# frozen_string_literal: true
require "nokogumbo"
require "securerandom"
class HtmlToMarkdown
def initialize(html, opts = {})
@opts = opts
# we're only interested in
@doc = Nokogiri::HTML5(html).at("body")
remove_not_allowed!(@doc)
remove_hidden!(@doc)
hoist_line_breaks!(@doc)
remove_whitespaces!(@doc)
end
def to_markdown
traverse(@doc)
.gsub(/\n{2,}/, "\n\n")
.strip
end
private
def remove_not_allowed!(doc)
allowed = Set.new
HtmlToMarkdown.private_instance_methods.each do |m|
if tag = m.to_s[/^visit_(.+)/, 1]
allowed << tag
end
end
@doc.traverse { |node| node.remove if !allowed.include?(node.name) }
end
HIDDEN_STYLES ||= /(display\s*:\s*none)|(visibility\s*:\s*hidden)|(opacity\s*:\s*0)|(transform\s*:\s*scale\(0\))|((width|height)\s*:\s*0)/i
def remove_hidden!(doc)
@doc.css("[hidden]").remove
@doc.css("[style]").each { |n| n.remove if n["style"][HIDDEN_STYLES] }
@doc.css("img[width]").each { |n| n.remove if n["width"].to_i <= 0 }
@doc.css("img[height]").each { |n| n.remove if n["height"].to_i <= 0 }
end
# When there's a
inside an inline element, split the inline element around the
def hoist_line_breaks!(doc)
klass = "_" + SecureRandom.hex
doc.css("br").each { |br| br.add_class(klass) }
loop do
changed = false
doc.css("br.#{klass}").each do |br|
parent = br.parent
if parent.description.block?
br.remove_class(klass)
else
before, after = parent.children.slice_when { |n| n == br }.to_a
if before.size > 1
b = Nokogiri::XML::Node.new(parent.name, doc)
before[0...-1].each { |c| b.add_child(c) }
parent.previous = b if b.inner_html.present?
end
if after.present?
a = Nokogiri::XML::Node.new(parent.name, doc)
after.each { |c| a.add_child(c) }
parent.next = a if a.inner_html.present?
end
parent.replace(br)
changed = true
end
end
break if !changed
end
end
# Removes most of the unnecessary white spaces for better markdown conversion
# Loosely based on the CSS' White Space Processing Rules (https://www.w3.org/TR/css-text-3/#white-space-rules)
def remove_whitespaces!(node)
return true if "pre" == node.name
node.children.chunk { |n| is_inline?(n) }.each do |inline, nodes|
if inline
collapse_spaces!(nodes) && remove_trailing_space!(nodes)
else
nodes.each { |n| remove_whitespaces!(n) }
end
end
end
def is_inline?(node)
node.text? || ("br" != node.name && node.description&.inline? && node.children.all? { |n| is_inline?(n) })
end
def collapse_spaces!(nodes, was_space = true)
nodes.each do |node|
if node.text?
text = String.new
node.text.chars.each do |c|
if c[/[[:space:]]/]
text << " " if !was_space
was_space = true
else
text << c
was_space = false
end
end
node.content = text
else
node.children.each { |n| was_space = collapse_spaces!([n], was_space) }
end
end
was_space
end
def remove_trailing_space!(nodes)
last = nodes[-1]
if last.text?
last.content = last.content[0...-1] if last.content[-1] == " "
elsif last.children.present?
remove_trailing_space!(last.children)
end
end
def traverse(node)
node.children.map { |n| visit(n) }.join
end
def visit(node)
visitor = "visit_#{node.name}"
send(visitor, node) if respond_to?(visitor, true)
end
ALLOWED_IMG_SRCS ||= %w{http:// https:// www.}
def allowed_hrefs
@allowed_hrefs ||= begin
hrefs = SiteSetting.allowed_href_schemes.split("|").map { |scheme| "#{scheme}:" }.to_set
ALLOWED_IMG_SRCS.each { |src| hrefs << src }
hrefs << "mailto:"
hrefs.to_a
end
end
def visit_a(node)
if node["href"].present? && node["href"].starts_with?(*allowed_hrefs)
"[#{traverse(node)}](#{node["href"]})"
else
traverse(node)
end
end
def visit_img(node)
return if node["src"].blank?
if @opts[:keep_img_tags]
node.to_html
elsif @opts[:keep_cid_imgs] && node["src"].starts_with?("cid:")
node.to_html
elsif node["src"].starts_with?(*ALLOWED_IMG_SRCS)
title = node["alt"].presence || node["title"].presence
width = node["width"].to_i
height = node["height"].to_i
dimensions = "|#{width}x#{height}" if width > 0 && height > 0
"![#{title}#{dimensions}](#{node["src"]})"
end
end
ALLOWED ||= %w{kbd del ins small big sub sup dl dd dt mark}
ALLOWED.each do |tag|
define_method("visit_#{tag}") do |node|
"<#{tag}>#{traverse(node)}"
end
end
def visit_blockquote(node)
text = traverse(node)
text.strip!
