Added a before_enqueue hook.

docs/HOOKS.md

@@ -66,6 +66,9 @@ An unnamed hook (`before_perform`) will be executed first.
 
 The available hooks are:
 
+* `before _enqueue`: Called with the job args before a job is placed on the queue.
+  If the hook returns `false`, the job will not be placed on the queue.
+
 * `after_enqueue`: Called with the job args after a job is placed on the queue.
   Any exception raised propagates up to the code which queued the job.
 

lib/resque.rb

@@ -224,6 +224,12 @@ def watch_queue(queue)
   #
   # This method is considered part of the `stable` API.
   def enqueue(klass, *args)
+    # Perform before_enqueue hooks. Don't perform enqueue if any hook returns false
+    before_hooks = Plugin.before_enqueue_hooks(klass).collect do |hook|
+      klass.send(hook, *args)
+    end
+    return if before_hooks.any? { |result| result == false }
+
     Job.create(queue_from_class(klass), klass, *args)
 
     Plugin.after_enqueue_hooks(klass).each do |hook|

lib/resque/plugin.rb

@@ -47,5 +47,10 @@ def failure_hooks(job)
     def after_enqueue_hooks(job)
       job.methods.grep(/^after_enqueue/).sort
     end
+
+    # Given an object, returns a list `before_enqueue` hook names.
+    def before_enqueue_hooks(job)
+      job.methods.grep(/^before_enqueue/).sort
+    end
   end
 end

test/job_hooks_test.rb

@@ -250,6 +250,46 @@ def self.perform(history)
   end
 end
 
+
+context "Resque::Job before_enqueue" do
+  include PerformJob
+
+  class ::BeforeEnqueueJob
+    @queue = :jobs
+    def self.before_enqueue_record_history(history)
+      history << :before_enqueue
+    end
+
+    def self.perform(history)
+    end
+  end
+
+  class ::BeforeEnqueueJobAbort
+    @queue = :jobs
+    def self.before_enqueue_abort(history)
+      false
+    end
+
+    def self.perform(history)
+    end
+  end
+
+  test "the before enqueue hook should run" do
+    history = []
+    @worker = Resque::Worker.new(:jobs)
+    Resque.enqueue(BeforeEnqueueJob, history)
+    @worker.work(0)
+    assert_equal history, [:before_enqueue], "before_enqueue was not run"
+  end
+
+  test "a before enqueue hook that returns false should prevent the job from getting queued" do
+    history = []
+    @worker = Resque::Worker.new(:jobs)
+    Resque.enqueue(BeforeEnqueueJobAbort, history)
+    assert_equal 0, Resque.size(:jobs)
+  end
+end
+
 context "Resque::Job all hooks" do
   include PerformJob