NatsMessageQueue

Extends: NatsAbstractMessageQueue

Description

The NatsMessageQueue class allows you to create a message queue that sends and receives messages via the NATS message broker.

Configuration parameters

• subject: name of NATS topic (subject) to subscribe
• queue_group: name of NATS queue group
• 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:
  • serialize_message: (optional) true to serialize entire message as JSON, false to send only the message payload (default: true)
  • retry_connect: (optional) turns on/off automated reconnect when connection is lost (default: true)
  • max_reconnect: (optional) maximum number of reconnection attempts (default: 3)
  • reconnect_timeout: (optional) number of milliseconds to wait on each reconnection attempt (default: 3000)
  • flush_timeout: (optional) number of milliseconds to wait on flushing messages (default: 3000)

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:nats:*:1.0 - (optional) shared connection to NATS service

Constructors

Creates a new instance of the message queue.

public constructor(name?: string)

• name: string - (optional) queue name.

Fields

Instance methods

clear

Clears a component’s state.

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

• context: string - (optional) a context to trace execution through a 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.

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.

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) a context to trace execution through a call chain.
• receiver: IMessageReceiver - receiver used to receive incoming messages.

onMessage

Checks if the message is not null. If this is the case, deserializes and sends it to the receiver if it’s set. Otherwise, puts it into the queue.

public onMessage(err: any, msg: any)

• err: any - error
• 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.

• Important: This method is not supported by NATS.

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 - checks if the message comes from the right topic. If this is the case, deserializes and sends it to the receiver if it’s set. Otherwise, puts it into the queue.
• waitTimeout: number - timeout (milliseconds) to wait for a message to come.
• returns: Promise<MessageEnvelope> - received message or null if nothing was received.

subscribe

Subscribes to a subject.

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

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

Examples

let queue = new NatsMessageQueue("myqueue");
queue.configure(ConfigParams.fromTuples(
  "topic", "mytopic",
  "connection.protocol", "nats"
  "connection.host", "localhost"
  "connection.port", 1883
));

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