(msg_split) Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit ...
(msg_split) ... anim id est laborum.

    def send(text, notice = false)
      # TODO deprecate `notice` argument, put splitting into own
      # method
      text = text.to_s
      split_start = @bot.config.message_split_start || ""
      split_end   = @bot.config.message_split_end   || ""
      command = notice ? "NOTICE" : "PRIVMSG"

      text.split(/\r\n|\r|\n/).each do |line|
        maxlength = 510 - (":" + " #{command} " + " :").size
        maxlength = maxlength - @bot.mask.to_s.length - @name.to_s.length
        maxlength_without_end = maxlength - split_end.bytesize

        if line.bytesize > maxlength
          splitted = []

          while line.bytesize > maxlength_without_end
            pos = line.rindex(/\s/, maxlength_without_end)
            r = pos || maxlength_without_end
            splitted << line.slice!(0, r) + split_end.tr(" ", "\u00A0")
            line = split_start.tr(" ", "\u00A0") + line.lstrip
          end

          splitted << line
          splitted[0, (@bot.config.max_messages || splitted.size)].each do |string|
            string.tr!("\u00A0", " ") # clean string from any non-breaking spaces
            @bot.irc.send("#{command} #@name :#{string}")
          end
        else
          @bot.irc.send("#{command} #@name :#{line}")
        end
      end
    end

(msg_split) 私はその人を常に先生と呼んでいた。だからここでもただ先生と書くだけで本名は打ち明けない。これは世間を憚かる遠慮というよりも、その方が私にとって自然だからである。私はその人の記憶を呼び起すごとに、すぐ「先生」といいたくなる。筆を執っても心持は同じ事である。よそよそしい頭文字などはとて�[CUT]
(msg_split) ...

while line.bytesize > maxlength_without_end
  pos = line.rindex(/\s/, maxlength_without_end) # (1)
  r = pos || maxlength_without_end
  splitted << line.slice!(0, r) + split_end.tr(" ", "\u00A0") # (2)
  line = split_start.tr(" ", "\u00A0") + line.lstrip
end

    def send(text, notice = false)
      text = text.to_s
      split_start = @bot.config.message_split_start || ""
      split_end   = @bot.config.message_split_end   || ""
      command = notice ? "NOTICE" : "PRIVMSG"
      max_bytesize = 510 - ":#{@bot.mask} #{command} #{@name} :".bytesize
      max_bytesize_without_end = max_bytesize - split_end.bytesize

      text.lines.map(&:chomp).each do |line|
        if line.bytesize > max_bytesize
          splitted = []

          rest = line
          while rest.bytesize > max_bytesize_without_end
            # 累積バイト数を求める
            accumulated_bytesize = line.each_char.reduce([]) do |acc, ch|
              acc << ((acc.last || 0) + ch.bytesize)
            end

            # バイト数が規定以下かつ最大となる位置を求める
            max_slice_bytesize, max_slice_length = accumulated_bytesize.
              select { |bytesize| bytesize <= max_bytesize_without_end }.
              each_with_index.
              to_a.
              last

            # max_slice_length より左にある空白の位置を求める
            last_space_index = rest.rindex(/\s/, max_slice_length)

            # 分割位置を決める
            r = if last_space_index
                  # max_slice_length より左に空白が存在する場合、最後の空白の左にする
                  accumulated_bytesize[last_space_index] - 1
                else
                  # max_slice_length より左に空白が存在しない場合、バイト数が規定以下かつ
                  # 最大となる位置にする
                  max_slice_bytesize
                end

            splitted << (rest.byteslice(0...r) +
                         split_end.tr(" ", "\u00A0"))
            rest = split_start.tr(" ", "\u00A0") +
              rest.byteslice(r...rest.bytesize).lstrip
          end
          splitted << rest

          splitted[0, (@bot.config.max_messages || splitted.size)].each do |string|
            string.tr!("\u00A0", " ") # clean string from any non-breaking spaces
            @bot.irc.send("#{command} #@name :#{string}")
          end
        else
          @bot.irc.send("#{command} #@name :#{line}")
        end
      end
    end

(msg_split) 私はその人を常に先生と呼んでいた。だからここでもただ先生と書くだけで本名は打ち明けない。これは世間を憚かる遠慮というよりも、その方が私にとって自然だからである。私はその人の記憶を呼び起すごとに、すぐ「先生」といいたくなる。筆を執っても心持は同じ事である。よそよそしい頭文字などはとても ...
(msg_split) ... 使う気にならない。

    private
    def split_message(msg, prefix, split_start, split_end)
      max_bytesize = 510 - prefix.bytesize
      max_bytesize_without_end = max_bytesize - split_end.bytesize

      if msg.bytesize <= max_bytesize
        return [msg]
      end

      splitted = []
      acc = 0
      # (*)
      acc_rune_sizes = msg.each_char.map {|ch|
        acc += ch.bytesize
      }
      while msg.bytesize > max_bytesize_without_end
        max_rune = acc_rune_sizes.rindex {|bs| bs <= max_bytesize_without_end} || 0
        r = [msg.rindex(/\s/, max_rune) || max_rune, 1].max
        splitted << (msg[0...r] + split_end.tr(" ", "\u00A0"))
        msg = split_start.tr(" ", "\u00A0") + msg[r..-1].lstrip
      end
      splitted << msg
    end

    private
    def split_message(msg, prefix, split_start, split_end)
      max_bytesize = 510 - prefix.bytesize
      max_bytesize_without_end = max_bytesize - split_end.bytesize

      if msg.bytesize <= max_bytesize
        return [msg]
      end

      splitted = []
      while msg.bytesize > max_bytesize_without_end
        # 繰り返しごとに累積バイト数を計算する
        acc = 0
        acc_rune_sizes = msg.each_char.map {|ch|
          acc += ch.bytesize
        }

        max_rune = acc_rune_sizes.rindex {|bs|
          bs <= max_bytesize_without_end
        } || 0
        r = [msg.rindex(/\s/, max_rune) || (max_rune + 1), 1].max

        splitted << (msg[0...r] + split_end)
        msg = split_start.tr(" ", "\z") + msg[r..-1].lstrip
      end
      splitted << msg

      # clean string from any substitute characters
      splitted.map {|string| string.gsub("\z", ' ')}
    end