text.gsub!(/\n{2,}/, "\n\n")
text.gsub!(/^/, "> ")
"\n\n#{text}\n\n"
end
BLOCKS ||= %w{div tr}
BLOCKS.each do |tag|
define_method("visit_#{tag}") do |node|
prefix = node.previous_element&.description&.block? ? "" : "\n"
"#{prefix}#{traverse(node)}\n"
end
end
def visit_p(node)
"\n\n#{traverse(node)}\n\n"
end
TRAVERSABLES ||= %w{aside font span thead tbody tfooter u}
TRAVERSABLES.each do |tag|
define_method("visit_#{tag}") do |node|
traverse(node)
end
end
def visit_tt(node)
"`#{traverse(node)}`"
end
def visit_code(node)
node.ancestors("pre").present? ? traverse(node) : visit_tt(node)
end
def visit_pre(node)
text = traverse(node)
fence = text["`"] ? "~~~" : "```"
code = node.at("code")
code_class = code ? code["class"] : ""
lang = code_class ? code_class[/lang-(\w+)/, 1] : ""
"\n\n#{fence}#{lang}\n#{traverse(node)}\n#{fence}\n\n"
end
def visit_br(node)
"\n"
end
def visit_hr(node)
"\n\n---\n\n"
end
def visit_abbr(node)
title = node["title"].presence
title_attr = title ? %[ title="#{title}"] : ""
"#{traverse(node)}"
end
def visit_acronym(node)
visit_abbr(node)
end
(1..6).each do |n|
define_method("visit_h#{n}") do |node|
"#{"#" * n} #{traverse(node)}"
end
end
CELLS ||= %w{th td}
CELLS.each do |tag|
define_method("visit_#{tag}") do |node|
"#{traverse(node)} "
end
end
def visit_table(node)
if rows = extract_rows(node)
headers = rows[0].css("td, th")
text = "| " + headers.map { |td| traverse(td).gsub(/\n/, "
") }.join(" | ") + " |\n"
text << "| " + (["-"] * headers.size).join(" | ") + " |\n"
rows[1..-1].each do |row|
text << "| " + row.css("td").map { |td| traverse(td).gsub(/\n/, "
") }.join(" | ") + " |\n"
end
"\n\n#{text}\n\n"
else
traverse(node)
end
end
def extract_rows(table)
return if table.ancestors("table").present?
return if (rows = table.css("tr")).empty?
headers_count = rows[0].css("td, th").size
return if rows[1..-1].any? { |row| row.css("td").size != headers_count }
rows
end
LISTS ||= %w{ul ol}
LISTS.each do |tag|
define_method("visit_#{tag}") do |node|
prefix = node.previous_element&.description&.block? ? "" : "\n"
suffix = node.ancestors("ul, ol, li").size > 0 ? "" : "\n"
"#{prefix}#{traverse(node)}#{suffix}"
end
end
def visit_li(node)
text = traverse(node)
lists = node.ancestors("ul, ol")
marker = "ol" == lists[0]&.name ? "1. " : "- "
indent = (" " * marker.size) * [1, lists.size].max
suffix = node == node.parent.elements[-1] ? "" : "\n"
text.gsub!(/\n{2,}/, "\n\n")
text.gsub!(/^(?!\s*$)/, indent)
text.lstrip!
"#{marker}#{text}#{suffix}"
end
EMPHASES ||= %w{i em}
EMPHASES.each do |tag|
define_method("visit_#{tag}") do |node|
text = traverse(node)
return "" if text.empty?
return " " if text.blank?
return "<#{tag}>#{text}" if text["\n"] || (text["*"] && text["_"])
prefix = text[0][" "]
suffix = text[-1][" "] if text.size > 1
wrap = text["*"] ? "_" : "*"
"#{prefix}#{wrap}#{text.strip}#{wrap}#{suffix}"
end
end
STRONGS ||= %w{b strong}
STRONGS.each do |tag|
define_method("visit_#{tag}") do |node|
text = traverse(node)
return "" if text.empty?
return " " if text.blank?
return "<#{tag}>#{text}" if text["\n"] || (text["*"] && text["_"])
prefix = text[0][" "]
suffix = text[-1][" "] if text.size > 1
wrap = text["*"] ? "__" : "**"
"#{prefix}#{wrap}#{text.strip}#{wrap}#{suffix}"
end
end
STRIKES ||= %w{s strike}
STRIKES.each do |tag|
define_method("visit_#{tag}") do |node|
text = traverse(node)
return "" if text.empty?
return " " if text.blank?
return "<#{tag}>#{text}" if text["\n"] || text["~~"]
prefix = text[0][" "]
suffix = text[-1][" "] if text.size > 1
"#{prefix}~~#{text.strip}~~#{suffix}"
end
end
def visit_text(node)
node.text
end
end