Pre-PR discussion: upload progress for Storage class

Hi all,

I’ve whipped up a modification to Storage.put that I wanted to run by the team before opening a PR. What do you think of the below? (also, see below the code for some questions)

@mlabieniec @mbahar

    public async put(key: string, object, options?): Promise<Object> {
        const credentialsOK = await this._ensureCredentials();
        if (!credentialsOK) { return Promise.reject('No credentials'); }

        const opt = Object.assign({}, this._options, options);
        const { bucket, region, credentials, level, track, progressCallback } = opt;
        const { contentType, contentDisposition, cacheControl, expires, metadata } = opt;
        const type = contentType ? contentType : 'binary/octet-stream';

        const prefix = this._prefix(opt);
        const final_key = prefix + key;
        const s3 = this._createS3(opt);
        logger.debug('put ' + key + ' to ' + final_key);

        const params: any = {
            Bucket: bucket,
            Key: final_key,
            Body: object,
            ContentType: type
        };
        if (cacheControl) { params.CacheControl = cacheControl; }
        if (contentDisposition) { params.ContentDisposition = contentDisposition; }
        if (expires) { params.Expires = expires; }
        if (metadata) { params.Metadata = metadata; }

        try {
            const upload = s3
                .upload(params)
                .on('httpUploadProgress', ({ loaded }) => {
                    if (progressCallback) {
                        progressCallback(loaded);
                    }
                });
            const data = await upload.promise();
            
            logger.debug('upload result', data);
            dispatchStorageEvent(
                track,
                { method: 'put', result: 'success' },
                null);
            
            return {
                key: data.Key.substr(prefix.length)
            };
        } catch (e) {
            logger.warn("error uploading", e);
            dispatchStorageEvent(
                track,
                { method: 'put', result: 'failed' },
                null);
            
            throw e;
        }
    }

Some questions that came to mind while I was working on this:

1. If we’re using TypeScript, we should use it to its fullest extent. Why aren’t we using an interface, for example, for the options parameter here?
2. If we’re using async/await, we might want to start moving towards using it universally (rather than Promise) and using try/catch blocks instead of an (err, res) => {} callback, just for the sake of code legibility.

[ffxsam]

PR opened, awaiting review.

[haverchuck]

This looks great to me!