Let's try this again...

lib/sidekiq.rb

@@ -82,4 +82,22 @@ def self.server_middleware
     @server_chain
   end
 
+  def self.load_json(string, options={})
+    # Can't reliably detect whether MultiJson responds to load, since it's
+    # a reserved word. Use adapter as a proxy for new features.
+    if MultiJson.respond_to?(:adapter)
+      MultiJson.load(string, options)
+    else
+      MultiJson.decode(string, options)
+    end
+  end
+
+  def self.dump_json(object, options={})
+    if MultiJson.respond_to?(:dump)
+      MultiJson.dump(object, options)
+    else
+      MultiJson.encode(object, options)
+    end
+  end
+
 end

lib/sidekiq/client.rb

@@ -45,7 +45,7 @@ def self.push(item)
 
       pushed = false
       Sidekiq.client_middleware.invoke(worker_class, item, queue) do
-        payload = MultiJson.encode(item)
+        payload = Sidekiq.dump_json(item)
         Sidekiq.redis do |conn|
           _, pushed = conn.multi do
             conn.sadd('queues', queue)

lib/sidekiq/manager.rb

@@ -110,7 +110,7 @@ def assign(msg, queue)
           processor = @ready.pop
           @in_progress[processor.object_id] = [msg, queue]
           @busy << processor
-          processor.process!(MultiJson.decode(msg), queue)
+          processor.process!(Sidekiq.load_json(msg), queue)
         end
       end
     end

lib/sidekiq/middleware/client/unique_jobs.rb

@@ -1,5 +1,5 @@
-require 'multi_json'
 require 'digest'
+require 'multi_json'
 
 module Sidekiq
   module Middleware
@@ -10,7 +10,7 @@ class UniqueJobs
         def call(worker_class, item, queue)
           enabled = worker_class.get_sidekiq_options['unique']
           if enabled
-            payload_hash = Digest::MD5.hexdigest(MultiJson.encode(item))
+            payload_hash = Digest::MD5.hexdigest(Sidekiq.dump_json(item))
             unique = false
 
             Sidekiq.redis do |conn|

lib/sidekiq/middleware/server/failure_jobs.rb

@@ -1,3 +1,5 @@
+require 'multi_json'
+
 module Sidekiq
   module Middleware
     module Server
@@ -14,8 +16,7 @@ def call(*args)
             :worker => args[1]['class'],
             :queue => args[2]
           }
-
-          Sidekiq.redis {|conn| conn.rpush(:failed, MultiJson.encode(data)) }
+          Sidekiq.redis {|conn| conn.rpush(:failed, Sidekiq.dump_json(data)) }
           raise
         end
       end

lib/sidekiq/middleware/server/retry_jobs.rb

@@ -1,3 +1,5 @@
+require 'multi_json'
+
 require 'sidekiq/retry'
 
 module Sidekiq
@@ -44,7 +46,7 @@ def call(worker, msg, queue)
             delay = DELAY.call(count)
             logger.debug { "Failure! Retry #{count} in #{delay} seconds" }
             retry_at = Time.now.to_f + delay
-            payload = MultiJson.encode(msg)
+            payload = Sidekiq.dump_json(msg)
             Sidekiq.redis do |conn|
               conn.zadd('retry', retry_at.to_s, payload)
             end

lib/sidekiq/middleware/server/unique_jobs.rb

@@ -1,11 +1,13 @@
+require 'multi_json'
+
 module Sidekiq
   module Middleware
     module Server
       class UniqueJobs
         def call(*args)
           yield
         ensure
-          json = MultiJson.encode(args[1])
+          json = Sidekiq.dump_json(args[1])
           hash = Digest::MD5.hexdigest(json)
           Sidekiq.redis {|conn| conn.del(hash) }
         end

lib/sidekiq/processor.rb

@@ -1,4 +1,5 @@
 require 'celluloid'
+require 'multi_json'
 require 'sidekiq/util'
 
