#Lambda - Sample Code: Resizing Images

.js

'use strict'
const AWS = require('aws-sdk')
const gm = require('gm').subClass({ imageMagick: true})
const util = require('util')
const path = require('path')
const parse = require('./parse')
const s3 = new AWS.S3()

// constants
const WEB_WIDTH_MAX = 150
const WEB_HEIGHT_MAX = 150

const download = (bucket, key) => {
    return s3.getObject({
            Bucket: bucket,
            Key: key
        }).promise()
        .then(data => data.Body)
        .catch(err => err)
}

const transformWebax = (response) => {
    return new Promise((resolve, reject) => {
        gm(response)
        .resize(WEB_WIDTH_MAX, WEB_HEIGHT_MAX)
        .gravity('Center')
        .crop(WEB_WIDTH_MAX, WEB_HEIGHT_MAX)
        .toBuffer('jpg', function (err, buffer) {
            if (err) {
                reject(err)
            } else {
                resolve(buffer)
            }
        })
    })
}

const uploadWebMax = (buffer, imageName, dstBucket) => {
    const dstKeyResized = 'resized/' + imageName
    return s3.putObject({
        Bucket: dstBucket,
        Key: dstKeyResized,
        Body: buffer,
    }).promise()
    .then(() => 'New resized image was uploaded')
    .catch(err => console.error(err))
}

module.exports.handler = async (event, context, callback) => {
    const srcBucket = parse.bucketName(event)
    const srcKey = parse.fileName(event)
    const imageName = path.basename(srcKey)
    const dstBucket = srcBucket
    

    const typeMatch = srcKey.match(/\.([^.]*)$/)

    if (!typeMatch) {
        callback('Could not determinse the image type')
    }

    const imageType = typeMatch[1]
    
    if (imageType.toUpperCase() !== 'jpg'.toUpperCase() && imageType.toUpperCase() !== 'png'.toUpperCase() && imageType.toUpperCase() !== 'jpeg'.toUpperCase()) {
        callback(`Unsupported image type: ${imageType}`)
        return
    }
    
    try {
    
    const response = await download(srcBucket, srcKey)
    const buffer = await transformWebax(response)
    const upload = await uploadWebMax(buffer, imageName, dstBucket)
    console.log(upload)
    callback(null, 'success')
    
    } catch (err) {
        callback(err)
    }
}