cos-downloader

If you want to download files from IBM's Cloud Object Storage to a web browser, but you don't want to hard code your service credentials in a client side app (for good reason) then this is one solution:

The web app makes an API call to an IBM Cloud Functions action to indicate that it wishes to download a file
The serverless action calculates a time-limited URL that allows the download of a single object. The URL is sent out as an HTTP 302 Redirect response
The the browser's request is redirected to a URL and fetches th file direct from Object Storage.

Sign up for IBM Cloud Object Storage

We're going to need an IBM Cloud Object storage service or an Amazon S3 account. IBM’s service supports a subset of the S3 API for easy migration. With a couple simple steps, we can use the same code on IBM Cloud Object Storage or Amazon S3.

Sign up for an IBM Cloud account. Once registered, you can add an IBM Cloud Object Storage service - the Lite plan gives you a generous free allocation to play with.

In the IBM Cloud Object Storage UI, you can

create a bucket - this is the "folder" where your uploaded files will be kept
create a set of credentials that we are going to use in our serverless script. When creating these credentials, you’ll need to pass in a flag to enable S3-style authentication: {"HMAC":true} to enable Amazon compatibility.

Make a note of the bucket name, the API endpoint and your keys for the next step.

Enable CORS

Enabling CORS on an object storage bucket enables it to be accessed directly from a web page without hitting any security restrictions.

Install the aws command-line tool and create a ~/.aws/credentials file containing your object storage service's key and secret:

[default]
aws_access_key_id=MY_PUBLIC_KEY
aws_secret_access_key=MY_PRIVATE_KEY

You should then be able to see the contents of your bucket:

aws --endpoint-url=https://s3-api.us-geo.objectstorage.softlayer.net/ s3 ls s3://mybucket

Create a file called cors.json that contains the same data as contained in the cors.json in this repository.

Then we can enable CORS with:

aws --endpoint-url=https://s3-api.us-geo.objectstorage.softlayer.net/ \
  s3api \
  put-bucket-cors \
  --bucket mybucket \
  --cors-configuration file://cors.json

Install the bx wsk tool

To deploy code to IBM Cloud Functions we need the bx wsk tool installed and configured on your machine. Follow the instuctions here

Deploy to Cloud Functions

Set some environment variables with your object storage credentials and endpoint:

export access_key='xxx'
export secret_key='yyy'
export bucket='mybucket'
export endpoint='https://s3-api.us-geo.objectstorage.softlayer.net'

and run the deployment script:

./deploy.sh

The deploy.sh script should output the URL of your serverless action. It will be something like:

https://openwhisk.ng.bluemix.net/api/v1/web/ORG_SPACE/default/download

You can call the API from curl to test it, passing the id of a file which exists in your Object Storage bucket:

curl -v 'https://openwhisk.ng.bluemix.net/api/v1/web/ORG_SPACE/default/download?id=test.txt'
< HTTP/1.1 302 Found
< Location: https://s3-api.us-geo.objectstorage.softlayer.net/mybucket/test.txt?AWSAccessKeyId=xxx&Signature=zzz&Expires=1520245061
<

If you visit the returned URL in a browser it should download your file. Note this link is time-limited so will only work for sixty seconds from creation.

Using in a web page

If your files are images, then you can construct <img> tags that contain links to your serverless action:

<img src="https://openwhisk.ng.bluemix.net/api/v1/web/ORG_SPACE/default/download?id=landscape.png" alt="photo">

Links

If you need to upload files from browser to Object Storage then this repostory can help.