query_parser.rb

# frozen_string_literal: true

module Rack
  class QueryParser
    (require_relative 'core_ext/regexp'; using ::Rack::RegexpExtensions) if RUBY_VERSION < '2.4'

    DEFAULT_SEP = /[&] */n
    COMMON_SEP = { ";" => /[;] */n, ";," => /[;,] */n, "&" => /[&] */n }

    # ParameterTypeError is the error that is raised when incoming structural
    # parameters (parsed by parse_nested_query) contain conflicting types.
    class ParameterTypeError < TypeError; end

    # InvalidParameterError is the error that is raised when incoming structural
    # parameters (parsed by parse_nested_query) contain invalid format or byte
    # sequence.
    class InvalidParameterError < ArgumentError; end

    # ParamsTooDeepError is the error that is raised when params are recursively
    # nested over the specified limit.
    class ParamsTooDeepError < RangeError; end

    def self.make_default(key_space_limit, param_depth_limit)
      new Params, key_space_limit, param_depth_limit
    end

    attr_reader :key_space_limit, :param_depth_limit

    def initialize(params_class, key_space_limit, param_depth_limit)
      @params_class = params_class
      @key_space_limit = key_space_limit
      @param_depth_limit = param_depth_limit
    end

    # Stolen from Mongrel, with some small modifications:
    # Parses a query string by breaking it up at the '&'.  You can also use this
    # to parse cookies by changing the characters used in the second parameter
    # (which defaults to '&').
    def parse_query(qs, separator = nil, &unescaper)
      unescaper ||= method(:unescape)

      params = make_params

      (qs || '').split(separator ? (COMMON_SEP[separator] || /[#{separator}] */n) : DEFAULT_SEP).each do |p|
        next if p.empty?
        k, v = p.split('=', 2).map!(&unescaper)

        if cur = params[k]
          if cur.class == Array
            params[k] << v
          else
            params[k] = [cur, v]
          end
        else
          params[k] = v
        end
      end

      return params.to_h
    end

    # parse_nested_query expands a query string into structural types. Supported
    # types are Arrays, Hashes and basic value types. It is possible to supply
    # query strings with parameters of conflicting types, in this case a
    # ParameterTypeError is raised. Users are encouraged to return a 400 in this
    # case.
    def parse_nested_query(qs, separator = nil)
      params = make_params

      unless qs.nil? || qs.empty?
        (qs || '').split(separator ? (COMMON_SEP[separator] || /[#{separator}] */n) : DEFAULT_SEP).each do |p|
          k, v = p.split('=', 2).map! { |s| unescape(s) }

          normalize_params(params, k, v, param_depth_limit)
        end
      end

      return params.to_h
    rescue ArgumentError => e
      raise InvalidParameterError, e.message, e.backtrace
    end

    # normalize_params recursively expands parameters into structural types. If
    # the structural types represented by two different parameter names are in
    # conflict, a ParameterTypeError is raised.
    def normalize_params(params, name, v, depth)
      raise ParamsTooDeepError if depth <= 0

      name =~ %r(\A[\[\]]*([^\[\]]+)\]*)
      k = $1 || ''
      after = $' || ''

      if k.empty?
        if !v.nil? && name == "[]"
          return Array(v)
        else
          return
        end
      end

      if after == ''
        params[k] = v
      elsif after == "["
        params[name] = v
      elsif after == "[]"
        params[k] ||= []
        raise ParameterTypeError, "expected Array (got #{params[k].class.name}) for param `#{k}'" unless params[k].is_a?(Array)
        params[k] << v
      elsif after =~ %r(^\[\]\[([^\[\]]+)\]$) || after =~ %r(^\[\](.+)$)
        child_key = $1
        params[k] ||= []
        raise ParameterTypeError, "expected Array (got #{params[k].class.name}) for param `#{k}'" unless params[k].is_a?(Array)
        if params_hash_type?(params[k].last) && !params_hash_has_key?(params[k].last, child_key)
          normalize_params(params[k].last, child_key, v, depth - 1)
        else
          params[k] << normalize_params(make_params, child_key, v, depth - 1)
        end
      else
        params[k] ||= make_params
        raise ParameterTypeError, "expected Hash (got #{params[k].class.name}) for param `#{k}'" unless params_hash_type?(params[k])
        params[k] = normalize_params(params[k], after, v, depth - 1)
      end

      params
    end

    def make_params
      @params_class.new @key_space_limit
    end

    def new_space_limit(key_space_limit)
      self.class.new @params_class, key_space_limit, param_depth_limit
    end

    def new_depth_limit(param_depth_limit)
      self.class.new @params_class, key_space_limit, param_depth_limit
    end

    private

    def params_hash_type?(obj)
      obj.kind_of?(@params_class)
    end

    def params_hash_has_key?(hash, key)
      return false if /\[\]/.match?(key)

      key.split(/[\[\]]+/).inject(hash) do |h, part|
        next h if part == ''
        return false unless params_hash_type?(h) && h.key?(part)
        h[part]
      end

      true
    end

    def unescape(s)
      Utils.unescape(s)
    end

    class Params
      def initialize(limit)
        @limit  = limit
        @size   = 0
        @params = {}
      end

      def [](key)
        @params[key]
      end

      def []=(key, value)
        @size += key.size if key && !@params.key?(key)
        raise ParamsTooDeepError, 'exceeded available parameter key space' if @size > @limit
        @params[key] = value
      end

      def key?(key)
        @params.key?(key)
      end

      # Recursively unwraps nested `Params` objects and constructs an object
      # of the same shape, but using the objects' internal representations
      # (Ruby hashes) in place of the objects. The result is a hash consisting
      # purely of Ruby primitives.
      #
      #   Mutation warning!
      #
      #   1. This method mutates the internal representation of the `Params`
      #      objects in order to save object allocations.
      #
      #   2. The value you get back is a reference to the internal hash
      #      representation, not a copy.
      #
      #   3. Because the `Params` object's internal representation is mutable
      #      through the `#[]=` method, it is not thread safe. The result of
      #      getting the hash representation while another thread is adding a
      #      key to it is non-deterministic.
      #
      def to_h
        @params.each do |key, value|
          case value
          when self
            # Handle circular references gracefully.
            @params[key] = @params
          when Params
            @params[key] = value.to_h
          when Array
            value.map! { |v| v.kind_of?(Params) ? v.to_h : v }
          else
            # Ignore anything that is not a `Params` object or
            # a collection that can contain one.
          end
        end
        @params
      end
      alias_method :to_params_hash, :to_h
    end
  end
end