Image Transformation with AWS Lambda

lambda.js

"use strict";

// Dependencies
const async = require("async");
const gm = require("gm").subClass({
    imageMagick: true
});

const aws = require("aws-sdk");
const s3 = new aws.S3();

exports.handle = (event, context, callback) => {
    // Get bucket key
    let imageUserId = event.pathParameters["user_id"];
    let imageFile = event.pathParameters["image_file"];
    let imageKey = `${imageUserId}/${imageFile}`;
  
    // Begin!
    async.waterfall([
        function downloadImage(nextStep) {
            console.time("DownloadImage");
            console.log("Downloading...");
            s3.getObject({
                Bucket: process.env.BUCKET,
                Key: imageKey
            }, nextStep);
            console.timeEnd("DownloadImage");
        },
        function transform(response, nextStep) {
            let imageType = response.ContentType;
            console.log("Image MIME Type before transformation: " + imageType);
            let image = gm(response.Body);
            image.resize(200, 200).quality(60).toBuffer(
                null,
                (err, buffer) => {
                    console.timeEnd("TransformImage");
                    if (err) {
                        nextStep(err);
                    } else {
                        nextStep(null, {
                            type: imageType,
                            image: buffer
                        });
                    }
                });
        },
        function respond(data, nextStep) {
            console.log("Image MIME Type after transformation: " + data.type);
            let response = {
                statusCode: 200,
                headers: {
                    "Content-Type": data.type
                },
                body: data.image.toString('base64'),
                isBase64Encoded: true
            };
            callback(null, response);
        }
    ], (err, result) => {
        if (err) {
            console.error(err);
        }
        callback();
    });
};