Kafka integration (#831)

Kafka integration with Fission enables invoking a function when a message arrives in a Kafka topic

pkg/apis/fission.io/v1/const.go

@@ -64,8 +64,9 @@ const (
 )
 
 const (
-	MessageQueueTypeNats = "nats-streaming"
-	MessageQueueTypeASQ  = "azure-storage-queue"
+	MessageQueueTypeNats  = "nats-streaming"
+	MessageQueueTypeASQ   = "azure-storage-queue"
+	MessageQueueTypeKafka = "kafka"
 )
 
 const (

pkg/apis/fission.io/v1/validation.go

@@ -36,6 +36,7 @@ const (
 
 var (
 	validAzureQueueName = regexp.MustCompile("^[a-z0-9][a-z0-9\\-]*[a-z0-9]$")
+	validKafkaTopicName = regexp.MustCompile("^[a-z0-9][a-z0-9\\-._]*[a-z0-9]$")
 )
 
 type (
@@ -164,10 +165,29 @@ func IsTopicValid(mqType MessageQueueType, topic string) bool {
 		return nsUtil.IsChannelNameValid(topic, false)
 	case MessageQueueTypeASQ:
 		return len(topic) >= 3 && len(topic) <= 63 && validAzureQueueName.MatchString(topic)
+	case MessageQueueTypeKafka:
+		return IsValidKafkaTopic(topic)
 	}
 	return false
 }
 
+// The validation is based on Kafka's internal implementation: https://github.com/apache/kafka/blob/trunk/clients/src/main/java/org/apache/kafka/common/internals/Topic.java
+func IsValidKafkaTopic(topic string) bool {
+	if len(topic) == 0 {
+		return false
+	}
+	if topic == "." || topic == ".." {
+		return false
+	}
+	if len(topic) > 249 {
+		return false
+	}
+	if !validKafkaTopicName.MatchString(topic) {
+		return false
+	}
+	return true
+}
+
 func IsValidCronSpec(spec string) error {
 	_, err := cron.Parse(spec)
 	return err
@@ -433,7 +453,7 @@ func (spec MessageQueueTriggerSpec) Validate() error {
 	result = multierror.Append(result, spec.FunctionReference.Validate())
 
 	switch spec.MessageQueueType {
-	case MessageQueueTypeNats, MessageQueueTypeASQ: // no op
+	case MessageQueueTypeNats, MessageQueueTypeASQ, MessageQueueTypeKafka: // no op
 	default:
 		result = multierror.Append(result, MakeValidationErr(ErrorUnsupportedType, "MessageQueueTriggerSpec.MessageQueueType", spec.MessageQueueType, "not a supported message queue type"))
 	}