CoCalc provides the best real-time collaborative environment for Jupyter Notebooks, LaTeX documents, and SageMath, scalable from individual users to large groups and classes!

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#
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#  Copyright (c) 2008 Kyle Maxwell, contributors
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#
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#  Permission is hereby granted, free of charge, to any person
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#  obtaining a copy of this software and associated documentation
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#  files (the "Software"), to deal in the Software without
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#  restriction, including without limitation the rights to use,
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#  copy, modify, merge, publish, distribute, sublicense, and/or sell
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#  copies of the Software, and to permit persons to whom the
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#  Software is furnished to do so, subject to the following
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#  conditions:
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#
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#  The above copyright notice and this permission notice shall be
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#  included in all copies or substantial portions of the Software.
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#
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#  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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#  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
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#  OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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#  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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#  HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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#  WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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#  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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#  OTHER DEALINGS IN THE SOFTWARE.
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#
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require "open-uri"
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require "uri"
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require "timeout"
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# https://github.com/fizx/robots
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class Robots
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  DEFAULT_TIMEOUT = 3
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  # Represents a parsed robots.txt file
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  class ParsedRobots
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    def initialize(uri, user_agent)
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      @last_accessed = Time.at(1)
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      io = Robots.get_robots_txt(uri, user_agent)
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      if !io || io.content_type != "text/plain" || io.status.first != "200"
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        io = StringIO.new("User-agent: *\nAllow: /\n")
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      end
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      @other = {}
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      @disallows = {}
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      @allows = {}
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      @delays = {} # added delays to make it work
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      agent = /.*/
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      io.each do |line|
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        next if line =~ /^\s*(#.*|$)/
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        arr = line.split(":")
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        key = arr.shift.to_s.downcase
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        value = arr.join(":").strip
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        value.strip!
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        case key
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        when "user-agent"
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          agent = to_regex(value)
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        when "allow"
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          @allows[agent] ||= []
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          @allows[agent] << to_regex(value)
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        when "disallow"
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          @disallows[agent] ||= []
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          @disallows[agent] << to_regex(value)
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        when "crawl-delay"
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          @delays[agent] = value.to_i
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        else
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          @other[key] ||= []
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          @other[key] << value
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        end
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      end
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      @parsed = true
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    end
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    def allowed?(uri, user_agent)
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      return true unless @parsed
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      allowed = true
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      path = uri.request_uri
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      @disallows.each do |key, value|
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        if user_agent =~ key
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          value.each do |rule|
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            allowed = false if path =~ rule
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          end
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        end
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      end
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      @allows.each do |key, value|
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        unless allowed
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          if user_agent =~ key
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            value.each do |rule|
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              if path =~ rule
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                allowed = true
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              end
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            end
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          end
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        end
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      end
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      if allowed && @delays[user_agent]
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        sleep @delays[user_agent] - (Time.now - @last_accessed)
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        @last_accessed = Time.now
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      end
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      return allowed
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    end
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    def other_values
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      @other
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    end
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    protected
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    def to_regex(pattern)
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      return /should-not-match-anything-123456789/ if pattern.strip.empty?
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      pattern = Regexp.escape(pattern)
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      pattern.gsub!(Regexp.escape("*"), ".*")
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      Regexp.compile("^#{pattern}")
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    end
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  end
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  def self.get_robots_txt(uri, user_agent)
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    begin
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      Timeout.timeout(Robots.timeout) do
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        begin
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          URI.join(uri.to_s, "/robots.txt").open("User-Agent" => user_agent)
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        rescue StandardError
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          nil
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        end
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      end
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    rescue Timeout::Error
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      dlog("robots.txt request timed out")
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    end
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  end
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  attr_writer :timeout
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  def self.timeout
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    @timeout || DEFAULT_TIMEOUT
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  end
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  def initialize(user_agent)
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    @user_agent = user_agent
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    @parsed = {}
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  end
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  def allowed?(uri)
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    uri = URI.parse(uri.to_s) unless uri.is_a?(URI)
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    host = uri.host
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    @parsed[host] ||= ParsedRobots.new(uri, @user_agent)
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    @parsed[host].allowed?(uri, @user_agent)
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  end
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  def other_values(uri)
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    uri = URI.parse(uri.to_s) unless uri.is_a?(URI)
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    host = uri.host
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    @parsed[host] ||= ParsedRobots.new(uri, @user_agent)
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    @parsed[host].other_values
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  end
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end
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