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# frozen_string_literal: true
module Gitlab
module WikiPages
class FrontMatterParser
# We limit the maximum length of text we are prepared to parse as YAML, to
# avoid exploitations and attempts to consume memory and CPU. We allow for:
# - a title line
# - a "slugs:" line
# - and up to 50 slugs
#
# This limit does not take comments into account.
MAX_SLUGS = 50
SLUG_LINE_LENGTH = (4 + Gitlab::WikiPages::MAX_DIRECTORY_BYTES + 1 + Gitlab::WikiPages::MAX_TITLE_BYTES)
MAX_FRONT_MATTER_LENGTH = (8 + Gitlab::WikiPages::MAX_TITLE_BYTES) + 7 + (SLUG_LINE_LENGTH * MAX_SLUGS)
ParseError = Class.new(StandardError)
class Result
attr_reader :front_matter, :content, :reason, :error
def initialize(content:, front_matter: {}, reason: nil, error: nil)
@content = content
@front_matter = front_matter.freeze
@reason = reason
@error = error
end
end
# @param [String] wiki_content
def initialize(wiki_content)
@wiki_content = wiki_content
end
def parse
return empty_result unless wiki_content.present?
return empty_result(block.error) unless block.valid?
Result.new(front_matter: block.data, content: strip_front_matter_block)
rescue ParseError => error
empty_result(:parse_error, error)
end
class Block
include Gitlab::Utils::StrongMemoize
def initialize(delim = nil, lang = '', text = nil)
@lang = lang.downcase.presence || Gitlab::FrontMatter::DELIM_LANG[delim]
@text = text&.strip!
end
def data
@data ||= YAML.safe_load(text, symbolize_names: true)
rescue Psych::DisallowedClass, Psych::SyntaxError => error
raise ParseError, error.message
end
def valid?
error.nil?
end
def error
strong_memoize(:error) { no_match? || too_long? || not_yaml? || not_mapping? }
end
private
attr_reader :lang, :text
def no_match?
:no_match if text.nil?
end
def not_yaml?
:not_yaml if lang != 'yaml'
end
def too_long?
:too_long if text.size > MAX_FRONT_MATTER_LENGTH
end
def not_mapping?
:not_mapping unless data.is_a?(Hash)
end
end
private
attr_reader :wiki_content
def empty_result(reason = nil, error = nil)
Result.new(content: wiki_content, reason: reason, error: error)
end
def block
@block ||= parse_front_matter_block
end
def parse_front_matter_block
wiki_content.match(Gitlab::FrontMatter::PATTERN) { |m| Block.new(m[:delim], m[:lang], m[:front_matter]) } || Block.new
end
def strip_front_matter_block
wiki_content.gsub(Gitlab::FrontMatter::PATTERN, '')
end
end
end
end
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