aws lambda reject file upload

Question

I created the below aws lambda function and set the trigger on all S3 upload events on my target bucket. The function attempt to reject file uploads greater than 2000000 bytes. The error message was logged, but neither context.fail('upload rejected') or context.fail(new Error('upload rejected')) did not prevent the fail upload. How to reject file upload, or in general, "reject/stop" an event with aws lambda?

//// nodejs aws lambda code: /////

exports.handler = (event, context, callback) => {
    var MAX_FILE_SIZE = 2000000;
    var msg = '';
    console.log('Received event:', JSON.stringify(event, null, 2));
    if (event.Records && event.Records.length && event.Records.length>0 && event.Records[0].s3 && event.Records[0].s3.object
        && event.Records[0].s3.object.size && event.Records[0].s3.object.size > MAX_FILE_SIZE) {
        msg = 'File ' + event.Records[0].s3.object.key + ' rejected, file size ' + event.Records[0].s3.object.size 
            + ' is greater than ' + MAX_FILE_SIZE + ' bytes.';
        console.log(msg);
        var err = new Error(msg);
        callback(err, {'disposition':'STOP_RULE'});
        context.fail(err);
    } else {
        msg = 'Upload succeeded.';
        console.log(msg);
        callback(null, msg);
        context.succeed(msg);
    }

};

Was answer, but it's more of a comment: Your lambda function, or your callback function, needs to actually be doing the upload in order to prevent it. Instead of having your lambda function trigger on upload, aka after it's already happening, you should use it with api gateway and call it, then on if it passes your validation, either send back to your server to do the upload, or have the lambda do the upload itself (which I would suggest) — Joe Lissner
– Joe Lissner, Commented Mar 31, 2017 at 21:22
if your goal is to limit size of an upload to s3, then you can use a bucket policy to do that. see aws.amazon.com/articles/1434. — Arthur Cinader
– Arthur Cinader, Commented Apr 5, 2017 at 0:24

Arafat Nalkhande · Accepted Answer · 2017-04-01 00:25:58Z

1

You can't do that if your lambda is triggered by s3 notification, simply because in that case it is not controlling the file upload in any way. It is simply called to do some processing based on file upload. If you want to control the file upload then your uploading should happen via the lambda function

What you can actually do in your current situation is that you can delete the file if you see that the size is greater than your required limit, but you cannot prevent the file from getting upload

edited Apr 1, 2017 at 0:25

answered Apr 1, 2017 at 0:20

Arafat Nalkhande

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