Sails.js File upload with Skipper to AWS S3

Instead of using skipper-s3 you can use the aws-sdk module. Upload the image to disk (original), process it, upload it, and delete the original.

var AWS = require('aws-sdk'),
    fs = require('fs');

sharp(original).resize(800).quality(90).toBuffer(function(err, outputBuffer) {
    if (err) {
    } else {
        new AWS.S3({
            accessKeyId: 'your access key', 
            secretAccessKey: 'your secret',
            params : { 
                Bucket : 'your bucket',
                Key: 'desired filename'

        s3client.upload({ACL:'public-read', Body: outputBuffer}, function(err, result) {
            if(err) {
                //handle error
            } else {
               // continue, handle returned data
               fs.unlinkSync(original); // delete original

Alternatively, some libraries (like gm) can take a remote URL. You could use skipper-s3 to upload, then carry out the process above (where original is the s3 URL) and it would work, too—really not performant, at all, though.