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module Banzai
module Filter
# Sanitize HTML
#
# Extends HTML::Pipeline::SanitizationFilter with a custom whitelist.
class SanitizationFilter < HTML::Pipeline::SanitizationFilter
UNSAFE_PROTOCOLS = %w(data javascript vbscript).freeze
def whitelist
whitelist = super
customize_whitelist(whitelist)
whitelist
end
private
def customized?(transformers)
transformers.last.source_location[0] == __FILE__
end
def customize_whitelist(whitelist)
# Only push these customizations once
return if customized?(whitelist[:transformers])
# Allow table alignment
whitelist[:attributes]['th'] = %w(style)
whitelist[:attributes]['td'] = %w(style)
# Allow span elements
whitelist[:elements].push('span')
# Allow html5 details/summary elements
whitelist[:elements].push('details')
whitelist[:elements].push('summary')
# Allow abbr elements with title attribute
whitelist[:elements].push('abbr')
whitelist[:attributes]['abbr'] = %w(title)
# Allow any protocol in `a` elements...
whitelist[:protocols].delete('a')
# ...but then remove links with unsafe protocols
whitelist[:transformers].push(self.class.remove_unsafe_links)
# Remove `rel` attribute from `a` elements
whitelist[:transformers].push(self.class.remove_rel)
whitelist
end
class << self
def remove_unsafe_links
lambda do |env|
node = env[:node]
return unless node.name == 'a'
return unless node.has_attribute?('href')
begin
uri = Addressable::URI.parse(node['href'])
uri.scheme = uri.scheme.strip.downcase if uri.scheme
node.remove_attribute('href') if UNSAFE_PROTOCOLS.include?(uri.scheme)
rescue Addressable::URI::InvalidURIError
node.remove_attribute('href')
end
end
end
def remove_rel
lambda do |env|
if env[:node_name] == 'a'
env[:node].remove_attribute('rel')
end
end
end
end
end
end
end
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