FIX: Topic view not working when Redis is readonly.

app/services/random_topic_selector.rb

@@ -47,7 +47,12 @@ class RandomTopicSelector
       $redis.ltrim(key, count, -1)
     end
 
-    results = results[0]
+    if !results.is_a?(Array) # Redis is in readonly mode
+      results = $redis.lrange(key, 0, count-1)
+    else
+      results = results[0]
+    end
+
     results.map!(&:to_i)
 
     left = count - results.length

spec/services/random_topic_selector_spec.rb

@@ -11,8 +11,15 @@ describe RandomTopicSelector do
       $redis.rpush key, t
     end
 
+    expect(RandomTopicSelector.next(0)).to eq([])
     expect(RandomTopicSelector.next(2)).to eq([0,1])
+
+    $redis.expects(:multi).returns(Discourse.received_readonly!)
     expect(RandomTopicSelector.next(2)).to eq([2,3])
+    $redis.unstub(:multi)
+
+    expect(RandomTopicSelector.next(2)).to eq([2,3])
+    expect(RandomTopicSelector.next(2)).to eq([])
   end
 
   it 'can correctly backfill' do