Websites/app/logical/file_download.rb

# frozen_string_literal: true

class FileDownload
  include ActiveModel::Validations
  class Error < StandardError; end

  RETRIABLE_ERRORS = [Errno::ECONNRESET, Errno::ETIMEDOUT, Errno::EIO, Errno::EHOSTUNREACH, Errno::ECONNREFUSED, Timeout::Error, IOError].freeze
  MAX_SIZE = 100.megabytes

  attr_reader :url

  validate :validate_url

  def initialize(url)
    begin
      unencoded = Addressable::URI.unencode(url)
      escaped = Addressable::URI.escape(unencoded)
      @url = Addressable::URI.parse(escaped)
    rescue Addressable::URI::InvalidURIError
      @url = nil
    end
    validate!
  end

  def size
    res = HTTParty.head(uncached_url, **httparty_options, timeout: 3)

    if res.success?
      res.content_length
    else
      raise(HTTParty::ResponseError, res)
    end
  end

  def download!(tries: 3, **)
    Retriable.retriable(on: RETRIABLE_ERRORS, tries: tries, base_interval: 0) do
      http_get_streaming(uncached_url, **)
    end
  end

  def validate_url
    errors.add(:base, "URL must not be blank") if url.blank?
    errors.add(:base, "'#{url}' is not a valid url") if url.host.blank?
    errors.add(:base, "'#{url}' is not a valid url. Did you mean 'https://#{url}'?") unless url.scheme.in?(%w[http https])
  end

  def http_get_streaming(url, file: Tempfile.new(binmode: true), max_size: MAX_SIZE)
    size = 0

    res = HTTParty.get(url, httparty_options) do |chunk|
      next if [301, 302].include?(chunk.code)

      size += chunk.size
      raise(Error, "File is too large (max size: #{max_size})") if size > max_size && max_size > 0

      file.write(chunk)
    end

    if res.success?
      file.rewind
      file
    else
      raise("HTTP error code: #{res.code} #{res.message}")
    end
  end

  # Prevent Cloudflare from potentially mangling the image
  def uncached_url
    return file_url unless is_cloudflare?(file_url)

    url = file_url.dup
    url.query_values = url.query_values.to_h.merge(nc: Time.now.to_i)
    url
  end

  alias file_url url

  def httparty_options
    {
      timeout:            10,
      stream_body:        true,
      connection_adapter: ValidatingConnectionAdapter,
    }.deep_merge(Websites.config.httparty_options)
  end

  def is_cloudflare?(url)
    ip_addr = IPAddr.new(Resolv.getaddress(url.hostname))
    CloudflareService.ips.any? { |subnet| subnet.include?(ip_addr) }
  end
end

# Hook into HTTParty to validate the IP before following redirects.
# https://www.rubydoc.info/github/jnunemaker/httparty/HTTParty/ConnectionAdapter
class ValidatingConnectionAdapter < HTTParty::ConnectionAdapter
  def self.call(uri, options)
    ip_addr = IPAddr.new(Resolv.getaddress(uri.hostname))
    raise(FileDownload::Error, "Downloads from #{ip_addr} are not allowed") if ip_blocked?(ip_addr)
    super
  end

  def self.ip_blocked?(ip_addr)
    ip_addr.private? || ip_addr.loopback? || ip_addr.link_local?
  end
end