KafkaMessageQueue

Implements: MessageQueue

Description

The KafkaMessageQueue class allows you to create message queues that send and receive messages via the Kafka message broker.

Configuration parameters

• topic: name of Kafka topic to subscribe
• group_id: (optional) consumer group id (default: default)
• from_beginning: (optional) restarts receiving messages from the beginning (default: false)
• read_partitions: (optional) number of partitions to be consumed concurrently (default: 1)
• autocommit: (optional) turns on/off autocommit (default: true)
• connection(s):
  • discovery_key: (optional) key to retrieve the connection from IDiscovery
  • host: host name or IP address
  • port: port number
  • uri: resource URI or connection string with all parameters in it
• credential(s):
  • store_key: (optional) key to retrieve the credentials from ICredentialStore
  • username: username
  • password: user’s password
• options:
  • read_partitions: (optional) list of partition indexes to be read (default: all, set for example: “1;5;7”)
  • write_partition: (optional) list of partition indexes to be read (default: auto (-1))
  • autosubscribe: (optional) true to automatically subscribe on option (default: false)
  • log_level: (optional) log level 0 - None, 1 - Error, 2 - Warn, 3 - Info, 4 - Debug (default: 1)
  • connect_timeout: (optional) number of milliseconds to connect to broker (default: 1000)
  • max_retries: (optional) maximum retry attempts (default: 5)
  • retry_timeout: (optional) number of milliseconds to wait on each reconnection attempt (default: 30000)
  • request_timeout: (optional) number of milliseconds to wait on flushing messages (default: 30000)

References

• *:logger:*:*:1.0 - (optional) ILogger components to pass log messages
• *:counters:*:*:1.0 - (optional) ICounters components to pass collected measurements
• *:discovery:*:*:1.0 - (optional) IDiscovery services
• *:credential-store:*:*:1.0 - (optional) ICredentialStore to resolve credentials
• *:connection:kafka:*:1.0 - (optional) shared connection to Kafka service

Constructors

NewKafkaMessageQueue

Creates a new instance of the message queue.

NewKafkaMessageQueue(name string) *KafkaMessageQueue

• name: string - (optional) queue name.

Fields

Methods

Abandon

Returns a message into the queue and makes it available for all subscribers to receive it again. This method is usually used to return a message which could not be processed at the moment, to repeat the attempt. Messages that cause unrecoverable errors shall be removed permanently or/and sent to the dead letter queue.

(c *KafkaMessageQueue) Abandon(ctx context.Context, message *MessageEnvelope) error

• ctx: context.Context - operation context.
• message: *MessageEnvelope - message to return.
• returns: error - error or nil no errors occured.

Clear

Clears a component’s state.

(c *KafkaMessageQueue) Clear(ctx context.Context, correlationId string) error

• ctx: context.Context - operation context.
• correlationId: string - (optional) transaction id used to trace execution through the call chain.
• returns: error - error or nil if no errors occurred.

Cleanup

Cleanup is run at the end of a session, once all ConsumeClaim goroutines have exited but before the offsets are committed for the very last time.

Cleanup(session kafka.ConsumerGroupSession) error

• session: kafka.ConsumerGroupSession - kafka session object.
• returns: error - setup error.

ConsumeClaim

ConsumeClaim must start a consumer loop of ConsumerGroupClaim’s Messages(). Once the Messages() channel is closed, the Handler must finish its processing loop and exit.

ConsumeClaim(session kafka.ConsumerGroupSession, group kafka.ConsumerGroupClaim) error

• session: kafka.ConsumerGroupSession - kafka session object.
• group: kafka.ConsumerGroupClaim - kafka consumer group.
• returns: error - setup error.

Close

Closes a component and frees used resources.

(c *KafkaMessageQueue) Close(ctx context.Context, correlationId string) (err error)

• ctx: context.Context - operation context.
• correlationId: string - (optional) transaction id used to trace execution through the call chain.
• returns: (err error) - error or nil if no errors occurred.

Complete

Permanently removes a message from the queue. This method is usually used to remove the message after successful processing.

(c *KafkaMessageQueue) Complete(ctx context.Context, message *MessageEnvelope) error

• ctx: context.Context - operation context.
• message: *MessageEnvelope - message to remove.
• returns: error - error or nil no errors occured.

Configure

Configures a component by passing its configuration parameters.

(c *KafkaMessageQueue) Configure(ctx context.Context, config *ConfigParams)

• ctx: context.Context - operation context.
• config:: *ConfigParams - configuration parameters to be set.

EndListen

Ends listening for incoming messages. When this method is called, Listen unblocks the thread and execution continues.

(c *KafkaMessageQueue) EndListen(ctx context.Context, correlationId string)

• ctx: context.Context - operation context.
• correlationId: string - (optional) transaction id used to trace execution through the call chain.

fromMessage

Returns the content of a message and information about it.

(c *KafkaMessageQueue) fromMessage(message *MessageEnvelope) (*kafka.ProducerMessage, error)

• message: *MessageEnvelope - message
• returns: (*kafka.ProducerMessage, error) - content of the message and information about it.

GetTopic

Returns the topic.

(c *KafkaMessageQueue) getTopic() string

• returns: string - topic

IsOpen

Checks if the component is open.

(c *KafkaMessageQueue) IsOpen() bool

• returns: bool - true if the component is open and false otherwise.

Listen

Listens for incoming messages and blocks the current thread until the queue is closed.

See IMessageReceiver

(c *KafkaMessageQueue) Listen(ctx context.Context, correlationId string, receiver IMessageReceiver) error

• ctx: context.Context - operation context.
• correlationId: string - (optional) transaction id used to trace execution through the call chain.
• receiver: IMessageReceiver - receiver used to receive incoming messages.
• returns: error - error or nil if no errors occurred.