 require 'sidekiq/middleware/server/active_record'
@@ -53,8 +54,8 @@ def stats(worker, msg, queue)
       redis do |conn|
         conn.multi do
           conn.set("worker:#{self}:started", Time.now.to_s)
-          conn.set("worker:#{self}", MultiJson.encode(:queue => queue, :payload => msg,
-                                                   :run_at => Time.now.strftime("%Y/%m/%d %H:%M:%S %Z")))
+          hash = {:queue => queue, :payload => msg, :run_at => Time.now.strftime("%Y/%m/%d %H:%M:%S %Z")}
+          conn.set("worker:#{self}", Sidekiq.dump_json(hash))
         end
       end
 

lib/sidekiq/retry.rb

@@ -46,7 +46,7 @@ def poll
 
             messages.each do |message|
               logger.debug { "Retrying #{message}" }
-              msg = MultiJson.decode(message)
+              msg = Sidekiq.load_json(message)
               conn.rpush("queue:#{msg['queue']}", message)
             end
           end

lib/sidekiq/web.rb

@@ -52,7 +52,7 @@ def workers
           Sidekiq.redis do |conn|
             conn.smembers('workers').map do |w|
               msg = conn.get("worker:#{w}")
-              msg = MultiJson.decode(msg) if msg
+              msg = Sidekiq.load_json(msg) if msg
               [w, msg]
             end.sort { |x| x[1] ? -1 : 1 }
           end
@@ -74,7 +74,7 @@ def retry_count
       def retries
         Sidekiq.redis do |conn|
           results = conn.zrange('retry', 0, 25, :withscores => true)
-          results.each_slice(2).map { |msg, score| [MultiJson.decode(msg), Float(score)] }
+          results.each_slice(2).map { |msg, score| [Sidekiq.load_json(msg), Float(score)] }
         end
       end
 
@@ -89,7 +89,7 @@ def queues
       def retries_with_score(score)
         Sidekiq.redis do |conn|
           results = conn.zrangebyscore('retry', score, score)
-          results.map { |msg| MultiJson.decode(msg) }
+          results.map { |msg| Sidekiq.load_json(msg) }
         end
       end
 
@@ -124,7 +124,7 @@ def relative_time(time)
     get "/queues/:name" do
       halt 404 unless params[:name]
       @name = params[:name]
-      @messages = Sidekiq.redis {|conn| conn.lrange("queue:#{@name}", 0, 10) }.map { |str| MultiJson.decode(str) }
+      @messages = Sidekiq.redis {|conn| conn.lrange("queue:#{@name}", 0, 10) }.map { |str| Sidekiq.load_json(str) }
       slim :queue
     end
 
@@ -142,7 +142,7 @@ def relative_time(time)
           results = conn.zrangebyscore('retry', score, score)
           conn.zremrangebyscore('retry', score, score)
           results.map do |message|
-            msg = MultiJson.decode(message)
+            msg = Sidekiq.load_json(message)
             conn.rpush("queue:#{msg['queue']}", message)
           end
         end

sidekiq.gemspec

@@ -17,7 +17,7 @@ Gem::Specification.new do |gem|
   gem.add_dependency                  'redis-namespace'
   gem.add_dependency                  'connection_pool', '~> 0.9.0'
   gem.add_dependency                  'celluloid', '~> 0.10.0'
-  gem.add_dependency                  'multi_json', '>= 1.0', '< 1.3'
+  gem.add_dependency                  'multi_json', '~> 1.0'
   gem.add_development_dependency      'minitest'
   gem.add_development_dependency      'sinatra'
   gem.add_development_dependency      'slim'

test/test_retry.rb

@@ -1,4 +1,5 @@
 require 'helper'
+require 'multi_json'
 require 'sidekiq/retry'
 require 'sidekiq/middleware/server/retry_jobs'
 
@@ -81,7 +82,7 @@ def @redis.with; yield self; end
     end
 
     it 'should poll like a bad mother...SHUT YO MOUTH' do
-      fake_msg = MultiJson.encode({ 'class' => 'Bob', 'args' => [1,2], 'queue' => 'someq' })
+      fake_msg = Sidekiq.dump_json({ 'class' => 'Bob', 'args' => [1,2], 'queue' => 'someq' })
       @redis.expect :multi, [[fake_msg], 1], []
       @redis.expect :rpush, 1, ['queue:someq', fake_msg]