Add rateLimit option to amqp gateway (#353)

gateways/core/stream/amqp/config.go

@@ -17,6 +17,7 @@ limitations under the License.
 package amqp
 
 import (
+	"errors"
 	"github.com/argoproj/argo-events/common"
 	"github.com/ghodss/yaml"
 	"github.com/sirupsen/logrus"
@@ -46,6 +47,10 @@ type amqp struct {
 	// Connection manages the serialization and deserialization of frames from IO
 	// and dispatches the frames to the appropriate channel.
 	conn *amqplib.Connection
+	// Maximum number of events consumed from the queue per RatePeriod.
+	RateLimit uint32 `json:"rateLimit,omitempty"`
+	// Number of seconds between two consumptions.
+	RatePeriod uint32 `json:"ratePeriod,omitempty"`
 }
 
 func parseEventSource(eventSource string) (interface{}, error) {
@@ -56,3 +61,11 @@ func parseEventSource(eventSource string) (interface{}, error) {
 	}
 	return a, nil
 }
+
+// Validate validates amqp
+func (a *amqp) Validate() error {
+	if (a.RateLimit == 0) != (a.RatePeriod == 0) {
+		return errors.New("RateLimit and RatePeriod must be either set or omitted")
+	}
+	return nil
+}

gateways/core/stream/amqp/start.go

@@ -18,6 +18,7 @@ package amqp
 
 import (
 	"fmt"
+	"time"
 	"github.com/argoproj/argo-events/common"
 	"github.com/argoproj/argo-events/gateways"
 	amqplib "github.com/streadway/amqp"
@@ -44,6 +45,30 @@ func (ese *AMQPEventSourceExecutor) StartEventSource(eventSource *gateways.Event
 	return gateways.HandleEventsFromEventSource(eventSource.Name, eventStream, dataCh, errorCh, doneCh, ese.Log)
 }
 
+func getLimitedDelivery(ch *amqplib.Channel, a *amqp, delivery chan amqplib.Delivery, queue string) {
+	period := time.Duration(a.RatePeriod) * time.Second
+	for {
+		startTime := time.Now()
+
+		for i := uint32(0); i < a.RateLimit; i++ {
+			msg, ok, err := ch.Get(queue, true)
+
+			if err != nil || ok == false {
+				break
+			}
+			delivery <- msg
+
+			if time.Now().After(startTime.Add(period)) {
+				startTime = time.Now()
+				i = 0
+			}
+		}
+
+		remainingTime := startTime.Add(period).Sub(time.Now())
+		time.Sleep(remainingTime)
+	}
+}
+
 func getDelivery(ch *amqplib.Channel, a *amqp) (<-chan amqplib.Delivery, error) {
 	err := ch.ExchangeDeclare(a.ExchangeName, a.ExchangeType, true, false, false, false, nil)
 	if err != nil {
@@ -60,6 +85,12 @@ func getDelivery(ch *amqplib.Channel, a *amqp) (<-chan amqplib.Delivery, error)
 		return nil, fmt.Errorf("failed to bind %s exchange '%s' to queue with routingKey: %s: %s", a.ExchangeType, a.ExchangeName, a.RoutingKey, err)
 	}
 
+	if a.RateLimit != 0 {
+		delivery := make(chan amqplib.Delivery)
+		go getLimitedDelivery(ch, a, delivery, q.Name)
+		return delivery, nil
+	}
+
 	delivery, err := ch.Consume(q.Name, "", true, false, false, false, nil)
 	if err != nil {
 		return nil, fmt.Errorf("failed to begin consuming messages: %s", err)