a lambda function to automatically take ownership of any objects written into an s3 bucket. Inspired by https://gist.github.com/joech4n/953c1cd6a36698c5d120

lake-s3-object-take-ownership.js

console.log('Loading event');
var aws = require('aws-sdk');
var s3 = new aws.S3({apiVersion: '2006-03-01'});

exports.handler = function(event, context) {
  // uses s3.listBuckets to fetch the canonical ID of the AWS account
  s3.listBuckets(function(err,data) {
    if (err) {
      console.log(err, err.stack);
    } else {
      var canonicalAccountId = data.Owner.ID;

      console.log('Received event:');
      console.log(JSON.stringify(event, null, '  '));

      // Get the data from the event
      var bucket = event.Records[0].s3.bucket.name;
      var key = event.Records[0].s3.object.key;

      var getOwnerParams = {
        Bucket: bucket, /* required */
        Key: decodeURIComponent(key), /* required */
      };

      // Gets the owner of the S3 Object
      s3.getObjectAcl(getOwnerParams, function(err, data) {
        if (err)
          console.log(err, err.stack); // an error occurred
        else {
          // If the owner is not the correct, then overwrite itself, else do nothing
          var objectOwnerId = data.Owner.ID;
          if (objectOwnerId != canonicalAccountId) {
            console.log("INFO: Object owner not correct. overwriting...");
            overwriteS3Object();
          } else {
            console.log("INFO: Object owner correct. Not doing anything...");
            context.done(null,'');
          }
        }
      });

      function overwriteS3Object() {
        // Configure params for CopyObject: http://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/S3.html#copyObject-property
        var copyParams = {
          Bucket: bucket,                 /* required */
          CopySource: bucket + '/' + key, /* required */
          Key: decodeURIComponent(key),   /* required; URL-decoded because event URL-encodes the key.
                                         For some reason, CopySource does not require this */
          StorageClass: 'STANDARD',       /* Must include this to be able to overwrite a file */
          ServerSideEncryption: 'AES256' /* server side encryption */
        };

        s3.copyObject(copyParams,
          function(err,data) {
            if (err) {
              console.log('ERROR: Problem overwriting ' + bucket + '/' +key + '. Make sure they exist and your bucket is in the same region as this function.');
              errorMessage = 'ERROR: Error from S3: '+err;
              console.log(errorMessage);
              context.done('error', errorMessage);
            }
            else {
              console.log('SUCCESS: Overwritten ' + bucket + '/' + key);
              context.done(null,'');
            }
          }
        );
      }
    }
  });
};