Overview

@shutterstock/chunker calls a blocking async callback before adding an item that would exceed a user-defined size limit OR when the count of items limit is reached.

A common use case for @shutterstock/chunker is as a "batch accumulator" that gathers up items to be processed in a batch where the batch has specific count and size constraints that must be followed. For example, sending batches to an AWS Kinesis Data Stream requires that there be 500 or less records totalling 5 MB or less in size (see AWS Kinesis PutRecords) . The record count part is easy, but the record size check and handling both is more difficult.

Getting Started

Installation

The package is available on npm as @shutterstock/chunker

npm i @shutterstock/chunker

Importing

import { Chunker } from '@shutterstock/chunker';

API Documentation

After installing the package, you might want to look at our API Documentation to learn about all the features available.

Chunker

Chunker has a BlockingQueue that it uses to store items until the size or count limits are reached. When the limits are reached, the Chunker calls the user-provided callback with the items in the queue. The callback is expected to return a Promise that resolves when the items have been processed. The Chunker will wait for the Promise to resolve before continuing.

See below for an example of using Chunker to write batches of records to an AWS Kinesis Data Stream.

Contributing

Setting up Build Environment

• nvm use
• npm i
• npm run build
• npm run lint
• npm run test

Running Examples

aws-kinesis-writer

1. Create Kinesis Data Stream using AWS Console or any other method
   1. Example: aws kinesis create-stream --stream-name chunker-test-stream --shard-count 1
   2. Default name is chunker-test-stream
   3. 1 shard is sufficient
   4. 1 day retention is sufficient
   5. No encryption is sufficient
   6. On-demand throughput is sufficient
2. npm run example:aws-kinesis-writer
   1. If the stream name was changed: KINESIS_STREAM_NAME=my-stream-name npm run example:aws-kinesis-writer
3. Observe in the log output that the enqueue method intermittently blocks when the count or size constraints would be breached. During the block the records are written to the Kinesis Data Stream, after which the block is released and the new item is added to the next batch.