parser_4.rb

require 'time'

class LogfileParser

  TIME_REGEXP = /\[\d{2}\/\w{3}\/\d{4}\:\d{2}:\d{2}:\d{2}\s.{5}\]/

  def initialize path, starting_at
    raise ArgumentError unless File.exists?( path )

    @log            = File.open( path )
    @starting_at    = Time.parse( starting_at )
    @min_timestamp  = @starting_at
    @max_timestamp  = (@starting_at + 300)
    @bytes_to_skip  = File.open( 'statefile' ) { |f| f.readline.to_i } rescue 0
  end

  def search
    @log.rewind

    filesize      = @log.stat.size
    buffer_size   = 128000
    position      = 0

    minute        = @starting_at.strftime("%M").chars.first

    # Generate dynamic Regexp for the given timerange
    time_range    = Regexp.new(
      @starting_at.strftime("\\[%d\\/%b\\/%Y\\:%H\\:#{minute}([0-4]\\:\\d{2}|5\\:00)\\s.{5}\\]")
    )

    while position <= filesize
     
      # Read in a 128kB chunk
      buffer = @log.read(buffer_size)

      # Check if time range is included
      if buffer =~ time_range
        # Seek backwards for precise line search ( just to be sure )
        @log.seek((position-buffer_size), File::SEEK_SET)

        @log.each_line do |line|
          next unless timestamp = line.match( TIME_REGEXP )


          entry_time = Time.parse( timestamp[0].sub(":", " ") )

          if entry_time >= @min_timestamp
            @bytes_to_skip = @log.tell
            File.open( 'statefile', 'w' ) { |f| f.write( @bytes_to_skip ) }
            return @bytes_to_skip
          end
        end

      end

      position += buffer_size
      @log.seek(position, File::SEEK_SET)
    end
  end

  def fast_forward
    if @bytes_to_skip > 0
      @log.seek(@bytes_to_skip, File::SEEK_SET)
    else
      search
    end
  end

  def emit &block
    fast_forward

    @log.each_line do |line|
      timestamp = line.match( TIME_REGEXP )
      next unless timestamp && timestamp[0]

      entry_time = Time.parse( timestamp[0].sub(":", " ") )

      if entry_time >= @min_timestamp && entry_time <= @max_timestamp
        yield line
      end

      if entry_time >= @max_timestamp
        break
      end
    end
  end

end

parser = LogfileParser.new( *ARGV )
parser.emit {|l| puts l }