Initialize pos_file for existing files

initialize-pos.rb

#!/usr/bin/env ruby
# -*- coding: utf-8 -*-

require 'fileutils'

POSITION_FILE_ENTRY_FORMAT = "%s\t%016x\t%016x\n".freeze
POSITION_FILE_ENTRY_REGEX = /^([^\t]+)\t([0-9a-fA-F]+)\t([0-9a-fA-F]+)/.freeze
DEFAULT_DIR_PERMISSION = 0755
DEFAULT_FILE_PERMISSION = 0644

[ { :pos_file => "/var/log/td-agent/fluentd-docker.pos", :files => Dir.glob("/var/lib/docker/containers/*/*-json.log") } ].each do |entry|
  pos_file_dir = File.dirname(entry[:pos_file])
  FileUtils.mkdir_p(pos_file_dir, mode: DEFAULT_DIR_PERMISSION) unless Dir.exist?(pos_file_dir)

  read_map = {}
  if File.exist? entry[:pos_file]
    content = File.open(entry[:pos_file]).read
    content.each_line do |line|
      m = POSITION_FILE_ENTRY_REGEX.match(line)
      next if m.nil?

      path = m[1]
      pos = m[2].to_i(16)
      ino = m[3].to_i(16)
      read_map[path] = {
        :pos => pos,
        :ino => ino
      }
    end
  end

  calc_map = {}
  entry[:files].each do |path|
    next if ! File.file?(path)

    s = File.stat(path)
    calc_map[path] = {
      :pos => s.size,
      :ino => s.ino
    }
  end

  # merge maps, using read value in case it's already in the file
  map = calc_map.merge(read_map)
  # backup pos_file
  FileUtils.cp entry[:pos_file], "#{entry[:pos_file]}.bak" if File.exist?(entry[:pos_file])

  puts "Updating #{entry[:pos_file]}"
  File.open(entry[:pos_file], "w") do |file|
    map.each do |key, value|
      file.write "#{POSITION_FILE_ENTRY_FORMAT % [key, value[:pos], value[:ino]]}"
    end
  end
end

Run it with:

docker run --rm -it --user root -v $(pwd)/initialize-pos.rb:/initialize-pos.rb -v /var/lib/docker/containers:/var/lib/docker/containers -v /var/log/td-agent:/var/log/td-agent fluent/fluentd:v1.11.5-1.0 ruby /initialize-pos.rb