Promise handling or similar behavior

[uded]

Hi,

It is very possible that I am doing something wrong here, but after giving a try for a while I am empty of any ideas.

When processing an image on AWS Lambda, I am using a regular tinify NodeJS API. My problem is that I am loosing control of the promise while executing the API call to do a remote store to S3. It seems, and this is just my guess based on the behavior of the app, that before the code can be executed in a controllable manner it's actually finished by context.succeed() call. As in the sample below (sizes is a simple array of objects here):

    var url = s3.getSignedUrl('getObject', params);

    var source = tinify.fromUrl(url);
    sizes.forEach(function (size, callback) {
        console.log("Processing size:", size);
        var resized = source.resize({
            method: "fit",
            width: size.width,
            height: size.height
        });

        resized.store({
            service: "s3",
            aws_access_key_id: "XXXX",
            aws_secret_access_key: "XXXX",
            region: "XXXX",
            path: "XXXX/" + name + "_" + size.height + "x" + size.width + "." + ext
        });
    });
   context.succeed("Done");

If I will remove the last line the app will never finish, but images will be handled correctly...

I tried o use async library and to figure out how the bluebird library is being used here, but no ideas till now and time is ticking. What I would like to achieve is a way to control the store() operation in a way that I will be notified about the progress and it's finish. Then, using async or any other technique I will be able to control calling context.succeed() properly...

Any suggestions?

[mattijsvandruenen]

There are various ways of making sure that the succeed() function is called when all images have been uploaded. One is indeed by using the async library. I've made a few small modifications to your code to use async.forEach

var url = s3.getSignedUrl('getObject', params);

var source = tinify.fromUrl(url);
async.forEach(sizes, function (size, callback) {
    console.log("Processing size:", size);
    var resized = source.resize({
        method: "fit",
        width: size.width,
        height: size.height
    });

    resized.store({
        service: "s3",
        aws_access_key_id: "XXXX",
        aws_secret_access_key: "XXXX",
        region: "XXXX",
        path: "XXXX/" + name + "_" + size.height + "x" + size.width + "." + ext
    }).location(function(err, result) {
        console.log("Image upload completed for size:", size);
        callback();
    });
}, function(err) {
    console.log("Finished uploading all sizes");
    context.succeed("Done");
});

The resized.store() call returns a ResultMeta object that we define in our tinify library. This object defines several functions such as location(), width() and height() that support a callback function. In the above example I use the location() fuction with a callback function. This allows us to know when an image size is completely uploaded to S3.

I hope this helps you on your way!