Lambda function to resize image from S3

index.js

var AWS = require('aws-sdk')
var gm = require('gm').subClass({ imageMagick: true })
var s3 = new AWS.S3()
 
exports.handler = function(event, context, callback) {
  var prefix    = 'resized-'
  var srcBucket = event.Records[0].s3.bucket.name
  var dstBucket = prefix + srcBucket
  var srcKey    = decodeURIComponent(event.Records[0].s3.object.key.replace(/\+/g, " "))
  var dstKey    = prefix + srcKey
  var typeMatch = srcKey.match(/\.([^.]*)$/)

  if (!typeMatch || typeMatch[1] != 'jpg') {
    callback('Unsupported image type.')
    return
  }
    
  s3.getObject({ Bucket: srcBucket, Key: srcKey }, function(err, data) {
    if (err) console.log(err, err.stack)
    else {
      gm(data.Body).size(function(err, size) {
        this.resize(100, 100).toBuffer(typeMatch[1], function(err, buffer) {
          if(err) console.log(err, err.stack)
          else {
            s3.putObject({ Bucket: dstBucket, Key: dstKey, Body: buffer }, function(err, data) {
              if (err) console.log(err, err.stack)
              else console.log(data)
            })
          }
        })
      })
    }
  })
}