KafkaMessageQueue

Extends: MessageQueue

Implements: IReferenceable, IUnreferenceable, IConfigurable, IOpenable, ICleanable

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:
  • autosubscribe: (optional) true to automatically subscribe on option (default: false)
  • acks: (optional) control the number of required acks: -1 - all, 0 - none, 1 - only leader (default: -1)
  • 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

Creates a new instance of the message queue.

public constructor(name?: string)

• name: string - (optional) queue name.

Fields

Instance 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 dead letter queue.

public abandon(message: MessageEnvelope): Promise<void>

• message: MessageEnvelope - message to return.

clear

Clears a component’s state.

public clear(context: IContext): Promise<void>

• context: IContext - (optional) transaction id used to trace execution through the call chain.

close

Closes a component and frees used resources.

public close(context: IContext): Promise<void>

• context: IContext - (optional) a context to trace execution through a call chain.

complete

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

public complete(message: MessageEnvelope): Promise<void>

• message: MessageEnvelope - message to remove.

configure

Configures a component by passing its configuration parameters.

public configure(config: ConfigParams): void

• config:: ConfigParams - configuration parameters to be set.

endListen

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

public endListen(context: IContext): void

• context: IContext - (optional) a context to trace execution through a call chain.

fromMessage

Returns the content of a message and information about it.

protected fromMessage(message: MessageEnvelope): any

• message: MessageEnvelope - message
• returns: any - content of the message and information about it.

getTopic

Returns the topic.

protected getTopic(): string

• returns: string - topic

isOpen

Checks if the component is open.

public isOpen(): boolean

• returns: boolean - 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

public listen(context: IContext, receiver: IMessageReceiver): void

• context: IContext - (optional) transaction id used to trace execution through the call chain.
• receiver: IMessageReceiver - receiver used to receive incoming messages.

moveToDeadLetter

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

• Important: This method is not supported by Kafka.

public moveToDeadLetter(message: MessageEnvelope): Promise<void>

• message: MessageEnvelope - message to be removed.

onMessage

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

public onMessage(topic: string, partition: number, msg: any): Promise<void>

• topic: string - topic
• partition: number - partition number
• msg: any - message

open

Opens the component.

public open(context: IContext): Promise<void>

• context: IContext - (optional) a context to trace execution through a call chain.

peek

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

public peek(context: IContext): Promise<MessageEnvelope>

• context: IContext - (optional) a context to trace execution through a call chain.
• returns: Promise<MessageEnvelope> - 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.

public peekBatch(context: IContext, messageCount: number): Promise<MessageEnvelope[]>

• context: IContext - (optional) a context to trace execution through a call chain.
• messageCount: number - maximum number of messages to peek.
• returns: Promise<MessageEnvelope[]> - list with peeked messages.

readMessageCount

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

public readMessageCount(): Promise<number>

• *returns: Promise<number> - number of messages in the queue.

receive

Receives an incoming message and removes it from the queue.

public receive(context: IContext, waitTimeout: number): Promise<MessageEnvelope>

• context: IContext - (optional) a context to trace execution through a call chain.
• waitTimeout: number - timeout in milliseconds to wait for a message to come.
• returns: Promise<MessageEnvelope> - received message or null 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.

public renewLock(message: MessageEnvelope, lockTimeout: number): Promise<void>

• message: MessageEnvelope - message to extend its lock.
• lockTimeout: number - locking timeout in milliseconds.

send

Sends a message into the queue.

public send(context: string, message: MessageEnvelope): Promise<void>

• context: IContext - (optional) a context to trace execution through a call chain.
• message: MessageEnvelope - message envelop to be sent.

setReferences

Sets references to dependent components.

public setReferences(references: IReferences): void

• references: IReferences - references to locate the component dependencies.

subscribe

Subscribes to a topic.

protected subscribe(context: IContext): Promise<void>

• context: IContext (optional) transaction id used to trace execution through the call chain.

toMessage

Creates a new MessageEnvelope.

protected toMessage(msg: any): MessageEnvelope

• msg: any - message
• returns: MessageEnvelope - message

unsetReferences

Unsets (clears) previously set references to dependent components.

public unsetReferences(): void

Examples

let queue = new KafkaMessageQueue("myqueue");
queue.configure(ConfigParams.fromTuples(
  "topic", "mytopic",
  "connection.protocol", "tcp"
  "connection.host", "localhost"
  "connection.port", 9092
));

await queue.open("123");

await queue.send("123", new MessageEnvelope(null, "mymessage", "ABC"));
let message = await queue.receive("123");

if (message != null) {
    ...
    await queue.complete("123", message);
}

See also

• MessageQueue

• MessagingCapabilities