add queue.Drain and redisClient.RPop method

queue.go

@@ -28,6 +28,7 @@ type Queue interface {
 	ReturnUnacked(max int64) (int64, error)
 	ReturnRejected(max int64) (int64, error)
 	Destroy() (readyCount, rejectedCount int64, err error)
+	Drain(count int64) ([]string, error)
 
 	// internals
 	// used in cleaner
@@ -459,6 +460,26 @@ func (queue *redisQueue) move(from, to string, max int64) (n int64, error error)
 	return n, nil
 }
 
+// Drain removes and returns 'count' elements from the queue. In case of an error,
+// Drain return all elements removed until the error occurred and the error itself.
+func (queue *redisQueue) Drain(count int64) ([]string, error) {
+	var (
+		n   int64
+		err error
+	)
+	out := make([]string, 0, count)
+
+	for n = 0; n < count; n++ {
+		val, err := queue.redisClient.RPop(queue.readyKey)
+		if err != nil {
+			return out, err
+		}
+		out = append(out, val)
+	}
+
+	return out, err
+}
+
 // Destroy purges and removes the queue from the list of queues
 func (queue *redisQueue) Destroy() (readyCount, rejectedCount int64, err error) {
 	readyCount, err = queue.PurgeReady()

queue_test.go

@@ -750,3 +750,25 @@ func Test_jitteredDuration(t *testing.T) {
 		assert.GreaterOrEqual(t, int64(110*time.Millisecond), int64(d))
 	}
 }
+
+func TestQueueDrain(t *testing.T) {
+	connection, err := OpenConnection("drain-connection", "tcp", "localhost:6379", 1, nil)
+	assert.NoError(t, err)
+	require.NotNil(t, connection)
+
+	queue, err := connection.OpenQueue("drain-queue")
+	assert.NoError(t, err)
+
+	for x := 0; x < 100; x++ {
+		queue.Publish(fmt.Sprintf("%d", x))
+	}
+
+	eventuallyReady(t, queue, 100)
+
+	for x := 1; x <= 10; x++ {
+		values, err := queue.Drain(10)
+		assert.NoError(t, err)
+		assert.Equal(t, 10, len(values))
+		eventuallyReady(t, queue, int64(100-x*10))
+	}
+}

redis_client.go

@@ -14,6 +14,7 @@ type RedisClient interface {
 	LRem(key string, count int64, value string) (affected int64, err error)
 	LTrim(key string, start, stop int64) error
 	RPopLPush(source, destination string) (value string, err error)
+	RPop(key string) (value string, err error)
 
 	// sets
 	SAdd(key, value string) (total int64, err error)

redis_wrapper.go

@@ -43,6 +43,10 @@ func (wrapper RedisWrapper) LTrim(key string, start, stop int64) error {
 	return wrapper.rawClient.LTrim(unusedContext, key, int64(start), int64(stop)).Err()
 }
 
+func (wrapper RedisWrapper) RPop(key string) (value string, err error) {
+	return wrapper.rawClient.RPop(unusedContext, key).Result()
+}
+
 func (wrapper RedisWrapper) RPopLPush(source, destination string) (value string, err error) {
 	value, err = wrapper.rawClient.RPopLPush(unusedContext, source, destination).Result()
 	// println("RPopLPush", source, destination, value, err)

test_queue.go

@@ -43,6 +43,7 @@ func (*TestQueue) ReturnRejected(int64) (int64, error) { panic(errorNotSupported
 func (*TestQueue) PurgeReady() (int64, error)          { panic(errorNotSupported) }
 func (*TestQueue) PurgeRejected() (int64, error)       { panic(errorNotSupported) }
 func (*TestQueue) Destroy() (int64, int64, error)      { panic(errorNotSupported) }
+func (*TestQueue) Drain(count int64) ([]string, error) { panic(errorNotSupported) }
 func (*TestQueue) closeInStaleConnection() error       { panic(errorNotSupported) }
 func (*TestQueue) readyCount() (int64, error)          { panic(errorNotSupported) }
 func (*TestQueue) unackedCount() (int64, error)        { panic(errorNotSupported) }

test_redis_client.go

@@ -11,7 +11,7 @@ import (
 type TestRedisClient struct {
 	store sync.Map
 	ttl   sync.Map
-	mx sync.Mutex
+	mx    sync.Mutex
 }
 
 // NewTestRedisClient returns a NewTestRedisClient
@@ -130,6 +130,29 @@ func (client *TestRedisClient) LPush(key string, values ...string) (total int64,
 	return int64(len(newList)), nil
 }
 
+// RPop removes and returns one value from the tail of the list stored at key.
+// When key holds a value that is not a list, an error is returned.
+func (client *TestRedisClient) RPop(key string) (value string, err error) {
+
+	client.mx.Lock()
+	defer client.mx.Unlock()
+
+	list, err := client.findList(key)
+	// not a list
+	if err != nil {
+		return "", ErrorNotFound
+	}
+	// list is empty
+	if len(list) == 0 {
+		return "", ErrorNotFound
+	}
+
+	// Remove the last element of source (tail)
+	client.storeList(key, list[0:len(list)-1])
+
+	return list[len(list)-1], nil
+}
+
 // LLen returns the length of the list stored at key.
 // If key does not exist, it is interpreted as an empty list and 0 is returned.
 // An error is returned when the value stored at key is not a list.

test_redis_client_test.go

@@ -157,3 +157,20 @@ func TestTestRedisClient_LPush_Len(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, int64(6), total)
 }
+
+func TestTestRedisClient_RPop(t *testing.T) {
+	client := NewTestRedisClient()
+	key := "list-key"
+
+	total, err := client.LPush(key, "1", "2", "3")
+	assert.NoError(t, err)
+	assert.Equal(t, int64(3), total)
+
+	value, err := client.RPop(key)
+	assert.NoError(t, err)
+	assert.Equal(t, "3", value)
+
+	total, err = client.LLen(key)
+	assert.NoError(t, err)
+	assert.Equal(t, int64(2), total)
+}