resize-image lambda@edge function

index.js

'use strict';

const querystring = require('querystring');
const AWS = require('aws-sdk');
const S3 = new AWS.S3({
	signatureVersion: 'v4',
});
const Sharp = require('sharp');

const BUCKET = 'bucket';
const BUCKET_DEV = 'bucket_dev';

// original image path: /{id}/{filename}
// resized image path: /{width}x{height}/{id}/{filename}
const parse = path => {
	let key = path.substring(1);
	let match = key.match(/(\d*)x(\d*)\/(.*)/);
	if (!match) {
		return null;
	}

	let width = parseInt(match[1], 10);
	let height = parseInt(match[2], 10);
	let originalKey = match[3];
	let ext = originalKey.substring(originalKey.lastIndexOf('.') + 1)
	let format = ext == 'jpg' ? 'jpeg' : ext;
	return {
		key, format, originalKey,
		width: width ? width : 0, 
		height: height ? height : 0, 
	}
}

const resize = async (srcBuff, w, h, format) => {
	// TODO resize options 
	return await Sharp(srcBuff)
		.resize(w)
		.toFormat(format)
		.toBuffer();
}

exports.handler = async (event, context) => {
	let response = event.Records[0].cf.response;

	//console.log(`event: ${JSON.stringify(event.Records[0].cf)}`);

	// check if image is not present 
	if (response.status == 404) {
		let request = event.Records[0].cf.request;		
		let path = request.uri;

		// parse data 
		let data = parse(path);
		// if there is no dimension attribute, just pass the response TODO 
		if (!data || (data.width == 0 && data.height == 0)) {
			return response;
		}

		try {
			// get the source image file 
			let srcImage = await S3.getObject({
					Bucket: BUCKET_DEV,
					Key: data.originalKey
				}).promise();
			// resize 
			let resized = await resize(
					srcImage.Body, data.width, data.height, data.format);
			// save the resized object to S3 bucket
			await S3.putObject({
				Body: resized,
				Bucket: BUCKET_DEV,
				ContentType: 'image/' + data.format,
				CacheControl: 'max-age=31536000',
				Key: data.key,
				StorageClass: 'STANDARD'
			}).promise();
			// generate a binary response with resized image 
			response.status = 200;
			response.body = resized.toString('base64');
			response.bodyEncoding = 'base64';
			response.headers['content-type'] = [{ key: 'Content-Type', value: 'image/' + data.format }];
			return response;
		} catch (err) {
			console.log('error occurs while resizing image.', err);
		}
	}
	else {
		// allow the response to pass through
		return response;
	}
}