chef/cookbooks/hostsfile/libraries/entry.rb

#
# Author:: Seth Vargo <sethvargo@gmail.com>
# Cookbook:: hostsfile
# Library:: entry
#
# Copyright:: 2012-2013, Seth Vargo
# Copyright:: 2012, CustomInk, LCC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

require 'ipaddr'

# An object representation of a single line in a hostsfile.
#
# @author Seth Vargo <sethvargo@gmail.com>
module HostsFile
  class Entry
    class << self
      # Creates a new Hostsfile::Entry object by parsing a text line. The
      # `line` attribute will be in the following format:
      #
      #     1.2.3.4 hostname [alias[, alias[, alias]]] [# comment [@priority]]
      #
      # @param [String] line
      #   the line to parse
      # @return [Entry]
      #   a new entry object
      def parse(line)
        entry, comment = extract_comment(line)
        comment, priority = extract_priority(comment)
        entries = extract_entries(entry)

        # Return nil if the line is empty
        return nil if entries.nil? || entries.empty?

        # If /etc/hosts has a broken content we throw a descriptive exception
        if entries[0].nil?
          raise ArgumentError, "/etc/hosts has a line without IP address: #{line}"
        end
        if entries[1].nil?
          raise ArgumentError, "/etc/hosts has a line without hostname: #{line}"
        end

        new(
          ip_address: entries[0],
          hostname:   entries[1],
          aliases:    entries[2..-1],
          comment:    comment,
          priority:   priority
        )
      end

      private

      def extract_comment(line)
        return nil if presence(line).nil?
        line.split('#', 2).collect { |part| presence(part) }
      end

      def extract_priority(comment)
        return nil if comment.nil?

        if comment.include?('@')
          comment.split('@', 2).collect { |part| presence(part) }
        else
          [comment, nil]
        end
      end

      def extract_entries(entry)
        return nil if entry.nil?
        entry.split(/\s+/).collect { |entry| presence(entry) }.compact
      end

      def presence(string)
        return nil if string.nil?
        return nil if string.strip.empty?
        string.strip
      end
    end

    # @return [String]
    attr_accessor :ip_address, :hostname, :aliases, :comment, :priority

    # Creates a new entry from the given options.
    #
    # @param [Hash] options
    #   a list of options to create the entry with
    # @option options [String] :ip_address
    #   the IP Address for this entry
    # @option options [String] :hostname
    #   the hostname for this entry
    # @option options [String, Array<String>] :aliases
    #   a alias or array of aliases for this entry
    # @option options[String] :comment
    #   an optional comment for this entry
    # @option options [Integer] :priority
    #   the relative priority of this entry (compared to others)
    #
    # @raise [ArgumentError]
    #   if neither :ip_address nor :hostname are supplied
    def initialize(options = {})
      if options[:ip_address].nil? || options[:hostname].nil?
        raise ArgumentError, ':ip_address and :hostname are both required options'
      end

      @ip_address = IPAddr.new(remove_ip_scope(options[:ip_address]))
      @hostname   = options[:hostname]
      @aliases    = [options[:aliases]].flatten.compact
      @comment    = options[:comment]
      @priority   = options[:priority] || calculated_priority
    end

    # Set a the new priority for an entry.
    #
    # @param [Integer] new_priority
    #   the new priority to set
    def priority=(new_priority)
      @calculated_priority = false
      @priority = new_priority
    end

    # The line representation of this entry.
    #
    # @return [String]
    #   the string representation of this entry
    def to_line
      hosts = [hostname, aliases].flatten.join(' ')

      comments = "# #{comment}".strip
      comments << " @#{priority}" unless priority.nil? || @calculated_priority
      comments = comments.strip
      comments = nil if comments == '#'

      [ip_address, hosts, comments].compact.join("\t").strip
    end

    # Returns true if priority is calculated
    #
    # @return [Boolean]
    #   true if priority is calculated and false otherwise
    def calculated_priority?
      @calculated_priority
    end

    private

    # Calculates the relative priority of this entry.
    #
    # @return [Integer]
    #   the relative priority of this item
    def calculated_priority
      @calculated_priority = true

      return 82 if ip_address == IPAddr.new('127.0.0.1')
      return 81 if ip_address == IPAddr.new('::1')
      return 80 if IPAddr.new('127.0.0.0/8').include?(ip_address) # local
      return 60 if ip_address.ipv4? # ipv4
      return 20 if ip_address.ipv6? # ipv6
      00
    end

    # Removes the scopes pieces of the address, because reasons.
    #
    # @see https://bugs.ruby-lang.org/issues/8464
    # @see https://github.com/customink-webops/hostsfile/issues/51
    #
    # @return [String, nil]
    #
    def remove_ip_scope(address)
      return nil if address.nil?
      address.to_s.sub(/%.*/, '')
    end
  end
end