Add (*rdb).forward method using lua script

rdb.go

@@ -185,3 +185,21 @@ func (r *rdb) moveAll(src, dst string) error {
 	}
 	return r.client.Watch(txf, src)
 }
+
+// forward moves all tasks with a score less than the current unix time
+// from the given zset to the default queue.
+func (r *rdb) forward(from string) error {
+	script := redis.NewScript(`
+	local msgs = redis.call("ZRANGEBYSCORE", KEYS[1], "-inf", ARGV[1])
+	for _, msg in ipairs(msgs) do
+		redis.call("ZREM", KEYS[1], msg)
+		redis.call("SADD", KEYS[2], KEYS[3])
+		redis.call("LPUSH", KEYS[3], msg)
+	end
+	return msgs
+	`)
+	now := float64(time.Now().Unix())
+	res, err := script.Run(r.client, []string{from, allQueues, defaultQueue}, now).Result()
+	fmt.Printf("[DEBUGGING LUA} %v, %v\n", res, err)
+	return err
+}

rdb_test.go

@@ -126,3 +126,40 @@ func TestMoveAll(t *testing.T) {
 		t.Errorf("LLEN %q = %d, want %d", defaultQueue, l, len(seed))
 	}
 }
+
+func TestForward(t *testing.T) {
+	r := setup()
+	t1 := randomTask("send_email", defaultQueue)
+	t2 := randomTask("generate_csv", defaultQueue)
+	secondAgo := time.Now().Add(-time.Second) // use timestamp for the past to avoid advancing time
+	json1, err := json.Marshal(t1)
+	if err != nil {
+		t.Fatalf("json.Marshal() failed: %v", err)
+	}
+	json2, err := json.Marshal(t2)
+	if err != nil {
+		t.Fatalf("json.Marshal() failed: %v", err)
+	}
+	client.ZAdd(scheduled, &redis.Z{
+		Member: string(json1),
+		Score:  float64(secondAgo.Unix()),
+	}, &redis.Z{
+		Member: string(json2),
+		Score:  float64(secondAgo.Unix()),
+	})
+
+	err = r.forward(scheduled)
+	if err != nil {
+		t.Fatalf("r.forward() failed: %v", err)
+	}
+
+	if c := client.ZCard(scheduled).Val(); c != 0 {
+		t.Errorf("ZCARD %q = %d, want 0", scheduled, c)
+	}
+	if l := client.LLen(defaultQueue).Val(); l != 2 {
+		t.Errorf("LLEN %q = %d, want 2", defaultQueue, l)
+	}
+	if c := client.SCard(allQueues).Val(); c != 1 {
+		t.Errorf("SCARD %q = %d, want 1", allQueues, c)
+	}
+}