Generate Thumbnail on S3 upload

generate-thum.js

// dependencies
const util = require('util');
const sharp = require('sharp');
const AWS = require('aws-sdk');

// get reference to S3 client
const s3 = new AWS.S3();

exports.handler = async (event, context, callback) => {

    // Read options from the event parameter.
    console.log("Reading options from event:\n", util.inspect(event, {depth: 5}));
    const thumbPrefix = "thumb-";
    const srcBucket = event.Records[0].s3.bucket.name;

    // Object key may have spaces or unicode non-ASCII characters.
    const srcKey = decodeURIComponent(event.Records[0].s3.object.key.replace(/\+/g, " "));
    const dstBucket = srcBucket;
    const dstKey = thumbPrefix + srcKey;

    if (srcKey.startsWith(thumbPrefix)) {
        console.log("image already processed.");
        return;
    }

    // Download the image from the S3 source bucket. 
    try {
        const params = {
            Bucket: srcBucket,
            Key: srcKey,
        };
        
        const origimage = await s3.getObject(params).promise();

    } catch (error) {
        console.log(error);
        return;
    }  

    // set thumbnail width. Resize will set the height automatically to maintain aspect ratio.
    const width  = 400;

    // Use the Sharp module to resize the image and save in a buffer.
    try { 
        const buffer = await sharp(origimage.Body)
        		.resize({width: width, withoutEnlargement: true})
        		.withMetadata()
        		.toBuffer();

    } catch (error) {
        console.log(error);
        return;
    } 

    // Upload the thumbnail image to the destination bucket
    try {
        const destparams = {
            Bucket: dstBucket,
            Key: dstKey,
            Body: buffer,
            ContentType: "image"
        };

        const putResult = await s3.putObject(destparams).promise(); 
        
    } catch (error) {
        console.log(error);
        return;
    } 
        
    console.log('Successfully resized ' + srcBucket + '/' + srcKey + ' and uploaded to ' + dstBucket + '/' + dstKey);
};