@parcellab/sqs-consumer

sqs-consumer

Build SQS-based applications without the boilerplate. Just define an async function that handles the SQS message processing. (Forked from bbc/sqs-consumer)

Installation

npm install @parcellab/sqs-consumer --save

Usage

const { Consumer } = require('@parcellab/sqs-consumer');

const app = Consumer.create({
  queueUrl: 'https://sqs.eu-west-1.amazonaws.com/account-id/queue-name',
  handleMessage: async (message) => {
    // do some work with `message`
  }
});

app.on('error', (err) => {
  console.error(err.message);
});

app.on('processing_error', (err) => {
  console.error(err.message);
});

app.start();

• The queue is polled continuously for messages using long polling.
• Messages are deleted from the queue once the handler function has completed successfully.
• Throwing an error (or returning a rejected promise) from the handler function will cause the message to be left on the queue. An SQS redrive policy can be used to move messages that cannot be processed to a dead letter queue.
• By default messages are processed one at a time – a new message won't be received until the first one has been processed. To process messages in parallel, use the batchSize option detailed below.

Credentials

By default the consumer will look for AWS credentials in the places specified by the AWS SDK. The simplest option is to export your credentials as environment variables:

export AWS_SECRET_ACCESS_KEY=...
export AWS_ACCESS_KEY_ID=...

If you need to specify your credentials manually, you can use a pre-configured instance of the AWS SQS client:

const { Consumer } = require('sqs-consumer');
const AWS = require('aws-sdk');

AWS.config.update({
  region: 'eu-west-1',
  accessKeyId: '...',
  secretAccessKey: '...'
});

const app = Consumer.create({
  queueUrl: 'https://sqs.eu-west-1.amazonaws.com/account-id/queue-name',
  handleMessage: async (message) => {
    // ...
  },
  sqs: new AWS.SQS()
});

app.on('error', (err) => {
  console.error(err.message);
});

app.on('processing_error', (err) => {
  console.error(err.message);
});

app.on('timeout_error', (err) => {
 console.error(err.message);
});

app.start();

Extra: handleMessageBatchControlled

Since handleMessageBatch won't delete any of the messages from the queue if the handler failed, you can use this if you want more control of the process.
handleMessageBatchControlled works same as handleMessageBatch BUT you HAVE to return an Array of messages that should be deleted from the list. If no Array is returned, no messages will be removed!
Whit handleMessageBatchControlled you can deal with a batch of messages and then handle the failed ones with the option to delete the succeeded messages.

Implementation example

const app = Consumer.create({
  queueUrl: 'https://sqs.eu-west-1.amazonaws.com/account-id/queue-name',
  sqs: new AWS.SQS(),
  batchSize: 10,
  handleMessageBatchControlled: async (messages) => {
    let succeededMessages = await Promise.all(messages.map(doSomeAsyncWork))
    .filter(msg => !!msg) // filter out all null/falsy
    return succeededMessages // return array of messages (to delete from SQS)
  },
});

// how you could handle the message batch:
// -> this function should not throw Errors and return a message if succeeded
// -> if this function will throw an Error, none of the messages will be deleted
async function doSomeAsyncWork (message) {
  try {
    // do some stuff ...
    return message // ... return the message if succeeded
  } catch (err) {
    console.log(err) // handle err ...
    return null // ... return e.g. null if failed
  }
}

API

Consumer.create(options)

Creates a new SQS consumer.

Options

• queueUrl - String - The SQS queue URL
• region - String - The AWS region (default eu-west-1)
• handleMessage - Function - An async function (or function that returns a Promise) to be called whenever a message is received. Receives an SQS message object as it's first argument.
• handleMessageBatch - Function - An async function (or function that returns a Promise) to be called whenever a batch of messages is received. Similar to handleMessage but will receive the list of messages, not each message individually. If both are set, handleMessageBatch overrides handleMessage.
• handleMessageBatchControlled - Function - An async function (or function that returns a Promise) to be called whenever a batch of messages is received. Similar to handleMessageBath but the Promise HAS to return a list of messages that should be deleted from SQS. If the Promise does not return a list of messages, handleMessageBatch won't delete anything from the queue!.
• handleMessageTimeout - String - Time in ms to wait for handleMessage to process a message before timing out. Emits timeout_error on timeout. By default, if handleMessage times out, the unprocessed message returns to the end of the queue.
• attributeNames - Array - List of queue attributes to retrieve (i.e. ['All', 'ApproximateFirstReceiveTimestamp', 'ApproximateReceiveCount']).
• messageAttributeNames - Array - List of message attributes to retrieve (i.e. ['name', 'address']).
• batchSize - Number - The number of messages to request from SQS when polling (default 1). This cannot be higher than the AWS limit of 10.
• visibilityTimeout - Number - The duration (in seconds) that the received messages are hidden from subsequent retrieve requests after being retrieved by a ReceiveMessage request.
• terminateVisibilityTimeout - Boolean - If true, sets the message visibility timeout to 0 after a processing_error (defaults to false).
• waitTimeSeconds - Number - The duration (in seconds) for which the call will wait for a message to arrive in the queue before returning.
• authenticationErrorTimeout - Number - The duration (in milliseconds) to wait before retrying after an authentication error (defaults to 10000).
• pollingWaitTimeMs - Number - The duration (in milliseconds) to wait before repolling the queue (defaults to 0).
• sqs - Object - An optional AWS SQS object to use if you need to configure the client manually

consumer.start()

Start polling the queue for messages.

consumer.stop()

Stop polling the queue for messages.

consumer.isRunning

Returns the current polling state of the consumer: true if it is actively polling, false if it is not.

Events

Each consumer is an EventEmitter and emits the following events:

Event	Params	Description
error	err, [message]	Fired when an error occurs interacting with the queue. If the error correlates to a message, that error is included in Params
processing_error	err, message	Fired when an error occurs processing the message.
timeout_error	err, message	Fired when handleMessageTimeout is supplied as an option and if handleMessage times out.
message_received	message	Fired when a message is received.
message_processed	message	Fired when a message is successfully processed and removed from the queue.
response_processed	None	Fired after one batch of items (up to batchSize) has been successfully processed.
stopped	None	Fired when the consumer finally stops its work.
empty	None	Fired when the queue is empty (All messages have been consumed).

AWS IAM Permissions

Consumer will receive and delete messages from the SQS queue. Ensure sqs:ReceiveMessage and sqs:DeleteMessage access is granted on the queue being consumed.

Contributing

See contributing guildlines