Class: NatsMessenger

NatsMessenger(config, logger)

Class representing a NATS connection and implements the Messenger interface

Constructor

new NatsMessenger(config, logger)

Create a NatsMessenger instance

Parameters:
Name Type Description
config Config

The connect configuration of the NATS server
logger Object

The central logger of the application

Classes

NatsMessenger

Methods

(async) close()

Shut down the NATS adapter

Drain the connection to the NATS server and close it.

(async) drain()

Drain the connection to NATS

Draining provides for a graceful way to unsubscribe or close a connection
without losing messages that have already been dispatched to the client.

In general, you can drain a subscription or all subscriptions in a connection.
When you drain a subscription, the client sends an unsubscribe protocol message to the server followed by a flush.
The subscription handler is only removed after the server responds.
Thus, all pending messages for the subscription have been processed.

Draining a connection, drains all subscriptions.
However, when you drain the connection it becomes impossible to make new subscriptions or send new requests.
After the last subscription is drained, it also becomes impossible to publish a message.
These restrictions do not exist when just draining a subscription.

(async) flush()

Flushes the pending messages with NATS

Flush sends a PING to the server.
When the server responds with PONG you are guaranteed that all pending data was sent and received by the server.

publish(topic, payload, msgHeaders)

Publish payload and header to a topic

Parameters:
Name Type Description
topic String

The name of the topic (subject in NATS terminology) to that the message must be published.
payload String

The payload of the message.
msgHeaders Object

A flat object (key-value pairs) that represent the headers.
Keys are the header names, and the values are the header values.

request(topic, payload, timeout, headers) → {Object}

Send payload as a request message through the topic subject and expects a response until timeout.
Calls the given callback with the response.

Parameters:
Name Type Description
topic String

The subject to which the request will be sent.
payload String

The content part of the message.
timeout Number

Timeout in milliseconds, until the request waits for the response.
headers Object

The key-value pairs of the request headers in the form of a plain old JavaScript object.
Returns:
  • It holds two properties:
    - payload: The payload of the response
    - headers: The key-value pairs of the response headers
Type
Object

response(topic, respCb) → {Object}

Setup response handler

Subscribes to the topic subject, and waits for incoming request messages.
When message arrives, calls the respCb with the incoming message
and headers and publish its return value and headers to the response subject defined by the incoming message.

Parameters:
Name Type Description
topic String

The name of the subject to wait for the request messages
respCb function

The response callback with arguments of err, requestPayload and requestHeaders.
Returns:
  • The subscription object
Type
Object

(async) start()

Start the NATS adapter

Create a connection to the NATS server using the configuration parameters

subscribe(topic, callback)

Subscribe to the topic subject, and calls the callback function with the inbound messages
so the messages will be processed asychronously.

Parameters:
Name Type Description
topic String

The subject that the subscriber will observe.
callback function

A function, that the subscriber will call, with the following parameters:
err, receivedPayload, receivedHeaders.