Generates image thumbnails using AWS Lambda

index.js

var async = require("async");
var AWS = require("aws-sdk");

var im = require("gm").subClass({imageMagick: true});
var s3 = new AWS.S3();

var path = require("path");

var CONFIG = require("./config.json");

function getImageType(objectContentType) {
	if (objectContentType === "image/jpeg") {
		return "jpeg";
	} else if (objectContentType === "image/png") {
		return "png";
	} else if (objectContentType === "image/gif") {
		return "gif";
	} else if (objectContentType === "image/svg+xml") {
		return "svg";
	} else {
		throw new Error("unsupported objectContentType " + objectContentType);
	}
}

exports.handler = function(event, context) {
	console.log("event ", JSON.stringify(event));
	async.mapLimit(event.Records, CONFIG.concurrency, function(record, cb) {
		var originalKey = decodeURIComponent(record.s3.object.key.replace(/\+/g, " "));
		s3.getObject({
			"Bucket": record.s3.bucket.name,
			"Key": originalKey
		}, function(err, data) {
			if (err) {
				cb(err);
			} else {
				cb(null, {
					"originalKey": originalKey,
					"contentType": data.ContentType,
					"imageType": getImageType(data.ContentType),
					"buffer": data.Body,
					"record": record
				});
			}
		});
	}, function(err, images) {
		if (err) {
			context.fail(err);
		} else {
			async.eachLimit(images, CONFIG.concurrency, function(image, cb) {
				  var sizes = [["/", "432x"], ["/thumbs/", "52x"]];
			          async.each(sizes, function(size, cb) {
			              if (image.imageType !== "image/svg+xml") {
			                  if (size[0].indexOf("/thumbs/") > -1)
			                      im(image.buffer).quality(99).strip().sharpen(6, 3).resize(size[1], "", "^>").toBuffer(image.imageType, function (err, buffer) {
			                          if (err) {
			                              cb(err);
			                          } else {
			                              s3.putObject({
			                                  "Bucket": image.record.s3.bucket.name,
			                                  "Key": (path.dirname(image.originalKey) + size[0] + path.basename(image.originalKey)).replace("originals/", ""),
			                                  "Body": buffer,
			                                  "ContentType": image.contentType
			                              }, function (err) {
			                                  cb(err);
			                              });
			                          }
			                      });
			                  else
			                      im(image.buffer).quality(99).strip().resize(size[1], "", "^>").toBuffer(image.imageType, function (err, buffer) {
			                          if (err) {
			                              cb(err);
			                          } else {
			                              s3.putObject({
			                                  "Bucket": image.record.s3.bucket.name,
			                                  "Key": (path.dirname(image.originalKey) + size[0] + path.basename(image.originalKey)).replace("originals/", ""),
			                                  "Body": buffer,
			                                  "ContentType": image.contentType
			                              }, function (err) {
			                                  cb(err);
			                              });
			                          }
			                      });
			              } else {
			                  s3.putObject({
			                      "Bucket": image.record.s3.bucket.name,
			                      "Key": (path.dirname(image.originalKey) + size[0] + path.basename(image.originalKey)).replace("originals/", ""),
			                      "Body": image.buffer,
			                      "ContentType": image.contentType
			                  }, function (err) {
			                      cb(err);
			                  });
			              }
			          });
			}, function(err) {
                if (err) {
                    context.fail(err);
                } else {
                    context.succeed();
                }
            });
        }
    });
};