add beforeEnqueue hook that allows the enqueue to be cancelled

README.md

@@ -413,6 +413,18 @@ Called whenever a job fails. Arguments passed (in this order) include:
 * Exception - The exception that was thrown when the job failed
 * Resque_Job - The job that failed
 
+#### beforeEnqueue ####
+
+Called immediately before a job is enqueued using the `Resque::enqueue` method.
+Arguments passed (in this order) include:
+
+* Class - string containing the name of the job to be enqueued
+* Arguments - array of arguments for the job
+* Queue - string containing the name of the queue the job is to be enqueued in
+* ID - string containing the token of the job to be enqueued
+
+You can prevent enqueing of the job by throwing an exception of `Resque_Job_DontCreate`.
+
 #### afterEnqueue ####
 
 Called after a job has been queued using the `Resque::enqueue` method. Arguments passed

lib/Resque.php

@@ -201,17 +201,24 @@ class Resque
 	 */
 	public static function enqueue($queue, $class, $args = null, $trackStatus = false)
 	{
-		$result = Resque_Job::create($queue, $class, $args, $trackStatus);
-		if ($result) {
-			Resque_Event::trigger('afterEnqueue', array(
-				'class' => $class,
-				'args'  => $args,
-				'queue' => $queue,
-				'id'    => $result,
-			));
+		$id         = Resque::generateJobId();
+		$hookParams = array(
+			'class' => $class,
+			'args'  => $args,
+			'queue' => $queue,
+			'id'    => $id,
+		);
+		try {
+			Resque_Event::trigger('beforeEnqueue', $hookParams);
+		}
+		catch(Resque_Job_DontCreate $e) {
+			return $id;
 		}
 
-		return $result;
+		Resque_Job::create($queue, $class, $args, $trackStatus, $id);
+		Resque_Event::trigger('afterEnqueue', $hookParams);
+
+		return $id;
 	}
 
 	/**
@@ -341,5 +348,15 @@ class Resque
 	    $result = self::redis()->del('queue:' . $queue);
 	    return ($result == 1) ? $counter : 0;
 	}
+
+	/*
+	 * Generate an identifier to attach to a job for status tracking.
+	 *
+	 * @return string
+	 */
+	public static function generateJobId()
+	{
+		return md5(uniqid('', true));
+	}
 }
 

lib/Resque/Job.php

@@ -50,14 +50,17 @@ class Resque_Job
 	 *
 	 * @return string
 	 */
-	public static function create($queue, $class, $args = null, $monitor = false)
+	public static function create($queue, $class, $args = null, $monitor = false, $id = null)
 	{
+		if (is_null($id)) {
+			$id = Resque::generateJobId();
+		}
+
 		if($args !== null && !is_array($args)) {
 			throw new InvalidArgumentException(
 				'Supplied $args must be an array.'
 			);
 		}
-		$id = md5(uniqid('', true));
 		Resque::push($queue, array(
 			'class'	=> $class,
 			'args'	=> array($args),

lib/Resque/Job/DontCreate.php

@@ -0,0 +1,12 @@
+<?php
+/**
+ * Exception to be thrown if while enqueuing a job it should not be created.
+ *
+ * @package		Resque/Job
+ * @author		Chris Boulton <chris@bigcommerce.com>
+ * @license		http://www.opensource.org/licenses/mit-license.php
+ */
+class Resque_Job_DontCreate extends Exception
+{
+
+}

test/Resque/Tests/EventTest.php

@@ -76,6 +76,18 @@ class Resque_Tests_EventTest extends Resque_Tests_TestCase
 		$this->assertContains($callback, $this->callbacksHit, $event . ' callback (' . $callback .') was not called');
 	}
 
+	public function testBeforeEnqueueEventCallbackFires()
+	{
+		$event = 'beforeEnqueue';
+		$callback = 'beforeEnqueueEventCallback';
+
+		Resque_Event::listen($event, array($this, $callback));
+		Resque::enqueue('jobs', 'Test_Job', array(
+			'somevar'
+		));
+		$this->assertContains($callback, $this->callbacksHit, $event . ' callback (' . $callback .') was not called');
+	}
+
 	public function testBeforePerformEventCanStopWork()
 	{
 		$callback = 'beforePerformEventDontPerformCallback';
@@ -88,10 +100,21 @@ class Resque_Tests_EventTest extends Resque_Tests_TestCase
 		$this->assertFalse(Test_Job::$called, 'Job was still performed though Resque_Job_DontPerform was thrown');
 	}
 
+	public function testBeforeEnqueueEventStopsJobCreation()
+	{
+		$callback = 'beforeEnqueueEventDontCreateCallback';
+		Resque_Event::listen('beforeEnqueue', array($this, $callback));
+		Resque_Event::listen('afterEnqueue', array($this, 'afterEnqueueEventCallback'));
+
+		Resque::enqueue('test_job', 'TestClass');
+		$this->assertContains($callback, $this->callbacksHit, $callback . ' callback was not called');
+		$this->assertNotContains('afterEnqueueEventCallback', $this->callbacksHit, 'afterEnqueue was still called, even though it should not have been');
+	}
+
 	public function testAfterEnqueueEventCallbackFires()
 	{
 		$callback = 'afterEnqueueEventCallback';
-		$event = 'afterEnqueue';
+		$event    = 'afterEnqueue';
 
 		Resque_Event::listen($event, array($this, $callback));
 		Resque::enqueue('jobs', 'Test_Job', array(
@@ -103,7 +126,7 @@ class Resque_Tests_EventTest extends Resque_Tests_TestCase
 	public function testStopListeningRemovesListener()
 	{
 		$callback = 'beforePerformEventCallback';
-		$event = 'beforePerform';
+		$event    = 'beforePerform';
 
 		Resque_Event::listen($event, array($this, $callback));
 		Resque_Event::stopListening($event, array($this, $callback));
@@ -117,13 +140,18 @@ class Resque_Tests_EventTest extends Resque_Tests_TestCase
 		);
 	}
 
-	
 	public function beforePerformEventDontPerformCallback($instance)
 	{
 		$this->callbacksHit[] = __FUNCTION__;
 		throw new Resque_Job_DontPerform;
 	}
 
+	public function beforeEnqueueEventDontCreateCallback($queue, $class, $args, $track = false)
+	{
+		$this->callbacksHit[] = __FUNCTION__;
+		throw new Resque_Job_DontCreate;
+	}
+
 	public function assertValidEventCallback($function, $job)
 	{
 		$this->callbacksHit[] = $function;
@@ -143,6 +171,11 @@ class Resque_Tests_EventTest extends Resque_Tests_TestCase
 		), $args);
 	}
 
+	public function beforeEnqueueEventCallback($job)
+	{
+		$this->callbacksHit[] = __FUNCTION__;
+	}
+
 	public function beforePerformEventCallback($job)
 	{
 		$this->assertValidEventCallback(__FUNCTION__, $job);