Fix Redis command errors when trying to start app with a readonly Redis.

lib/discourse_redis.rb

@@ -135,9 +135,10 @@ class DiscourseRedis
     options.dup.merge!(host: options[:slave_host], port: options[:slave_port])
   end
 
-  def initialize(config = nil)
+  def initialize(config = nil, namespace: true)
     @config = config || DiscourseRedis.config
     @redis = DiscourseRedis.raw_connection(@config)
+    @namespace = namespace
   end
 
   def self.fallback_handler
@@ -183,29 +184,35 @@ class DiscourseRedis
    :sunion, :ttl, :type, :watch, :zadd, :zcard, :zcount, :zincrby, :zrange, :zrangebyscore, :zrank, :zrem, :zremrangebyrank,
    :zremrangebyscore, :zrevrange, :zrevrangebyscore, :zrevrank, :zrangebyscore].each do |m|
     define_method m do |*args|
-      args[0] = "#{namespace}:#{args[0]}"
+      args[0] = "#{namespace}:#{args[0]}" if @namespace
       DiscourseRedis.ignore_readonly { @redis.send(m, *args) }
     end
   end
 
   def mget(*args)
-    args.map! { |a| "#{namespace}:#{a}" }
+    args.map! { |a| "#{namespace}:#{a}" }  if @namespace
     DiscourseRedis.ignore_readonly { @redis.mget(*args) }
   end
 
   def del(k)
     DiscourseRedis.ignore_readonly do
-      k = "#{namespace}:#{k}"
+      k = "#{namespace}:#{k}"  if @namespace
       @redis.del k
     end
   end
 
   def keys(pattern = nil)
     DiscourseRedis.ignore_readonly do
-      len = namespace.length + 1
-      @redis.keys("#{namespace}:#{pattern || '*'}").map {
-        |k| k[len..-1]
-      }
+      pattern = pattern || '*'
+      pattern = "#{namespace}:#{pattern}" if @namespace
+      keys = @redis.keys(pattern)
+
+      if @namespace
+        len = namespace.length + 1
+        keys.map! { |k| k[len..-1] }
+      end
+
+      keys
     end
   end