Fix #4125: Detect forum and comment spam.

app/logical/danbooru_logger.rb

@@ -1,4 +1,12 @@
 class DanbooruLogger
+  def self.info(message, params = {})
+    Rails.logger.info(message)
+
+    if defined?(::NewRelic)
+      ::NewRelic::Agent.record_custom_event(:spam, message: message, **params)
+    end
+  end
+
   def self.log(exception, expected: false, **params)
     if expected
       Rails.logger.info("#{exception.class}: #{exception.message}")

app/logical/spam_detector.rb

@@ -4,7 +4,7 @@
 class SpamDetector
   include Rakismet::Model
 
-  attr_accessor :user, :user_ip, :content, :comment_type
+  attr_accessor :record, :user, :user_ip, :content, :comment_type
   rakismet_attrs author: proc { user.name },
                  author_email: proc { user.email },
                  blog_lang: "en",
@@ -24,13 +24,26 @@ class SpamDetector
     false
   end
 
-  def initialize(record)
+  def initialize(record, user_ip: nil)
     case record
     when Dmail
+      @record = record
       @user = record.from
       @content = record.body
       @comment_type = "message"
-      @user_ip = record.creator_ip_addr.to_s
+      @user_ip = user_ip || record.creator_ip_addr.to_s
+    when ForumPost
+      @record = record
+      @user = record.creator
+      @content = record.body
+      @comment_type = record.is_original_post? ? "forum-post" : "reply"
+      @user_ip = user_ip
+    when Comment
+      @record = record
+      @user = record.creator
+      @content = record.body
+      @comment_type = "comment"
+      @user_ip = user_ip || record.creator_ip_addr.to_s
     else
       raise ArgumentError
     end
@@ -39,6 +52,16 @@ class SpamDetector
   def spam?
     return false if !SpamDetector.enabled?
     return false if user.is_gold?
-    super
+
+    is_spam = super
+
+    if is_spam
+      DanbooruLogger.info("Spam detected: user_name=#{user.name} comment_type=#{comment_type} content=#{content.dump}", record.as_json)
+    end
+
+    is_spam
+  rescue => exception
+    DanbooruLogger.log(exception)
+    false
   end
 end

app/models/comment.rb

@@ -2,6 +2,7 @@ class Comment < ApplicationRecord
   include Mentionable
 
   validate :validate_creator_is_not_limited, :on => :create
+  validate :validate_comment_is_not_spam, on: :create
   validates_presence_of :body, :message => "has no content"
   belongs_to :post
   belongs_to_creator
@@ -124,6 +125,10 @@ class Comment < ApplicationRecord
     end
   end
 
+  def validate_comment_is_not_spam
+    errors[:base] << "Failed to create comment" if SpamDetector.new(self).spam?
+  end
+
   def update_last_commented_at_on_create
     Post.where(:id => post_id).update_all(:last_commented_at => created_at)
     if Comment.where("post_id = ?", post_id).count <= Danbooru.config.comment_threshold && !do_not_bump_post?

app/models/forum_post.rb

@@ -15,6 +15,7 @@ class ForumPost < ApplicationRecord
   after_destroy :update_topic_updated_at_on_destroy
   validates_presence_of :body
   validate :validate_topic_is_unlocked
+  validate :validate_post_is_not_spam, on: :create
   validate :topic_is_not_restricted, :on => :create
   before_destroy :validate_topic_is_unlocked
   after_save :delete_topic_if_original_post
@@ -133,6 +134,10 @@ class ForumPost < ApplicationRecord
     votes.where(creator_id: user.id, score: score).exists?
   end
 
+  def validate_post_is_not_spam
+    errors[:base] << "Failed to create forum post" if SpamDetector.new(self, user_ip: CurrentUser.ip_addr).spam?
+  end
+
   def validate_topic_is_unlocked
     return if CurrentUser.is_moderator?
     return if topic.nil?

test/unit/spam_detector.rb

@@ -6,8 +6,8 @@ class SpamDetectorTest < ActiveSupport::TestCase
       skip "SpamDetector not working: API key not configured, not valid, or akismet is down" if !SpamDetector.working?
       SpamDetector.stubs(:enabled?).returns(true)
 
-      @user = create(:gold_user)
-      @spammer = create(:user, email: "akismet-guaranteed-spam@example.com")
+      @user = create(:gold_user, created_at: 1.month.ago)
+      @spammer = create(:user, created_at: 1.month.ago, email: "akismet-guaranteed-spam@example.com")
     end
 
     context "for dmails" do
@@ -26,6 +26,66 @@ class SpamDetectorTest < ActiveSupport::TestCase
         refute(SpamDetector.new(dmail).spam?)
         refute(dmail.is_spam?)
       end
+
+      should "log a message when spam is detected" do
+        Rails.logger.expects(:info)
+        Dmail.create_split(from: @spammer, to: @user, title: "spam", body: "wonderful spam", creator_ip_addr: "127.0.0.1")
+      end
+
+      should "pass messages through if akismet is down" do
+        Rakismet.expects(:akismet_call).raises(StandardError)
+        dmail = create(:dmail, from: @spammer, to: @user, owner: @user, title: "spam", body: "wonderful spam", creator_ip_addr: "127.0.0.1")
+
+        refute(SpamDetector.new(dmail).spam?)
+      end
+    end
+
+    context "for forum posts" do
+      setup do
+        @forum_topic = as(@user) { create(:forum_topic) }
+      end
+
+      should "detect spam" do
+        as(@spammer) do
+          forum_post = build(:forum_post, topic: @forum_topic)
+          forum_post.validate
+
+          assert(SpamDetector.new(forum_post, user_ip: "127.0.0.1").spam?)
+          assert(forum_post.invalid?)
+          assert_equal(["Failed to create forum post"], forum_post.errors.full_messages)
+        end
+      end
+
+      should "not detect gold users as spammers" do
+        as(@user) do
+          forum_post = create(:forum_post, topic: @forum_topic)
+
+          refute(SpamDetector.new(forum_post).spam?)
+          assert(forum_post.valid?)
+        end
+      end
+    end
+
+    context "for comments" do
+      should "detect spam" do
+        as(@spammer) do
+          comment = build(:comment)
+          comment.validate
+
+          assert(SpamDetector.new(comment).spam?)
+          assert(comment.invalid?)
+          assert_equal(["Failed to create comment"], comment.errors.full_messages)
+        end
+      end
+
+      should "not detect gold users as spammers" do
+        as(@user) do
+          comment = create(:comment)
+
+          refute(SpamDetector.new(comment).spam?)
+          assert(comment.valid?)
+        end
+      end
     end
   end
 end