Revert "Bump redis to 4.2.0."

Revert “Bump redis to 4.2.0.”

This reverts commit 98bc28cea259b823552e1b953506bcf2f76347a9.

diff --git a/Gemfile.lock b/Gemfile.lock
index 3aee171..2870d86 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -310,7 +310,7 @@ GEM
       msgpack (>= 0.4.3)
       optimist (>= 3.0.0)
     rchardet (1.8.0)
-    redis (4.2.0)
+    redis (4.1.4)
     redis-namespace (1.7.0)
       redis (>= 3.0.4)
     regexp_parser (1.7.1)
diff --git a/config/initializers/002-rails_failover.rb b/config/initializers/002-rails_failover.rb
index 2b84cf1..54692b7 100644
--- a/config/initializers/002-rails_failover.rb
+++ b/config/initializers/002-rails_failover.rb
@@ -65,7 +65,7 @@ if ENV["ACTIVE_RECORD_RAILS_FAILOVER"]
   end
 
   RailsFailover::ActiveRecord.register_force_reading_role_callback do
-    Discourse.redis.exists?(
+    Discourse.redis.exists(
       Discourse::PG_READONLY_MODE_KEY,
       Discourse::PG_FORCE_READONLY_MODE_KEY
     )
diff --git a/lib/admin_confirmation.rb b/lib/admin_confirmation.rb
index 28f305b..dc132b7 100644
--- a/lib/admin_confirmation.rb
+++ b/lib/admin_confirmation.rb
@@ -43,7 +43,7 @@ class AdminConfirmation
   end
 
   def self.exists_for?(user_id)
-    Discourse.redis.exists? "admin-confirmation:#{user_id}"
+    Discourse.redis.exists "admin-confirmation:#{user_id}"
   end
 
   def self.find_by_code(token)
diff --git a/lib/discourse.rb b/lib/discourse.rb
index 2706629..67ac64c 100644
--- a/lib/discourse.rb
+++ b/lib/discourse.rb
@@ -489,7 +489,7 @@ module Discourse
   end
 
   def self.readonly_mode?(keys = READONLY_KEYS)
-    recently_readonly? || Discourse.redis.exists?(*keys)
+    recently_readonly? || Discourse.redis.exists(*keys)
   end
 
   def self.pg_readonly_mode?
diff --git a/lib/discourse_redis.rb b/lib/discourse_redis.rb
index 9ca18dc..096c86b 100644
--- a/lib/discourse_redis.rb
+++ b/lib/discourse_redis.rb
@@ -193,7 +193,7 @@ class DiscourseRedis
   end
 
   # Proxy key methods through, but prefix the keys with the namespace
-  [:append, :blpop, :brpop, :brpoplpush, :decr, :decrby, :expire, :expireat, :exists, :exists?, :get, :getbit, :getrange, :getset,
+  [:append, :blpop, :brpop, :brpoplpush, :decr, :decrby, :expire, :expireat, :get, :getbit, :getrange, :getset,
    :hdel, :hexists, :hget, :hgetall, :hincrby, :hincrbyfloat, :hkeys, :hlen, :hmget, :hmset, :hset, :hsetnx, :hvals, :incr,
    :incrby, :incrbyfloat, :lindex, :linsert, :llen, :lpop, :lpush, :lpushx, :lrange, :lrem, :lset, :ltrim,
    :mapped_hmset, :mapped_hmget, :mapped_mget, :mapped_mset, :mapped_msetnx, :move, :mset,
@@ -207,6 +207,19 @@ class DiscourseRedis
     end
   end
 
+  # Implement our own because https://github.com/redis/redis-rb/issues/698 has stalled
+  def exists(*keys)
+    keys.map! { |a| "#{namespace}:#{a}" }  if @namespace
+
+    DiscourseRedis.ignore_readonly do
+      @redis.synchronize do |client|
+        client.call([:exists, *keys]) do |value|
+          value > 0
+        end
+      end
+    end
+  end
+
   def mget(*args)
     args.map! { |a| "#{namespace}:#{a}" }  if @namespace
     DiscourseRedis.ignore_readonly { @redis.mget(*args) }
diff --git a/spec/components/discourse_redis_spec.rb b/spec/components/discourse_redis_spec.rb
index abc9a59..8e44116 100644
--- a/spec/components/discourse_redis_spec.rb
+++ b/spec/components/discourse_redis_spec.rb
@@ -87,6 +87,31 @@ describe DiscourseRedis do
         expect(Discourse.recently_readonly?).to eq(true)
       end
     end
+
+    describe '.exists' do
+      it 'should return false when key is not present' do
+        expect(Discourse.redis.exists('test')).to eq(false)
+      end
+
+      it 'should return false when keys are not present' do
+        expect(Discourse.redis.exists('test', 'test2')).to eq(false)
+      end
+
+      it 'should return true when key is present' do
+        Discourse.redis.set('test', 1)
+
+        expect(Discourse.redis.exists('test')).to eq(true)
+      end
+
+      it 'should return true when any key is present' do
+        Discourse.redis.set('test', 1)
+        Discourse.redis.set('test2', 1)
+
+        expect(Discourse.redis.exists('test')).to eq(true)
+        expect(Discourse.redis.exists('test', 'test2')).to eq(true)
+        expect(Discourse.redis.exists('test2', 'test3')).to eq(true)
+      end
+    end
   end
 
   context '.slave_host' do

GitHub sha: a3dfd553