end