Ruby on Rails 项目里面字符串过滤html标签

    Ruby on Rails 项目里面字符串去掉html标签没有特别直接的办法， 需要借助第三方lib：
1 . 比较简单的方式， 不支持换行：

require 'nokogiri'

item = Nokogiri::HTML('<a href="#">string</a>')
puts item.to_html

2. 第二种, 代码来自Github， 稍作修改：

require 'nokogiri'

# The main method on this module +plain_text+ will convert a string of HTML to a plain text approximation.
class PlainText
IGNORE_TAGS = %w(script style object applet iframe).inject({}){|h, t| h[t] = true; h}.freeze
PARAGRAPH_TAGS = %w(p h1 h2 h3 h4 h5 h6 table ol ul dl dd blockquote dialog figure aside section).inject({}){|h, t| h[t] = true; h}.freeze
BLOCK_TAGS = %w(div address li dt center del article header header footer nav pre legend tr).inject({}){|h, t| h[t] = true; h}.freeze
WHITESPACE = [" ", "\n", "\r"].freeze
PLAINTEXT = "plaintext".freeze
PRE = "pre".freeze
BR = "br".freeze
HR = "hr".freeze
TD = "td".freeze
TH = "th".freeze
TR = "tr".freeze
OL = "ol".freeze
UL = "ul".freeze
LI = "li".freeze
A = "a".freeze
TABLE = "table".freeze
NUMBERS = ["1", "a"].freeze
ABSOLUTE_URL_PATTERN = /^[a-z]+:\/\/[a-z0-9]/i.freeze
HTML_PATTERN = /[<&]/.freeze
TRAILING_WHITESPACE = /[ \t]+$/.freeze
BODY_TAG_XPATH = "/html/body".freeze
CARRIDGE_RETURN_PATTERN = /\r(\n?)/.freeze
LINE_BREAK_PATTERN = /[\n\r]/.freeze
NON_PROTOCOL_PATTERN = /:\/?\/?(.*)/.freeze
NOT_WHITESPACE_PATTERN = /\S/.freeze
SPACE = " ".freeze
EMPTY = "".freeze
NEWLINE = "\n".freeze
HREF = "href".freeze
TABLE_SEPARATOR = " | ".freeze

# Helper instance method for converting HTML into plain text. This method simply calls HtmlToPlainText.plain_text.

class << self
# Convert some HTML into a plain text approximation.

def plain_text(html)
return nil if html.nil?
return html.dup unless html =~ HTML_PATTERN
body = Nokogiri::HTML::Document.parse(html).xpath(BODY_TAG_XPATH).first
return unless body
convert_node_to_plain_text(body).strip.gsub(CARRIDGE_RETURN_PATTERN, NEWLINE)
end

private

# Convert an HTML node to plain text. This method is called recursively with the output and
# formatting options for special tags.
def convert_node_to_plain_text(parent, out = '', options = {})
if PARAGRAPH_TAGS.include?(parent.name)
append_paragraph_breaks(out)
elsif BLOCK_TAGS.include?(parent.name)
append_block_breaks(out)
end

format_list_item(out, options) if parent.name == LI
out << "| " if parent.name == TR && data_table?(parent.parent)

parent.children.each do |node|
if node.text? || node.cdata?
text = node.text
unless options[:pre]
text = node.text.gsub(LINE_BREAK_PATTERN, SPACE).squeeze(SPACE)
text.lstrip! if WHITESPACE.include?(out[-1, 1])
end
out << text
elsif node.name == PLAINTEXT
out << node.text
elsif node.element? && !IGNORE_TAGS.include?(node.name)
convert_node_to_plain_text(node, out, child_options(node, options))

if node.name == BR
out.sub!(TRAILING_WHITESPACE, EMPTY)
out << NEWLINE
elsif node.name == HR
out.sub!(TRAILING_WHITESPACE, EMPTY)
out << NEWLINE unless out.end_with?(NEWLINE)
out << "-------------------------------\n"
elsif node.name == TD || node.name == TH
out << (data_table?(parent.parent) ? TABLE_SEPARATOR : SPACE)
elsif node.name == A
href = node[HREF]
if href &&
href =~ ABSOLUTE_URL_PATTERN &&
node.text =~ NOT_WHITESPACE_PATTERN &&
node.text != href &&
node.text != href[NON_PROTOCOL_PATTERN, 1] # use only text for <a href="mailto:a@b.com">a@b.com</a>
out << " (#{href}) "
end
elsif PARAGRAPH_TAGS.include?(node.name)
append_paragraph_breaks(out)
elsif BLOCK_TAGS.include?(node.name)
append_block_breaks(out)
end
end
end
out
end

# Set formatting options that will be passed to child elements for a tag.
def child_options(node, options)
if node.name == UL
level = options[:ul] || -1
level += 1
options.merge(:list => :ul, :ul => level)
elsif node.name == OL
level = options[:ol] || -1
level += 1
options.merge(:list => :ol, :ol => level, :number => NUMBERS[level % 2])
elsif node.name == PRE
options.merge(:pre => true)
else
options
end
end

# Add double line breaks between paragraph elements. If line breaks already exist,
# new ones will only be added to get to two.
def append_paragraph_breaks(out)
out.sub!(TRAILING_WHITESPACE, EMPTY)
if out.end_with?(NEWLINE)
out << NEWLINE unless out.end_with?("\n\n")
else
out << "\n\n"
end
end

# Add a single line break between block elements. If a line break already exists,
# none will be added.
def append_block_breaks(out)
out.sub!(TRAILING_WHITESPACE, EMPTY)
out << NEWLINE unless out.end_with?(NEWLINE)
end

# Add an appropriate bullet or number to a list element.
def format_list_item(out, options)
if options[:list] == :ul
out << "#{'*' * (options[:ul] + 1)} "
elsif options[:list] == :ol
number = options[:number]
options[:number] = number.next
out << "#{number}. "
end
end

def data_table?(table)
table.attributes['border'].to_s.to_i > 0
end
end
end

使用方式：
require 'plain_text'

content = PlainText.plain_text(desc)