Sample Lambda Code for Image Conversion on S3

image-conversion-lambda-s3.js

'use strict';

const AWS = require('aws-sdk');

const S3 = new AWS.S3({ apiVersion: '2006-03-01' });

const Sharp = require('sharp');

const outputBucket = 'output-bucket-name';

const config = [
{
  'key': 'small',
  'maxHeight': 320,
  'format': 'webp',
  'options': {'quality': 100}
},
{
  'key': 'med',
  'maxHeight': 640,
  'format': 'webp',
  'options': {'quality': 100}
},
{
  'key': 'large',
  'maxHeight': 960,
  'format': 'webp',
  'options': {'quality': 100}
},
{
  'key': 'preview',
  'maxHeight': 42,
  'format': 'webp',
  'options': {'quality': 10}
}
];

let resizeParams = {
  fit: Sharp.fit.inside,
  withoutEnlargement: true
};

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

  // get the bucket name for uploaded image
  const bucket = event.Records[0].s3.bucket.name;
  // get the path for the uploaded image
  const key = decodeURIComponent(event.Records[0].s3.object.key.replace(/\+/g, ' '));
  console.log('New image uploaded: ', key);
  // get filename by removing the extension
  const name = key.split('.')[0];

  const params = {
    Bucket: bucket,
    Key: key,
  };

  // get the image data from S3
  S3.getObject(params).promise().then(data => {
    
    const image = data.Body;
    let promises = [];
    console.log('image data fetched');

    // iterate over output image configurations
    for (let i = 0; i < config.length; i++) {
      
      let c = config[i];

      // set the height param to max allowed height for current config
      resizeParams['height'] = c['maxHeight'];
      // resize the image using Sharp
      let bufferPromise = Sharp(image).resize(resizeParams).toFormat(c['format'], c['options']).toBuffer()
      let s = Promise.all([bufferPromise, c])
      .then(([buffer, c]) => {
        // put the new image back in S3 output bucket
        return S3.putObject({
          Body: buffer,
          Bucket: outputBucket,
          ContentType: `image/${c['format']}`,
          Key: `resized/${name}-${c['key']}.${c['format']}`
        }).promise()
      });
      promises.push(s);
    }
    return Promise.all(promises);
  })
  .then(() => {
    callback(null, 'success');
  })
  .catch(err => {
    console.log('error: ', err);
    callback(`error: ${err}`);
  });
};