parse_header

# File lib/webrick/httputils.rb, line 143
    def parse_header(raw)
      header = Hash.new([].freeze)
      field = nil
      raw.each_line{|line|
        case line
        when /^([A-Za-z0-9!\#$%&'*+\-.^_`|~]+):\s*(.*?)\s*\z/m
          field, value = $1, $2
          field.downcase!
          header[field] = [] unless header.has_key?(field)
          header[field] << value
        when /^\s+(.*?)\s*\z/m
          value = $1
          unless field
            raise HTTPStatus::BadRequest, "bad header '#{line}'."
          end
          header[field][-1] << " " << value
        else
          raise HTTPStatus::BadRequest, "bad header '#{line}'."
        end
      }
      header.each{|key, values|
        values.each{|value|
          value.strip!
          value.gsub!(/\s+/, " ")
        }
      }
      header
    end