config: remove banned_ip_for_download? option.

* Remove `banned_ip_for_download?` config option. This isn't something that usually needs
  to be configured.
* Replace the `ipaddress` gem with `ipaddress_2`. The `ipaddress` gem has several methods
  we need (`link_local?`, etc) that are only available in master because the gem hasn't had
  an official release in several years. `ipaddress_2` is a fork that is more actively
  maintained.

Gemfile

@@ -42,7 +42,7 @@ gem 'builder'
 # gem 'did_you_mean' # github.com/yuki24/did_you_mean/issues/117
 gem 'puma'
 gem 'scenic'
-gem 'ipaddress'
+gem 'ipaddress_2'
 gem 'http'
 gem 'activerecord-hierarchical_query'
 gem 'pundit'

Gemfile.lock

@@ -171,7 +171,7 @@ GEM
       multi_xml (>= 0.5.2)
     i18n (1.8.2)
       concurrent-ruby (~> 1.0)
-    ipaddress (0.8.3)
+    ipaddress_2 (0.13.0)
     jmespath (1.4.0)
     jquery-rails (4.3.5)
       rails-dom-testing (>= 1, < 3)
@@ -443,7 +443,7 @@ DEPENDENCIES
   flamegraph
   http
   httparty
-  ipaddress
+  ipaddress_2
   jquery-rails
   listen
   mail

app/logical/downloads/file.rb

@@ -95,15 +95,25 @@ module Downloads
       ip_addr = IPAddr.new(Resolv.getaddress(url.hostname))
       CloudflareService.new.ips.any? { |subnet| subnet.include?(ip_addr) }
     end
+
+    def self.banned_ip?(ip)
+      ip = IPAddress.parse(ip.to_s) unless ip.is_a?(IPAddress)
+
+      if ip.ipv4?
+        ip.loopback? || ip.link_local? || ip.multicast? || ip.private?
+      elsif ip.ipv6?
+        ip.loopback? || ip.link_local? || ip.unique_local? || ip.unspecified?
+      end
+    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))
+      ip_addr = IPAddress.parse(::Resolv.getaddress(uri.hostname))
 
-      if Danbooru.config.banned_ip_for_download?(ip_addr)
+      if Downloads::File.banned_ip?(ip_addr)
         raise Downloads::File::Error, "Downloads from #{ip_addr} are not allowed"
       end
 

config/danbooru_default_config.rb

@@ -392,39 +392,6 @@ module Danbooru
       "zDMSATq0W3hmA5p3rKTgD"
     end
 
-    # For downloads, if the host matches any of these IPs, block it
-    def banned_ip_for_download?(ip_addr)
-      raise ArgumentError unless ip_addr.is_a?(IPAddr)
-
-      if ip_addr.ipv4?
-        if IPAddr.new("127.0.0.1") == ip_addr
-          true
-        elsif IPAddr.new("169.254.0.0/16").include?(ip_addr)
-          true
-        elsif IPAddr.new("10.0.0.0/8").include?(ip_addr)
-          true
-        elsif IPAddr.new("172.16.0.0/12").include?(ip_addr)
-          true
-        elsif IPAddr.new("192.168.0.0/16").include?(ip_addr)
-          true
-        else
-          false
-        end
-      elsif ip_addr.ipv6?
-        if IPAddr.new("::1") == ip_addr
-          true
-        elsif IPAddr.new("fe80::/10").include?(ip_addr)
-          true
-        elsif IPAddr.new("fd00::/8").include?(ip_addr)
-          true
-        else
-          false
-        end
-      else
-        false
-      end
-    end
-
     # The url of the Discord server associated with this site.
     def discord_server_url
       nil