MoveToDeadLetter

Permanently removes a message from the queue and sends it to the dead letter queue.

• Important: This method is not supported by Kafka.

(c *KafkaMessageQueue) MoveToDeadLetter(ctx context.Context, message *MessageEnvelope) error

• ctx: context.Context - operation context.
• message: *MessageEnvelope - message to be removed.
• returns: error - error or nil if no errors occurred.

OnMessage

Deserializes a message. Then, sends it to a receiver if its set or puts it into the queue.

(c *KafkaMessageQueue) OnMessage(ctx context.Context, msg *KafkaMessage)

• ctx: context.Context - operation context.
• msg: *KafkaMessage - topic

Open

Opens the component.

(c *KafkaMessageQueue) Open(ctx context.Context, correlationId string) (err error)

• ctx: context.Context - operation context.
• correlationId: string - (optional) transaction id used to trace execution through the call chain.
• returns: (err error) - error or nil if no errors occurred.

Peek

Peeks a single incoming message from the queue without removing it. If there are no messages available in the queue, it returns nil.

(c *KafkaMessageQueue) Peek(ctx context.Context, correlationId string) (*MessageEnvelope, error)

• ctx: context.Context - operation context.
• correlationId: string - (optional) transaction id used to trace execution through the call chain.
• returns: (*MessageEnvelope, error) - peeked message.

PeekBatch

Peeks multiple incoming messages from the queue without removing them. If there are no messages available in the queue, it returns an empty list.

(c *KafkaMessageQueue) PeekBatch(ctx context.Context, correlationId string, messageCount int64) ([]*MessageEnvelope, error)

• ctx: context.Context - operation context.
• correlationId: string - (optional) transaction id used to trace execution through the call chain.
• messageCount: int64 - maximum number of messages to peek.
• returns: ([]*MessageEnvelope, error) - list with peeked messages.

ReadMessageCount

Reads the current number of messages in the queue to be delivered.

(c *KafkaMessageQueue) ReadMessageCount() (int64, error)

• *returns: (int64, error) - number of messages in the queue.

Receive

Receives an incoming message and removes it from the queue.

(c *KafkaMessageQueue) Receive(ctx context.Context, correlationId string, waitTimeout time.Duration) (*MessageEnvelope, error)

• ctx: context.Context - operation context.
• correlationId: string - (optional) transaction id used to trace execution through the call chain.
• waitTimeout: time.Duration - timeout in milliseconds to wait for a message to come.
• returns: (*MessageEnvelope, error) - received message or nil if nothing was received.

RenewLock

Renews a lock on a message that makes it invisible from other receivers in the queue. This method is usually used to extend the message processing time.

• Important: This method is not supported by Kafka.

(c *KafkaMessageQueue) RenewLock(ctx context.Context, message *MessageEnvelope, lockTimeout time.Duration) (err error)

• ctx: context.Context - operation context.
• message: *MessageEnvelope - message to extend its lock.
• lockTimeout: time.Duration - locking timeout in milliseconds.
• returns: (err error) - error or nil if no errors occurred.

Ready

Gets channel with flag.

(c *KafkaMessageQueue) Ready() chan bool

• returns: chan bool - channel with bool flag ready.

SetReady

Set new channel for consumer

(c *KafkaMessageQueue) SetReady(chFlag chan bool)

• chFlag: chan bool - channel with ready flag value.

Send

Sends a message into the queue.

(c *KafkaMessageQueue) Send(ctx context.Context, correlationId string, envelop *MessageEnvelope) error

• ctx: context.Context - operation context.
• correlationId: string - (optional) transaction id used to trace execution through the call chain.
• message: *MessageEnvelope - message envelop to be sent.
• returns: error - error or nil if no errors occurred.

SetReferences

Sets references to dependent components.

(c *KafkaMessageQueue) SetReferences(ctx context.Context, references IReferences)

• ctx: context.Context - operation context.
• references: IReferences - references to locate the component’s dependencies.

Setup

Setup is run at the beginning of a new session, before ConsumeClaim.

Setup(session kafka.ConsumerGroupSession) error

• session: kafka.ConsumerGroupSession - kafka session object.
• returns: error - setup error.

subscribe

Subscribes to a topic.

(c *KafkaMessageQueue) subscribe(correlationId string) error

• correlationId: (optional) transaction id used to trace execution through the call chain.
• returns: error - error or nil if no errors occurred.

toMessage

Creates a new MessageEnvelope.

(c *KafkaMessageQueue) toMessage(msg *KafkaMessage)

• msg: *KafkaMessage - message
• returns: (*MessageEnvelope, error) - message

UnsetReferences

Unsets (clears) previously set references to dependent components.

(c *KafkaMessageQueue) UnsetReferences(ctx context.Context)

• ctx: context.Context - operation context.

Examples

ctx := context.Context()
queue := NewKafkaMessageQueue("myqueue")
queue.Configure(ctx, cconf.NewConfigParamsFromTuples(
  "subject", "mytopic",
  "connection.protocol", "kafka",
  "connection.host", "localhost",
  "connection.port", 1883,
))

_ = queue.Open(ctx, "123")

_ = queue.Send(ctx, "123", NewMessageEnvelope("", "mymessage", "ABC"))

message, err := queue.Receive(ctx, "123", 10000*time.Milliseconds)
if (message != nil) {
	...
	queue.Complete(ctx, message)
}

See also

• MessageQueue

• MessagingCapabilities