Sample Node.js script for resizing images with the Sharp library

index.js

'use strict';

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

const BUCKET  = process.env.BUCKET  ? process.env.BUCKET : "mybucket";
const URL     = process.env.URL     ? process.env.URL    : "http://localhost:5858"; // for local development
const PRESETS = process.env.PRESETS ? JSON.parse(process.env.PRESETS) : "{}";

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

  const key      = event.queryStringParameters.key;
  const ext      = key.match(/(?:\.([^.]+))?$/)[1].toLocaleLowerCase();
  const format   = ext === "png" ? "png" : "jpeg";
  const writeKey = key;

  let url, preset, resource, dimension, width, height, originalKey = null;
  let quality    = 80;
  let redirect_status = '302';
  let redirect_headers = process.env.URL ? {
    'location': `${URL}/${key}`
  } : {};

  /**
   *  
   * This script will resize images based on pre-defined keywords. 
   * 
   * Sample request:
   *
   *    <bucket>/resized/full/my_picture.jpg
   *
   * The script will parse the path to keyword and picture name. The script will look 
   * for the original resource in <bucket>/original/my_picture.jpg and resize
   * according to the dimension of "full". The mapping of the keyword "full" to actual pixel
   * dimensions is defined in the environment variable PRESETS.
   *
   * The script accepts full dimension requests (width and height specified)
   * and single dimension requests (just width). If both are provided the image
   * will be scaled to this specific dimension. If only width is provided
   * the height will be matched accordingly.
   *
   */

  // get preset (keyword) from URL
  if(url = key.match(/^(resized)\/([a-z_]+)\/(.*)/)) {

    // URL:     resized/full/picture.jpg
    // url         [1]  [2]      [3]
    preset   = url[2]
    resource = url[3]

    if (preset in PRESETS) {

      quality 	  = parseInt(PRESETS[preset].quality);
      originalKey = "original/" + resource // path to original image resource

      // get dimension from keyword
      if (dimension = PRESETS[preset].res.match(/((\d+)x(\d+))/)) {

        // if dimension as WIDTH x HEIGHT (560x430)
        width   = parseInt(dimension[2], 10);
        height  = parseInt(dimension[3], 10);

      } else if (dimension = PRESETS[preset].res.match(/(^(\d+))/)) {

        // if dimension as WIDTH ONLY (560)
        width = parseInt(dimension[2], 10);

      }

    } else {

      callback(null, {
        statusCode: '400',
        headers: {},
        body: 'Not a valid keyword requested [2].',
      });
      return;

    }

  } else {

    callback(null, {
        statusCode: '400',
        headers: {},
        body: 'Not a valid keyword requested [1].',
    });
    return;

  }

  if(width == null){
    callback(null, {
      statusCode: '400',
      headers: {},
      body: 'Not a valid keyword requested [3].',
    });
    return;
  }
 

  /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 
    
    OUTPUT
    
   * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

  if(ext === "gif"){

    /**
     * Pass through *.gif's as it could be animated
     */

    // get original key from S3 with Sharp library, resize and put back to S3
    S3.getObject({Bucket: BUCKET, Key: originalKey}).promise()
      .then(data => S3.putObject({
        Body: data.Body,
        Bucket: BUCKET,
        ContentType: 'image/gif',
        Key: writeKey,
      }).promise())
      .then(() => callback(null, {
        statusCode: redirect_status,
        headers: redirect_headers,
        body: 'Success!',
      }))
      .catch(err => {
        if(err.code === "NoSuchKey") err.message = "Image not found.";
        callback(null, {
          statusCode: err.statusCode,
          body: err.message,
        });
        return;
      })

  } else {

    /**
     * Resize *.jpg and *.png
     */

    // get original key from S3 with Sharp library, resize and put back to S3
    S3.getObject({Bucket: BUCKET, Key: originalKey}).promise()
      .then(data => sharp(data.Body)
        .withoutEnlargement(height==null)
        .resize(width, height)
        .toFormat(format, {quality: quality})
        .toBuffer()
      )
      .then(buffer => S3.putObject({
        Body: buffer,
        Bucket: BUCKET,
        ContentType: 'image/' + format,
        Key: writeKey,
      }).promise()
      )
      .then(() => callback(null, {
        statusCode: redirect_status,
        headers: redirect_headers,
        body: 'Success!',
      })
      )
      .catch(err => {
        if(err.code === "NoSuchKey") err.message = "Image not found.";
        callback(null, {
          statusCode: err.statusCode,
          body: err.message,
        });
        return;
      })

  }

}