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Sample JavaScript code for resizing pictures on AWS Lambda
/**
* 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();
}
);
};
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