Sample JavaScript code for resizing pictures on AWS Lambda

aws-lambda-picture-resize

/**
 * This is based on: http://docs.aws.amazon.com/lambda/latest/dg/walkthrough-s3-events-adminuser.html
 */
// dependencies
var async = require('async');
var AWS = require('aws-sdk');
var gm = require('gm').subClass({ imageMagick: true }); // Enable ImageMagick integration.
var util = require('util');

var MAX_WIDTH;
var MAX_HEIGHT;

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

exports.handler = function(event, context) {
  // Read options from the event.
  console.log("Reading options from event:\n", util.inspect(event, {depth: 5}));
  var srcBucket = event.Records[0].s3.bucket.name;
  var srcKey    = event.Records[0].s3.object.key;
  var dstBucket = "";
  var dstKey    = srcKey;
  if (srcBucket  == "source-bucket") {
      // This is the original picture, so it is Stage 1
      // which resizes to a 100x100 thumbnail
      dstBucket = "thumbnails-bucket";
      MAX_HEIGHT = 100;
      MAX_WIDTH = 100;

  } else {

      console.error("Resize stage not recognized.");
      return;

  }

  // Sanity check: validate that source and destination are different buckets.
  if (srcBucket == dstBucket) {
    console.error("Destination bucket must not match source bucket.");
    return;
  }

  // Infer the image type.
  var typeMatch = srcKey.match(/\.([^.]*)$/);
  if (!typeMatch) {
    console.error('unable to infer image type for key ' + srcKey);
    return;
  }
  var imageType = typeMatch[1];
  if (imageType != "jpg" && imageType != "jpeg" && imageType != "png") {
    console.log('skipping non-image ' + srcKey);
    return;
  }

  // Download the image from S3, transform, and upload to a different S3 bucket.
  async.waterfall([
    function download(next) {
      // Download the image from S3 into a buffer.
      s3.getObject({
          Bucket: srcBucket,
          Key: srcKey
        },
        next);
      },
    function tranform(response, next) {
      gm(response.Body).size(function(err, size) {
        // Infer the scaling factor to avoid stretching the image unnaturally.
        //var scalingFactor = Math.min(
        //  MAX_WIDTH / size.width,
        //  MAX_HEIGHT / size.height
        //);
        //var width  = scalingFactor * size.width;
        //var height = scalingFactor * size.height;
        var width  = MAX_WIDTH;
        var height = MAX_HEIGHT;

        // Transform the image buffer in memory.
        this.resize(width, height)
          .toBuffer(imageType, function(err, buffer) {
            if (err) {
              next(err);
            } else {
              next(null, response.ContentType, buffer);
            }
          });
      });
    },
    function upload(contentType, data, next) {
      // Stream the transformed image to a different S3 bucket.
      s3.putObject({
          Bucket: dstBucket,
          Key: dstKey,
          Body: data,
          ContentType: contentType
        },
        next);
      }
    ], function (err) {
      if (err) {
        console.error(
          'Unable to resize ' + srcBucket + '/' + srcKey +
          ' and upload to ' + dstBucket + '/' + dstKey +
          ' due to an error: ' + err
        );
      } else {
        console.log(
          'Successfully resized ' + srcBucket + '/' + srcKey +
          ' and uploaded to ' + dstBucket + '/' + dstKey
        );
      }

      context.done();
    }
  );
};